Identification of myeloid cells in the human enthesis as the main source of local IL-23 production

Abstract

ObjectiveWe investigated whether the normal human spinal enthesis contained resident myeloid cell populations, capable of producing pivotal proinflammatory cytokines including tumour necrosis factor (TNF) and interleukin (IL)-23 and determined whether these could be modified by PDE4 inhibition.MethodsNormal human enthesis soft tissue (ST) and adjacent perientheseal bone (PEB) (n=15) were evaluated using immunohistochemistry (IHC), digested for myeloid cell phenotyping, sorted and stimulated with different adjuvants (lipopolysaccharide and mannan). Stimulated enthesis fractions were analysed for inducible production of spondyloarthropathy disease-relevant mediators (IL-23 full protein, TNF, IL-1β and CCL20). Myeloid populations were also compared with matched blood populations for further mRNA analysis and the effect of PDE4 inhibition was assessed.ResultsA myeloid cell population (CD45+ HLADR+ CD14+ CD11c+) phenotype was isolated from both the ST and adjacent PEB and termed ‘CD14+ myeloid cells’ with tissue localisation confirmed by CD14+ IHC. The CD14− fraction contained a CD123+ HLADR+ CD11c− cell population (plasmacytoid dendritic cells). The CD14+ population was the dominant entheseal producer of IL-23, IL-1β, TNF and CCL20. IL-23 and TNF from the CD14+ population could be downregulated by a PDE4I and other agents (histamine and 8-Bromo-cAMP) which elevate cAMP. Entheseal CD14+ cells had a broadly similar gene expression profile to the corresponding CD14+ population from matched blood but showed significantly lower CCR2 gene expression.ConclusionsThe human enthesis contains a CD14+ myeloid population that produces most of the inducible IL-23, IL-1β, TNF and CCL20. This population has similar gene expression profile to the matched blood CD14+ population.

Interleukin‐23 pathway at the enthesis: The emerging story of enthesitis in spondyloarthropathy

“…It is worth pointing out that in human SpA and AS in particular, that 50% of cases have subclinical IBD and the thought was that the IL‐23 in disease might be coming from remote sites as in the IL‐23 minicircle above and the SKG model. However, as previously discussed it has now emerged that the human enthesis has robust inducible IL‐23 from myeloid cells …”

“…129 Peripheral monocytes isolated from patients with enthesitis also show enhanced IL-23 secretion when stimulated, when compared to healthy controls. 129 Psoriatic DCs are capable of producing IL-23 and are capable of activating CD4+ T-cells to produce IL-17. 130 Moreover, both macrophages and DC show IL-23 staining within psoriasis plaques.…”

“…Despite these models, the literature strongly supports myeloid cells as being the chief orchestrators of IL‐23–mediated disease. However, it still remains to be seen whether IL‐23 is dominantly produced by enthesis‐resident myeloid cells or those that are tissue‐infiltrating during inflammation . Our group recently investigated myeloid cells in healthy human enthesis and found a CD14+ population, which was the dominant producer of IL‐23 at the normal enthesis .…”

“…However, it still remains to be seen whether IL‐23 is dominantly produced by enthesis‐resident myeloid cells or those that are tissue‐infiltrating during inflammation . Our group recently investigated myeloid cells in healthy human enthesis and found a CD14+ population, which was the dominant producer of IL‐23 at the normal enthesis . Peripheral monocytes isolated from patients with enthesitis also show enhanced IL‐23 secretion when stimulated, when compared to healthy controls …”

“…129 Our group recently investigated myeloid cells in healthy human enthesis and found a CD14+ population, which was the dominant producer of IL-23 at the normal enthesis. 129 Peripheral monocytes isolated from patients with enthesitis also show enhanced IL-23 secretion when stimulated, when compared to healthy controls. 129 Psoriatic DCs are capable of producing IL-23 and are capable of activating CD4+ T-cells to produce IL-17.…”