Asymptomatic carriage of Neisseria meningitidis is common (5–35% of individuals) while the incidence of invasive meningococcal disease is fairly low (<1–5 per 100000 per annum in Europe). Naturally acquired protective immunity may account for this difference. In this study, we investigated the relationship between anti-meningococcal salivary IgA and age and carriage. We showed that salivary IgA to a range of meningococcal antigens increased successively with age with some specificity for commonly circulating serosubtypes. In a group of 258 students 37 (14%) of whom were carriers of N. meningitidis serogroup B, higher levels of specific IgA were associated with carriage. Stratified analysis revealed a positive relationship between smoking and specific anti-N. meningitidis IgA independent of current carriage, weighted odds ratio (OR) 4·1 (95% CI 1·1–18) and OR 3·8 (95% CI 0·96–16) for reference strains B:1:P1.14 and B:4:P1.5,4 respectively. These data implicate IgA as a factor in host defence from meningococcal invasion, although the precise mechanisms remain uncertain.
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