The function of the intraepithelial lymphocyte (IEL) network of T cell receptor (TCR) γδ+ (Vγ5+) dendritic epidermal T cells (DETC) was evaluated by examining several mouse strains genetically deficient in γδ T cells (δ−/− mice), and in δ−/− mice reconstituted with DETC or with different γδ cell subpopulations. NOD.δ−/− and FVB.δ−/− mice spontaneously developed localized, chronic dermatitis, whereas interestingly, the commonly used C57BL/6.δ−/− strain did not. Genetic analyses indicated a single autosomal recessive gene controlled the dermatitis susceptibility of NOD.δ−/− mice. Furthermore, allergic and irritant contact dermatitis reactions were exaggerated in FVB.δ−/−, but not in C57BL/6.δ−/− mice. Neither spontaneous nor augmented irritant dermatitis was observed in FVB.β−/− δ−/− mice lacking all T cells, indicating that αβ T cell–mediated inflammation is the target for γδ-mediated down-regulation. Reconstitution studies demonstrated that both spontaneous and augmented irritant dermatitis in FVB.δ−/− mice were down-regulated by Vγ5+ DETC, but not by epidermal T cells expressing other γδ TCRs. This study demonstrates that functional impairment at an epithelial interface can be specifically attributed to absence of the local TCR-γδ+ IEL subset and suggests that systemic inflammatory reactions may more generally be subject to substantial regulation by local IELs.

Aggregation of the high-affinity IgE receptor (Fc RI) on mast cells activates a tyrosine phosphorylation cascade that is required for adhesion and degranulation events leading to the release of histamine and other inflammatory mediators. The full range of intracellular mediators that regulate this process is unknown. Recent studies have identified a group of immune cell-specific adaptor proteins that include linker for activation of T-cell (LAT), SH2-domain-containing leukocyte protein (SLP-76), and Fyn-Tbinding protein (FYB)͞SLP-76-associated protein (SLAP). In this study, we demonstrate that FYB can up-regulate integrin-mediated adhesion to fibronectin and mediator release in RBL-2H3 mast cells. The regulation of these two events could be distinguished from each other by the requirement of the FYB SH3 domain in ␤-hexosaminidase release, but not adhesion, and the up-regulation of mediator release by FYB in nonadherent cells. Fc RI aggregation increased FYB tyrosine phosphorylation, whereas confocal immunofluorescence microscopy showed that FYB colocalizes with Factin in membrane ruffles and plaques. Our findings identify FYB as a regulator of integrin-mediated adhesion and degranulation events, which, in the case of mast cells, has potential applications to inflammatory and allergic responses. R ecent studies have identified a spectrum of immune cellspecific adaptors that integrate signals from surface receptors (1-3). These adaptors include linker for activation of T-cell (LAT), Grb2-related adaptor down-stream of Shc (Gads), SH2-domain-containing leukocyte protein of 76 kDa (SLP-76), Fyn-T-binding protein (FYB)͞SLP-76-associated protein of 130 kDa (SLAP-130), and src kinase-associated phosphoprotein of 55 kDa (SKAP55). LAT and SLP-76 are essential for proper thymic differentiation, T cell proliferation, and platelet-mast-cell function (4-8). The major binding partner of SLP-76 is the SH2 domain-binding protein FYB͞SLAP (9, 10). FYB also binds to and is preferentially phosphorylated by src kinase FYN-T (9, 11). Two isoforms of FYB at 120 and 130 kDa (FYB-120͞130) have been cloned and are restricted to T cells, monocytes, platelets (11,12), and mast cells (this article). Each isoform has Y 595 DDV͞Y 651 DDV and Y 624 DGI motifs for SLP-76 and FYN-T SH2 domain binding, respectively (11, 13), a proline-rich region that binds to the SH3 domain of SKAP-55 (14, 15), two putative nuclear localization sites (9), a C-terminal SH3-like domain that binds to a tyrosine-based RKxxYxxY motif in SKAP55 (16), and an Ena (Enabled)͞VASP (vasodilatorstimulated phosphoprotein) homology 1 domain (EVH1) binding site (17).The role of FYB͞SLAP as a positive or negative regulator of immune cell signaling has been the subject of much debate (9-12). FYB overexpression has been reported to either weakly potentiate (9) or to inhibit T cell antigen receptor (TcR) ͞CD3-driven IL-2 production (10). However, cotransfection of FYB with its binding partners Fyn-T and SLP-76 cooperates in the potent up-regulation of IL-2 transcription (11,12). T...

γδ T cells, a lineage of innate-like lymphocytes, are distinguished from conventional αβ T cells in their antigen-recognition, cell activation requirements and effector functions. γδ T cells have been implicated in the pathology of several human autoimmune and inflammatory diseases and their corresponding mouse models, but their specific roles in these diseases have not been elucidated. We report that γδTCR+ cells including both the CD27−CD44hi and CD27+CD44lo subsets infiltrate islets of pre-diabetic non-obese diabetic (NOD) mice. Moreover, NOD CD27−CD44hi and CD27+CD44lo γδ T cells were pre-programmed to secrete IL-17, or IFN-γ upon activation. Adoptive transfer of T1D to T and B lymphocyte-deficient NOD recipients was greatly potentiated when γδ T cells, and specifically the CD27− γδ T cell subset, were included compared to transfer of αβ T cells alone. Antibody-mediated blockade of IL-17 prevented T1D transfer in this setting. Moreover, introgression of genetic Tcrd deficiency onto the NOD background provided robust T1D protection, supporting a non-redundant, pathogenic role of γδ T cells in this model. The potent contributions of CD27− γδ T cells and IL-17 to islet inflammation and diabetes reported here suggest that these mechanisms may also underlie human T1D.