Homocytotropic response to guinea-pigs to antigen extracts from formalized and unformalized Parascaris equorum.

A homocytotropic anaphylactic response is described in guinea-pigs sensitized with antigen from Parascaris equorum. This antigen was not sensitive to prolonged storage in formalin. Some adult ascarid extracts prepared from worms that had been stored for 14 days in 10 per cent formalin before use, retained their ability to produce an allergenic response. The antisera withstood heat inactivation at 56 degrees for up to 7 h or treatment with 2-mercaptoethanol and were still capable of eliciting a skin response. The skin response persisted for 96 h after sensitization. The serum of animals sensitized with a single dose of P. equorum antigen remained capable of producing a positive passive cutaneous anaphylactic response up to 245 days after the sensitizing dose. It appears, from the results obtained, that this antibody resembles IgG1, rather than IgE.