Some properties of the plasma membrane of macrophages from germ-free rats

The mobility of plasma membrane receptors for lectins concanavalin A (Con A), phytohemagglutinin (PHA), garden pea agglutinin (PSA), lentil agglutinin (LCA), peanut agglutinin (PNA), soybean agglutinin (SBA), wheat germ agglutinin (WGA), and perch spawn agglutinin (PFA), the presence of binding sites for sheep erythrocytes, the presence of Fc and complement receptors, as well as pinocytic and phagocytic activities were investigated in normal peritoneal macrophages from conventionally reared (CV) and germ-free (GF) rats. Differences varying according to the lectin used were found in lectin-receptor-complex lateral mobilities measured as a function of patch and cap formation. Germ-free-rat-derived macrophages showed a significant decrease in the average amount of SBA binding sites per cell as determined by 125I-SBA labeling. The percentage of complement- and Fc-receptor-bearing macrophages was lower in GF rats, in contrast to the higher percentage of macrophages forming spontaneous rosettes with sheep erythrocytes. The pinocytic activity as determined by the neutral red uptake assay exhibited a threefold increase in GF rat-derived macrophages in comparison to CV ones. On the other hand, phagocytosis was more intense in macrophages from conventional rats, as detected by the engulfing of CdCO3 microcrystals. Our results, together with other recent reports, indicate that the earlier opinion that the peritoneal macrophages of GF animals do not differ essentially from those of conventional ones needs to be revised.