Expression of major histocompatibility complex antigens on macrophages: correlative study using flow cytometry, radioimmunoassay, and colloidal gold immunolabeling.

Correlative scanning electron microscopy (SEM), radioimmunoassay (RIA), and flow cytometric analysis were used to characterize levels of class I and class II major histocompatibility complex-encoded (MHC) antigen expression on peritoneal exudate cells of mice chronically infected with Chlamydia psittaci. Analysis of peritoneal macrophages by all three techniques revealed a marked induction of H-2 K,D (class I) and I-A, I-E (class II) antigens on cells from infected C3H mice when compared to uninfected controls. Scanning electron micrographs further document that the increases in class I and II MHC antigens are due to an increase in Ia/H-2 bearing cells as well as an increase in MHC molecules/cell. These immune macrophages have a flattened morphology, almost completely devoid of the membrane ruffles and villi which are characteristic of control peritoneal macrophages. These studies suggest that while both flow cytometry and RIA can provide an accurate quantitative estimate of antigen expression in a cell population, the immunogold labeling technique can allow visualization of individual cells and additional analysis of the topographical distribution of cell surface antigens.