Arrest of DNA Replication of Macrophages in BCG Granuloma and Peritoneal Exudates by Bacteria

Previously we found that bacterial surface substances induced the suppression of DNA synthesis of macrophages. We examined in the present study whether DNA synthesis of macrophages could be similarly suppressed by whole bacteria themselves. For this purpose we isolated macrophages from BCG granuloma of guinea pigs and rats. The macrophages from both of the animals gave essentially the same results. No isolated macrophages containing bacilli were found to incorporate 3H-thymidine when tested by autoradiography. Further, DNA replication of peritoneal exudate macrophages was markedly and rapidly suppressed in vitro upon phagocytosis of various kinds of bacteria but not of non-bacterial preparations. A close correlation was found between granuloma formation and inhibition of 3H-thymidine incorporation by MDP, its analogs, and various bacteria. These findings suggest that macrophages suppress their DNA replication when they phagocytose bacteria and that they can discriminate between bacteria and non-bacterial preparations.