Inheritance of T helper immunodeficiency (thid) in LEC mutant rats

Contiguous gene deletion of Ptprk and Themis causes T-helper immunodeficiency (thid) in the LEC rat

The LEC rat has a spontaneous mutation of T-helper immunodeficiency (thid), which causes a marked defect in T cell maturation from double positive (DP) to CD4 single positive (SP) cells in the thymus. Previously, we identified the contiguous gene deletion of Ptprk and Themis genes in the thid locus that causes the simultaneous loss of expression of both genes, and the exogenous Ptprk expression partially rescued this phenotype. To determine whether the deletion of Themis influences thid phenotype, bone marrow (BM) cells were transduced with lentiviral vector expressing Themis gene, and were transplanted into X-ray-irradiated LEC rats. Interestingly, the exogenous Themis expression rescued the development of CD4 SP cells as well as Ptprk. The result suggests that the deficiency of both genes is responsible for the thid mutation, and that both genes are indispensable for the development of SP cells from DP cells in the thymus.

Gasp, a Grb2-associating protein, is critical for positive selection of thymocytes

T cells develop in the thymus through positive and negative selection, which are responsible for shaping the T cell receptor (TCR) repertoire. To elucidate the molecular mechanisms involved in selection remains an area of intense interest. Here, we identified and characterized a gene product Gasp (Grb2-associating protein, also called Themis) that is critically required for positive selection. Gasp is a cytosolic protein with no known functional motifs that is expressed only in T cells, especially immature CD4/CD8 double positive (DP) thymocytes. In the absence of Gasp, differentiation of both CD4 and CD8 single positive cells in the thymus was severely inhibited, whereas all other TCR-induced events such as beta-selection, negative selection, peripheral activation, and homeostatic proliferation were unaffected. We found that Gasp constitutively associates with Grb2 via its N-terminal Src homology 3 domain, suggesting that Gasp acts as a thymocyte-specific adaptor for Grb2 or regulates Ras signaling in DP thymocytes. Collectively, we have described a gene called Gasp that is critical for positive selection.

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.

High sensitivity of thymocytes of LEC strain rats to induction of apoptosis by X-irradiation

It is known that physical disruption of cell contacts induces apoptosis of thymocytes. When thymocytes from LEC and WKAH rats were incubated in vitro at 37 degrees C for 0-6 hr and then the proportion of apoptotic cells was determined using a flow cytometer, it was found that the percentages of apoptotic thymocytes from both LEC and WKAH rats increased with incubation time and that the proportion of apoptotic cells from LEC rats was significantly higher than that from WKAH rats at each incubation time. The fact that cycloheximide, an inhibitor of protein synthesis, did not show significant inhibitory effects on induction of apoptosis of thymocytes indicates that induction of apoptosis during in vitro cultivation did not require de novo protein synthesis. When thymocytes from LEC and WKAH rats were X-irradiated in vitro at 4 and 8 Gy, the percentages of radiation-induced apoptotic cells increased with post-incubation time after X-irradiation in both LEC and WKAH rat thymocytes and the proportions of apoptotic cells from LEC rats were significantly higher than those from WKAH rat cells at 2 and 4 hr post-incubation after X-irradiation. When thymocytes from LEC and WKAH rats were X-irradiated in the presence of cycloheximide, the induction of apoptosis was substantially inhibited, indicating that radiation-induced apoptosis of thymocytes from LEC and WKAH rats required de novo protein synthesis. The present results showed high sensitivities of thymocytes of LEC rats to induction of apoptosis during in vitro cultivation and by X-irradiation.

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.

Absence of linkage between radiosensitivity and the predisposing atp7b gene mutation for heritable hepatitis in the LEC rat

The LEC rat is known to be a mutant strain that spontaneously develops heritable hepatitis due to copper accumulation, caused by mutation of the copper-transporting ATPase gene (Atp7b). Immunodeficiency and radiosensitivity have also been observed. Hayashi et al. extensively examined the radiosensitivity of the LEC rat and concluded that its hypersensitivity is controlled by a single autosomal gene. Furthermore, they suggested the possibility that it correlates to copper accumulation due to the Atp7b gene mutation, because ionizing radiation-induced hydroxyl radicals might act in concert with copper-induced hydroxyl radicals. In the present experiment, we analyzed linkage between radiosensitivity and the mutation responsible for hepatitis in F(1) animals of a cross with the F344 rat. Our results clearly demonstrated an absence of any significant association. In addition, partial dominance for radiosensitivity was observed, and radiosensitive (F(1) x LEC) backcross rats were twice as numerous as their radioresistant counterparts, suggesting the possibility of control by two or more recessive genes.

