FUNCTIONAL IMPLICATIONS OF THE EXPRESSION OF PILC PROTEINS IN MENINGOCOCCI

Multiple forms of PilC were found in Neisseria meningitidis (Nm) strai ns isolated from the oropharynx, blood or cerebrospinal fluid expressi ng either Class I or Class II pili. PilC expression was observed less frequently in case as opposed to carrier isolates. Moreover, PilC and pili were not always co-expressed. Several heavily piliated strains ha d no detectable PilC protein as determined by Western blotting using a n antiserum previously used to detect such proteins in adhesive varian ts (Nassif et al, 1994). Serogroup B strain MC58 produced large number s of pili, but expressed barely detectable amounts of PilC. A clonal v ariant of this strain with increased expression of PilC concurrently e xhibited increased adherence to Chang conjunctival epithelial cells an d human umbilical vein endothelial cells (Huvecs), but with more rapid binding to the former. No alteration in pilin sequence occurred in th is variant, suggesting the involvement of PilC in increased adhesion. A Pil(-) backswitcher isolated from the hyper-adherent variant was Pil C(+) but was non-adherent, indicating that any PilC adherence function requires pilus expression. Parental variant (low PilC) produced pili in bundles that were easily detached from the bacterial surface and we re frequently associated with Huvec surfaces after bacteria had been s heared off, but pili infrequently replaced bacteria during infection w ith the PilC-expressing variant. The hyper-adherent variant, which app eared to produce morphologically distinct pilus bundles, was able to w ithstand considerable shearing force and remained firmly attached to H uvecs. This raises the possibility that the observed hyper-adherence m ay arise from better anchorage of pili to the bacterial surface in add ition to increased adhesion to some host cell surfaces.