Effect of quantity and quality of IgG antibodies on blocking of allergenic histamine release in vitro

In a study of the protective role of IgG antibodies in allergen injection therapy, serum antibodies to timothy grass allergens were raised in rabbits and tested for inhibition of histamine release from basophils of grass pollen-sensitive human subjects. Rabbit sera were not inhibitory until late in the immune response when large amounts of relatively low affinity IgG antibodies were detected by primary binding. Inhibition of histamine release by late sera required preincubation of allergen and antibody prior to addition of sensitive basophils, and could not be demonstrated when basophils and IgG antibodies had simultaneous access to allergen. Hence intravascular inhibition of mediator release in allergen-treated patients may require high affinity IgG antibodies. The predominantly low affinity of antibodies raised in the rabbits precluded testing of this possibility.