Induction and Differentiation of IL-10-Producing Regulatory B Cells from Healthy Blood Donors and Rheumatoid Arthritis Patients.

The most important feature of B cells is the production of Abs upon activation; additionally, B cells produce pro- and anti-inflammatory cytokines in response to certain stimuli. IL-10-producing B cells represent a major subset of regulatory B cells (Bregs) that suppress autoimmune and inflammatory responses. B cells play a crucial role in the development and maintenance of the chronic inflammatory autoimmune disease rheumatoid arthritis (RA); however, controversial data are available on IL-10- producing Bregs in RA. Our aim was to identify the optimal conditions that induce IL-10+ Bregs and, furthermore, to shed light on the signaling pathways that are responsible for their expansion. The results show that dual stimulation by CpG and CD40L for 48 h is optimal for IL-10 induction, and this can be synergistically boosted by IL-21. We identified the CD19+CD27+ memory B cell population as the major source of IL-10+ Bregs. We detected significantly fewer CD19+CD27+IL-10+ cells in RA patients compared with healthy controls, and these were functionally defective in suppressing IFN-γ production by CD4+ T cells in coculture. IL-21 drastically increased the number of IL-10+ Bregs within the CD19+CD27+ and CD19+CD27- populations; furthermore, it induced the appearance of IL-10+Blimp-1+ plasmablasts. Monitoring the phosphorylation of key signaling molecules revealed that activation of ERK, p38, and CREB is indispensable for the induction of IL-10 production, whereas phosphorylation of STAT3 further enhances IL-10 expression in human Bregs. We conclude that CREB and STAT3 are the key transcription factors responsible for the expansion and differentiation of human IL-10-producing Bregs.

Regulatory B cells in rheumatoid arthritis: Alterations in patients receiving anti-TNF therapy.

Cytokines, including tumor necrosis factor alpha (TNFα) are involved in Rheumatoid arthritis (RA) pathogenesis by augmenting autoimmunity, sustaining long term inflammation in the synovium, and promoting joint damage. Anti-TNF therapy is one of the most efficient and widely used therapies for RA, although its mechanism is not clarified yet. Earlier we demonstrated that RA patients have a reduced number of IL-10 producing regulatory B cells (B10 cells) as compared to healthy individuals and they are functionally impaired. Our aim was to study the influence of anti-TNF therapy on B10 cells in RA, to follow the alteration of B cell activation markers (CD25, CD69) and to monitor the level of citrullinated peptid-specific antibodies and the secreted IL-10 in patients' sera during the therapy. We have observed that at six month after starting the therapy the frequency of B10 cells remarkably increased, while the expression of the activation marker, CD69 decreased on B cells. In contrast, serum levels of IL-10 and anti-citrullinated peptide antibodies did not change post-treatment. CONCLUSION: The reduced activation state of B cells and the increasing number of regulatory B10. cells might contribute to the therapeutic efficacy of anti-TNF agents in RA.

Suppression of innate and adaptive B cell activation pathways by antibody coengagement of FcγRIIb and CD19.

The Fc receptor (FcγRIIb) inhibits B cell responses when coengaged with B cell receptor (BCR), and has become a target for new autoimmune disease therapeutics. For example, BCR and FcγRIIb coengagement via the Fc-engineered anti-CD19 XmAb5871 suppresses humoral immune responses. We now assess effects of XmAb5871 on other activation pathways, including the pathogen-associated molecular pattern receptor, TLR9. Since TLR9 signaling is implicated in autoimmune diseases, we asked if XmAb5871 could inhibit TLR9 costimulation. We show that XmAb5871 decreases ERK and AKT activation, cell proliferation, cytokine, and IgG production induced by BCR and/or TLR9 signals. XmAb5871 also inhibited differentiation of citrullinated peptide-specific plasma cells from rheumatoid arthritis patients. XmAb5871 may therefore have potential to suppress pathogenic B cells in autoimmune diseases.

TGFß activated kinase 1 (TAK1) at the crossroad of B cell receptor and Toll-like receptor 9 signaling pathways in human B cells.

B cell development and activation are regulated by combined signals mediated by the B cell receptor (BCR), receptors for the B-cell activating factor of the tumor necrosis factor family (BAFF-R) and the innate receptor, Toll-like receptor 9 (TLR9). However, the underlying mechanisms by which these signals cooperate in human B cells remain unclear. Our aim was to elucidate the key signaling molecules at the crossroads of BCR, BAFF-R and TLR9 mediated pathways and to follow the functional consequences of costimulation.Therefore we stimulated purified human B cells by combinations of anti-Ig, B-cell activating factor of the tumor necrosis factor family (BAFF) and the TLR9 agonist, CpG oligodeoxynucleotide. Phosphorylation status of various signaling molecules, B cell proliferation, cytokine secretion, plasma blast generation and the frequency of IgG producing cells were investigated. We have found that BCR induced signals cooperate with BAFF-R- and TLR9-mediated signals at different levels of cell activation. BCR and BAFF- as well as TLR9 and BAFF-mediated signals cooperate at NFκB activation, while BCR and TLR9 synergistically costimulate mitogen activated protein kinases (MAPKs), ERK, JNK and p38. We show here for the first time that the MAP3K7 (TGF beta activated kinase, TAK1) is responsible for the synergistic costimulation of B cells by BCR and TLR9, resulting in an enhanced cell proliferation, plasma blast generation, cytokine and antibody production. Specific inhibitor of TAK1 as well as knocking down TAK1 by siRNA abrogates the synergistic signals. We conclude that TAK1 is a key regulator of receptor crosstalk between BCR and TLR9, thus plays a critical role in B cell development and activation.