Background/Purpose: Rheumatoid arthritis (RA) is an autoimmune disease affecting 1% of the worldwide population and characterized by synovial hypertrophy and chronic joint inflammation. In recent work, it has been shown that release of catecholamines by the sympathetic nervous system (SNS) modulates development and course of arthritis. In this context, we were able to show that catecholamines increase the production of the anti-inflammatory cytokine IL-10, which can ameliorate joint inflammation. In the current study, we investigated whether regulatory B cells have enzymes for catecholamine biosynthesis and adrenergic receptors to determine if autocrine mechanisms could contribute to controlling regulatory B cell function.

Methods: In in vitro experiments on IgM/CpG-activated murine primary B cells, the basics for the mechanism(s) of increased regulatory B cell function and its targeted influence were investigated. Tyrosine hydroxylase (TH) as well as the expression of adrenergic receptors were analyzed in naïve (0h) or IgM/CpG activated B cells after 24h and 48h by FACS, Western Blot and qRT-PCR. For analysis of IL-10 production released IL-10 from inactivated and activated B cells were quantified in supernatant of B cell cultures by ELISA or directly in B cells by intracellular FACS staining.

Results: Here, we demonstrated that tyrosine hydroxylase (TH), the rate limiting enzyme of catecholamine biosynthesis are strongly expressed by splenic mouse B cells after activation with the BCR/TLR9 stimulus IgM/CpG. Analysis of B cells by FACS showed a raised expression of tyrosine hydroxylase with duration of IgM/CpG activation (0h vs. 24h, n=7-12, p***<0,0001; 0h vs. 48h, n=7-12, p***<0,0001; 24h vs. 48h, n = 12, p**=0,0091). A sign that catecholamines are not only provided by the sympathetic nervous system, but also produced by B cells. Furthermore, qRT-PCR and FACS showed that all adrenergic receptors (ADR) determined (ADRα1a, ADRα1b, ADRα2b, ADRß1 and ADRß2) are expressed on the surface of IgM/CpG-activated B cells (n=12). The number of TH+ cells, as determined by FACS correlates with the expression of ADRα1a (r=0.575, p=0.2, n=6), ADRα2b (r=0.582, p=0.046, n=12), and ADRβ2 (r=0.742, p=0.006, n=12) ADRβ1 (r=0.575, p=0.2, n=6). After activation with IgM/CpG B cells produce IL-10 as determined by ELISA (n=6, p***<0,0001) and FACS (n=5, p***<0,0001) and the production can be increased by addition of isoproterenol, a ADR-beta agonist (n=12, p**=0,006), an effect that was blocked by nadolol (n=12, p*=0,0293). FACS analysis showed that IL-10 was mainly produced by TH+ B cells (n=6, p***<0,0001; TH+:23%, IL-10+:1,68% TH+IL-10+:2,13%; 99,3% of IL-10+ cells are TH+).

Conclusion: In conclusion, our data suggest that IgM/CpG-induced expression of TH in murine, primary B cells is associated with an increase in IL-10 mediated by stimulation of betaAR adrenergic receptors. This might point to an autocrine mechanism to control regulatory B cells, which could be exploited for therapeutic purposes in RA.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/hints-for-catecholamine-driven-autocrine-mechanisms-to-regulate-regulatory-b-cells/