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 CD45RB^high cells were the major CD4⁺ subpopulation in primary infected mice, while CD45RB^low cells predominated in 60 days re-infected animals. Moreover, the great majority of activated (large) CD4⁺ cells in the primary infection belonged to the CD45RB^high subset, while after re-infection most of the CD4⁺ large had a CD45RB^low phenotype.