THE IMMUNE SYSTEMCH 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

http://www.uic.edu/classes/bios/bios100/lectures/two_lines_of_defense.htm

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

• http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__antigenic_determinants__epitopes_.html

A. Components of adaptive immune response1. 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

http://highered.mheducation.com/sites/0072556781/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• http://highered.mheducation.com/sites/007

2507470/student_view0/chapter22/animation__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