Brief report: enrichment of activated group 3 innate lymphoid cells in psoriatic arthritis synovial fluid.

OBJECTIVE: Innate lymphoid cells (ILCs) are a recently discovered group of cells that are essential to epithelial homeostasis and are implicated in psoriasis pathogenesis, yet they have never been reported in psoriatic arthritis (PsA). METHODS: ILC classes and subsets were characterized in the peripheral blood (PB) of healthy controls, patients with psoriasis, and patients with PsA and in the synovial fluid (SF) of patients with PsA and patients with rheumatoid arthritis (RA). Cell surface marker expression and intracellular cytokine production following stimulation were analyzed using flow cytometry. RESULTS: ILCs were identified in the SF and were 4-fold more abundant in PsA SF than in PsA PB. Fewer CCR6+ ILCs were found in PsA PB than in healthy control PB, while PsA SF was enriched for CCR6+ ILCs compared to PsA PB and RA SF. Natural cytotoxicity receptor NKp44+ group 3 ILCs were rare in PB and RA SF, but abundant in PsA SF. Increased numbers of interleukin-17A (IL-17A)-producing ILCs were present in PsA SF compared to RA SF. CCR6, NKp44, and melanoma cell adhesion molecule (MCAM) were expressed on the cell surface of SF ILCs that produced IL-17A. The number of circulating NKp44+, CCR6+, and MCAM+ ILCs in blood was inversely correlated with PsA disease activity. CONCLUSION: Our findings indicate that PsA SF is enriched for group 3 ILCs that express CCR6 and NKp44, which distinguishes the synovial compartment from RA. The increased IL-17A production by SF ILCs indicates a novel role for ILCs in PsA.

Proinflammatory mediator-induced reversal of CD4+,CD25+ regulatory T cell-mediated suppression in rheumatoid arthritis.

OBJECTIVE: We previously demonstrated that CD4+,CD25+ regulatory T (Treg) cells are present in increased numbers in the synovial fluid (SF) of rheumatoid arthritis (RA) patients and display enhanced suppressive activity as compared with their peripheral blood (PB) counterparts. Despite the presence of these immunoregulatory cells in RA, chronic inflammation persists. The purpose of the present study was to investigate whether particular proinflammatory mediators that are associated with RA could abrogate CD4+,CD25+ Treg-mediated suppression. METHODS: Monocyte phenotype was determined by flow cytometry and cytokine levels by enzyme-linked immunosorbent assay. Magnetically sorted CD4+,CD25- and CD4+,CD25+ T cells derived from the PB and SF obtained from RA patients were stimulated alone or in coculture with anti-CD3 monoclonal antibody (mAb) and autologous antigen-presenting cells, in the absence or presence of anti-CD28 mAb or the proinflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha), or IL-7. RESULTS: Monocytes from the SF of RA patients displayed increased expression of HLA class II molecules, CD80, CD86, and CD40 as compared with PB-derived monocytes, indicating their activated status. Mimicking this increased costimulatory potential, addition of anti-CD28 mAb to cocultures of CD4+,CD25- and CD4+,CD25+ T cells resulted in reduced CD4+,CD25+ Treg-mediated suppression in both PB and SF. Furthermore, IL-7 and, to a limited extent, TNFalpha, both of which are produced by activated monocytes and were detected in SF, abrogated the CD4+,CD25+ Treg-mediated suppression. In contrast, IL-6 did not influence Treg-mediated suppression. CONCLUSION: Our findings suggest that the interaction of CD4+,CD25+ Treg cells with activated monocytes in the joint might lead to diminished suppressive activity of CD4+,CD25+ Treg cells in vivo, thus contributing to the chronic inflammation in RA.

Modulation of monocyte/macrophage function by human CD4+CD25+ regulatory T cells.

The suppressive effects of CD4+CD25+ regulatory T cells (Tregs) on T cells have been well documented. Here we investigated whether human CD4+CD25+ Tregs can inhibit the proinflammatory properties of monocytes/macrophages. Monocytes and T cells were isolated from peripheral blood of healthy volunteers by magnetic cell separation and cocultured for 40 h. Monocytes were analyzed directly for cytokine production and phenotypic changes or repurified and used in T-cell stimulation and lipopolysaccharide challenge assays. Coculture with CD4+CD25+ Tregs induced minimal cytokine production in monocytes, whereas coculture with CD4+CD25- T cells resulted in large amounts of proinflammatory (tumor necrosis factor-alpha, interferon-gamma, interleukin-6) and regulatory (interleukin-10) cytokines. Importantly, when these CD4+CD25+ Treg-treated monocytes were repurified after coculture and challenged with lipopolysaccharide, they were severely inhibited in their capacity to produce tumor necrosis factor-alpha and interleukin-6 compared with control-treated monocytes. In addition, monocytes that were precultured with CD4+CD25+ Tregs displayed limited upregulation of human leukocyte antigen class II, CD40 and CD80, and downregulation of CD86 compared with control-treated monocytes. This altered phenotype had functional consequences, as shown by the reduction in T cell-stimulatory capacity of Treg-treated monocytes. Together, these data demonstrate that CD4+CD25+ Tregs can exert direct suppressive effects on monocytes/macrophages, thereby affecting subsequent innate and adaptive immune responses.

CD4(+)CD25(+) regulatory T cells in rheumatoid arthritis: differences in the presence, phenotype, and function between peripheral blood and synovial fluid.

OBJECTIVE: In mice, CD4(+)CD25(+) regulatory T cells play a pivotal role in preventing autoimmunity. Regulatory T cells are also present and functional in healthy humans. We investigated the presence, phenotype, and function of CD4(+)CD25(+) regulatory T cells in peripheral blood (PB) and synovial fluid (SF) from patients with rheumatoid arthritis (RA). METHODS: The presence and phenotype of CD4(+)CD25(+) regulatory T cells were determined by flow cytometry. Anergy and suppressive activity were assessed by culturing CD4(+)CD25(-) and CD4(+)CD25(+) T cells with anti-CD3 monoclonal antibodies and antigen-presenting cells, followed by proliferation and cytokine detection. RESULTS: The percentage of CD4(+)CD25(+) T cells in RA SF was significantly increased compared with that in RA PB, and both of these percentages were higher than that in PB from controls. The cells in RA PB were similar in phenotype and function to CD4(+)CD25(+) regulatory T cells from controls. In SF, however, approximately 40-50% of CD4(+)CD25(+) T cells expressed an activated phenotype, i.e., CD69+, class II MHC(+), OX-40(+), with high levels of CTLA-4 and glucocorticoid-induced tumor necrosis factor receptor. These synovial CD4(+)CD25(+) T cells displayed an increased suppressive capacity compared with blood CD4(+)CD25(+) T cells. However, this enhanced suppressive activity was counterbalanced, because activated responder T cells from SF were less susceptible to CD4(+)CD25(+) T cell-mediated suppression than were responder cells from PB. CONCLUSION: We demonstrate that CD4(+)CD25(+) regulatory T cells are present and functional in patients with RA, with higher numbers of regulatory T cells with increased suppressive activity found in SF compared with PB. These findings suggest a negative feedback system that is active at the site of inflammation. The balance between activated responder and regulatory T cells appears to influence the extent of immunoregulation in RA.