T regulatory cells and the germinal center

Germinal center (GC) reactions are central features of T cell-driven B cell responses, and the site where antibody (Ab) producing cells and memory B cells are generated. Within GCs, a range of complex cellular and molecular events occur which are critical for the generation of high affinity Abs. These processes require exquisite regulation not only to ensure the production of desired Abs, but to minimize unwanted autoreactive or low affinity Abs.

To assess whether T regulatory cells (Treg) participate in the control of GC responses, immunized mice were treated with either an anti-glucocorticoid-induced TNFR-related protein (GITR) mAb or an anti-CD25 mAb to disrupt Treg activity. In both groups of treated mice, the GC B cell pool was significantly larger compared with control treated animals, with switched GC B cells composing an abnormally high proportion of the response. With these results indicating Tregs influence on GC dynamics, experiments were conducted to determine if Tregs were located in the GC, which subset of Treg was involved and by which mechanisms were their functions being effected. Within the spleens of immunized mice, CXCR5+ and CCR7- Tregs were documented by flow cytometry and Foxp3+ cells were found within GCs using immunohistology. Studies demonstrated administration of either anti-TGF-β or anti-IL-10R blocking mAb to likewise result in dysregulated GCs, suggesting that generation of inducible Tregs is important in controlling the GC response. Blockade of two Treg methods of suppression, PD-1/PD-L1 pathway and CTLA-4, also resulted in disrupted GCs, indicating the possible use of them for suppression by Treg. Collectively, these findings indicate that Tregs contribute to the overall size and quality of the humoral response by controlling homeostasis within GCs.