The role of IL-7 in thymic and extrathymic development of TCR gamma delta cells

IL-7-deficient (IL-7(-/-)) mice have reduced numbers of B and TCR alpha beta cells, but lack mature TCR gamma delta cells. Although most T cell development occurs in the thymus, some intestinal intraepithelial lymphocytes (IEL), including TCR gamma delta cells, can develop extrathymically. Epithelial cells in both thymus and intestine synthesize IL-7, suggesting that TCR gamma delta cell development could occur in either site. To evaluate the role of thymic IL-7 in development of TCR gamma delta cells, newborn TCR beta-deficient (TCR beta(-/-)) thymi were grafted to IL-7(-/-) mice. Donor- and host-derived TCR gamma delta cells were recovered from thymus grafts, spleen, and IEL. However, when IL-7(-/-) thymi were grafted to TCR beta(-/-) mice, no development of graft-derived TCR gamma delta cells occurred, indicating that extrathymic IL-7 did not support TCR gamma delta IEL generation from newborn thymic precursors. In contrast, TCR gamma delta IEL development occurred efficiently in adult, thymectomized, irradiated C57BL/6J mice reconstituted with IL-7(-/-) bone marrow. This demonstrated that extrathymic development of TCR gamma delta IEL required extrathymic IL-7 production. Thus, intrathymic IL-7 was required for development of thymic TCR gamma delta cells, while peripheral IL-7 was sufficient for development of extrathymic TCR gamma delta IEL.

The Role of IL-7 in Thymic and Extrathymic Development of TCRγδ Cells

IL-7-deficient (IL-7−/−) mice have reduced numbers of B and TCRαβ cells, but lack mature TCRγδ cells. Although most T cell development occurs in the thymus, some intestinal intraepithelial lymphocytes (IEL), including TCRγδ cells, can develop extrathymically. Epithelial cells in both thymus and intestine synthesize IL-7, suggesting that TCRγδ cell development could occur in either site. To evaluate the role of thymic IL-7 in development of TCRγδ cells, newborn TCRβ-deficient (TCRβ−/−) thymi were grafted to IL-7−/− mice. Donor- and host-derived TCRγδ cells were recovered from thymus grafts, spleen, and IEL. However, when IL-7−/− thymi were grafted to TCRβ−/− mice, no development of graft-derived TCRγδ cells occurred, indicating that extrathymic IL-7 did not support TCRγδ IEL generation from newborn thymic precursors. In contrast, TCRγδ IEL development occurred efficiently in adult, thymectomized, irradiated C57BL/6J mice reconstituted with IL-7−/− bone marrow. This demonstrated that extrathymic development of TCRγδ IEL required extrathymic IL-7 production. Thus, intrathymic IL-7 was required for development of thymic TCRγδ cells, while peripheral IL-7 was sufficient for development of extrathymic TCRγδ IEL.

Age-dependent intestinal lymphoproliferative disorder due to stem cell factor receptor deficiency: parameters in small and large intestine

Signaling through c-Kit/stem cell factor (SCF) is crucial for normal development of erythroid and myeloid hematopoietic precursors and of melanocytes and germ cells. While peripheral lymphoid populations of W/Wv and SI/SId mice appear normal, we demonstrated that the intraepithelial lymphocyte (IEL) populations of small (SI) and large (LI) intestine were significantly affected. IEL populations of young W/Wv animals were indistinguishable from those of their control littermates, but an age-dependent decrease in SI and LI TCRgamma delta IEL occurred in c-Kit mutant mice. In SI, but not in LI, this diminution was accompanied by gross expansion of TCRalpha beta IEL that resulted in significantly increased IEL:epithelial cell ratios in c-Kit mutant mice. Bromodeoxyuridine labeling studies revealed that the increase in cell numbers was due to lymphoproliferation that occurred in situ. Interestingly, TCRgamma delta IEL expressed cell surface c-Kit, while the expanding population of TCRalpha beta IEL did not. Analysis of radiation bone marrow chimeras demonstrated that the dysregulation required either disruption of stromal cell SCF or IEL c-Kit and showed that the effect on IEL or their precursors was not due to other changes in the intestinal microenvironment. Lamina propria T cell populations in these mice were unaffected, reinforcing the idea that the developmental requirements of these gut-resident lymphocyte populations are distinct. Overall, the results demonstrated that the development of intestinal TCRgamma delta IEL, regardless of location, shares common requirements for SCF, while SI and LI TCRalpha beta IEL may develop along distinct pathways. Possible mechanisms for the loss of proliferative regulation in gut T cells in c-Kit/SCF deficiency are discussed.

