Physical Characteristics of Blood

• Thicker (more viscous) than water and flows more slowly than water

• Temperature of 100.4 degrees F

• pH 7.4 (7.35-7.45)

• 8 % of total body weight

• Blood volume– 5 to 6 liters in average male

– 4 to 5 liters in average female

– hormonal negative feedback systems maintain constant blood volume and osmotic pressure

Components of Blood• Hematocrit

– 55% plasma

– 45% cells • 99% RBCs• < 1% WBCs and platelets

Blood components• 55% plasma: 7 to 8% dissolved substances (sugars, amino acids,

lipids & vitamins), ions, dissolved gases, hormones– ions are involved in membrane excitability, determination of fluid pH

and osmotic pressure– most of the proteins in plasma are plasma proteins: provide a role in

balancing osmotic pressure and water flow between the blood and extracellular fluid/tissues

– loss of plasma proteins from blood – increases osmotic pressure in blood and results in water flow out of blood into tissues – swelling

– do not exit the blood due to their size – creates a protein gradient between blood and interstitial fluid

– partially responsible for the plasma’s capacity to buffer pH– most common plasma proteins: albumin, globulins, clotting proteins

(fibrinogen)• albumins – most abundant

• globulins – three classes– alpha, beta and gamma

• fibrinogen – cleaved by thrombin to produce a very stick mass of fibers made of fibrin

– participate in clot formation

Blood: Cellular elements

• 45% of blood is the cellular elements or formed elements• 99% of this is erythrocytes or RBCs

– formed by differentiation of hematopoietic stem cells (HSCs) in the red bone marrow of long bones and pelvis – makes about 2 million per second!

• immature RBCs = reticulocytes• still possess a nucleus and organelles• lack mitochondria and cannot use the oxygen they transport for ATP synthesis• maturation of the reticulocyte causes loss of nucleus and organelles and the filling of

the RBC with close to 250 million Hb molecules• also contain crucial erythrocytic enzymes

– 1. glycolytic enzymes – 2. carbonic anhydrase – converts the soluble form of CO2 (HCO3 in carbonic acid) into

CO2 gas at the lungs and CO2 gas into HCO3 at the tissues

– most numerous cell type in the body – 4 to 6 million per ul blood– flat, biconcave discs

• provides a larger surface area for diffusion of oxygen across their membrane• thinness of the membrane allows rapid diffusion• very flexible membrane that allows their deformation for travel through thin

capillaries

Hematopoiesis

Erythrocytes: Red Blood cells & their development

• hemoglobin • pigment – naturally colored that is red due to its iron content• combines with

– oxygen• binding sites

– carbon dioxide– the acidic portion of carbonic acid

• oxidation of CA occurs at the tissue level– carbon monoxide

• occupies the oxygen binding sites– nitric oxide

• binds to Hb in the lungs where it vasodilates pulmonary arterioles to ensure efficient transport of oxygenated blood from the lungs back to the heart

– composed of a: – 1. globin portion

• four, highly folded protein chains– 2. heme component

• four molecules of iron-based heme bound to each globin protein chain• each heme can bind one oxygen – total binding capacity of 4 oxygen molecules per Hb

•

Erythropoiesis• produced first by the yolk sac• then from myeloid stem cells in the red bone marrow• controlled at the level of the kidneys by the secretion of erythropoietin (EPO)

– increased differentiation of the myeloid stem cell– release of mature RBCs or, if needed, the release of reticulocytes– synthetic EPO – can now be made in the lab

• used to boost RBC production during chemotherapy, diminishes the need for transfusions• role in blood-doping

Feedback Control of RBC Production

• Tissue hypoxia (cells not getting enough O2)– high altitude since air has less O2

– anemia• RBC production falls below RBC

destruction

– circulatory problems

• Kidney response to hypoxia– release erythropoietin

– speeds up development of proerythroblasts into reticulocytes

RBC life-span and recycling– RBC lives only about 120 days – destroyed by macrophages in the liver, bone marrow and

spleen– most RBCs are destroyed in the spleen – small vessels tend to lyze the fragile RBCs as they

travel through this organ– 1. liver/spleen/bone marrow degrades the hemoglobin to its globin component and heme– 2. heme is degraded into free iron and biliverdin – Fe released into the blood

• transported in blood attached to transferrin protein (4&5)• stored in liver, muscle or spleen (6)• attached to ferritin or hemosiderin protein• sent to the bone marrow for hemoglobin synthesis (7&8)

– 9. biliverdin is converted into bilirubin in the liver (11) which travels to the small intestine in the bile where it is converted into a series of compounds – end up expelled in urine as urobilin (13) or in the feces as stercobilin (14)

