Macrophage cell cycling: influence of proliferative state on the antibody-mediated activities of rat resident peritoneal macrophages

Countercurrent centrifugal elutriation (CCE) was used to isolate fractions of rat resident peritoneal macrophages that were enriched in different phases of the cell cycle. The purpose was to assess the influence of the proliferative status of these cells on their antibody-mediated phagocytic activity. Autoradiographic analysis of the resident peritoneal cell population isolated 1 hr after an intravenous injection of [3H] thymidine showed that about 3% of the macrophages were in S-phase of the cell cycle. CCE yielded fractions of macrophages in which the proportions of S-phase cells ranged from 0% to about 10%. Results of flow cytometric analysis of propidium iodine-stained cells were consistent with the autoradiographic findings. Essentially all of the macrophages in the CCE fractions ingested antibody-coated particles, but there were marked differences in phagocytic capacity and in expression of Fc-receptors among discrete groups of cells. CCE fractions with the smallest cells and no S-phase macrophages ingested approximately six- to eightfold fewer particles than did macrophages from CCE fractions with the largest cells and enriched in S-phase macrophages. Similarly, smaller macrophages bound fewer antibody-coated particles than did larger macrophages. These results, which are identical to those previously reported for murine macrophage cell lines, show that the number of Fc-receptors and the phagocytic capacity of cycling resident peritoneal macrophages increase as the cells progress from G1 to G2. Thus, the proliferative state of macrophages does not determine whether they are phagocytic but rather their phagocytic capacity.