This implies that thymically derived natural Treg cells may also play a role in controlling the overall size of the GC response, or upon systemic TGF-β neutralization, other factors or cytokines may partially compensate leading to nominal induction of iTreg cells. The potential role of IL-10 was also examined by repeated administration of a blocking anti-IL-10R mAb. Mice were injected i.p. on day 0 with 1 mg of anti-IL-10R (1B1.3a) mAb or control rat IgG. Starting AZD6738 in the second week, 500 μg of anti-IL-10R mAb

or rat IgG was injected twice weekly and continued until the mice were killed. The SRBC were given i.p. on day 0. Similar to anti-TGF-β-treated mice, blockade of the IL-10R resulted in an inability to control the balance of IgM+ to switched GC B cells in the spleen. Although not evident at days 8 and 12, this imbalance became marked at days 18 and 24 and reflected a significant increase in both the frequency and Palbociclib order total number of IgM− GC B cells (Fig. 9b). Examination of the frequency and number of total B220+ PNAhi B cells showed little difference between anti-IL-10R mAb and control-treated mice, except at day 24 (Fig. 9a). This is again similar to the result observed after TGF-β neutralization, and may likewise reflect the activity of natural Treg cells or the ability of other cytokines to partially compensate.

Finally, to ensure that anti-IL-10R mAb treatment did not directly modulate responding B cells, the GC population was tested for expression of IL-10R. As shown in the Supplementary material, Fig. S3, no expression above background was detected. A large number of studies have documented the role of Treg cells in controlling antibody responses.16–46 Using either in vivo disruption (anti-GITR mAb) or depletion (anti-CD25 mAb) protocols, investigators have shown that loss of Treg-cell activity results in enhanced humoral

responses to experimental antigens,16–22 pathogens23,24 and auto-antigens.17,25–29 In all of these reports, antibody levels directed against the specific 4-Aminobutyrate aminotransferase antigen or infectious agent were significantly elevated, including IgG,16–27,29 IgA18,25 and even IgE.19,26 Additional studies examined whether adoptive transfer of polyclonal21,30–32,35,37–40 or TCR transgenic33,34,36,41 Treg cells could dampen antibody responses to defined allo-antigens or auto-antigens. In all cases, the transfer of Treg cells significantly lowered or even eliminated serum antibodies directed against these antigens. As GCs serve as the basis for T-cell-driven humoral responses, the current study examined the behaviour of primary splenic GC reactions induced to a number of antigens in mice treated with an anti-GITR mAb (Figs 1–4). After disruption of Treg-cell activity, total SRBC-induced GC B-cell numbers were increased at all time-points examined (days 8–24). A higher proportion of IgM− switched B cells within the GC compartment largely accounted for this increase.