Hematocrit• Percentage of blood occupied by cells – since

RBCs are 99% of these cells, hematocrit is a measurement of RBC count– female normal range

• 38 - 46% (average of 42%)

– male normal range• 40 - 54% (average of 46%)

• testosterone

Polycythemia– too many RBCs (hematocrit over 65%) – dehydration, tissue hypoxia, blood doping in athletes– primary polycthemia

• caused by a tumor-like condition of the bone marrow• overproduction of RBCs through increased differentiation of the myeloid stem

cell• too many RBCs can increase the viscosity of the blood and result in dramatic

decreases in blood pressure as frictional forces in the vessels increase – increases the workload of the heart

• increased viscosity also slows the velocity of blood flow - reduce oxygen delivery to tissues

– secondary polycthemia• appropriate EPO-induce adaptive mechanism to improve the blood’s oxygen

carrying capacity• occurs at high altitudes or in people with chronic lung diseases

Anemia• Symptoms

– oxygen-carrying capacity of blood is reduced

– fatigue, cold intolerance & paleness• lack of O2 for ATP & heat production

• Types of anemia– iron-deficiency = lack of absorption or loss of iron

• type of nutritional anemia• failure to take in essential raw ingredients not made by the body

– pernicious = lack of intrinsic factor for vitamin B12 absorption from the digestive tract• B12 is essential for normal RBC formation and maturation• binding of B12 to intrinsic factor allows its absorption• intrinsic factor – synthesized by the small intestine

– hemorrhagic = loss of RBCs due to bleeding (ulcer)

– hemolytic = defects in cell membranes cause rupture• rupture of too many RBCs by external factors such as malaria (normal RBCs) or genetic disorders like sickle

cell anemia (defective RBCs)

– thalassemia = hereditary deficiency of hemoglobin

– aplastic = destruction of bone marrow (radiation/toxins)• failure of the bone marrow to produce enough RBCs • may selectively destroy the ability to produce RBCs only• but may also destroy the myeloid stem cells – affect WBCs and platelets

Sickle-cell Anemia (SCA)

• Genetic defect in hemoglobin molecule (Hb-S) that changes 2 amino acids in the globin protein– at low very O2 levels, RBC becomes deformed by

changes in hemoglobin molecule within the RBC• sickle-shaped cells do not pass through capillaries well

and get stuck = causing occlusions and decreased blood flow to organs

• also rupture easily = causing anemia & clots

• Found among populations in malaria belt– Mediterranean Europe, sub-Saharan Africa & Asia

• Person with only one sickle cell gene– increased resistance to malaria because RBC

membranes leak K+ & lowered levels of K+ kill the parasite infecting the red blood cells

Blood disorders

• http://members.aol.com/Sheffbp/products/bludphys.htm (Simulation of anemia diagnosis)

• http://www.udel.edu/Biology/Wags/histopage/colorpage/ch/ch.htm (Hematopoiesis)

• http://www.bloodline.net (Hematology education and news)• http://www.thrombosis.net/lframes/intro.htm (Introduction to thrombosis)• http://www.vh.org/adult/patient/cancercenter/blooddisorders/index.html

(Blood disorders)• http://www.bmtnews.org (Blood and Marrow Transplant Information

Network)• http://www.psbc.org/hematology (Introduction to hematology)• http://www.pediatrics.emory.edu/ (Sickle cell anemia)• http://www.bloodjournal.org (Journal of the American Society of

Hematology)• http://medir.ohsu.edu/cliniweb/C15/C15.378.html (Blood protein disorders)

Blood Groups and Blood Types

• RBC surfaces are marked by genetically determined glycoproteins & glycolipids – agglutinogens or isoantigens– distinguishes at least 24 different blood groups

• ABO, Rh, Lewis, Kell, Kidd and Duffy systems

RH blood groups

• Antigen was discovered in blood of Rhesus monkey

• People with Rh agglutinogens on RBC surface are Rh+. Normal plasma contains no anti-Rh antibodies

• Antibodies develop only in Rh- blood type & only with exposure to the antigen– transfusion of positive blood– during a pregnancy with a positive blood type fetus

• Transfusion reaction upon 2nd exposure to the antigen results in hemolysis of the RBCs in the donated blood

• Rh negative mom and Rh+ fetus will have mixing of blood at birth• Mom's body creates Rh antibodies unless she receives a RhoGam shot

soon after first delivery, miscarriage or abortion– RhoGam binds to loose fetal blood and removes it from body before she reacts

• In 2nd child, hemolytic disease of the newborn may develop causing hemolysis of the fetal RBCs

