A deletion mutation of the protein tyrosine phosphatase kappa (Ptprk) gene is responsible for the T-helper immunodeficiency (thid) in the LEC rat

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Bone marrow (BM)-derived T-cell progenitors differentiate into CD4 or CD8 single positive (SP) cells in the thymus. We have previously reported that a single autosomal mutation, thid, causes a defect in maturation of CD4 SP thymocytes and an abnormality of peripheral helper-T cells in the LEC rat. In this study, we attempted to identify a gene responsible for the thid mutation. We first performed genetic linkage analysis and mapped thid locus between Myb and D1Rat392 on Chr 1. In this region, we found a ~380 kb deletion from intron 3 of the Ptprk gene, which encodes a receptor-like protein tyrosine phosphatase type κ (RPTPκ), to intron 1 of RGD1560849 predicted gene in the LEC rat genome. Reconstitution with syngenic BM cells transduced Ptprk but not RGD1560849 predicted gene rescued development of CD4 SP cells in the LEC rat thymus. It is confirmed by this result that the Ptprk gene is responsible for the thid mutation in the LEC rat. Our results further suggest that RPTPκ plays a critical role in the development of CD4 SP cells in the thymus.