Macrophage-Eosinophil Interactions in the Inflammatory Response to Trichinella spiralis

Little is understood of the reasons why eosinophils accumulate in vivo, although a tissue reaction to administered antigen has been shown to be a prerequisite for the response. The present experiments aim to understand the significance of the tissue reaction to parasitic larvae in the chain of events leading to eosinophilia. Trichinella spiralis larvae were injected intraperitoneally in rats, and the peritoneal exudate was examined at intervals. Eosinophils were closely associated with macrophages rather than with other cell types or with parasites. A striking collection of eosinophils around individual macrophages was noted 48 hr after injection, and in particular following a second challenge. Use of indirect immunofluorescence techniques showed that these coincided with presence of immunoglobulin on macrophage surfaces. Incubation of peritoneal cells in medium containing 0.25% trypsin reduced macrophage surface immunofluorescence and numbers of rosettes. Rosettes could be constituted in vitro by incubation of normal peritoneal cells in medium containing antigen and antibody. These findings suggest that in the tissue reaction to parasitic larvae a close association exists between eosinophils and macrophages.