Hemolytic Disease of Newborn

Thrombocytes: Platelets & clotting

• Disc-shaped, 2 - 4 micron cell fragment with no nucleus– not whole cells!– do have organelles and cytosolic enzymes for generating energy from glucose

• Normal platelet count is 150,000-400,000/drop of blood• Platelets form in bone marrow by following steps:

– myeloid stem cells to megakaryocyte-colony forming cells to megakaryoblast to megakaryocytes whose cell fragments form platelets

– one megakaryocyte forms 1000 platelets• Short life span (5 to 9 days in bloodstream)

– formed in bone marrow– few days in circulating blood– aged ones removed by fixed macrophages in liver and spleen– 30% of platelets are stored in the spleen – in blood-filled spaces since platelets do

not leave the blood

Platelet Plug Formation• hemostasis = arrest of bleeding from a broken vessel

– 3 steps:– 1) vascular spasm – constriction of smooth muscle layer in damaged vessel

• intrinsic response triggered by physical damage– 2) platelet plug formation– 3) blood clotting

• Platelets store chemicals in granules needed for platelet plug formation– platelets do not stick to the smooth endothelium– damage to the endothelial lining exposes collagen fibers to the platelet – results

in their activation and adhesion to the collagen fibers to form a plug– alpha granules

• clotting factors –clot formation• platelet-derived growth factor – repair of damaged vessel wall

– dense granules• ADP, ATP, Ca+2, serotonin, fibrin-stabilizing factor, & enzymes that produce

thromboxane A2– thromboxane – chemotactic factor for other platelets – platelet aggregation– ADP causes circulating platelets to become sticky – adhere to the first layer of aggregating

platelets – results in the secretion of more ADP by the incoming platelets– release of serotonin, epinephrine and thromboxane act as vasoconstrictors to reinforce the

initial vascular spasm– aspirin – inhibits COX enzyme which inhibits the production of thromboxane A2

Steps in the process:(1) platelet adhesion & activation – by collagen interaction(2) platelet release reaction – from their storage granules

-Release thromboxane A2 & ADP - arrival and activation of other

platelets-Serotonin & thromboxane A2 are alsovasoconstrictors decreasing blood flow through the injured vessel

(3) platelet aggregation – self-perpetuating-inhibited at a specific level by the release of inhibiting factors by the adjacent normal endothelium-actin-myosin interactions contract within the aggregating platelets – strengthens the plug-plug becomes reinforced through the formation of sticky fibrin strands

Platelet Plug formation

Blood Clotting– in a test tube gel separates into liquid (serum) and a clot of insoluble

fibers (fibrin) in which the cells are trapped– in the body the clot stabilizes the weaker platelet plug and initiates healing– ultimate step is conversion of fibrinogen (soluble plasma protein) into

insoluble fibrin

• Substances required for clotting are Ca+2, clotting factors and plasma proteins from the liver and substances released by platelets or damaged tissues

• Clotting is a cascade of reactions in which each clotting factor activates the next in a fixed sequence resulting in the formation of fibrin threads– prothrombinase & Ca+2 convert prothrombin into thrombin– thrombin converts fibrinogen into fibrin threads

Overview of the Clotting Cascade

-may be triggered through two possiblepaths

1. extrinsic pathway2. intrinsic pathway

-either path leads to activation of thefinal pathway in which thrombin cleaves fibrinogen to form fibrin

Extrinsic Pathway

• short-cut to clot formation• requires contact with tissue factors

produced externally from the blood• damaged tissues produce and release

Tissue Factor or thromboplastin into bloodstream

• In the presence of Ca+2, clotting factor X becomes activated and combines with clotting factor V to form prothrombinase

• Prothrombinase forms in seconds

Intrinsic Pathway• drives clotting in damaged vessels and also induces

clotting in blood samples in test tubes

• Activation of this pathways occurs either when:– endothelium is damaged & platelets come in contact

with collagen of blood vessel wall – initiates plug formation by activated platelets

– OR platelets themselves become damaged & release phospholipids which activate incoming platelets

• Requires several minutes for reaction to occur – occurs concurrently with platelet plug formation and the extrinsic pathway

• Substances involved: Ca+2 and clotting factors XII, X and V

• first factor – Factor XII (Hageman factor)

• activated by contact with exposed collagen or glass surfaces

• activated Factor XII requires calcium – which then combines with Factor V to produce prothrombinase

Final Common Pathway• activated prothrombinase and Ca+2

– catalyze the conversion of prothrombin to thrombin

• Thrombin– in the presence of Ca+2 converts soluble

fibrinogen to insoluble fibrin threads– activates fibrin stabilizing factor – clotting

factor XIII• stabilizes the forming fibrin mesh

– positive feedback effects of thrombin• accelerates formation of prothrombinase• activates platelets to release phospholipids which

acts to activate more Factor X and therefore produces more thrombin (positive feedback)

