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The Immune System




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After activation the cell divides to form:

T-helper cells – secrete CYTOKINES

 help B cells divide

 stimulate macrophages

Cytotoxic T cells (killer T cells)

 Kill body cells displaying antigen

Memory T cells

 remain in body

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The Immune System

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The Immune System

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Active and Passive Immunity

Active and Passive Immunity

Active immunity

Lymphocytes are activated by antigens on the surface of pathogens

Natural active immunity - acquired due to infection

Artificial active immunity – vaccination

Takes time for enough B and T cells to be produced to mount an effective response.

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Active and Passive Immunity

Active and Passive Immunity

Passive immunity

B and T cells are not activated and plasma cells have not produced antibodies.

The antigen doesn’t have to be encountered for the body to make the antibodies.

Antibodies appear immediately in blood but protection is only temporary.

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Active and Passive Immunity

Active and Passive Immunity

Artificial passive immunity

Used when a very rapid immune response is needed e.g. after infection with tetanus.

Human antibodies are injected. In the case of tetanus these are antitoxin antibodies.

Antibodies come from blood donors who have recently had the tetanus vaccination.

Only provides short term protection as abs destroyed by phagocytes in spleen and liver.

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Active and Passive Immunity

Active and Passive Immunity

Natural passive immunity

A mother’s antibodies pass across the placenta to the foetus and remain for several months.

Colostrum (the first breast milk) contains lots of IgA which remain on surface of the baby’s gut wall and pass into blood

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Active and Passive Immunity

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A preparation containing antigenic


Whole live microorganism

Dead microorganism

Attenuated (harmless) microorganism

Toxoid (harmless form of toxin)

Preparation of harmless ags

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Injection into vein or muscle


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