Fc- And Non-Fc-Mediated Phagocytosis Of Borrelia Burgdorferi By Maerophages

The Fe receptor (FeR) for immunoglobulin has been assigned a major role in the ingestion of Borrelia burgdorferi,</it> the Lyme disease spirochete, by macrophages. Yet macrophages readily take up and kill B. burgdorferi</it> that have not been opsonized. By use of doubly-labeled macrophages infected with spirochetes and analyzed by confocal fluorescence microscopy, simultaneous localization of both FeR and spirochetes (opsonized and unopsonized) was quantified. After infection with unopsonized spirochetes, bacterial surface antigen and the FeR remained distinct, confirming the expectation that unopsonized uptake of B. burgdorferi</it> is largely independent of the FeR. A similar lack of colocalization was seen when opsonized spirochetes were ingested by macrophages whose FcRs were sequestered by an immune complex-coated substrate. Furthermore, comparable efficiency of uptake was observed whether or not the FcR was engaged.