PMC

Bactericidal activity of convalescent-phase serum HCC010 against strain 9162 L3,7 was depleted by incubation with different solid-phase antigens, including conjugates of sialylated and nonsialylated LNnT. The concentration of NOMV is based on LPS content by KDO assay, and LPS and lacto-N-neotetraose conjugates are based on dry weight.

The bactericidal depletion curves shown were obtained with serum 145-18 and are typical of those obtained with sera from Chilean children having naturally occurring bactericidal antibodies to test strain 8532(B:15:P1.7-2,3:L3,7,8). The antigen concentration is the concentration of antigen that was put in the wells of the plate. A series of concentrations was tested for each antigen. Antigen concentrations were based on protein for NOMV and on dry weight for purified LPS. NOMV contained about 25% LPS.

The representative bactericidal depletion curves shown were obtained with the human convalescent-phase serum HC010 by preincubation with different solid-phase antigens. The test strain was 9162 L3,7. Strain 8532 PorA(−) was a spontaneous mutant of strain 8532, an isolate from the same epidemic clone as 9162 and with the same antigenic profile. The values are the means from duplicate tests, and the error bars show the standard deviations. The antigen concentrations for both NOMV and purified LPS are based on LPS content, using a value of 25% LPS relative to protein for the NOMV.

A normal human serum (HN026) was tested for specificity of bactericidal activity toward strain 9162(B:15:P1.7-2,3:L3,7) using the bactericidal depletion assay. “WC” indicates whole cells. The concentration is based on protein for NOMV and on dry weight for purified LPS. In the case of the whole cells, a concentration of 100 corresponds to an optical density at 650 nm (OD₆₅₀) of approximately 1.0 for the suspension of cells applied to the wells, and the other concentrations are 2-fold dilutions of that suspension.

The maximum depletion of bactericidal activity obtained with NOMV from the test strain 8532(B:15:P1.7-2,3:L3,7,8), an epidemic outbreak isolate, or an L8 phase variant of the test strain or with purified L1 or L3,7 LPS was determined for sera from 9 Chilean children with bactericidal titers as shown in . The particular sera assayed are indicated in boldface in and are identified by subject number and week/month of bleed. The control serum (17-8) was taken from volunteer 17 at 8 weeks following initial vaccination (2 weeks after the second dose) with a meningococcal group B outer membrane protein vaccine essentially free of LPS (). BSA, bovine serum albumin.