A monoclonal mouse anti-rat Ia antibody which cross reacts with a human HLA-DRw determinant.

A mouse monoclonal antibody, called MRC OX 3, which detects a polymorphic Ia determinant in the rat and cross reacts with an Ia determinant coded for by the I-A subregion in the mouse, detects a polymorphic determinant on human B cell lines. MRC OX 3 antibody binds to human B cell lines which express HLA-DRw specificities DRw 1, DRw2 and DRw6 but does not bind to those cells which only express other HLA-DRw specificities. No significant binding of MRC OX 3 antibody to either normal or mitogen stimulated human peripheral blood leukocytes, some of which are typed as HLA-DRw1, DRw2 or DRw6, could be detected. The binding of MRC OX 3 antibody to a human B cell line could be completely inhibited by pre-absorbing the antibody with purified rat Ia antigen.