Inheritance of Immunoglobulin Subclass Regulator-1 (Igsr-1) in LEC Mutant Rats

Abstract

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.