Chromosomal mapping of the T-helper immunodeficiency (thid) locus in LEC rats

Development of inflammatory bowel disease in Long-Evans Cinnamon rats based on CD4+CD25+Foxp3+ regulatory T cell dysfunction

A mutant strain with defective thymic selection of the Long-Evans Cinnamon (LEC) rat was found to spontaneously develop inflammatory bowel disease (IBD)-like colitis. The secretion of Th1-type cytokines including IFN-gamma and IL-2 from T cells of mesenteric lymph node cells (MLNs) and lamina propria mononuclear cells, but not spleen cells, in LEC rats was significantly increased more than that of the control Long-Evans Agouti rats through up-regulated expression of T-bet and phosphorylation of STAT-1 leading to NF-kappaB activation. In addition, the number of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells of the thymus, MLNs, and lamina propria mononuclear cells from LEC rats was significantly reduced, comparing with that of the control rats. Moreover, bone marrow cell transfer from LEC rats into irradiated control rats revealed significantly reduced CD25(+)Foxp3(+) Treg cells in thymus, spleen, and MLNs compared with those from control rats. Indeed, adoptive transfer with T cells of MLNs, not spleen cells, from LEC rats into SCID mice resulted in the development of inflammatory lesions resembling the IBD-like lesions observed in LEC rats. These results indicate that the dysfunction of the regulatory system controlled by Treg cells may play a crucial role in the development of IBD-like lesions through up-regulated T-bet, STAT-1, and NF-kappaB activation of peripheral T cells in LEC rats.

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

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 the 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 the thid locus between Myb and D1Rat392 on Chr 1. In this region we found an approximately 380-kb deletion from intron 3 of the Ptprk gene, which encodes a receptor-like protein tyrosine phosphatase type kappa (RPTPkappa) to intron 1 of the RGD1560849 predicted gene in the LEC rat genome. Reconstitution with syngenic BM cells transduced Ptprk but not the 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 RPTPkappa plays a critical role in the development of CD4 SP cells in the thymus.

Maturational arrest of thymocyte development is caused by a deletion in the receptor-like protein tyrosine phosphatase kappa gene in LEC rats

The Long-Evans Cinnamon (LEC) rat has a spontaneous mutation, T helper immunodeficiency (thid), which causes a markedly reduced CD4(+) thymocyte population. Here we positionally clone the locus and identify a deletion in the gene encoding a receptor-like protein tyrosine phosphatase kappa (Ptprk) that led to complete loss of the transcript. The rat Ptprk gene exhibits 98% identity with the human and mouse counterparts and is expressed most abundantly in the CD4(-)CD8(-) double-negative stage. The downregulation of Ptprk in mouse immature thymocytes by RNA interference mimicked the thid phenotype. These results indicate that thid maps to the Ptprk locus and that functional Ptprk is crucial for lineage commitment or progression of CD4(+) T cells. We also found that Ptprk appears to function in parallel with or downstream of Th-POK/cKrox (also known as ZBTB7B), a master regulator of T cell lineage decision.

Role of Atp7b gene in spontaneous and N-diethylnitrosamine-induced carcinogenesis in a new congenic strain, WKAH.C-Atp7b rats

To examine whether Long-Evans Cinnamon (LEC) rats, a mutant rat model of Wilson's disease, have a susceptibility gene(s) to hepatocarcinogenesis in addition to the causative gene, Atp7b, we established a new congenic strain, WKAH.C-Atp7b rats, in which the Atp7b gene of the LEC rats is inserted into the normal Wistar-King Aptekman Hokkaido (WKAH) background. Hepatocellular tumors developed spontaneously in both sexes of WKAH.C-Atp7b rats, their incidence being slightly lower than that in LEC rats. Incidences of spontaneous liver tumors in LEC, WKAH.C-Atp7b and WKAH rats correlated with hepatic copper and iron concentrations. Medium-term liver bioassay showed that LEC rats were more susceptible to the induction of glutathione S-transferase placental form-positive preneoplastic foci than WKAH.C-Atp7b rats, and WKAH.C-Atp7b rats were more susceptible than WKAH rats. In an N-diethylnitrosamine (DEN)-induced long-term carcinogenicity study, 1) LEC rats were similarly or rather less susceptible to hepatocellular tumors than WKAH.C-Atp7b and WKAH rats, indicating that the progression of the preneoplastic foci to liver cancer in LEC rats was worse than that in WKAH.C-Atp7b and WKAH rats, 2) the incidences of kidney tumors in LEC and WKAH.C-Atp7b rats were higher than that in WKAH rats and high copper concentrations in the kidneys were observed in LEC and WKAH.C-Atp7b rats, 3) LEC rats were resistant to lung carcinogenesis. These data indicate that the susceptibility of LEC rats to liver and kidney carcinogenesis could be explained by Atp7b gene mutation and that the susceptibility to lung carcinogenesis is controlled by gene(s) other than Atp7b.

