Interspecific neisserial high molecular weight proteins able to induce natural immunity responses are strongly correlated with in vitro bactericidal activity.

Human sera from healthy volunteers and patients convalescent from meningitis were used to search for widely cross-reactive antigens implicated in vivo protective responses. Using the type strain Neisseria meningitidis B16B6 and a wide variety of both N. meningitidis and N. lactamica strains, several cross-reactive antigens and bactericidal sera were found, although the cross-reactivity patterns did not correlate with bactericidal activity, a total correlation was found between bactericidal activity and reaction with one or two high molecular weight proteins (162 and 138 kDa), and a mouse serum against the purified proteins showed a high bactericidal activity. Our results suggest that the high molecular weight proteins found are immunogenic and cross-reactive, eliciting bactericidal responses during infection and as a result of natural immunity. These proteins should be taken into account in studies for future vaccine formulations.