IL-21 and CD40L Synergistically Promote Plasma Cell Differentiation through Upregulation of Blimp-1 in Human B Cells

Abstract

After undergoing Ig somatic hypermutation and antigen selection, germinal center (GC) B cells terminally differentiate into either memory or plasma cells (PCs). It is known that the CD40L and IL-21/STAT3 signaling pathways play critical roles in this process, yet it is unclear how the B cell transcription program interprets and integrates these two types of T cell derived signals. In this study, we characterized the role of STAT3 in the GC-associated PC differentiation using purified human tonsillar GC B cells and a GC B cell-like cell line. When primary GC B cells were cultured under PC differentiation condition, STAT3 inhibition by AG490 prevented the transition from GC centrocytes to pre-plasmablast (pre-PB) suggesting that STAT3 is required for the initiation of PC development. In a GC B cell-like human B cell line, although IL-21 alone can induce low-level Blimp-1 expression, maximum Blimp-1 upregulation and optimal PC differentiation required both IL-21 and CD40L. CD40L, while having no effect on Blimp-1 as a single agent, greatly augmented the amplitude and duration of IL-21 triggered Jak-STAT3 signaling. In the human PRDM1 locus, CD40L treatment enhanced the ability of STAT3 to upregulate Blimp-1 by removing BCL6, a potent inhibitor of Blimp-1 expression, from a shared BCL6/STAT3 site in intron 3. Thus, IL-21 and CD40L collaborate through at least two distinct mechanisms to synergistically promote Blimp-1 activation and PC differentiation.

EZH2 Inhibition by Tazemetostat Results in Altered Dependency on B-cell Activation Signaling in DLBCL

“…4E, tazemetostat has only a modest effect on PRDM1 levels in the SU-DHL-5 line as a single agent and neither CD40L nor IL21 affect PRDM1 protein levels in SU-DHL-5 cells (Supplementary Fig. S5), while they have been shown to induce PRDM1 expression in normal B-cells (39). However, we observe that treatment with combinations of CD40L and tazemetostat strongly upregulate PRDM1 in SU-DHL-5s (Fig.…”

Tolerant Kidney Transplant Patients Produce B Cells with Regulatory Properties

“…12,20 Here again, this is in accordance with the fact that in vitro unstimulated T cells from TOLs produce less IL-21, a molecule that directly acts on B cell differentiation. 62,63 We hypothesize that these properties may contribute to a favorable tolerogeneic environment and favorable inversion of the B effector-plasma cell/Bregs balance in these patients and their lower antibody production. These data support a role for B cells in patients with operational tolerance.…”

The forkhead transcription factor FOXP1 represses human plasma cell differentiation

“…The observed low expression of FOXP1 in PCs, combined with the repression of the PC gene signature by FOXP1, suggests that FOXP1 downregulation might be required for PC differentiation, whereas aberrantly high expression of FOXP1 might prevent PC differentiation. To investigate the putative repressive role of FOXP1 in PC differentiation, we first assessed the effects of ectopic FOXP1 overexpression 29,30 When cultured in normal culture medium, these cell lines do not secrete immunoglobulins and express low levels of PRDM1, IRF4, and XBP1. Stimulation of these cell lines with interleukin (IL) 21 and CD40 ligand (CD40L)-expressing L cells (OCI-Ly7) or IL-21 alone (SKW6.4) rapidly induced immunoglobulin secretion and the expression of PC-specific genes.…”