Genetic association between low expression phenotype of CD62L (L-selectin) in peripheral CD4+ T cells and the thid (T-helper immunodeficiency) phenotype in the LEC rat

Genetic linkage analysis was performed between the low expression phenotype of peripheral CD4+ T cells and the thid (T-helper immunodeficiency) phenotype using (BN x LEC)F1 x LEC backcross progenies. In contrast to a previous result using a thid congenic strain that the low expression phenotype of CD62L was not correlated with the thid phenotype, our result in this study indicated that the low expression phenotype of CD62L was genetically linked with the thid phenotype. The discrepancy between the previous and present results may be due to the source of animals, congenic strain versus backcross progenies. It is suggested by this study that the thid locus controls the expression level of CD62L in peripheral CD4+ T cells.

X-ray hypersensitivity in the LEA rat: genetic linkage analysis of responsible loci

The LEA rat was established from a Long-Evans rat closed colony as the control strain of the LEC rat, which is reported to exhibit several mutant phenotypes such as hepatic disorder (hts), blockage of the T cell differentiation (thid) and X-ray hypersensitivity (xhs1 and xhs2). Here we report that the LEA rat is hypersensitive to X-rays to a similar degree as the LEC rat, although it is normal with respect to the hts and thid phenotypes. We further performed genetic linkage analysis of X-ray hypersensitivity in the LEA rat. The quantitative trait loci (QTL) linkage analysis revealed that xhs1 but not xhs2 is the locus responsible for X-ray hypersensitivity in the LEA rat.

Unresponsiveness of CD4-8+/- thymocytes to lectin stimulation in LEC mutant rats

A mutant strain of rat, LEC, shows a novel arrest of T-cell maturation from CD4+8+ to CD4+8-, but not to CD4-8+ cells in the thymus. The responsible mutant locus is designated the thid, which was acted upon in a recessive manner of inheritance. We found that LEC rat thymocytes failed to respond to interleukin (IL)-1, IL-6 and IL-7 in the presence of the mitogenic lectins, Allo A or concanavalin A (Con A). The unresponsiveness appeared to be due to unresponsiveness to the lectin stimulation rather than because of cytokine stimulation. Normal rat CD4-8+/- (consisting of CD4-8+ and CD4-8- thymocytes), CD4+/-8- (consisting of CD4+8- and CD4-8- thymocytes), and CD4-8- thymocyte subsets normally responded to mitogenic stimulation, while CD4+8+ thymocytes did not. In contrast, all LEC rat CD4-8+/-, CD4+/-8-, CD4-8- and CD4-8+ thymocytes did not respond to the mitogenic stimulation, suggesting that the unresponsiveness of the CD4-8+/- thymocytes seems to be responsible for the unresponsiveness of whole thymocytes in LEC rats. LEC rat CD4-8+/- thymocytes normally expressed Con A receptor (R), lymphocyte function-associated antigen-1 (LFA-1), and CD45, which are thought to be important molecules for lectin stimulation. When backcross rats from (F344xLEC)F1xLEC were examined, the phenotype for the thid mutation correlated with the [3H]thymidine deoxyribose (TdR) incorporation level in response to Con A stimulation; thymocytes from backcross rats showing +/thid phenotype responded to Con A stimulation normally, whereas thymocytes from backcross rats showing thid/thid phenotype showed significantly lower responsiveness compared with +/thid rats. However, in WKAH.C-thid congenic rat thymocytes that carry the thid mutation, the responsiveness to mitogenic stimulation was comparable to that of normal rat thymocytes. These results suggest that a defect in responsiveness to mitogenic stimulation in LEC rat thymocytes is controlled by multiple genetic loci and the thid locus is one of the important loci for the development of this abnormal phenotype.