Germinal centre and marginal zone B cells expand quickly in a second Plasmodium chabaudi malaria infection producing mature plasma cells.

Antibodies and B cells are critical in the protective immune response to the blood stage of the malaria parasite, Plasmodium chabaudi. However, little is known about the development of memory B cells and their differentiation into plasma cells during infection or after re-infection. Here we have shown that B cells with phenotypic characteristics of memory cells (CD19(+)IgD(-) CD38(+), IgG1(+)) are generated in a primary Plasmodium chabaudi chabaudi infection of mice. In addition, we observed that germinal centre cells (CD19(+), GL7(+), MHCII(hi)) and Marginal Zone B cells (CD19(+)CD23(-)IgD(-)) show faster expansion on re-infection than in the primary, though other subsets do not. Interestingly, though both IgM(-) and IgM(+) memory cells are produced, IgM(+) memory cells do not expand on second infection. The second infection quickly produced mature bone marrow plasma cells (intracellular Ig(hi), CD138(hi), CD9(+), B220(-)), compared to primary infection; which generates a very large population of immature splenic plasma cells (B220+). This analysis suggests that a memory B cell population is generated after a single infection of malaria, which on re-infection responds quickly producing germinal centres and generating long-lived plasma cells making the second encounter with parasite more efficient.