Analysis of the human CD36 leucocyte differentiation antigen by means of the monoclonal antibody NL07

The murine monoclonal antibody (MoAb) NL07 was generated by immunization with human platelet extracts. NL07 MoAb recognized a molecule expressed by human platelets, monocytes, and endothelial cells, as well as by the myelomonocytic line U937 and by some melanoma cells or lines. Normal endothelial cells and the melanoma cells express the NL07 epitope only while adhering to a substrate. SDS-polyacrylamide gel electrophoresis and two-dimensional gel analysis indicate that the molecule recognized by NL07 MoAb on platelets is a single chain structure featuring a molecular weight of 85 kDa under reducing conditions, with an acidic isoelectric point ranging from 5.2 to 5.5. The specific phenotype distribution and the biochemical structure indicate that NL07 MoAb recognizes the platelet GPIV (CD36) molecule, a surface glycoprotein with a functional role of thrombospondin receptor. The results of competition tests with OKM5 MoAb (specific for the CD36 molecule) confirm the molecular specificity and epitope coincidence. Furthermore, upon binding to the platelets, NL07 MoAb is able to transmit via CD36 an activation signal which is followed by a potent aggregation. On the contrary, there is lack of evidence concerning the ability of the CD36 molecule of transmitting signal(s) on the U937 cells.