Secretion of parasite-specific immunoglobulin G by purified blood B lymphocytes from immune individuals after in vitro stimulation with recombinant Plasmodium falciparum merozoite surface protein-1 sub(19) antigen

The C-terminal 19 000 MW fragment of merozoite surface protein-1 (MSP1 sub(19)) is one of the most promising candidate antigens for a malaria vaccine. Baculovirus recombinant Plasmodium falciparum MSP1 sub(19) has been used to define conditions for the in vitro production of specific antibodies by purified human blood B cells in a culture system where T-cell signals were provided by the engagement of CD40 molecules and exogenous cytokines. MSP1 sub(19) preferentially induced surface immunoglobulin G (IgG) -positive (s gamma super(+)) B lymphocytes from P. falciparum-immune donors to differentiate and produce antigen-specific IgG. In contrast, naive B cells or cells from non-immune donors could not be induced to secrete parasite-specific IgG in vitro. Although IgG secretion was obtained in the absence of exogenous cytokines, it was dependent on B-cell-derived interleukin-10 (IL-10) and/or B-cell factor(s) under the control of IL-10, since IgG levels were significantly decreased in the presence of neutralizing anti-IL-10 antibodies. These results demonstrate at the cellular level that a single malaria vaccine candidate polypeptide can direct parasite-specific antibody production mediated by the secretion of potentiating factors.