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.

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