Recombinant haplotype bearing the lymphopenia gene of the BB rat

The development of insulin-dependent diabetes mellitus in the BB rat requires the presence of the class II major histocompatibility complex alleles of the RT1u haplotype and a T cell lymphopenia. The lymphopenia gene (lyp) behaves as an autosomal recessive trait that co-segregates with markers of rat chromosome 4. The current study examines two congenic and four recombinant inbred rat strains derived from BB and Buffalo rat strains using markers for simple-sequence length polymorphisms to confirm the linkage of the lymphopenia gene to chromosome 4. In two of these lines the lymphopenia associates with a recombinant haplotype that is BB-like at the D4Mit6 marker and Buffalo-like at D4Mit7 (neuropeptide Y locus) thus placing the lyp locus between these two closely linked markers.