immunity, types of

Immunity is the ability of the body to resist becoming infected upon exposure to a microorganism or parasite. The body's various modes of resistance to attack give rise to different terminology to describe the types of immunity.

Term	Definition	Example
active immunity	immunity acquired actively, as when exposure to a vaccine induces formation of antibodies that mark foreign substances for destruction	DPT immunization exposure to an upper respiratory virus
passive immunity	immunity transferred to the patient "passively,"rather than formed by the patient himself; usually in the form of antibody protein substances	gamma-globulin injections for immunodeficient patients maternal immunity to infections transferred via the bloodstream prior to delivery or in breast milk
cellular immunity	produced by the T-cell lymphocyte white cells of the body; basically, T-cells remember exposure, and tell the B-cells to make the antibodies	life-long immunity to chickenpox after childhood infection
humoral immunity	produced by the B-cell lymphocyte white cells of the body; B-cells produce antibodies ("humors") upon direction from the T-cells	expectant mothers are tested for their antibody levels to rubella to determine if they are immune
herd immunity	protection of any one individual from a disease by the fact that everyone around him is immune to the disease and thus he can never be exposed directly	herd immunity is the principal behind rubella immunization: if all the kids who could possibly transmit the disease to expectant mothers are immune, the expectant mothers will be protected even if their antibodies are low

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