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.

HD mice: a novel mouse mutant with a specific defect in the generation of CD4(+) T cells

We have identified a spontaneous mutation in mice, which we term HD for "helper T cell deficient." This mouse is distinguished by the virtual absence of peripheral T cells of the CD4(+)8(-) major histocompatibility complex (MHC) class II-restricted T helper subset due to a specific block in thymic development. The developmental defect is selective for CD4(+)8(-) cells; the maturation of CD4(-)8(+) and gamma delta T cells is normal. The autosomal recessive mutation underlying the HD phenotype is unrelated to MHC class II, since it segregates independently of the MHC class II locus. Moreover, the HD phenotype is not caused by a defect of the CD4 gene. Bone marrow transfer experiments demonstrate that the defect is intrinsic to cells of the hematopoietic lineage, i.e., most likely to developing thymocytes themselves. The frequency of CD4(+)8(low) intermediate cells is markedly increased in HD mice, suggesting that class II-restricted thymocytes are arrested at this stage. This is the first genetic defect of its kind to be described in the mouse and may prove highly informative in understanding the molecular pathways underlying lineage commitment.

Development of functional rat-derived T cells in SCID mice engrafted with the fetal thymus of LEC rats which are defective in CD4+ T cells

We reported that LEC rats are genetically deficient in the development of thymic CD4+8- cells and that this defect is caused by bone marrow (BM)-derived stem cells. To determine which BM-derived cells are responsible for the arrest of T-cell development in LEC rats, fetal thymuses of LEC rats, or LEA rats which bear the same major histocompatibility complex (MHC) as LEC rats but are immunologically normal, were engrafted under the kidney capsule of severe combined immunodeficiency (SCID) mice (LEC-TG and LEA-TG mice, respectively). We than examined the differentiation of T cells and their immunological functions in the SCID mice. A large number of rat-derived CD4+ T cells appeared in the peripheral blood, lymph nodes (LN) and spleens in LEC-TG mice. Furthermore, the peripheral LN cells in LEC-TG mice appeared to be functional. These cells produced IL-2 upon Con A stimulation, whereas LN cells from LEC rats produced no IL-2 in the same conditions. Thymopoiesis was observed at 3 weeks in LEC-TG as well as LEA-TG mice. The distribution of thymocyte subsets with respect to CD4 and CD8 expression in LEC-TG mice closely resembled that of LEA rat thymus and that in LEA-TG mice, suggesting that normal T-cell differentiation occurred in LEC-TG mice. The results indicated that BM-derived progenitor T cells of LEC rats could differentiate to functional CD4+ T cells.

Abnormal CD45RC expression and elevated CD45 protein tyrosine phosphatase activity in LEC rat peripheral CD4+ T cells

LEC rats are known to show a maturational arrest in the development of CD4+8+ to CD4+8- cells in the thymus. Despite the blockade of maturation of CD4+8-thymocytes, CD4+ T cells were observed in peripheral lymphoid organs, and these cells exhibit a defect in interleukin-2 (IL-2) production upon concanavalin A (Con A) stimulation. Although peripheral CD4+ cells in normal rat highly expressed CD45RC (CD45RChigh), the level of CD45RC expression was low (CD45RClow) in LEC rat peripheral CD4+ cells. However, CD4+ cells from both strains highly expressed CD45 when those cells were stained by pan-CD45 mAb, suggesting that LEC rat CD4+ cells are deficient in expression of the CD45RC isoform, but not of CD45 molecules. When backcross rats from (F344 x LEC)F1 x LEC were examined, the phenotype for CD45 expression pattern in CD4+ cells was clearly correlated with IL-2 production level in response to Con A stimulation. Thus, CD45RClow cells exhibit a defect in IL-2 production, while CD45RChigh cells show normal IL-2 production. Protein tyrosine phosphatase (PTPase) activity in the membrane fraction of LEC rat CD4+ cells was threefold higher than that of normal rat CD4+ cells. Con A stimulation led to an increase in tyrosine phosphorylation levels, especially 100- and 40-kDa proteins, in normal rat CD4+ cells. In LEC rat CD4+ cells, however, the level of tyrosine phosphorylation in those proteins were very low. These results suggest that an elevated CD45 PTPase activity is responsive for a defect in IL-2 production in LEC rat peripheral CD4+ T cells.

