The Immune System

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10

antigen-stimulated

proliferation and

differentiation of

B cells (clonal

selection)

Slide 57

The Role of Antibodies in Immunity

Neutralization occurs when a pathogen can no longer infect a host because it is bound to an antibody.

Opsonization occurs when antibodies bound to antigens increase phagocytosis.

Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis.

Slide 58

Antibody-mediated mechanisms of antigen disposal

Viral neutralization

Virus

Opsonization

Bacterium

Macrophage

Activation of complement system

and pore formation

Complement proteins

Formation of

membrane

attack complex

Flow of water

and ions

Pore

Foreign

cell

Slide 59

Active Immunization

Active immunity develops naturally in response to an infection.

It can also develop following/ from immunization, also called vaccination.

In immunization, a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory.

Slide 60

Passive Immunity

Passive immunity provides immediate, short-term protection.

It is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk.

It can also be conferred artificially by injecting antibodies into a nonimmune person.

Slide 61

Passive immunization of an infant occurs during breast-feeding

Slide 62

Immune Rejection

Cells transferred from one person to another can be attacked by immune defenses.

This complicates blood transfusions or the transplant of tissues or organs.

MHC molecules are different among genetically nonidentical individuals.

Differences in MHC molecules stimulate rejection of tissue grafts and organ transplants.

Slide 63

Chances of successful transplantation increase if donor and recipient MHC tissue types are well matched.

Immunosuppressive drugs facilitate transplantation.

Lymphocytes in bone marrow transplants may cause the donor tissue to reject the recipient.

Slide 64

Blood Groups

Antigens on red blood cells surface determine whether a person has blood type A (A antigen), B (B antigen), AB (both A and B antigens), or O (neither antigen).