Inheritance of immunoglobulin subclass regulator-1 (Igsr-1) in LEC mutant rats

Long-Evans Cinnamon (LEC) mutant rats were reported to exhibit a deficiency in the serum immunoglobulin (Ig) G1. The phenotype determining the basal level of IgG1 was tentatively designated as immunoglobulin subclass regulator-1 (Igsr-1), and normal rats and LEC rats were categorized into Igsr-1A (normal expression of IgG1) and Igsr-1B (low expression of IgG1), respectively. In this report we examined genetic trait of this phenotype in LEC rats. The serum IgG1 levels in F1 hybrids produced by mating LEC rats (Igsr-1B) with normal rats (Igsr-1A) were intermediate level, indicating that Igsr-1 behaves as a co-dominant genetic trait. When backcross rats were examined, serum IgG1 levels varied between those in normal and LEC rats without clear segregation, indicating that Igsr-1 is controlled by multiple genes. Furthermore, the serum IgG1 level in each backcross rat did not correlate to another recessive mutant genotype, thid (T-helper immunodeficiency). These data suggest that the deficiency in serum IgG in LEC rats is independent of the deficiency in helper T cell function, but might be due to the multiple deficiency in as-yet-unidentified mechanisms.