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Hapten:
a non-protein substance that can evoke an immune response through combination with a carrier protein. On its own, however, it is not antigenic.
Histamine:
a chemical present in many animal tissues, but particularly in the granules of mast cells and basophils. It is released during allergic reactions and dilates capillaries (causing vascular permeability and a drop in blood pressure) and causes bronchial constriction (closing of the airways).
Histology:
the study of the minute structure, composition and function of tissue.
Hives:
a vascular reaction of the skin marked by the transient appearance of smooth, slightly elevated patches (wheals) which are redder or paler than the surrounding skin and often severely itchy. Also called urticaria.
Hormone:
a chemical, produced in the body by an organ, or cells of an organ, that has a specific effect on the activity of a target organ; e.g. epinephrine.
Humoral Immunity:
acquired immunity in which circulating antibodies (immunoglobulins) play a key role.
Hydrolysis:
the chemical process by which a compound is split into fragments by the addition of water.
HPP:
hydrolyzed plant protein.
Hydrolysed Plant protein:
protein of a plant source that has been fragmented by hydrolysis (usually corn, soy, wheat or peanut).
Hymenoptera:
an order of insects usually having two pairs of well-developed membranous wings; includes bees, wasps, ants, etc.
Hypersensitivity:
a state of altered immunological reactivity in which the body displays an exaggerated response to a foreign agent. Anaphylaxis is classified as a Type I immediate hypersensitivity reaction.
Hypotension:
abnormally low blood pressure, as seen in shock.
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