RAT MACROPHAGE LYSOSOMAL MEMBRANE ANTIGEN RECOGNIZED BY MONOCLONAL-ANTIBODY ED1

The monoclonal antibody (mAb) ED1 is being used widely as a marker for rat macrophages. The distribution of the recognized antigen in tissue s and isolated cells strongly supports this use as a macrophage marker , since the majority of macrophages are recognized and only seldomly a re other cell types stained by mAb ED 1. In the present study we furth er characterized the recognized antigen by a detailed description of t he localization of the antigen and by determining biochemical and func tional properties. We show that the antigen is expressed on the membra nes of cytoplasmic granules, like phagolysosomes, as well as on the ce ll surface. The amount of ED1 expression in a single cell can be corre lated to phagocytic activity of the respective cell type, but the mAb ED1 is not able to block latex phagocytosis or bacterial killing. The mAb ED1 appears to recognize a heavily glycosylated protein of 90 000- 110 000 MW, depending on the cell type used as antigen source. A possi ble relation with other known lysosomal glycoproteins with a similar m olecular weight is discussed.