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Ch. 43 The Immune System
Objectives
LO 2.28 The student is able to use representations or models to analyze quantitatively and qualitatively the effects of disruptions to dynamic homeostasis in biological systems.LO 2.29 The student can create representations and models to describe immune responses.LO 2.30 The student can create representations or models to describe nonspecific immune defenses in plants and animals.LO 2.34 The student is able to describe the role of programmed cell death in development and differentiation, the reuse of molecules, and the maintenance of dynamic homeostasis.
Overview
• Innate Immunity – defenses are activated immediately upon infection; same response for all pathogens.
• Adaptive (Acquired) Immunity – defenses based on recognition of the pathogen.
Pathogens(such as bacteria,fungi, and viruses)
INNATE IMMUNITY(all animals)
• Rapid response
Recognition of traits sharedby broad ranges ofpathogens, using a smallset of receptors
•
Recognition of traits specific to particularpathogens, using a vastarray of receptors
•
• Slower response
Barrier defenses:
SkinMucous membranesSecretions
Internal defenses:
Phagocytic cellsNatural killer cellsAntimicrobial proteinsInflammatory response
Humoral response:
Antibodies defend againstinfection in body fluids.
Cell-mediated response:
Cytotoxic cells defendagainst infection in body cells.
ADAPTIVE IMMUNITY(vertebrates only)
Ch. 43.1 In Innate Immunity, Recognition and Response Rely on Traits Common to Groups of Pathogens
Invertebrates• Exoskeleton (chitin)• Chitin-based barriers and lysozymes
(break down bacterial walls) in intestines
• Hemocytes– Phagocytosis– Chemicals– Antimicrobial peptides (disrupt fungi
and bacterial plasma membranes)– Specialized recognition proteins
Pathogen
PHAGOCYTICCELL
VacuoleLysosomecontainingenzymes
Vertebrates• Barrier defenses
– Skin– Cilia: sweep mucus and any entrapped microbes
upward, preventing the microbes from entering the lungs
– Lysozymes in• Mucus – traps microbes• Saliva• Tears
– Acidic• Skin• Sweat• Stomach juices
• Cellular Innate Defenses– Phagocytosis after Toll-like receptor recognizes
pathogen• Neutrophils: circulate in blood• Macrophages: live in cells/organs (spleen)• Dendritic cells: tissue in contact with environment (skin)• Eosinophils: beneath mucosal surfaces; multicellular
pathogens.
– Natural Killer Cells: secrete chemical when they come in contact with a pathogen
• Antimicrobial Peptides and Proteins– Interferons
• Made by virally infected cells to warn surrounding cells.
• Inflammatory Response
– Histamine is released by mast cells in response to tissue damage• Trigger dilation and increased permeability of nearby capillaries• Increased blood flow delivers clotting factors to the injury (marks
beginning of repair process/blocks spread of microbes)– Cytokines from macrophages/neutrophils promote blood flow causing
redness and increased temp in the area.– Pus—the accumulation of dead phagocytic cells and fluid leaked from
capillaries
Pathogen Splinter
Mastcell
Macro-phage
Capillary
Redblood cells
Neutrophil
Signalingmolecules
Movementof fluid
Phagocytosis
43.2 In Adaptive Immunity, Receptors Provide Pathogen-Specific Recognition
• Pathogens have antigens that trigger lymphocytic responses.– B cells
• Binding of Y shaped antigen receptor on membrane to antigen causing it to secrete soluble receptors called antibodies.
– T cells• Single rod shaped antigen receptor only binds to already infected host cells that
display the antigen.Antibody
Antigenreceptor
B cell
Antigen Epitope
Pathogen(a) B cell antigen receptors and antibodies
Antibody C
Antibody BAntibody A
Antigen
(b) Antigen receptor specificity
Displayedantigenfragment
MHC molecule
Antigenfragment
Pathogen
Host cell
T cell
T cell antigenreceptor
(a) Antigen recognition by a T cell
Characteristics of Adaptive Immunity1. Immense diversity of lymphocytes and receptors.
– > 1 million different B cell antigen receptors; 10 million different T cell antigens; each cell carries a specific set of these
2. Self-tolerance.– Lymphocytes are tested; any with “self” receptors go through
apoptosis.