The diversity of T-cell receptor repertoire of peripheral CD4+ lymphocytes in LEC mutant rats

A novel mutant strain of rats, LEC, exhibits an arrest of T-cell maturation from CD4+CD8+ to CD4+CD8- but not the CD4-CD8+ cells in the thymus. Nevertheless, CD4+T cells arise in lymph nodes of LEC rats, implying extrathymic T-cell maturation. We analyzed the variable (V) and junctional region diversity of T-cell receptor (TCR) beta- chains in this population, since several reports have provided evidence that extrathymically matured T cells exhibit a biased expression of the TCR repertoire. CD4+ T cells in LEC rat lymph nodes exhibited a polymorphic V beta gene expression pattern. However, biased V beta gene expression was not identified in peripheral CD4+ T cells of LEC rats when compared with V beta gene expression in their thymocytes. Furthermore, junctional regions of TCR beta chains exhibited a vast diversity created by non-germline- encoded nucleotide (N nucleotide) additions. These results indicate that peripheral CD4+ T cells in LEC rats possess a vast diversity in the TCR repertoire as do thymocytes of the same rat, suggesting that they derive from the thymus.

Intestinal intra-epithelial lymphocytes in LEC mutant rats

LEC rat is a novel strain showing a maturational arrest from CD4+8+ to CD4+8- cells but not to CD4-8+ cells in the thymus. In this study, we examined if this mutation affects the differentiation of intestinal intra-epithelial lymphocytes (IEL) in LEC rats. In normal rat IEL, all 4 subsets with respect to the CD4/CD8 expression were observed. The CD4-8+ population was dominant and a unique population, CD4+8+, was observed as already shown in previous papers. Both CD4+8- and CD4+8+ cells were CD3+, TCR-alpha/beta +, CD45RC-, and CD5+, whereas CD4-8+ cells consisted of a heterogeneous population, being CD3+, TCR-alpha/beta +/-, CD45RC+/-, and CD5-. In LEC rat IEL, CD4+8- and CD4+8+ cells existed normally and distribution of CD4/CD8 subsets was not different from that of normal rat IEL. Furthermore, the expression pattern of CD3, TCR-alpha/beta, CD45RC and CD5 was not different from that of normal rat IEL in each subset. These results suggest that maturational arrest of CD4+8- thymocytes does not affect IEL maturation, especially maturation of CD4+8- IEL, suggesting that the IEL maturation mechanism for CD4+8- cells is independent of that of thymocytes.

Radiation hypersensitivity of LEC strain rats controlled by a single autosomal recessive gene

LEC strain rats (LEC rats), which are known to develop hereditarily spontaneous fulminant hepatitis 4-5 months after birth, were highly sensitive to whole-body X-irradiation when compared to WKAH strain rats. The radiosensitivity of F1 hybrids of LEC and WKAH rats was similar to that of WKAH rats and significantly lower than that of LEC rats. Segregation data of backcross hybrids (F1 x LEC and LEC x F1) suggested that the hypersensitivity of LEC rats to whole-body irradiation is controlled by a single autosomal recessive gene. The radiosensitivity of fibroblasts from LEC rats was higher than that of fibroblasts from WKAH rats. The repair process of DNA double-strand breaks in LEC cells was slower than that in WKAH cells. LEC rats could provide a useful animal model to assist in understanding the mechanism of radiation-induced DNA damage and repair.

