INTERNALIN-A CAN MEDIATE PHAGOCYTOSIS OF LISTERIA-MONOCYTOGENES BY MOUSE MACROPHAGE CELL-LINES

Listeria monocytogenes internalin A (InlA) is a surface protein that m ediates the attachment of Listeria to, and invasion of, hepatocytes, e pithelial, and endothelial cells, In this study, we tested whether Inl A could also mediate phagocytosis oft. monocytogenes by the non-lister icidal mouse macrophage cell lines J774A.1 and H36.12j. Recombinant In lA (rInlA) was used to derive mouse monoclonal anti-InlA antibodies (m Ab) and rabbit anti-InlA antibodies, Fluorescence microscopy demonstra ted that these anti-InlA antibodies reacted with wild-type L. monocyto genes, L. ivanovii, and L. innocua(+), a mutant transformed with the i nlAB operon that expresses surface InlA but failed to react with Bug 8 , an InlA/InlB-negative transposon mutant of L. monocytogenes or with noninvasive Listeria sp. Fluorescence microscopy, radiolabeling, and f low cytometry showed that rInlA bound specifically to both macrophage cell lines, Incubation of macrophages and wild-type L. monocytogenes i n the presence of rInlA or pretreatment of Listeria with anti-InlA ant ibodies specifically inhibited, by at least 50%, the phagocytosis of l isteria by both of these cells, By comparison, treatment with these re agents failed to affect the phagocytosis of Streptococcus pyogenes by either macrophage cell line nor did these reagents alter the ability o f macrophages to internalize wildtype L. monocytogenes. We found that Bug 8, but not wild-type L, monocytogenes, failed to grow within both of these non-listericidal macrophage cell lines, In contrast to infect ion by wild-type L. monocytogenes, Bug 8 was rapidly eliminated from t he spleens of both C57Bl/6 and DBA/2 mice, Data presented here show th at only invasive Listeria sp, have surface InlA and that L. monocytoge nes can enter non-listericidal macrophage cell lines by binding of bac terial InlA to the macrophage cell surface.