Differential contribution of Lck and Fyn protein tyrosine kinases to intraepithelial lymphocyte development

The developmental stages and the role of protein tyrosine kinases (PTK) in the maturation of CD3(+)CD8 alpha alpha(+) intraepithelial lymphocytes (IEL) have not been extensively characterized. However, comparisons of thymic and extrathymic T cell development indicate that these processes involve some distinct signaling and selection events. We used mice deficient in Lck, Fyn, or both Lck and Fyn to analyze the role that these src-family PTK play in IEL development. In contrast to thymocyte development, we found that all IEL subsets develop in mice deficient for either kinase alone. However, lck(-/-) animals exhibited reduced numbers of TcR alpha beta(+)CD8 alpha alpha(+) IEL, indicating that Lck is important in the development of these cells. Mice which lack both Lck and Fyn fail to generate TcR alpha beta(+) IEL, suggesting that signaling through the preTcR, mediated by Lck and, to a lesser extent Fyn, is required for maturation of all TcR alpha beta(+) IEL lineages. Interestingly, a small population of TcR gamma delta(+)CD8 alpha alpha(+) cells are apparent in lck(-/-)fyn(-/-) animals, demonstrating that TcR alpha beta(+)CD8 alpha alpha(+) and TcR gamma delta(+)CD8 alpha alpha(+) IEL have distinct PTK requirements for their development or expansion. CD3(-)-CD8 alpha(-)CD44(+) and CD3(-)CD8 alpha alpha(+)CD16/32(+)B220(+) cells comprise the majority of IEL in both lck(-/-)fyn(-/-) and rag(-/-) mice, while they are poorly represented in wild-type controls. Comparison of the cell surface phenotype of these putative precursor IEL in lck(-/-)fyn(-/-) and rag(-/-) animals suggests that IEL maturation in these animals is arrested at an equivalent developmental stage. Overall, the data presented demonstrate that signals mediated by Lck or Fyn direct TcR alpha beta(+)CD8 alpha alpha(+) IEL maturation but are dispensable for the development of TcR gamma delta(+)CD8 alpha alpha(+) IEL.