This is an immediate type of hypersensitivity; a pre sensitized host produces immediate pathological changes after subsequent exposure to the same allergen.
The pathological changes are due to de granulation of mast cells or basophils, following an antigen binding to their surface bound IgE antibodies. IgE Abs production is very low in normal people, usually at an average of 0.0004mg/ml of serum.
Individuals prone to allergy produce more number of IgE antibodies than the normal people. The exact reason for the production of IgE antibodies instead of IgG antibodies in allergic persons is not yet known.
Antigens such as pollen grains helminthes antigens are potent stimulators of IgE Abs in all individuals.
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Clinical symptoms developed in sensitized persons after exposure to allergen are referred as anaphylactic reactions. (Ana- without, phylaxis – protection) and high level IgE antibodies producing tendency is referred as atopic condition.
The factors that are influencing the production of IgE antibodies are mostly genetic and the analysis of conditions suggests that the interaction of IgE regulatory gene and one or more genes of HLA region are responsible for generating atopic conditions.