Increase of surface Ia-like antigen expression on human monocytes independent of antigenic stimuli.

Abstract

Abstract The temporal expression of la-like antigen (la antigen) on the surface of isolated peripheral blood monocytes and peritoneal washing cells was quantitated by using a fluorescence-activated cell sorter. Regardless of the specific technique of isolation, all such cells demonstrated the presence of la antigen on the surface membrane, although in widely varying amounts per cell. No la-negative subpopulation was detected. When cells were cultured in vitro with or without serum and without the addition of any specific phagocytic or antigen stimulus, a marked increase (2- to 3-fold) in the average amount of surface antigen per cell measured by quantitative immunofluorescence occurred over the first 12 hr of culture. Thereafter, the amount of antigen declined slightly over the next 3 days. This increase in la antigen did not occur on human B cells under similar culture conditions. Moreover, the expression of another well-defined monocyte surface antigen (mac-1) failed to show an increase; it declined with time on cultured monocytes. The increase in la antigen on monocytes was not influenced by the method that was used to prepare the cells, the concomitant presence of T cells, the addition of supernatant from phytohemagglutinin- (PHA) stimulated lymphocyte cultures, the presence of autologous serum, or by the phagocytosis of opsonized latex particles or heat-killed bacteria by the monocytes. The increase was, however, inhibited by cycloheximide and puromycin and by keeping the cells at 2°C. We conclude that all the monocytes recoverable from human blood express the la antigen, that this antigen shows a unique increase in expression on the surface of these cells over the first several hours after their removal from the blood that is independent of any phagocytic or immunologic stimulus, and that this increase requires both metabolic energy and protein synthesis.