Immune SystemBody’s Defenses

Immune Responses

• Passive• Formation of antibodies• To the fetus thru the placenta, thru breast milk, thru administration of plasma (artificial)

• Active• Formation of your own antibodies• Vaccinations • by contracting an infectious disease by exposure of an antigen

Innate immune system Adaptive immune system

Response is non-specific Pathogen and antigen specific response

Exposure leads to immediate maximal response

Lag time between exposure and maximal response

Cell-mediated and humoral components

Cell-mediated and humoral components

No immunological memory Exposure leads to immunological memory

Found in nearly all forms of life Found only in jawed vertebrates

Components of the immune system

2 categories of Defenses

• Non-specific • Specific

Types of Defenses

•Nonspecific defense

• mechanisms are general and protect against many types of pathogens

• Barriers to entry

• Inflammatory rxns

• Protective proteins

Types of Defenses: non-specific

•Pathogens: • bacteria, fungi, protozoa, and viruses that cause

infection

Barriers to entry: non-specific

Layered Defenses• Physical barriers prevent pathogens such as

bacteria and viruses from entering the organism.

Barriers to entry: Bodily secretions

Barriers to entry

Chemical Barriers to Entry• Enzymes• Acids: stomach acid

Chemical Barriers• Complement System

http://www.youtube.com/watch?v=vbWYz9XDtLw

Figure 16.21

Inflammatory Response

WBCs

Neutrophils1st WBC to

scence• Phagocytes

capable of diapedesis

• Hallmark of acute infection

• First to arrive on scene

• 40-70%

Eosinophils

• Mediate for allergies• Limited phagocytic

activity• Strong Chemotaxis

• Attract to injury and infection

• Destroys Antigen/Ab complex

• 2-4%

Basophils

• Mast cells• Releases histamine:

vasodialator• Heparine: anticoagulant• Releases serotonin/Kinin• .5-1% (smallest

population)

Monocytes

• Scavengers• Transform into

macrophages, eating bacteria, viruses and tissue debris

• 3rd line of defense• 3-8%

Monocyte

Lymphocytes

• Acquired immune response

• SPECIFIC defense system

• 20-25%

• Forms 2 types: • T cells: attack all foreign cells• B cells: produce Ab to get rid

of bacteria and viruses

Blood cells are produced in the bone marrow from a pluripotent stem cell that can become either a WBC, RBC or Platelet

http://www.dnatube.com/video/2441/Uptake-of-Bacteria-by-Phagocytes

Specific DefensesImmunity is a specific defense mechanism.

It is resistance to a particular pathogen or its toxin or metabolic by-product.

Immunity is based upon the ability to distinguish self molecules from non-self.

Molecules that can elicit an immune response are antigens.

Antigens• The lymphatic system responds to non-self or foreign

antigens, but not to self antigens.

• Shape of antigens allow immune system to be specific

• Antigens: molecules that can elicit an immune response and each having their own receptor• may be proteins, polysaccharides, glycoproteins, or

glycolipids.

Antigen-Presenting Cells• Macrophages alert

lymphocytes by displaying antigens from engulfed cells.

• Foreign antigens are attached to the macrophage surface by a self protein, part of the major histocompatibility complex (MHC).

Cellular Immune Response• Helper T cells destroy infected cells and clean up pathogens

• T cells attach to foreign, antigen-bearing cells, cell-to-cell contact.

• Cytokines or lymphokines enhance cellular response to antigens.

• Helper T cells produce chemical signals to activate cytotoxic T cells, which are WBC carrying pathogen-specific receptors on their surface

• Kill cancer cells and attack foreign tissue

Lymphocytes Origin• Red bone marrow

releases undifferentiated lymphocytes into the circulation.

• Some become T lymphocytes or T cells in the thymus.

Figure 16.16

The Immune Response

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter24/animation__the_immune_response.html

Humoral ImmunityRemoving Pathogens at large

• B cells secrete antibodies into the blood: antibody-mediated immunity.

• Helper T cells activate B cells in response to macrophage presentation of antigens.

• Stimulated B cells produce plasma cells or memory cells.

• Plasma cells produce antibodies.

• AB are released by plasma cells and circulate in blood and lymph

• Ab attach to pathogens, similar to specific binding of cytotoxic T cells

• AB/Antigen complex are then destroyed by general defense like macrophages or proteins that puncture pathogen’s membranes

• http://bcs.whfreeman.com/thelifewire/content/chp18/1804s.swf

Types of T Cells• Helper T cells

• stimulate B cells to produce antibodies• CD4 cells are prime targets of HIV

• Memory T cells• produced upon initial antigen exposure and protect

against delay in future exposure• Cytotoxic T cells

• release perforin to destroy cells that present foreign antigens

B Cell Activation

• Activated helper T cell releases cytokines.

• Cytokines stimulate B cell proliferation.

Figure 16.19

B Cell Activation• Some B cells become

plasma cells that secrete antibodies that bind antigens.

• Antibodies (immunoglobulins) are globular proteins composed of four chains.

• Ends of the molecule contain antigen-binding sites.

Long Term Protection• Memory Cells

Long Term• Vaccines

Long Term• How pathogens evade immunity

• Antigen shifting

Immunoglobulins

• Immunoglobulin G• IgG, gamma globulin, 80% of

antibodies• defends against bacteria,

viruses, toxins• found in blood plasma and

tissue fluid• activates complement

Figure 16.20

Immunoglobulins• Immunoglobulin A

• IgA, 13% of antibodies• found in exocrine secretions• defends against bacteria and

viruses

Immunoglobulins• Immunoglobulin M

• IgM, 6% of antibodies, found in plasma• activates complement

• Immunoglobulin D• IgD, found on mast cells• activates B cells

• Immunoglobulin E• IgE, found in exocrine secretions• promotes inflammation and allergic reactions

Antibody Actions

• Antibodies attach directly to antigens• agglutination, precipitation, neutralization

• Antibodies activate complement• Combination with antigens exposes reactive sites on

complement which results in• opsonization increasing phagocytosis susceptibility• chemotaxis attracting neutrophils and

macrophages• inflammation to prevent spread of antigens• lysis of cell membranes

Innate Immunity• Humoral

Innate Immunity• Cellular Barriers

Adaptive Immunity

• http://gtm-media.discoveryeducation.com//downloaddirector/downloadFile.aspx?thefile=10053\sec9296_256.mov&realname=The_Immune_System