Mac-1 antigen: quantitative expression in macrophage populations and tissues, and immunofluorescent localization in spleen.

The extent of Mac-1 expression by different macrophage populations and tissues has been examined and contrasted to that of la. Mac-1 is expressed on >86% of unelicited peritoneal macrophages as well as on macrophages elicited by thioglycollate, Con A, LPS, Listeria monocytogenes, or peptone, as determined by immunofluorescent flow cytometry analysis. All populations express similar quantities of Mac-1 /cell. The number of ''% M1/70 MAb bound per thioglycollate-elicited macrophage is 1.6 x lo5 at saturation. Immunoprecipitation from 35S-methionine labeled cells confirmed that macrophages elicited by diverse agents contain similar amounts of Mac-1 polypeptides of 170,000 and 95,000 M,. In contrast, the amount of la antigen in Con Aor Listeria-elicited macrophages is much higher than in unelicited macrophages or macrophages elicited by LPS or thioglycoflate. Mac-1 is thus a general marker for macrophages elicited by different means, even though the macrophages differ widely in functional activities and in la antigen expression. Tissue absorption studies show that the amount of Mac-1 expressed by spleen and bone marrow is 5 and 7% that of thioglycollate-elicited peritoneal exudate cells (PEC), respectively. Lung and liver weakly .absorb lZ5l-M1 / 7 0 whereas heart, kidney, and brain are not absorptive. When used in indirect immunofluorescent staining of frozen spleen sections, M1/70 intensely stains cells with macrophage morphology in splenic red pulp and marginal zone, but not the T-dependent areas of white pulp.