ANTIGEN ON MACROPHAGES TABLE I Monoclonal Antibodies

An antigen that clearly marked T helper cells was first identified when the W 3 / 2 5 mouse monoclonal ant ibody was raised against rat thymocytes (1, 2). T h e W 3 / 2 5 antigen appears to be equivalent to human T 4 antigen, which is now called CD4 (3), and to mouse L 3 T 4 antigen (4-6). Hencefor th , we will call the rat ant igen "CD4 (W3/25) ." Antibodies to CD4 antigens inhibit T helper cell responses in vitro (5, 7, 8) and the CD4 molecule has been sugested as a recogni t ion s t ructure for class II antigens (5, 9, 10). Since the CD4 (W3/25) ant igen seemed to have an impor tant role in T helper cell responses (7, 8), it was a surprise when Barclay (11) showed that the W3/25 ant ibody labeled rat peri toneal macrophages. In humans, ant i -T4 antibodies have also been shown to label macrophages (12, 13). However , thus far the molecular characteristics o f the CD4 antigens f rom macrophages have not been established in any species. In this paper we examine this point to de te rmine whether rat macrophages express authent ic CD4 (W3/25) antigen.