Anti-Mac-1 selectively inhibits the mouse and human type three complement receptor

Monoclonal antibodies (MAb) 1 have proven to be of great value in identifying the cellular lineages and subsets that give rise to the diversity of the immune system. Recently, interest has focused on the use of such antibodies to evaluate macrophage heterogeneity (1-5), and these reagents have added measurably to the information attained using heterospecific antisera (6). The first and perhaps best characterized of these antibodies, the rat anti-mouse M1/70 (anti-Mac-i) MAb, defines an antigen containing two polypeptides of 170,000 and 95,000 mol wt found on the surface of mouse macrophages, polymorphonuclear leukocytes (PMNL), and natural killer cells (1, 2, 7). The M1/70 MAb cross-reacts with human cells. Mac-1 has the same distribution in humans as in the mouse (8). To date, no function has been attributed to this antigen. The difficulty in ascribing function to antibody-defined cell surface structures has been a characteristic of studies on differentiation and cell type-specific antigens. Current evidence indicates that cells of the myeloid lineage (mononuclear phagocytes and PMNL) bear two distinct cell surface receptors for fragments of activate