Mouse Anti-Human CD6 Hybridoma [4Qu23C9]

Background and Aims CD6 is a crucial regulator of T cell activation and is implicated in the pathogenesis of multiple autoimmune diseases. ALCAM is the first identified endogenous ligand of CD6. We sought to investigate potential roles of CD6 in regulating intestinal mucosal inflammation in inflammatory bowel disease [IBD]. Methods We analysed the expression of CD6 and ALCAM in the inflamed mucosa of IBD patients using qRT-PCR and immunohistochemistry. Phenotypic properties of CD6(low/-) and CD6(high)CD4(+) T cells were determined by flow cytometry, qRT-PCR, and ELISA. ALCAM Fc chimeric protein was used to evaluate the role of CD6-ALCAM engagement in regulating IBD CD4(+) T cell activation and differentiation. Results Expression of CD6 and its ligand ALCAM was markedly increased in the inflamed mucosa of IBD patients compared with that in normal controls, and was significantly correlated with disease activity indices of IBD patients. Interestingly, CD6(high)CD4(+) T cells of IBD patients exhibited significantly higher pathogenicity compared with CD6(low/-)CD4(+) T cells, characterized by enhanced T cell activation and preferential Th1 and Th17 cell phenotypes, but a markedly decreased proportion of nTreg [CD25(high)Foxp3(+), CD25(high)CD127(low)] cells. Importantly, inclusion of ALCAM Fc chimeric protein significantly facilitated IBD CD4(+) T cell, especially CD6(high)CD4+ T cell, differentiation into Th1/Th17 cells compared with hIgG1 Fc-treated controls. Conclusions These data indicate that overexpression of CD6 and ALCAM in the inflamed mucosa of IBD patients accelerates intestinal mucosal immune responses via promoting CD4(+) T cell proliferation and differentiation into Th1/Th17 cells. Thus, CD6 may serve as a novel therapeutic target for treatment of IBD.

CD6 is a 130 000 MW T-cell surface glycoprotein that can deliver coactivating signals to mature T lymphocytes. Studies using monoclonal antibodies (mAb) have defined at least four epitopes on CD6, and distinct functional responses are elicited by mAb to the different epitopes. The function of CD6 is unknown. Multiple CD6 ligands are predicted, based on data that a soluble CD6 fusion protein precipitates at least three peptides. A cDNA clone for one of these ligands, termed activated leucocyte-cell adhesion molecule (ALCAM) has recently been isolated. In order to further characterize the role of CD6 in cell-cell interactions, we have examined the role of CD6 in a variety of responses by tetanus toroid (TT) specific human T-cell clones. Anti-CD6 mAb UMCD6 (epitope 3) inhibits antigen-specific responses of such clones to TT, but not to the superantigen SEA. Responses of clones to nominal antigen are CD6-dependent using either peripheral blood mononuclear cells (PBMC) or macrophage-depleted E rosette negative cells as the antigen-presenting cell (APC) population. Furthermore, these clones made autoreactive with DNA methyltransferase inhibitors express increased CD6, and autoreactivity is inhibited by UMCD6. Taken together, the data suggests the existence of a functional CD6 ligand in peripheral blood which is expressed by APC, including cells other than macrophages. Interactions between CD6 and CD6 ligands may regulate both antigen specific and autoreactive responses of human T lymphocytes.