Age-dependent intestinal lymphoproliferative disorder due to stem cell factor receptor deficiency: parameters in small and large intestine

Signaling through c-Kit/stem cell factor (SCF) is crucial for normal development of erythroid and myeloid hematopoietic precursors and of melanocytes and germ cells. While peripheral lymphoid populations of W/Wv and SI/SId mice appear normal, we demonstrated that the intraepithelial lymphocyte (IEL) populations of small (SI) and large (LI) intestine were significantly affected. IEL populations of young W/Wv animals were indistinguishable from those of their control littermates, but an age-dependent decrease in SI and LI TCRgamma delta IEL occurred in c-Kit mutant mice. In SI, but not in LI, this diminution was accompanied by gross expansion of TCRalpha beta IEL that resulted in significantly increased IEL:epithelial cell ratios in c-Kit mutant mice. Bromodeoxyuridine labeling studies revealed that the increase in cell numbers was due to lymphoproliferation that occurred in situ. Interestingly, TCRgamma delta IEL expressed cell surface c-Kit, while the expanding population of TCRalpha beta IEL did not. Analysis of radiation bone marrow chimeras demonstrated that the dysregulation required either disruption of stromal cell SCF or IEL c-Kit and showed that the effect on IEL or their precursors was not due to other changes in the intestinal microenvironment. Lamina propria T cell populations in these mice were unaffected, reinforcing the idea that the developmental requirements of these gut-resident lymphocyte populations are distinct. Overall, the results demonstrated that the development of intestinal TCRgamma delta IEL, regardless of location, shares common requirements for SCF, while SI and LI TCRalpha beta IEL may develop along distinct pathways. Possible mechanisms for the loss of proliferative regulation in gut T cells in c-Kit/SCF deficiency are discussed.

Stem cell factor augments tumor necrosis factor-granulocyte-macrophage colony-stimulating factor-mediated dendritic cell hematopoiesis

We describe the effects of stem cell factor (SCF) on the dendritic cell (DC) pathway and provide evidence for the existence of a post granulocyte-macrophage colony-forming unit (GM-CFU) DC progenitor. When employed with cytokines regulating DC development (tumor necrosis factor [TNF] + GM colony-stimulating factor [GM-CSF]), SCF increased the size of monocyte (mono) and mono-DC colonies arising from cord blood CD34+ progenitor cells. The overall plating efficiency of these colonies increased approximately threefold, as compared with growth in TNF + GM-CSF. Most (approximately 70%) of the CFUs were mono-DC CFU, and SCF did not alter the proportion of mono-DC CFU to mono-CFU obtained with TNF + GM-CSF alone. Proliferation, as measured by thymidine uptake and manual cell counts, at least doubled and occurred earlier (by day 4). In long-term cultures established with TNF + GM-CSF + SCF, high levels of proliferation were prolonged for up to three weeks. These were associated with extended DC development and the capacity to form 2 degree mono-DC colonies. There was no induction of polymorphonuclear (PMN) cells in 2 degree cultures treated with either GM-CSF, GM-CSF + SCF or GM-CSF + granulocyte CSF (G-CSF), implying that the DC progenitor being replated was post GM-CFU. DC progeny arising in the presence of SCF exhibited typical DC features including: the lack of nonspecific esterase and phagocytic activity, the presence of class II major histocompatibility complex (MHC) antigens, the absence of CD14 antigens, and the ability to induce a potent mixed leukocyte reaction. Thus, SCF augments DC growth from progenitor cells without altering the developmental commitment instituted by TNF + GM-CSF. This enhancement follows the same general mechanisms previously reported for SCF-mediated lineage enhancement, i.e., increased colony size, number and plating capacity.