Function of lipopolysaccharide in the invasion of Neisseria gonorrhoeae into human mucosal cells.

The variable incorporation of sialic acid into the LPS of Neisseria gonorrhoeae modulates the invasive behavior of this bacterium towards cultured human epithelial cells. Here we report that the inhibitory effect of LPS sialylation on the gonococcal entry into Chang epithelial cells and ME-180 endocervical cells (van Putten, EMBO J 12:4043-4051, 1993) is located early in the uptake pathway upstream of the invasion-associated recruitment of F-actin at the sites of bacterial entry, but beyond the level of bacterial adherence. Receptor equilibrium studies using purified radiolabelled opacity protein receptor demonstrated that LPS sialylation caused a 3-5 fold reduction in binding of the bacterial invasion-promoting opacity outer membrane protein to its receptor. In HEC-1B and PC-3 cells, LPS sialylation did only partially inhibit the bacterial entry process, suggesting the existence of a second uptake mechanism for gonococci in these cell lines. Experiments with non-sialylatable and truncated isogenic LPS variants, and with genetically defined LPS mutants demonstrated that the invasive phenotype of N. gonorrhoeae requires a minimum of an Rc (or Rd1) chemotype of LPS. Variation within the LPS outer core region did not influence the invasive properties of the bacteria as long as there was no attached sialic acid.