This study investigated B cell kinetics of the candidate vaccine, glycosylphosphatidylinositol (GPI) and memory B cell (MBC) reactivation upon P. berghei (PBA) challenge in the murine model.
C57Bl/6 mice were allocated to the following groups: GPI-KLH, NP-KLH, KLH, naïve, or PBA. Mice were primed and boosted (previous protocols), or challenged twice with PBA and drug treated. A subset of mice were euthanised for B cell phenotyping (flow cytometry, ELISPOTS). Naïve, GPI-KLH or PBA-challenged mice were rested (10 weeks) and “challenged” with GPI-KLH or PBA or nothing (GPI “no-challenge” controls). Five days later mice were euthanised and B cells phenotyped (flow cytometry, ELISPOT and ELISA). Kruskal-Wallis and paired t-tests were used to assess significance.
GPI-KLH vaccination generated GPI-specific class-switched B cells. Plasma cells (PCs) were formed and resided in bone marrow (BM). MBCs reactivated when “re-challenged” with synthetic GPI-KLH as observed by significant increases in GPI-specific B cells and sera levels compared to naives (GPI-KLH/PBA challenged). Whilst GPI-vaccinated PBA-challenged mice had significant reactivation compared to naives (GPI/PBA challenged), B cell counts were significantly suppressed when compared to GPI controls (no challenge). Conversely, GPI-vaccinated PBA-challenged mice had significantly higher B cell frequencies than GPI controls (no challenge). Anti-GPI IgG levels post-PBA-challenge were variable.
GPI-KLH vaccination induced B cell activation, class-switching, plasma cells, and GPI-specific IgG1 MBCs. MBCs were functional as demonstrated by reactivation when “challenged” with GPI or PBA. However, for the latter, B cell counts were suppressed compared to baseline GPI controls (no challenge), yet cell frequencies were significantly increased. This may reflect suppression of proliferation in response to infection, a common trademark of malaria. Nonetheless, MBCs were responsive as reflected by increases in cell frequencies and changes in sera titres. GPI-KLH shows promising potential as a vaccine for generating functional MBCs. Further studies should elucidate the longevity of this response.