The appearance of IgG1+ cells after IgG2a agrees with earlier observations on serum antibody kinetics in P. chabaudi infections, and coincides with the gradual increase in malaria-specific IgG1 antibodies and T helper cell precursors and the gradual decrease in IgG2a serum antibody and IFN-γ producing Th1 cells observed in this infection (30). This evidence concerns the gene IFNG and infection.