The quality or state of being specific, as of an antigen to its corresponding antibody.


The extent to which an individual is liable to infection or to the effects of substances, such as toxicants, allergens, or other influences. The antithesis of resistance.


T cell.

A lymphocyte produced in the bone marrow that matures in the thymus and is integral to cell-mediated immunity. T cells regulate the growth and differentiation of other lymphocytes and are involved in antibody production.



The administration of vaccine orally or by injection to protect against a given disease.


Dilation of the blood vessels.


Wheal and flare.

Wheal—A smooth, slightly elevated area on the body surface, which is redder or paler than the surrounding skin; it is often attended with severe itching, and is usually evanescent, changing its size or shape, or disappearing within a few hours. It is the typical lesion of urticaria, the dermal evidence of allergy, and in sensitive persons may be provoked by mechanical irritation of the skin. Known as also hive and welt. Flare—(1) The red outermost zone of the ''triple response" (Sir Thomas Lewis) urticarial wheal reaction, a manifestation of immediate, as opposed to delayed, allergy or hypersensitivity; (2) a spreading flush or area of redness on the skin, spreading out around an infective lesion or extending beyond the main point of reaction to an irritant; and (3) sudden exacerbation of a disease.

White cell.

A colorless cell in the blood, lymph, or tissues that is an important component of the immune system. See leukocyte.

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