Rat lymphokine (LK) components of 500-2500 MW separated on Sephadex G-15 column (FrA) were tested for their effect on Fc and C3b receptor activities of rat resident (rPM) and thioglycollate-provoked (pPM) peritoneal macrophages. Functions of the receptors were studied by measuring the adherence and uptake of 51Cr-labeled sheep red blood cells (SRBC) mediated by isolated rat anti-SRBC IgM or IgG2a antibodies and human C3, respectively. On rPMs mainly Fcμ receptors (FcμRs) were affected by FrA; at low concentration (20 μ/ml) adherence was increased and phagocytosis was inhibited. At higher concentrations (40-80 μ/ml) a reverse effect was observed: adherence was inhibited and phagocytosis increased. On pPMs IgG2a-mediated functions were mainly affected by FrA with a concentration dependence like that observed with FcμRs on rPM monolayers. A concentration-dependent enhancement of C3b receptor (C3bR)-mediated adherence by FrA was observed on both PM types. On pPMs C3bR-mediated phagocytosis was enhanced as well.
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