The (alpha2-->8)-linked polysialic acid capsule of group B Neisseria meningitidis modifies multiple steps during interaction with human macrophages

Abstract

Group B Neisseria meningitidis causes systemic disease, including meningitis, after initial colonization and subsequent penetration of nasopharyngeal mucosa, a tissue which is richly populated by macrophages. In an initial effort to characterize the interaction of N. meningitidis and mature human macrophages, the influence of the (␣238)-linked polysialic acid capsule on the interaction of N. meningitidis with human monocyte-derived macrophages was investigated with a capsulate case isolate and an isogenic Tn916-derived noncapsulate transformant. The capsulate strain was fourfold less adherent to the macrophage surface after cold incubation, although adherence of both strains was significantly increased after opsonization with nonimmune C5-depleted serum. When opsonized inocula were adjusted so that they adhered to macrophages in equal numbers, the two strains were internalized at equivalent rates and both entered membrane-bound compartments (phagosomes). Colocalization of bacteria with the late endosomal and lysosomal marker lysosome-associated membrane protein revealed that fusion of lysosomes with phagosomes containing the capsulate organism was significantly reduced 10 and 30 min after entry, but by 1 h, no difference between the strains was observed. Once internalized, meningococci were effectively killed, although more rapid killing of the capsulate strain was observed over the first 3 h. These results indicate that the (␣238)-linked polysialic acid capsule modifies the interaction of meningococci with human macrophages at multiple steps, including adherence to the macrophage surface and phagosome-lysosome fusion. Moreover, the discordance between the kinetics of phagosomelysosome fusion and bacterial killing suggests that a nonlysosomal mechanism may be responsible for a significant fraction of macrophage killing of N. meningitidis.

Glutamate utilization promotes meningococcal survival in vivo through avoidance of the neutrophil oxidative burst

“…We successfully isolated primary human PMNs (demonstrated by their expression of surface markers including CD68, CD11b, CD18 and CEACAMs, and neutrophil elastase), and showed the anti-phagocytic effect of the polysaccharide capsule of N. meningitidis as demonstrated previously (Read et al, 1996;Unkmeir et al, 2002). Interestingly, our assays showed that, compared with E. coli and S. flexneri, wild-type N. meningitidis exhibits enhanced survival when in association with PMNs as does N. gonorrhoeae (Veale et al, 1979).…”

Critical determinants of the interactions of capsule-expressing Neisseria meningitidis with host cells: the role of receptor density in increased cellular targeting via the outer membrane Opa proteins

“…Down-modulation of meningococcal OMP-mediated adherence by surface sialic acids has been frequently observed (Stephens et al, 1993;Virji et al, 1995a;Read et al, 1996;McNeil and Virji, 1997;Hardy et al, 2000). As adhesins such as Opa and Opc are integral OMPs located beneath the capsule, one obvious explanation for such down-modulation is steric hindrance/physical masking by the polysaccharide.…”

Co-ordinate action of bacterial adhesins and human carcinoembryonic antigen receptors in enhanced cellular invasion by capsulate serum resistant Neisseria meningitidis

“…Our previous studies and those of others have shown that under the influence of invasins, meningococci lacking capsule invade target cells more readily than fully capsulate bacteria (Virji et al, 1993;Read et al, 1996;Deghmane et al, 2000;Hardy et al, 2000). As capsule is subject to natural phase variation and capsule expression may also be controlled by environmental conditions or signals from target cells (Masson and Holbein, 1985;Deghmane et al, 2002), we assessed the internalized phenotype with respect to the expression of capsule and other major surface factors.…”