Rats resistant to the dextran anaphylactoid reaction.

In one colony of Wistar albino rats 23% were resistant to dextran and to egg-white, these animals (non-reactors) failing to show an anaphylactoid reaction after the intraperitoneal or intravenous injection of either of the two substances. Non-reactors were also found in a few other colonies of Wistar rats but not in colonies of other strains. Procedures which potentiated the anaphylactoid reaction in sensitive rats (reactors) did not alter the response of non-reactors. Dextran failed to release histamine from the perfused hind-quarters of non-reactors although other chemical liberators of histamine were effective. Lack of anaphylactoid reaction was not due to a deficiency of skin histamine or 5-hydroxytryptamine, and the blood sugar and serum protein levels of non-reactors were also normal. Non-reactors could be sensitized to antigens and their serum was antigenic to guinea-pigs. It is suggested that non-reactors lack a blood or tissue component with which dextran normally combines to produce an intermediate substance active in releasing amines.