Host age determines the effects of helminthic parasite infestation upon expression of allergic reactivity in rats.

Comparisons were drawn between the effects of Nippostrongylus brasiliensis infestation upon IgE synthesis and the in vivo expression of allergic reactions to ovalbumin (OV) in weanling, juvenile and adult rats. Parameters examined included total and antigen (OV)-specific IgE levels in serum and the relationship between serum levels of antigen-specific IgE in individual parasitized rats and the magnitude of their subsequent reactions to intravenous or intradermal antigenic challenge. On the basis of parallel trials employing non-infested age-matched controls, parasitized adult and juvenile animals manifested allergic reactivity to the full potential of their individual specific antibody levels. In contrast, the magnitude of allergic reactions in parasitized weanlings was markedly depressed below that expected from their IgE antibody scores. The most notable additional feature distinguishing parasitized weanling rats from infested animals of other ages was the presence in their serum of extremely high levels of 'irrelevant' IgE.