Interactions of Phagocytes with the Lyme Disease Spirochete: Role of the Fc Receptor

The phagocytic capacity of murine and human mononuclear and polymorphonuclear phagocytes (including peripheral blood monocytes and neutrophils), rabbit and murine peritoneal exudate cells, and the murine macrophage cell line P388D1 against the Lyme disease spirochete was studied. All of these cells were capable of phagocytosing the spirochete; phagocytosis was measured by the uptake of radiolabeled spirochetes, the appearance of immunofluorescent bodies in phagocytic cells, and electron microscopy. Both opsonized and nonopsonized organisms were phagocytosed. The uptake of opsonized organisms by neutrophils was blocked by a monoclonal antibody specific for the Fc receptor and by immune complexes; these findings suggested that most phagocytosis is mediated by the Fc receptor. Similarly, the uptake of opsonized organisms by human monocytes was inhibited by human monomeric IgG1 and by immune complexes. These results illustrate the role of immune phagocytosis of spirochetes in host defense against Lyme disease.