Characterization of Humoral and Cellular Immune Responses Elicited by Meningococcal Carriage

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Abstract
In order to study the immune response elicited by asymptomatic carriage ofNeisseria meningitidis, samples of serum, peripheral blood mononuclear cells (PBMCs), and saliva were collected from a cohort of more than 200 undergraduate students in Nottingham, United Kingdom, who were subject to high rates of acquisition and carriage of meningococci. Serum immunoglobulin G levels were elevated following increases in the rate of carriage, and these responses were specific for the colonizing strains. In order to investigate T-cell responses, PBMCs from 15 individuals were stimulated with a whole-cell lysate of the H44/76 meningococcal strain (B:15:P1.7,16), stained to detect cell surface markers and intracellular cytokines, and examined by flow cytometry. The cells were analyzed for expression of CD69 (to indicate activation), gamma interferon (IFN-γ) (a representative T-helper 1 subset [Th1]-associated cytokine), and interleukin-5 (IL-5) (a Th2-associated cytokine). Following a brief meningococcal stimulation, the numbers of CD69+IFN-γ+CD56/16+NK cells were much higher than cytokine-positive CD4+events. Both IFN-γ+and IL-5+events were detected among the CD69+CD4+population, leading to the conclusion that an unbiased T-helper subset response was elicited by meningococcal carriage.