• also acts to promote platelet aggregation

Clotting: A summary12

Platelet aggregation

Clot Retraction & Blood Vessel Repair• Fibroblasts & endothelial cells repair the blood

vessel– Formation of PDGF

• release of the fibrinolytic enzyme plasmin dissolves the clot– plasmin – plasma protein present in the

blood as inactive plasminogen– activated by Factor XII– plasminogen becomes trapped in the forming

clot, becomes activated to plasmin and slowly dissolves the clot as the tissue repairs itself

Role of Vitamin K in Clotting

• Normal clotting requires adequate vitamin K– fat soluble vitamin absorbed if lipids are present– absorption slowed if bile release is insufficient

• Required for synthesis of 4 clotting factors by the hepatocytes– factors II (prothrombin), VII, IX and X

• Produced by bacteria in large intestine• anti-coagulants called the coumarin drugs (heparin and

warfarin) act by competing with vitamin K in the liver– inhibits the formation of the vitamin K-dependent clotting factors

• Inherited deficiency of clotting factors – bleeding spontaneously or after minor trauma

– subcutaneous & intramuscular hemorrhaging

– nosebleeds, blood in urine, articular bleeding & pain

• Hemophilia A lacks factor VIII (males only)– most common

– over 150 point mutations in the DNA identified

– factor VIII acts as a cofactor for the activation of factor X

• Hemophilia B lacks factor IX (males only)– less common

– over 300 mutations in the DNA identified

• Hemophilia C (males & females)– less severe because alternate clotting activators exist

• Treatment is transfusions of fresh plasma or concentrates of the missing clotting factor

Clotting Disorders: Hemophilia

Clotting Disorders• If clotting occurs in an unbroken vessel is called a thrombosis

– clots can form in undamaged vessels if the body’s clotting and anti-clotting mechanisms are not kept balanced and in check

– inappropriate clot attached to a vessel wall = thrombus– freely floating clot = embolus– thrombosis can result from several factors

• 1. roughening of the endothelial lining during arterosclerotic plaque formation• 2. slow moving blood• 3. unbalanced fibrin-plasmin production• 4. widespread release of thromboplastin by tissues

• Disseminated Intravascular Clotting : – Life threatening paradoxical presence of blood clotting and bleeding at the same time

throughout the whole body– so many clotting factors are removed by widespread clotting that too few remain to

permit normal clotting– Associated with infections, hypoxia, low blood flow rates, trauma, hypotension &

hemolysis– Clots cause ischemia and necrosis leading to multisystem organ failure

Immunity

• Immunity: ability of the body to defend itself from infectious agents, foreign cells, cancer cells

• immune system has two functional divisions• innate immune system

– non-specific immunity– cell-mediated and humoral (secreted) mediated– chemical and physical barriers– chemical: complement and inflammation– no memory– all forms of life

• adaptive immune system– pathogen and antigen specific response– cell-mediated and humoral mediated– chemical barriers– memory results– only jawed vertebrates

1) Non-specific defenses: Innate immunity

A)Mechanical barriers: first line of defense- Skin and mucus membranes lining the respiratory tract, digestive & reproductive systemse.g. ciliated epithelium of respiratory system - coated with mucus, coughed outB) Chemical barriers (humoral mediated defense): first line of defense-acidic pH of the stomach interior-E.coli within the small intestine-gastric enzymes in gastric juice-high salt in perspiration kills some bacteriaC) Fever: second line of defense-secretion of pyrogen by lymphocytes - raises body temp-rise in body temp enhances the phagocytic activity of immune cellsD) Inflammation & complement: second line of defenseE) Phagocytosis by phagocytic cells (cell-mediated defense)-dendritic cells, macrophages, neutrophils

-cells of the innate system: WBCs with the exclusion of the T and B lymphocytes

Complement

• group of about 20 proteins who control inflammation

• several of these proteins are called acute phase proteins (serum proteins that dramatically increase upon infection)

• complement proteins interact with many components of both the innate and adaptive immune systems

• similar to a blood clotting system – one complement protein activates another which activated another etc…..

