Identification of two subpopulations of rat monocytes expressing disparate molecular forms and quantities of CD43

Expression of CD43 (leukosialin, sialophorin) by rat blood monocytes was analyzed by flow cytometric, microscopic, and biochemical techniques. Monocytes were identified cytometrically using a combination of light-scatter parameters and binding of the anti-monocyte/macrophage monoclonal antibody (mAb) OX-41. Two-color flow cytometry studies with W3/13 and HIS 17, two anti-CD43 mAb that react with different antigenic epitopes, revealed two subpopulations of monocytes expressing disparate levels of CD43 (referred to hereafter as hi-CD43 MO and lo-CD43 MO). In three-color flow cytometry studies, hi-CD43 MO were found to express higher levels of CD4 than lo-CD43 MO; in contrast, lo-CD43 MO bound higher levels of RP-3, a mAb raised against rat neutrophils. Hi- and lo-CD43 MO expressed comparable amounts of CD14, CD45, and intercellular adhesion molecule-1 (CD54); hi-CD43 MO expressed somewhat more lymphocyte function-associated antigen-1 alpha chain (CD11a) and CD18 than their lo-CD43 MO counterparts. A minority of cells in both subpopulations expressed class II histocompatibility antigens. Hi- and lo-CD43 MO isolated by fluorescence-activated cell sorting had features typical of monocytes as assessed by light and electron microscopy. In Western blotting experiments, lo-CD43 MO and elicited peritoneal macrophages were found to express a less heavily sialylated form of CD43 than hi-CD43 MO.