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Expression of Fc receptors on the plasma membrane of guinea pig peritoneal exudate macrophages (PEM) was suppressed to almost one-half of that of the controls by long-term exposure to lipopolysaccharide (LPS) or muramyl dipeptide (MDP) in culture. The effect of the reagents was dose and time dependent, and as little as 0.5 ng/ml LPS or 5 ng/ml MDP was effective for the suppression. The expression of the Fc receptors decreased to 60 to 70% of the control level at 48 hr and to 45 to 50% at 72 hr after incubation of the cells in the presence of LPS or MDP. A Scatchard plot of the binding of 125I-soluble immune complexes (I.C.) to the cells revealed that the decrease in the binding of 125I-I.C. is due to a reduction in the number of Fc receptors on the cell membrane and not to a decreased affinity of the receptors. The membrane protein was radio-labeled with 125I, and the Fc receptors were purified by being bound to insoluble I.C. The specific binding of the 125I-labeled Fc receptors, from the LPS-treated macrophages, to the insoluble I.C. was almost one-half of that from the untreated control cells. SDS-PAGE analysis of the purified 125I-labeled Fc receptors revealed that the major peak of the m.w. 44,000 molecule in the LPS-treated cells was almost one-half of that of the control. Contrary to the effect of LPS or MDP, 72-hr incubation of macrophages with MIF-rich supernatant, cultured from lymph node cells, enhanced the expression of Fc receptors. Macrophages were treated with I.C. for 4 hr at 37 degrees C to remove the Fc receptors from the surface membrane. The reappearance of the receptors on the plasma membrane of the cells was significantly suppressed by LPS and MDP. The effect of LPS on the binding of five murine monoclonal antibodies (Ab) raised against PEM to the macrophage membrane and also that of 125I-wheat germ agglutinin (WGA) or 125I-insulin was studied. The monoclonal Ab were selected for their activity to induce superoxide anion generation in the macrophages, as do I.C., although the binding sites for the monoclonal Ab were not related to Fc receptors. The bindings of the five monoclonal Ab were not affected by exposure of the cells to LPS or MDP. Macrophages treated with the reagents bound as much 125I-insulin or WGA as did the untreated control cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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