Human Immunity to the Meningococcus

Abstract

Results of the present study suggest that natural immunity to meningococcal disease is initiated, reinforced, and broadened by intermittent carriage of different strains of meningococci throughout life. In young adults, carriage of meningococci in the nasopharynx is an efficient process of immune sensitization. 92% of carriers of serogroup B, C, or Bo meningococci were found to develop increased titers of serum bactericidal activity to their own meningococcal isolate, and 87% developed bactericidal activity to heterologous strains of pathogenic meningococci. The rise in bactericidal titer occurred within 2 wk of onset of the carrier state, and was accompanied by an increase in titer of specific IgG, IgM, and IgA antibodies to meningococci. In early childhood, when few children have antibodies to pathogenic meningococci, active immunization seems to occur as a result of carriage of atypical, nonpathogenic strains. Immunity to systemic meningococcal infection among infants in the neonatal period is associated with the passive transfer of IgG antibodies from mother to fetus. The antigenic determinants which initiate the immune response to meningococci include the group-specific C polysaccharide, cross-reactive antigens, and type-specific antigens.

The natural history of meningococcal carriage and disease

“…Individuals are likely to experience many episodes of carriage with N. meningitidis and N. lactamica through their lifetimes, which is probably important in developing and maintaining immunity to meningococcal disease [2,15]. The force of infection is clearly variable by age and serogroup, with meningococcal carriage being most common in teenagers and carriage of N. lactamica most common in young children.…”

“…The SIS model is a much simpler starting point from which these relationships can be investigated further. Third, there is clear evidence from immunological studies that carriage episodes are important in generating immunity against disease [2] but not necessarily against infection resulting in carriage. This immunity can be accounted for implicitly in the risk of disease given infection in the current model structures.…”

“…Of course this relationship may just be an artefact of age, but since carriage has been shown experimentally to be an immunizing event [2,3] it may be due to immunity built up from exposure to carriage, in which case, cross-protection from N. lactamica and other serogroups is likely to be important. An understanding of these mechanisms may be essential when considering vaccines against strains more commonly carried than serogroup C or vaccines based on N. lactamica outer membrane vesicles that are currently being developed [22].…”

“…N. meningitidis carriage strains are diverse and only a subset of these (known as hyperinvasive lineages) cause disease. Asymptomatic infection with pathogenic and non-pathogenic strains, including the closely related Neisseria lactamica, which is carried frequently in children, may help contribute to the development of protection against meningococcal disease [2,3]. However, large-scale carriage studies are expensive and difficult to conduct, limiting the availability of these data.…”

Secretor status and humoral immune responses to Neisseria lactamica and Neisseria meningitidis

“…Protective immunity to disease due to Neisseria meningitidis is associated with the presence of an intact complement system and opsonizing or bactericidal antibodies specific for the invading strain [9][10][11]. These antibodies can be formed through nasopharyngeal carriage of meningococci [12].…”