Antigens of activated rat T lymphocytes including a molecule of 50,000 M sub(r) detected only on CD4 positive T blasts

Mouse monoclonal antibodies (MAbs) have been prepared against rat T cell blasts. One MAb called MRC OX-40 recognized an antigen that differed from any previously described in that its expression was detected only on T blasts that also expressed the CD4 antigen. The OX-40 MAb did not detect an activation determinant of CD2 or CD4 molecules but recognized a distinct chain of mol. wt 50,000. The OX-40 MAb augmented T cell proliferation at late stages on in vitro responses. Other MAbs without obvious counterparts in other species were MRC OX-48 and MRC OX-49, 50 which recognized cell surface molecules of mol. wts of about 95,000 and 90,000, respectively. The MRC OX-39 MAb was found to bind the rat IL-2 receptor.