• functions– 1. attraction of phagocytes upon activation

of the pathway – chemotaxis– 2. coating of foreign cells with complement

– recognition of the foreign particle by the incoming phagocytes

– 3. intrinsic ability to coat bacteria (opsonization) and lead to their lysis

Inflammation:1) injury to tissue2) release of histamine and kinins (pain) by damaged cells – along with prostaglandins3) histamine - dilation of capillaries & increased blood flow

-histamine causes the gaps between endothelial cells to widen to allow thepassage of larger molecules – immune cells and complement proteins

4) delivery of proteins (e.g .clotting, immune cells), increase of fluid in damaged area, reddening of skin – swelling/edema5) migration of neutrophils and monocytes/macrophages (WBCs) via capillaries - phagocytosis of foreign particles6) clotting response by blood - cascade/positive feedback - to minimize blood loss7) macrophages release Colony stimulating factors - differentiation of more WBCs by the bone marrow and increased distribution systemically8) production and release of lymphocytes from lymph nodes - travel to infection site

-anti-inflammatories (ibuprofen, aspirin, cortisones) can be administered to combactchronic or persistent inflammation

-act against chemicals produced by WBCs and prostaglandins made by damaged cells

-anti-histamines - block the binding of histamine to receptors

WBCs

• cells of the lymphoid lineage– T and B lymphocytes

• cells of the myeloid lineage– phagocytes and other cells

-Leukocytes are 1% of the total cellular elements- found in the Buffy coat together with the platelets:

-granular and agranular classification-neutrophils: phagocytic properties

-release lysozymes which destroy/digest bacteria-release defensin proteins that act like antibiotics & poke holes

in bacterial cell walls destroying them-release strong oxidants (bleach-like, strong chemicals ) that

destroy bacteria

- releases cytokines that attract other neutrophils-eosinophils: parasitic defense cells -also involved in the allergic response

-release histaminase slows down inflammation caused by basophils

-basophils: heparin, histamine & serotonin -heighten the inflammatory response and account for hypersensitivity (allergic) reaction-monocytes: enter various tissues and differentiate into phagocytic macrophages-lymphocytes: T and B cells

Leukocytes: White Blood cells & the Immune system

WBC Physiology• Less numerous than RBCs

– 5000 to 10,000 cells per drop of blood– 1 WBC for every 700 RBC

• Leukocytosis is a high white blood cell count– microbes, strenuous exercise, anesthesia or surgery

• Leukopenia is low white blood cell count– radiation, shock or chemotherapy

• Only 2% of total WBC population is in circulating blood at any given time– rest is in lymphatic fluid, skin, lungs, lymph nodes &

spleen

Lymphatic & Immune System

Lymphatic system: system of lymphatic vessels and organs-multiple functions

1. defense against disease – lymph flows through lymph nodes-the lymph is filtered by the nodes and microorganisms are destroyed2. transport of absorbed fat3. return of filtered proteins – return of plasma proteins that have leaked from capillaries

-larger lymphatic vessels are similar to blood vessels - presence of valves-lymphatic vessels - for the transport of lymph-lymph: filtrate produced in tissues and NOT reabsorbed by the CV system-lymphatic capillaries join to form lymphatic vessels-lymphatic vessels join to form:

1) thoracic duct2) lymphatic duct

- Right side head, arm & chest empty into lymphatic duct and rest of body empties into thoracic duct-then dumped directly into left & right subclavian veins -lymphatic system is ONE WAY(from tissues to heart)

Lymphatic organs:1)lymph nodes: found at certain points along the lymphatic system

-for the cleaning of lymph-capsule surrounding an outer cortex and inner medulla-cortex contains immune cells = lymphocytes (fight pathogens)-medulla contains immune cells = macrophages (clean lymph)

2) tonsils: lymphatic tissue located in the pharynx (adenoids) or oral cavity (palatine tonsils) -defense against pathogens ingested through food and drink3) spleen: upper left region of the abdomen -cleanses the blood -capsule, white and red pulp -white pulp contains lymphocytes -red pulp contains red blood cells & macrophages4) bone marrow (red): adult - within the spongy bone of the epiphyses, pelvis, skull, clavicle, sternum -site of origin for all blood cells (RBCs, WBCs) -derived from hematopoietic stem cells (hematopoiesis) -also the site of origin for all mesodermal cells (bone, muscle, cartilage, fat…..)

-derived from mesenchymal stem cells 5) thymus gland: located below the trachea, on top of the heart -divided into lobules -larger in children -production of T lymphocytes -production of hormones - thymosin - stimulates the lymphocytes located in other tissues

Cells of Innate and Adaptive Immunity: Phagocytes

• one of the first cells to arrive upon inflammation• Two major kinds: monocytes/macrophages and

polymorphonuclear granulocytes (neutrophils)• attracted through the process of chemotaxis (soluble

chemicals that attract cells)• need a method of recognizing the foreign antigen – use

antibodies/immunoglobulins (macrophages)• or can use non-specific attachment to microorganisms

