Interleukin 23 (IL-23) plays a major role in differentiation and survival of IL-17-secreting CD4+ Th17 cells. Having noted a higher frequency of Th17 cells in ankylosing spondylitis (AS) and rheumatoid arthritis (RA) than in healthy donors (HD), we investigated whether IL-23 secretion is increased in these conditions.
Monocyte-derived dendritic cells (moDC) were obtained from peripheral blood of 17 HD, 16 patients with RA, and 30 patients with AS, and stimulated with ligands for several pathogen recognition receptors. Messenger RNA (mRNA) expression and cytokine secretion were analyzed by real-time polymerase chain reaction and ELISA, respectively.
The combination of ligands for Toll-like receptors (TLR) 7/8 and TLR3 led to synergistic secretion of both IL-23 and IL-12p70 from all subjects; similar synergy was seen with TLR2 ligands and curdlan. However, for both combinations, moDC from patients with RA produced significantly lower amounts of IL-23 than moDC from patients with AS; in contrast, IL-12p70 secretion did not differ. Similarly, tumor necrosis factor-α, IL-6, and IL-10 were secreted at comparable levels in all subjects, whereas CXCL8 and CCL3 production was actually enhanced in moDC of patients with RA. Equivalent levels of mRNA for both IL-23p19 and IL-12p35 subunits were found in moDC from all donors, suggesting posttranscriptional regulation of IL-23 production in RA.
Our observations show that IL-23 production is decreased in RA and maintained in AS. Because increased numbers of CD4+IL-17+ T cells are seen in both diseases, these observations imply that there are different mechanisms underlying chronic inflammation in these 2 forms of inflammatory arthritis.