Memory B-cell developmental program requires learn more antigen-specific CD4+ T-cell help [22]. A reported study showed that children of all ages can produce in vitro cellular immune responses following meningococcal infection [23]. To better understand the potential of the Cuban vaccine to induce immunological

memory we performed a longitudinal analysis of memory B-cell frequency, the kinetics of functional inhibitors antibody response as well as the memory T-cell frequencies and activation status after immunisation of adult volunteers with the Cuban MenB vaccine (VA-MENGOC-BC®). Despite the small number of individuals in this study, our results indicated a short duration of the humoral immunity in terms of both frequency of memory B-cells and functional antibody titers. The frequencies

of memory B-cells varied from 0.14% to 0.95% (median of 0.46%) 14 days after the third vaccination. This is in agreement with results of Sasaki at al. [24], who found a rather constant frequency of approximately 0.5% influenza-specific memory B-cells in circulating blood from 27 to 42 days after vaccination. However, for 5 out of 6 individuals, the MenB specific memory B-cells declined to undetectable values 6 months after the primary series. The booster dose induced a recall response only in 2 of 5 individuals. These data are in check details contrast with the results of Nanan et al. [15] who showed that specific memory B-cells accumulate with every immunisation dose of tetanus or diphtheria vaccine and remain elevated over several years. Similar to the memory B-cell response, post-boosting bactericidal Sclareol antibody levels were significantly lower than after 3 doses of vaccine, with 3 of 5 individuals presenting a 4-fold increase in antibody titers. A similar antibody response pattern was observed for opsonic antibodies.

Due to the continuous re-circulation of memory B-cells through the blood and secondary lymphoid organs it is assumed that memory B-cells found in the circulation should be representative for the entire B-cell pool [15] and [25]. A recent report of long-term presence of memory B-cells specific for tetanus, pertussis, measles and influenza virus found that the frequencies of these cells varied between 0.02% and 0.87% of the total IgG producing cells. Of note, memory B-cells were detected in all individuals for all antigens tested [25], indicating a high sensitivity of the assay, which used CpG, IL-2, IL-10 and IL-15 as polyclonal stimulators of B-cells. The assay used in our study may be of lower sensitivity compared with the latter, since we used only IL-2 and SAC as polyclonal stimulators of B-cells. Nonetheless, our results showed that the profile of memory B-cell response of vaccinated volunteers was kinetically accompanied by serum bactericidal and opsonic antibody responses indicating the presence of short lived memory B-cells or poor activation of these cells.