(neutrophils)• Phagocytosis enhanced if the microorganism has been

coated with complement protein

Cells of Innate and Adaptive Immunity: Neutrophils (Polymorphonuclear Granulocytes)

• are over 90% of the circulating granulocytes

• Nuclei = 2 to 5 lobes connected by thin strands– older cells have more lobes

– young cells called band cells because of horseshoe shaped nucleus (band)

• Fine, pale lilac practically invisible granules

• Diameter is 10-12 microns

• Fastest response of all WBC to bacteria

• Direct actions against bacteria– release lysozymes which destroy/digest bacteria

– release defensin proteins that act like antibiotics & poke holes in bacterial cell walls destroying them

– release strong oxidants (bleach-like, strong chemicals ) that destroy bacteria

Cells of Innate and Adaptive Immunity: Monocyte (Agranulocyte)

• two main functions– 1. “professional” phagocytic macrophages – derived from monocytes

– 2. antigen-presenting cells

• Nucleus is kidney or horse-shoe shaped

• Largest WBC in circulating blood– does not remain in blood long before migrating to the tissues

– differentiate into macrophages

– form the reticuloendothelial system (RES)• Destroy microbes and clean up dead tissue following an infection

• fixed group found in specific tissues

• Or as “wandering cells” gathers at sites of infection

• express an Fc receptor on their surface – important for recognizing the foreign microorganism

• Diameter is 12 - 20 microns

• Cytoplasm is a foamy blue-gray

• 3 to 8% of circulating WBCs – form a circulating pool of monocytes

• Take longer to get to site of infection, but arrive in larger numbers

Cells of Innate and Adaptive Immunity: Eosinophils (Granulocyte)

• Nucleus with 2 or 3 lobes connected by a thin strand• Large, uniform-sized granules stain orange-red with acidic

dyes– do not obscure the nucleus

• Diameter is 10 to 12 microns• 2 to 4% of circulating WBCs• Leave capillaries to enter tissue fluid• Release histaminase

– slows down inflammation caused by basophils

• Attack parasitic worms• Phagocytize antibody-antigen complexes

Cells of Innate and Adaptive Immunity: Basophils (Granulocyte)

• Large, dark purple, variable-sized granules stain with basic dyes– obscure the nucleus

• Irregular, s-shaped, bilobed nuclei • Diameter is 8 to 10 microns• Less than 1% of circulating WBCs• Involved in inflammatory and allergy reactions• Leave capillaries & enter connective tissue as mast cells• Release heparin, histamine & serotonin

– heighten the inflammatory response and account for hypersensitivity (allergic) reaction

Cells of Adaptive Immunity: Lymphocytes (Agranulocyte)

• Dark, oval to round nucleus• Cytoplasm sky blue in color

– amount varies from rim of blue to normal amount• Small cells 6 - 9 microns in diameter• Large cells 10 - 14 microns in diameter

– increase in number during viral infections• 20 to 25% of circulating WBCs• produced in the primary lymphoid tissues – thymus and adult bone marrow• B cells

– destroy bacteria and their toxins– turn into plasma cells that produces antibodies

• T cells– attack viruses, fungi, transplanted organs, cancer cells & some bacteria

• Natural killer cells = sometimes classified as large granular lymphocytes– attack many different microbes & some tumor cells– destroy foreign invaders by direct attack– kill by binding directly to the target = cytotoxicity

2) Specific Defenses (Cell-mediated Immunity)

Antigens:-before birth, the body takes an “inventory” of all self proteins = antigens-lymphocytes develop receptors that allow them to distinguish between self andforeign-non-self antigens combine with T and B cell receptors and stimulate an immunereaction

T Cell-mediated immunity:/Cell-mediated immunity-T = thymus derived-respond to antigens by cell-cell contact - attach to foreign cells directly-antigens are processed before interacting with T cells

-antigen-presenting cells (B cells, macrophages)

• Foreign antigen in body fluid is phagocytized by APC– macrophage, B cell, dendritic cell (communicates with the B cell in the lymph node and spleen)

• Antigen is digested and fragments are bound to MHC-II molecules stuck into antigen presenting cell membrane

• APC migrates to lymphatic tissue to find T cells

• found primarily in skin, lymph nodes, spleen and the thymus

• typical APC – Langerhans cell in the skin– migrate out of the skin

– enter into the lymph node where they interdigitate with the T lymphocytes

Antigen Presenting Cell (APC)

• APC displays the foreign antigen to the T cell

• this requires cell-cell contact between the APC and T cell in order to activate the T cell

• both T helper and cytotoxic T cells can be activated by an APC

• interaction between the MHC complex with the Ag and a complex of proteins on the T cell called the T cell receptor

