EXPRESSION OF THE L8 LIPOPOLYSACCHARIDE DETERMINANT INCREASES THE SENSITIVITY OF NEISSERIA-MENINGITIDIS TO SERUM BACTERICIDAL ACTIVITY

The influence of lipopolysaccharide (LPS) expression on the sensitivit y of Neisseria meningitidis to serum bactericidal activity was investi gated by using a series of variants that expressed different LPS deter minants. For each of two different strains, a series of three LPS vari ants that expressed L3,7,L8, or both were analyzed. LPS variants were identified and monitored by colony blotting with murine monoclonal ant ibodies specific for the L8 or the L3,7,9 immunotype determinants. Dif ferences in LPS expression were verified by analysis of proteinase K l ysates of whole cells by sodium dodecyl sulfate polyacrylamide gel ele ctrophoresis and then by silver staining or immunoblotting. The varian ts were used as test strains in bactericidal assays with human sera an d with murine sera and monoclonal antibodies. Expression of the L8 LPS epitope was correlated with increased sensitivity to serum bactericid al activity. The geometric mean bactericidal titers of 12 to 16 sets o f 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 p rotein monoclonal antibodies also increased with increased L8 expressi on.