Epitopic Heterogeneity of the CD36 Antigen Expressed by Normal and Neoplastic Endothelial Cells: An Immunohistochemical Study with a Novel Monoclonal Antibody 8C9

Phenotypic and functional heterogeneity of endothelial cells (ECs) is being recognized with increasing frequency. Here we report a novel murine monoclonal antibody (MoAb), named 8C9, that detects a unique epitope on the leukocyte differentiation antigen CD36 (platelet glyco‐protein IV or Illb) expressed by both normal and neoplastic ECs. In immunohistochemical and flow cytometric studies, 8C9 immunoreactivity was detected on capillary ECs, adipocytes, monocytes, platelets and a human monocytoid cell line U 937, which are known to express the CD36 antigen. Blocking experiments using U ‐937 cells and studies on cryostat sections revealed that a murine MoAb OKM5, which detects the CD36 antigen, blocked the binding of 8C9 to its antigen. lmmunoblot analysis showed that 8C9 bound to a 97‐kDa membrane protein expressed by U 937 cells treated with phorbol ester. These results indicate that 8C9 detects the CD36 antigen. However, the findings that some OKMS‐ positive normal ECs in the liver, spleen and lymph nodes as well as neoplastic ECs in a cutaneous angiosarcoma did not react with 8C9, together with the fact that the CD36 antigen does not form a complex or associate with other proteins, suggest epitopic heterogeneity of the CD36 antigen expressed by these tissues. Acta Pathol Jpn 42: 807–817, 1992.