The role of resident and exudate macrophages in multinucleate giant cell formation

Peroxidase cytochemistry which differentiates "resident" from "exudate" peritoneal macrophages in guinea pigs, was used in the investigation of the multinucleate giant cells in foreign body granulomas in the peritoneal cavity of guinea pigs. Only a few, small syncytia (two to three nuclei) displayed the cytochemical characteristics of "resident" macrophages. On the other hand, most of the polykarya at the site of inflammation displayed a distribution of peroxidase activity similar to that of "exudate" macrophages. Irrespective of whether peroxidase cytochemistry distinguishes between a distinct type of macrophage or a specific functional stage, the evidence indicates that fusion is much more frequent between macrophages with "exudate" characteristics. Thus, fusion of these latter cells is responsible for the vast majority of multinucleate giant cells in inflammatory sites. In addition, some form of recognition mechanism between macrophages of similar cytochemical characteristics probably also operates since syncytia exhibited characteristics of either "exudate" or "resident" macrophages, but never both.