The mucosal T cell integrin αM290β7 recognizes a ligand on mucosal epithelial cell lines

The integrin αM290β7 is expressed at high levels on mucosal T cells, particularly on those within the epithelium of the gut. We now report that a mouse T cell hybridoma, MTC‐1, with similar surface expression of this molecule, adhered strongly to cells of the mouse rectal carcinoma line CMT93 and that adhesion was blocked completely by the monoclonal antibody (mAb) M290. Other mAb to the αM290 or β7 subunits had little or no inhibitory effect. M290 also inhibited adhesion of the hybridoma to cells of the mouse lung carcinomas CTM64/61 and KLN205 but had little or no effect on adhesion to seven other mouse epithelial cell lines or to the human colon carcinoma line, HT29. Intraepithelial lymphocytes (IEL) isolated from the small intestine of BALB/c mice displayed potent Tcell receptor‐dependent cytotoxic effector function against CMT93 in the presence of low concentrations of Phytolacca americana lectin. This cytotoxic activity also was inhibited by the M290 mAb. Treatment of CMT93 cells with tumor necrosis factor‐a and interferon‐γ induced expression de novo of ICAM‐1 and reduced the inhibitory effect of M290 in tests both for adhesion and cytotoxicity. In further experiments cytotoxic activity of IEL against the mastocytoma P815 was investigated. This target cell was considered not to possess a ligand for the integrin. In this case cytotoxic effector function was triggered by anti‐CD3 mAb and, in contrast to results with CMT93, target cell lysis was increased in the presence of M290 and other antibodies to the integrin, suggesting a co‐stimulatory effect. These results show that αM290β7 recognizes a ligand on the surface of certain epithelial cell lines. Further, they provide the first clear indication that this integrin may play an important role in functional interactions between T cells and the mucosal epithelium.