Germinal center organization mediated by T-bet dependent expression of CXCR3 and CCR6

Abstract

Abstract The germinal center (GC) is composed of distinct regions with proliferation and affinity maturation of GC B cells (GCB) occurring in the dark zone (DZ) and antigen-mediated selection and commitment of the long-lived plasma cell (LL-PCs) precursors occurring in the light zone (LZ). Despite the key role for GCs in establishing enduring humoral immunity, we know little about the dynamics of the GCB cell response. We showed that the transcription factor T-bet is expressed by GCB cells and that B cell intrinsic T-bet is required for the LL-PC response following influenza (flu) infection. To test whether the loss of LL-PCs in these mice was due to a role for T-bet in regulating the GCB response, we infected 50:50 Tbx21−/−: pepboy chimeric mice with flu and enumerated GCB cells. We found that Tbx21−/− B cells were overrepresented in the GC relative to the pepboy cells and that Tbx21−/− GCB cells were enriched in the LZ. Partitioning of GCB cells in the LZ/DZ is regulated by chemokines and we showed that T-bet controls transcription of two chemokine receptors, CXCR3 and CCR6, which are expressed by GCB cells. Using 50:50 Tbx21−/−: pepboy chimeras, we tested whether T-bet regulates GCB cell positioning by inducing CXCR3 and repressing CCR6. We observed that the CCR6+ GCB cell subset, which is known to localize in the LZ, was very enriched in Tbx21−/− GCB cells. By contrast, the CXCR3+ GCB subset, which was dominated by WT cells, was enriched in the DZ. To determine the role for CXCR3 in GCB cell localization, we infected 50:50 Cxcr3−/− :pepboy chimeras and found that the Cxcr3−/− GCB cells are enriched in the LZ. Therefore, T-bet regulates GCB cell localization and potentially the dynamics of the GC response by controlling CXCR3 and CCR6 expression.