Ig‐Isotype Patterns of Primary and Secondary B Cell Responses to Plasmodium Chabaudi Chabaudi Correlate with IFN‐γ and IL‐4 Cytokine Production and with CD45RB Expression by CD4+ Spleen Cells

In this work, the authors analysed T and B lymphocyte subsets and cytokine production in the spleen of BALB/c mice during polyclonal lymphocyte activation (primary infection) and parasite‐specific response to Plasmodium chabaudi chabaudi (secondary infection). The secondary response was evaluated in fully immunoprotected animals, 60 days after a chloroquine‐cured infection. The authors observed that in polyclonal lymphocyte activation antibody‐secreting cells of all isotypes increased, with predominance of IgG2a and IgG3 classes. At that time, IFN‐γ was largely produced, but IL‐4/IL‐5 were just slightly enhanced. In mice re‐infected after 60 days, the Ig‐isotype pattern was restricted to IgG1 and only IL–4/IL‐5 were produced. In both responses, however, the levels of IL‐2 were greatly reduced, while those of IL‐10 were enhanced to similar levels. The different involvement of Th1 and Th2 cells in both responses was confirmed through analysis of CD45RB expression by CD4+ cells. The authors observed that CD45RBhigh cells were the major CD4+ subpopulation in primary infected mice, while CD45RBlow cells predominated in 60 days re‐infected animals. Moreover, the great majority of activated (large) CD4+ cells in the primary infection belonged to the CD45RBhigh subset, while after re‐infection most of the CD4+ large had a CD45RBlow phenotype.