3. Once recognized, increasing the number of specific lymphocytes for an antigen.
– Active lymphocyte divides by mitosis making cloned effector cells (begin fighting immediately; B=plasma cells; T= helper T cells and cytotoxic T cells) and memory cells (long lived cells that activate if antigen enters the body again)
4. Stronger and quicker response to previously encountered antigens.
– Memory cells
43.3 Adaptive Immunity Defends Against Infection of Body Fluids and Body Cells
Cell-Mediated Immune Response (attacks infected body cells)• Active helper T cells secrete cytokines which activate cytotoxic T cells.• Cytotoxic T cells bind to infected host cells
– Secretes proteins that disrupt membrane integrity and trigger apoptosis.– Once destroyed, antibodies attach to antigens from within the host cell.
Antigen-presentingcell
Pathogen
Antigen fragment
Class II MHC molecule
Accessory protein
Antigen receptor
Helper T cell
Cytokines
Cell-mediatedimmunity
Cytotoxic T cell
2
1
Cytotoxic T cell
31 2
Accessoryprotein
Class I MHCmolecule
Infectedcell
Antigenreceptor
Antigenfragment
Perforin
Pore
Gran-zymes
ReleasedcytotoxicT cell
Dyinginfected cell
© 2011 Pearson Education, Inc.
Animation: Helper T Cells Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Animation: Cytotoxic T Cells Right-click slide / select “Play”
Humoral Immune Response (attacks pathogen)• Helper T cells activate B cells.• B cells divide into memory or plasma cells.• Plasma cells give secrete 2,000 antibodies/sec!• Antibodies:
– Prevent the pathogen from infecting cells (neutralization)– Increase phagocytosis due to easy recognition (opsonization)– Complement system of proteins opens a pore in the pathogen causing water
to rush in the pathogen to lyse.
Pathogen
31 2
Antigen-presentingcell Antigen
fragment
Class IIMHC
molecule
Antigenreceptor
Accessoryprotein
Helper T cell
B cell
Cytokines
Activatedhelper T cell
Memory B cells
Plasma cells Secretedantibodies
OpsonizationNeutralization
Antibody
VirusBacterium
Macrophage
Activation of complement system and poreformation
Complement proteins
Formation of membraneattack complex
Flow of waterand ions
Pore
AntigenForeigncell
Humoral (antibody-mediated) immune response Cell-mediated immune response
Antigen (1st exposure)
Engulfed by
Antigen-presenting cell
Helper T cell
Memoryhelper T cells
Antigen (2nd exposure)
B cell
Plasma cells
Secretedantibodies
Defend against extracellularpathogens
Memory B cellsMemory
cytotoxic T cellsActive
cytotoxic T cells
Defend against intracellularpathogens and cancer
Cytotoxic T cell
Key
Stimulates
Gives rise to
Active and Passive Immunization• Active (cell mediated and humoral responses)
– Can be induced by vaccinations – weakened, killed, or parts of pathogens to – to create memory cells and can lead to immunization.
• Passive (passed on from mother to child for first few months of life)– Injection of antibodies from an immune animal to
a non-immune animal.
Immune Rejection
• Cells from another person’s body can be recognized as foreign due to different carbohydrate found on the cell membranes, causing an immune response.– Blood groups (ABO)– Tissue and Organ Transplant
43.4 Disruptions in Immune System Function Can Elicit or Exacerbate Disease
• Allergies– Exaggerated responses to allergens.
• Autoimmune diseases– Immune system does not recognize “self-cells”
• Lupus• Arthritis• Diabetes• MS
Immunodeficiency Diseases
• Inborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses
• Acquired immunodeficiency develops later in life and results from exposure to chemical and biological agents
• Acquired immunodeficiency syndrome (AIDS) is caused by a virus
Evolutionary Adaptations of Pathogens
Antigenic Variation• Changes its antigens so the host does not recognize it
– Ex: Flu
Latency• Inactive state which does not trigger an immune
response (lysogenic cycle).Attacking the Immune System Itself• HIV – attacks helper T cells preventing both cell
mediated and humoral responses to infections.
Cancer and Immunity
• The frequency of certain cancers increases when adaptive immunity is impaired– 20% of all human cancers involve viruses
• The immune system can act as a defense against viruses that cause cancer and cancer cells that harbor viruses
• In 2006, a vaccine was released that acts against human papillomavirus (HPV), a virus associated with cervical cancer.