Larval exoantigens from ascarid nematodes are potent inducers of histamine release from human blood basophils.

Histamine release (HR) from washed human blood cells after challenge with the excretory-secretory antigens (ES) of the parasitic nematodes Toxocara canis and Ascaris suum was studied, employing a recently developed microfibre-based assay combined with hyperosmolar release media for maximal sensitivity. Blood samples were obtained from 30 patients suspected of parasite infection and 11 healthy volunteers serving as controls. Specific antibodies of IgE, IgG1 and IgG4 subclasses were determined by ELISA. Virtually no HR could be provoked by ES in the 11 controls. In contrast, HR was seen in 16 patients after challenge with T. canis ES and in 11 patients with A. suum ES. In the majority of these, HR was detectable after challenge with ES protein concentrations of less than 1 ng/ml, and the maximal HR obtained with ES was greater than that seen with optimal concentrations of anti-IgE. The HR after ES antigen challenge correlated with the amount of specific IgE in patient plasma, and coincided with the presence of specific IgG1 and IgG4.