THE IMMUNE SYSTEM CH 43 A group of cells, molecules, and organs that act together to fight off foreign invaders

All animals have innate immunity Vertebrates have adaptive immunity

I. The innate immune response in mammals Involves nonspecific responses to pathogens Barrier defenses: prevent pathogen entry Skin is a physical barrier Tears mucus and saliva are inhospitable to invaders Mucus is thick and traps invaders

cellular defenses: If the invader passes thru skin – White blood cells phagocytose invader – Damaged cells release signals like histamine causing increased blood supply to the area and clot formation and inflammation/swelling/heat – Fevers to generate heat which can inhibit growth of microbes and increases phagocytosis

II. The adaptive (or specific) immune response launches a SPECIFIC attack against the invader Properties of the adaptive immune response – Only works if the invader is present – Is specific to that invader – Has memory – Can distinguish between self and nonself

The adaptive immune response is the result of the production of antibodies against a specific antigen Antigen: a specific molecule, usually a protein that is foreign to the organism (nonself) and stimulates the immune system to make antibodies hill.com/sites/ /student_view0/chapt er22/animation__antigenic_determinants__epito pes_.html hill.com/sites/ /student_view0/chapt er22/animation__antigenic_determinants__epito pes_.html

A. Components of adaptive immune response 1. macrophages or white blood cells circulate thru blood and phagocytose foreign invaders and present the antigen on their surface with MHC protein Macrophages are antigen presenting cells

2. Lymphocytes – involved in antibody production – Originate from stem cells – Two types: B-cells T- cells

B-cell Make antibodies Each different B- cell makes only one type of antibody They sit dormant until the antigen stimulates them to make antibodies Has B cell receptor on it

T-cells Helper T-cells helps the B-cells make antibodies Killer T-cells kill cells with foreign invader Supressor T-cells suppress T-helper and B-cells Has T cell receptor on it

3. Antibodies (Compare b t antibody) Bind to the foreign invader and inactivate it Produced by B cells Each antibody will only inactivate one antigen

Antibodies are secreted form of B cell receptor T cell receptor is one side of B cell receptor/antibody There is a single B cell, T cell, antibody for each antigen

B. Gene rearrangement explains why there are so many T and B cells: gene rearrangements of T cell and B cell receptor genes begins to occur producing millions of different B and T cells. This is maturation/differentiation on.com/sites/ / student_view0/chapter32/ animation_quiz_2.html

Self Tolerance: – During maturation and differentiation of B and T cells, if any produce receptors to body cells what would happen? – What occurs naturally?

C. The Primary immune response: first exposure to pathogen 1. APC phagocytoses pathogen, digests it, and presents the antigen along with MHC class II protein. A specific helper T cell binds to presented antigen with its receptor and becomes activated

2 and 3. Activated helper T binds to B cell with antigen on the B cell receptor. Helper T secretes cytokines that cause proliferation of B cell producing plasma cells, which make antibodies, and memory B cells

Circulating antibodies bind free pathogens, preventing their activity and inducing their destruction

Activated helper T also activates a specific killer T cell. Infected cell present antigen on MHC class I molecule. Killer T binds to antigen, secretes perforin, and infected cell dies.

D. Secondary Immune response Subsequent exposure to same pathogen Activated B, helperT and killer T from primary response proliferate forming memory cells Second exposure activates memory cells to immediately destroy pathogen /student_view0/chapter22/animatio n__the_immune_response.html /student_view0/chapter22/animatio n__the_immune_response.html

Summary of adaptive immune response:

The humoral immune response results in production of antibodies The cell-mediated immune response results in death of infected cells What cells are involved in humoral response? What cells are involved in cell-mediated response?

III. Active vs Passive Immunity A. active immunity Production of antibodies and memory cells from exposure to pathogen – Becoming sick – Getting immunized

B. passive immunity Acquisition of antibodies without exposure to pathogen – Naturally from maternal to fetal blood or mom to baby thru breast milk – Artificially by injection of IgG

What is the main difference between active and passive immunity?

IV. Self vs Nonself Where are MHC class I found? Where are MHC class II found?

All cells have MHC class I proteins on cell membrane There are about 600 different forms and each cell has 6-8 of them There are many different combinations in the human population Immune system recognizes its own MHC combinations as self and all others as nonself resulting in rejection