• TCR = multiple proteins associated with a co-receptor (CD4 for a T helper or CD8 for a cytotoxic T cells)

- Activated T cells synthesize specific soluble chemicals called cytokines -also “decide” to become either helper or cytotoxic T cells-if the foreign Ag is bacterial = T helper-if the foreign Ag is viral = T cytotoxic

-T cells secrete chemicals called cytokines - enhance other cell responses to antigens-cytokine = secreted signaling molecules-cytokines made by lymphocytes may be called lymphokines

e.g. interleukins, interferons

-interleukins - over 23 made by various WBCs-several made by T cells-play various roles in activating the many components of the immune system

-interferons: play a role in viral infections-released by virally-infected cells or by activated T cells in response to the infection-three types of IFNs are made naturally by T cells – alpha, beta and gamma IFN-also made synthetically

T cell types• 1. Cytotoxic T cells (Tc cells) destroy virally infected cells and tumor cells

– also implicated in transplant rejection. – are also known as CD8+ T cells, since they express the CD8 glycoprotein at their

surface. – secrete perforin which punches holes in the foreign membrane

• 2. Helper T cells, (Th cells) participate in bacterial infections– need to be activated by an APC– once activated - divide rapidly (clonal expansion) and secrete small proteins

called cytokines that regulate or "help" the immune response. – also called CD4+ T cells– are a target of HIV infection - virus infects the cell by using the CD4 protein to

gain entry. The loss of Th cells . • 3. Memory T cells - T cells that persist long-term after an infection has

resolved. – quickly expand to large numbers of effector T cells upon re-exposure to their

cognate antigen, – provide the immune system with "memory" against past infections. – comprise two subtypes: central memory T cells (TCM cells) and effector

memory T cells (TEM cells). – may be either CD4+ or CD8+.

• 4) Regulatory T cells (Treg cells), formerly known as suppressor T cells• 5) Natural Killer T cells (NKT cells) – also called natural killer (NK) cells

Interactions among the cells of the immune system

TH

Activated T

B Cell-mediated immunity/Antibody mediated immunity (HumoralImmunity)

-antibody producing cells – B cells-activated by interacting with an antigen that fits with the B cell’s specific receptors (B cell receptor or immunoglobulin)-activation is helped by T helper cells - releases cytokines that induce the B cell toproliferate - clonal expansion-activated B cell differentiates into a plasma cell - secretes antibodies specific to thebound antigen and therefore similar in structure to the antigen receptor on the B cellsurface

Antibodies• Antibodies = Immunoglobulins• B cells produce a polyclonal response - several

types of antibodies against one type of foreign particle

• comprised of 4 chains of amino acids linked by pairs of sulfur atoms (disulfide bonds)

• two light chains, two heavy chains• each light and heavy chain is comprised of

constant regions that do not change significantly from antibody class to class

• each light and heavy chain also has a variable region that recognizes a specific antigen

• also called an antigen-binding site• heavy chain defines the class of antibody along

with isoforms (subtypes) within that class

Antibody types: 5 major types

1) IgG = immunoglobulin G-plasma and tissue fluids-effective against bacteria, viruses and toxins-activates the complement system

2) IgA - exocrine gland secretionse.g. breast milk, tears, nasal discharge, gastric juices

3) IgM - blood plasma -develops in response to contact with certain antigens in foods and bacteria -also activates complement

4) IgE - exocrine secretions with IgA-associated with the allergic response

5) IgD - surfaces of most B cells-activation of B cells

Antibodies• immunoglobulins• flexible adaptor for helping cells without inherent

recognition systems to recognize microorganisms• when activated, the B cell produces soluble

antibodies that recognizes a specific microbe via its variable region

• these antibodies can act as an adaptor to link a microorganism to an immune cell

• however, the antibody also binds onto phagocytic cells at the other end of the antibody (via the constant region of the heavy chain)

• OR also can act to activate the complement system which coats microorganisms – aids in recognition by phagocytic cells

B cell types

• 1) Plasma B cells (also known as plasma cells) – large B cells that have been exposed to antigen – produce and secrete large amounts of antibodies

• 2) Memory B cells - formed from activated B cell– activation requires interaction with between the B cell and an antigen encountered

during the primary immune response. – are able to live for a long time – respond quickly following a second exposure to the same antigen.

• 3) B-1 cells - B cells that express CD5– thought to mediate B cell-B cell interaction– express IgM on their surface in greater quantities than IgG – have a preference for binding other immunoglobulins, self antigens and common

bacterial polysaccharides. – present in low numbers in the lymph nodes and spleen – found predominantly in the peritoneal and pleural cavities.

• 4) B-2 cells are the conventional B cells most texts refer to.

