No abstract

A major neurotransmitter dopamine transmits signals via five different seven transmembrane G protein-coupled receptors termed D1-D5. It is now evident that dopamine is released from leukocytes and acts as autocrine or paracrine immune modulator. However, the role of dopamine for dendritic cells (DCs) and T(h) differentiation remains unclear. We herein demonstrate that human monocyte-derived dendritic cells (Mo-DCs) stored dopamine in the secretary vesicles. The storage of dopamine in Mo-DCs was enhanced by forskolin and dopamine D2-like receptor antagonists via increasing cyclic adenosine 3',5'-monophosphate (cAMP) formation. Antigen-specific interaction with naive CD4(+) T cells induced releasing dopamine-including vesicles from Mo-DCs. In naive CD4(+) T cells, dopamine dose dependently increased cAMP levels via D1-like receptors and shifts T-cell differentiation to T(h)2, in response to anti-CD3 plus anti-CD28 mAb. Furthermore, we demonstrated that dopamine D2-like receptor antagonists, such as sulpiride and nemonapride, induced a significant DC-mediated T(h)2 differentiation, using mixed lymphocyte reaction between human Mo-DCs and allogeneic naive CD4(+) T cells. When dopamine release from Mo-DCs is inhibited by colchicines (a microtubule depolymerizer), T-cell differentiation shifts toward T(h)1. These findings identify DCs as a new source of dopamine, which functions as a T(h)2-polarizing factor in DC-naive T-cell interface.

A major neurotransmitter dopamine transmits signals via five different seven-transmembrane G protein-coupled receptors termed D1–D5. Several studies have shown that dopamine not only mediates interactions into the nervous system, but can contribute to the modulation of immunity via receptors expressed on immune cells. We have previously shown an autocrine/paracrine release of dopamine by dendritic cells (DCs) during Ag presentation to naive CD4+ T cells and found efficacious results of a D1-like receptor antagonist SCH-23390 in the experimental autoimmune encephalomyelitis mouse model of multiple sclerosis and in the NOD mouse model of type I diabetes, with inhibition of Th17 response. This study aimed to assess the role of dopaminergic signaling in Th17-mediated immune responses and in the pathogenesis of rheumatoid arthritis (RA). In human naive CD4+ T cells, dopamine increased IL-6–dependent IL-17 production via D1-like receptors, in response to anti-CD3 plus anti-CD28 mAb. Furthermore, dopamine was localized with DCs in the synovial tissue of RA patients and significantly increased in RA synovial fluid. In the RA synovial/SCID mouse chimera model, although a selective D2-like receptor antagonist haloperidol significantly induced accumulation of IL-6+ and IL-17+ T cells with exacerbated cartilage destruction, SCH-23390 strongly suppressed these responses. Taken together, these findings indicate that dopamine released by DCs induces IL-6–Th17 axis and causes aggravation of synovial inflammation of RA, which is the first time, to our knowledge, that actual evidence has shown the pathological relevance of dopaminergic signaling with RA.

Neutrophils may play an important role in the pathogenesis of severe asthma. Their infiltration into the airway is increased. Interleukin (IL)-8 is involved in this process, and is actually upregulated in the airways of patients. We have observed that in the absence of eosinophil chemoattractants, neutrophils stimulated by IL-8 augment eosinophil trans-basement membrane migration by releasing superoxide anion, matrix metalloproteinase, leukotriene B₄ and platelet-activating factor. These findings suggest that IL-8-stimulated neutrophils could lead eosinophils to accumulate in the airways of asthmatic patients, which might be a mechanism for corticosteroid resistance in severe asthma. However, the mechanisms of IL-8 upregulation in the airway are not completely understood. Several studies suggest that IL-17 (or T helper 17 cells; Th17) is involved in the IL-8 upregulation observed in severe asthma. We clarified that dopamine induces Th17 differentiation through dopamine D1-like receptor (D1-like-R), and that the D1-like-R antagonist attenuates Th17-mediated diseases like experimental autoimmune encephalomyelitis. Furthermore, we demonstrated that a D1-like-R antagonist significantly suppressed ovalbumin (OVA)-induced neutrophilic airway inflammation in OVA T cell receptor-transgenic DO11.10 mice through inhibiting Th17-mediated immune responses. Therefore, dopamine D1-like-R antagonists could become useful for treating Th17-mediated neutrophil-dominant severe asthma. As inhaled corticosteroids are known to be less effective for controlling neutrophilic inflammation, a more effective therapeutic strategy for neutrophil-dominant asthma should still be elucidated.