Roles of the Src Tyrosine Kinases Lck and Fyn in Regulating γδTCR Signal Strength

Abstract

Lck and Fyn, members of the Src family of tyrosine kinases, are key components of the αβTCR-coupled signaling pathway. While it is generally accepted that both Lck and Fyn positively regulate signal transduction by the αβTCR, recent studies have shown that Lck and Fyn have distinct functions in this signaling pathway, with Lck being a positive regulator and Fyn being a negative regulator of αβTCR signal transduction. To determine whether Lck and Fyn also differentially regulate γδTCR signal transduction, we analyzed γδ T cell development and function in mice with reduced Lck or Fyn expression levels. We found that reducing Lck or Fyn levels altered the strength of the γδTCR signaling response, with low levels of Lck weakening γδTCR signal strength and low levels of Fyn augmenting γδTCR signal strength. These alterations in γδTCR signal strength had profound effects not only on αβ/γδ lineage choice, but also on γδ thymocyte maturation and γδ T cell effector function. These results indicate that the cellular levels of Lck and Fyn play a role in regulating the strength of the γδTCR signaling response at different stages in the life of the γδ T cell.

Unexpected Role for the B Cell-Specific Src Family Kinase B Lymphoid Kinase in the Development of IL-17–Producing γδ T Cells

“…Paradoxically, although the thymic and peripheral γδ T cells in γδTCR Tg Blk −/− mice had all the earmarks of cells that have received a strong TCR signal, αβ/γδ lineage commitment was not affected, as evidenced by the comparable numbers ofαβ and γδ lineage cells in the thymuses of γδTCR Tg Blk −/− and γδTCR Tg Blk +/+ mice. This is in contrast with the results of previous studies, in which augmenting γδTCR signal strength consistently resulted in fewer αβ lineage cells (18,52,53). An explanation for these findings is that TCR-induced Blk activity is not required at the stage when αβ/γδ lineage commitment occurs but instead is required at a later developmental stage, after adoption of the γδ lineage fate.…”

“…Because γδ T cells from the Vγ6/Vδ1 γδTCR Tg mouse have the ability to acquire different effector fates (18), which match those reported for this γδ T subset following activation in vivo (34), we used our γδTCR Tg system to assess the effects of Blk-deficiency on γδ T cell effector function. To this end, we examined cytokine production by γδ T cells following TCR activation and found that the percentage of stimulated γδ T cells producing IL-17 is drastically reduced in γδTCR Tg Blk −/− mice compared to γδTCR Tg Blk +/+ mice (Fig.…”

“…1 B ), we estimate that these γδ T cells express ~200,000 molecules of Blk per cell. This amount is even more striking given that LN γδ T cells express significantly less Lck and Fyn than γδ thymocytes (18). These data indicated that Blk is the predominant SFK expressed in γδ thymocytes and in the mature Blk + γδ T cell subset.…”

“…Flow cytometric analysis for both surface and intracellular Ags was performed as previously described (18). …”

“…γδ T cells from γδTCR Tg Blk −/− and γδTCR Tg Blk +/+ mice were stimulated as previously described (18). …”