Interactions of invasive and noninvasive strains of Neisseria meningitidiswith monkey epithelial cells, mouse monocytes and human macrophages

Adherence and phagocytosis of invasive and noninvasive Neisseria meningitid is strains was investigated using light, fluorescence and electron microsco py. Invasive strains were isolated from the cerebrospinal fluid and/or bloo d of the patients with invasive meningococcal disease and noninvasive strai ns from the nasopharynx and/or larynx of healthy carriers. Adherence/endocy tosis was studied on monkey kidney cells (the LLC-MK2 cell line) and phagoc ytosis on mouse monocytes and human macrophages (the P388D1 and U-937 cell lines, respectively). Although invasive and noninvasive meningococci isolat ed in the same cluster showed identical genotype and phenotype markers, the y were found to interact differently with epithelial cells as well as with monocytes/macrophages. Invasive isolates displayed higher adherence to the surface of LLC-MK2 cells compared to noninvasive ones. Phagocytosis by P388 D1 cells of noninvasive strains was effective and the bacteria were damaged by cytolysis. In contrast, invasive bacteria frequently persisted in "coil ing" vacuoles and in effect could destroy the host cell. This is the first demonstration of coiling phagocytosis induced by meningococci. Efficiency o f phagocytosis by U-937 cells was significantly higher for the noninvasive than invasive strains. Different behaviour of invasive and noninvasive stra ins of N. meningitidis observed during 4 hours of interactions with epithel ial cells and monocytes/macrophages reflects well the higher pathogenic pot ential of invasive bacteria.