Endogenous CD4+CD25+Regulatory T Cells Play No Apparent Role in the Acute Humoral Response to IntactStreptococcus pneumoniae

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Abstract
Immunoglobulin G (IgG) antiprotein and antipolysaccharide responses to intactStreptococcus pneumoniaeare CD4+-T-cell dependent and therefore might be under the negative control of CD4+CD25+regulatory T cells. Injection of anti-interleukin 2 receptor α (anti-IL-2Rα) MAb to deplete regulatory T cells, injection of agonistic MAb against glucocorticoid-induced tumor necrosis factor receptor family-related protein to inhibit regulatory-T-cell function, and adoptive transfer of regulatory-T-cell-depleted CD4+T cells into athymic nude mice each had no effect on either the primary or secondary protein- or polysaccharide-specific IgG response to intactS. pneumoniae. Surprisingly, anti-IL-2Rα MAb also had no effect on the IgG response to intactS. pneumoniaein MyD88−/−mice or to a soluble protein-polysaccharide conjugate injected into wild-type mice in the absence of adjuvant. Collectively, these data are the first to suggest that, in contrast to their role in limiting chronic cell-mediated immunity, regulatory T cells may play no significant role in an acute humoral immune response to an intact extracellular bacterial pathogen.