Age-dependent modulation of serum IgE and mast cell sensitization by Nippostrongylus brasiliensis infestation in rats.

The capacity of N. brasiliensis (Nb) infestation to modify synthesis of ovalbumin (OV) specific IgE antibody was monitored in weanling, juvenile and adult female WAG rats by both passive cutaneous anaphylaxis (PCA) activity and by a rat radio-allergosorbent test (RAST). Infestation with Nb larvae 10 days after immunization with OV produced marginal potentiation of anti-OV Ig antibody production by both RAST and PCA in weanlings, marginal suppression by both parameters in juveniles and was without effect in adults. However, immunization with OV after infestation with Nb partially suppressed anti-OV IgE antibody production in weanlings (RAST) and totally abolished the PCA activity. Although this regime did not impair anti-OV IgE antibody synthesis (RAST) in juveniles, the sera were PCA-negative. In contrast, normal responses were found in adult rats. Negative PCA titres in sera containing high levels of specific antibody occurred when serum total IgE levels were elevated, and are explained on the basis of competition for binding sites on mast cells. The ratio of OV-specific IgE to 'total' IgE is a critical factor in detecting PCA activity.