Enhancement of carrier-mediated transport after immunologic activation of peritoneal macrophages

Abstract

Immunologically activated peritoneal macrophages from inbred mice and Hartley strain guinea pigs demonstrate a markedly greater than normal transport of 2-deoxy-D-glucose and L-leucine. The degree of nutrilite transport enhancement was greatest when animals were injected with the appropriate eliciting antigens before harvesting and also, if antigen was included in the tissue culture medium during the initial hours of in vitro culture. Enhanced hexose and amino acid uptake could also be achieved by exposure of macrophages from nonimmunized animals for 48 hr to supernatants of sensitized splenic lymphocyte cultures incubated with specific antigens. The animal systems in which this phenomenon was observed included CBA/J and C57BL/6J mice immunized with Staphylococcus aureus or sub-lethal doses of Listeria monocytogens, and the Hartley strain, albino guinea pig immunized with S. aureus or BCG. In all cases, immunization resulted in a state of delayed hypersensitivity as measured by skin testing or footpad swelling. Splenic cell supernatants contained lymphokines as detected by the presence of macrophage inhibitory factor (MIF), and by the supernatants' capacity to stimulate incorporation of 14C-glucosamine by macrophages in vitro. No increase of glucose or leucine transport by macrophages was observed in the absence of appropriate antigen stimulation in vivo or in vitro. We previously showed that a phagocytic stimulus results in a significant increase in hexose transport by normal macrophages; leucine transport by these same cells was unaltered after phagocytosis. In contrast, immunologically activated macrophages do not transport measurably more 2-deoxy-C-glucose after particle ingestion; activation or the phagocytic stimulus enhance 2-deoxy-C-glucose uptake to approximately the same extent. Analysis of nutrilite transport kinetics revealed that immunologic activation of macrophages increases the initial velocity (V1) and Vmax but does not change the Km values of hexose or amino acid transport. The kinetics of transport by the immunologically activated macrophages do not change measurably after phagocytosis. We conclude that either immunological activation or phagocytosis results in augmented 2-deoxy-D-glucose transport via identical or related mechanisms and that transport of the sugar can't be increased above that level induced by either event. The reasons why immunologic activation increases both glucose and leucine transport but phagocytosis increases only the former are not yet understood.