Maturational arrest from CD4+8+ to CD4+8- thymocytes is caused by the bone marrow-derived cells in LEC mutant rats

LEC rats exhibit a congenital maturational arrest from CD4+8+ to CD4+8- but not to CD4-8+ cells in the thymus. To elucidate a cause of this mutation, bone marrow (BM) chimera rats were made between LEC and normal (WKAH) rats. In (WKAH-->LEC) BM chimera rats, donor-derived T cells matured normally, suggesting that LEC rat thymic stroma has a normal ability in supporting thymocyte differentiation. On the other hand in (LEC-->WKAH) BM chimera rats, LEC rat BM-derived T cells showed the arrest of maturation from CD4+8+ to CD4+8- cells in spite of having normal functions of WKAH rat-derived thymic stroma. In these chimeric rats, even though the maturational arrest from CD4+8+ to CD4+8- cells occurred in the thymus, CD4+ cells were found in peripheral lymph nodes (LNs), suggesting that these CD4+ cells differentiated extrathymically. These results suggest that the maturational arrest from CD4+8+ to CD+8- thymocytes is caused by BM-derived cells but not by thymic stroma.

Strain differences in change in airway responsiveness after repeated antigenic challenge in three strains of rats

1. The strain differences in 2,4-dinitrophenylated-Ascaris antigen-induced airway hyperresponsiveness (AHR) were investigated in three strains of rats: Brown-Norway (BN), Long-Evans Cinnamon (LEC) and Wistar. 2. Fourty-eight hour-passive cutaneous anaphylaxis titers after repeated challenge were highest in BN and lowest in LEC. 3. Twenty-four hours after the last challenge, a marked AHR and significant increase in wet/dry weight ratio of the main bronchus were observed only in Wistar. 4. Only the isolated bronchus of the challenged Wistar among the strains showed hyperresponsiveness to acetylcholine. 5. Wistar may be the best strain for antigen-induced AHR.

Ontogeny of T cell maturation in LEC mutant rats which bear a congenital arrest of maturation from CD4+CD8+ to CD4+CD8- thymocytes

LEC rats bear a congenital deficiency in CD4+CD8- thymocytes and peripheral CD4+ T cells, and consequently a deficiency in Th cell functions. Ontogeny of T cell maturation in normal and LEC mutant rats was, therefore, investigated. Prenatal development of thymocytes in normal rat strains, with respect to the expression of CD4/CD8 and TcR antigens, was similar to that of mice except that its kinetics was delayed by approximately 24 h. The kinetics of T cell maturation in LEC rats was comparable with that of normal rats up to day 19 of gestation, at which stage double-negative thymocytes (CD4-CD8-) developed into double positives (CD4+CD8+) through immature CD4-CD8+ subset. At day 19 of gestation in LEC as well as normal rats, double positives occupied approximately 80% of the total thymocytes, half of which were TcR-dull positive, indicating that TcR was normally rearranged and then expressed in LEC rat thymocytes. These data indicate that double negatives normally mature into at least double positives in LEC rats. Both single positives appeared after day 19 of gestation in normal rats, while in LEC rats CD4+CD8- cells did not appear, suggesting that the deficiency in CD4+CD8- cells is due to a congenital arrest of maturation from CD4+CD8+ to CD4+CD8- cells, but not due to a postnatal deletion.

Bone marrow-derived progenitor T cells convey the origin of maturational arrest from CD4+CD8+ to CD4-CD8+ thymocytes in LEC mutant rats

A mutant strain of rats, LEC, shows a novel arrest of T cell maturation from CD4+CD8+ to CD4+CD8- but not to CD4-CD8+ cells in the thymus. Transplantation of LEC rat fetal thymuses into the subcapsule of the kidney of athymic nude rats resulted in a normal maturation of thymocytes in the thymus graft. Furthermore, both single-positive thymocytes and peripheral lymph node T cells expressed T cell receptor alpha/beta antigen, and lymph node T cells acquired the ability to produce interleukin 2 upon mitogen stimulation. Transplantation of fetal thymuses from LEA rats, which express the same major histocompatibility complex haplotype as LEC rats, into LEC rat kidney subcapsule resulted in the maturational arrest from CD4+CD8+ to CD4+CD8- cells in the thymus graft. These data strongly suggest that bone marrow-derived progenitor T cells carry the cause of maturational arrest and that the thymic stroma of LEC rats has a normal potential to nurse thymocytes.