Anti-(human LFA-1) monoclonal antibodies bind P815 murine tumour cells

Using anti-CD11a and anti-CD18 monoclonal antibodies (mAbs) directed respectively against the α and the β chains of LFA-1, we obtained an important and specific staining of P815 murine tumour cells. Both ascitic and cultured cells displayed a positive staining. Other murine tumours of haematopoietic origin, as well as lymphocytes or lymphoblasts from DBA/2 mice, were not labelled by the same monoclonal antibodies. These results were surprising since, to our knowledge, no case of cross-reaction between species has been reported with LFA-1. Moreover, competition assays showed that epitopes recognized by the two anti-CD11a antibodies were different from those identified by H35.89.9, a mAb raised against the murine LFA-1 α chain. Using allogeneic cytotoxic T lymphocytes, we also showed that anti-(human LFA-1) mAbs were unable to block the lysis of P815 by these effector cells. Thus, the putative functional properties of these structures, as well as their importance from an antigeneic point of view, remain to be assessed.