IMMUNE-RESPONSE IN THE HAMSTER - DEFINITION OF A NOVEL IGG NOT EXPRESSED IN ALL HAMSTER STRAINS

A new IgG isotype is described in serum from Syrian hamsters. This 7S- IgG is called IgG3 and was isolated from IgG1 and IgG2 because of its great affinity for protein A. The unique antigenic determinants of IgG 3 were identified with a specific rabbit antisera. IgG3 is the least e xpressed IgG subclass in Syrian hamsters, but serum levels increase mo re than 10-fold after immunization or infection. Although found in all tested outbred strains, IgG3 is expressed in only some of the commerc ially available inbred strains of Syrian hamsters. Five inbred hamster strains were examined, and in three strains (CB, LHC and MHA) IgG3 wa s not detected in normal serum or in immune serum, indicating serum le vels at least 100-fold less than other normal inbred/outbred hamsters. The results of breeding experiments suggests a single gene defect is responsible for this non-expression of IgG3. Immunodeficiency was not associated with this IgG3 deficiency. Selective deficiencies of immuno globulin classes/subclasses in experimental animals are rare. The evol ution of a similar IgG3 deficiency in these three hamster strains duri ng inbreeding suggests a novel and efficient mechanism for regulation of IgG3 synthesis in the Syrian hamster.