Expression of the L8 lipopolysaccharide determinant increases the sensitivity of Neisseria meningitidis to serum bactericidal activity.

The influence of lipopolysaccharide (LPS) expression on the sensitivity of Neisseria meningitidis to serum bactericidal activity was investigated by using a series of variants that expressed different LPS determinants. For each of two different strains, a series of three LPS variants that expressed L3,7, L8, or both were analyzed. LPS variants were identified and monitored by colony blotting with murine monoclonal antibodies specific for the L8 or the L3,7,9 immunotype determinants. Differences in LPS expression were verified by analysis of proteinase K lysates of whole cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and then by silver staining or immunoblotting. The variants were used as test strains in bactericidal assays with human sera and with murine sera and monoclonal antibodies. Expression of the L8 LPS epitope was correlated with increased sensitivity to serum bactericidal activity. The geometric mean bactericidal titers of 12 to 16 sets of pre- and postvaccination sera were determined for each variant. Mean serum titers increased progressively with increased expression of L8 on the target strain. The bactericidal titers of anti-outer membrane protein monoclonal antibodies also increased with increased L8 expression.