FC-MEDIATED AND NON-FC-MEDIATED PHAGOCYTOSIS OF BORRELIA-BURGDORFERI BY MACROPHAGES

The Fc receptor (FcR) for immunoglobulin has been assigned a major rol e in the ingestion of Borrelia burgdorferi, the Lyme disease spirochet e, by macrophages. Yet macrophages readily take up and kill B. burgdor feri that have not been opsonized. By use of doubly-labeled macrophage s infected with spirochetes and analyzed by confocal fluorescence micr oscopy, simultaneous localization of both FcR and spirochetes (opsoniz ed and unopsonized) was quantified. After infection with unopsonized s pirochetes, bacterial surface antigen and the FcR remained distinct, c onfirming the expectation that unopsonized uptake of B. burgdorferi is largely independent of the FcR. A similar lack of colocalization was seen when opsonized spirochetes were ingested by macrophages whose FcR s were sequestered by an immune complex-coated substrate. Furthermore, comparable efficiency of uptake was observed whether or not the FcR w as engaged.