Journal of leukocyte biology
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LL-37/hCAP-18 is the only human member of the cathelicidin family and plays an important role in killing various pathogens, as well as in immune modulation. In this study, we investigated the effect of LL-37 on bacterial phagocytosis by macrophages and demonstrate that LL-37 enhances phagocytosis of IgG-opsonized Gram-negative and Gram-positive bacteria in a dose- and time-dependent manner by dTHP-1 cells. In addition, LL-37 enhanced phagocytosis of nonopsonized Escherichia coli by human macrophages. ⋯ However, TLR4 signaling was also coupled to the phagocytic response, as a specific TLR4 antibody significantly suppressed phagocytosis of IgG-opsonized E. coli and nonopsonized E. coli by dTHP-1 cells. Finally, macrophages from Cnlp(-/-) mice exhibited diminished bacterial phagocytosis compared with macrophages from their WT littermates. In conclusion, we demonstrate a novel, immune-modulatory mechanism of LL-37, which may contribute to bacterial clearance.