B cell activation• requires binding of a foreign antigen to

the antibody displayed on the surface of the B cell

– antigen is internalized and processed into fragments which are displayed in association with the MHC-II complex = APC

• the membrane bound antibody is called a B cell receptor (BCR)

– the BCR recognizes the unprocessed form of an antigen

– the TCR recognizes a processed form of the antigen

• interaction of the B cell displaying the antigen activates the T helper cell

• interaction leads to the differentiation of the B cells into a plasma cell and production of soluble antibodies

– activated T cells secrete lymphokines which stimulates the differentiation of the B cell

B cell activation

• Scenario #1: B cells acts as an APC– Internalizes the foreign invader and displays Ag– Both B and T cell are activated– If bacterial antigen – B cell makes Abs to bacteria and T

cell becomes a T helper– If viral antigen – B cell makes Abs to virus and T cell

becomes a cytotoxic T cell

• Scenario #2: naïve B cell– Naïve B cell activated through binding with activated T

helper cell

• Scenario #3: B cell receptor activation– B cell binds foreign Ag via its BCR (IgD/IgM complex)– Stimulates differentiation into plasma cells

Immune Responses

Primary response: when B or T cells become activated after an intial exposure-release of IgM then IgG by plasma cells into the lymph-several weeks

-several B and T cells become dormant but persist in the lymph = memory cells-if an identical antigen is encountered - clonal expansion and an immediate responsecalled a Secondary response

-lasts years

Immunity Types

1) Passive - when an individual is given prepared antibodies to combat a disease-temporary because the Ig’s are not produced by the individual-passed from mother to child in breast milk-usually given as a gamma globulin injection (blood serum) from a person who have recovered from an infection

2) Active - develops after exposure to an antigen-also can be induced through exposure to small amounts of the pathogen

Immunization = administration of a vaccine-vaccine = contains small amounts of an antigen to which theimmune system responds-antigens are treated so that they are no longer virulent (i.e.no longer replicates or no longer viable)-today - bacteria can be engineered to mass produce specificproteins from a pathogen

e.g. Hepatitis B vaccines

-active immunity depends on the presence of memory T and B cells-long lasting - although booster shots may be required

e.g. Diptheria, tetanus, pertussis - age 4 to 6 years, tetanus boosters at 11 and 14 yearsand older

e.g. Polio - age 2, 4 and 6 months, 4 to 6 years, no boostere.g. measles, mumps, rubella - 12 to 15 months, 4 to 6 years, booster at 11-12 years

Allergies

-type I hypersensitivity-hypersensitivities to substances such as pollen, dander, or other substancesthat normally do no damage to others-these antigens = allergens

1. Immediate response: Immediate hypersensitivity-within seconds of contact-cold-like symptoms or increased swelling and redness at area of contact-caused by release of IgE antibodies-IgE antibody release is a local event – occurs at the site of the allergen’s entranceinto the bodye.g. mucosal surfaces and lymph nodes-IgE antibodies are produced by B cells-IgE binds to the cell surface of mast cells in tissues and basophils in the blood

-via the Fc receptor-allergen-IgE interaction causes release of histamine-severe reaction = anaphylatic shocke.g. bee sting - first exposure results in high sensitivity

-second exposure can be fatal due to massive histamine release,resulting in increased vessel permeability and a drastic drop inblood pressure

-allergy shots - build up of IgG which will react with the allergen beforethe allergens can interact with IgE

Mast cell• often indistinguishable from the basophil• expel their granule contents via exocytosis

– release of histamine is triggered by the crosslinking of IgE antibodies on the cell surface to the microorganism

– but also can be triggered by crosslinking by lectin (high doses in strawberries)

– can also be directly activated by synthetic compounds like codeine and morphine

– following exocytosis – there is the production of new compounds derived from arachidonic acid (prostaglandins and leukotrienes)

• two types– 1. connective tissue mast cells

• located around the blood vessels is most connective tissues– 2. mucosal mast cells

• dependent on T cells for proliferation• highest in concentration in the mucosa of the lung and gut

-also a role for the T helper cell in allergies in regulating IgE production-presentation of an Ag to a T helper cell results in the production of a IgE binding factor (IgE-BF)-this factor potentiates the production of IgE by the B cell and the production of IgE memory cells-IgE production can be limited by a class of T cell = T suppressor cells-Ts cells produce a factor which limits the activation of B cells and production of IgE

Allergies

• 2. Delayed response:• -initiated by memory T cells• -regulated by cytokines secreted by T

cells• e.g. tuberculosis skin test - positive =

red and hardened at injection site • e.g. contact dermatitis - poison ivy,

jewelry, cosmetics