Peripheral blood CD8+ T-cell profiles in patients with psoriatic arthritis: a cross-sectional case-control study

E. Colombo, G. Galleri, G.L. Erre, C. Piras, G. Biondi, L. Taras, A. Zinellu, A.A. Mangoni, R. Manetti, M. Montesu, G. Passiu

Rheumatology Unit, Department of Clinical and Experimental Medicine, University of Sassari, Sassari, Italy. e.gianluca@libero.it

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• Rheumatology

OBJECTIVE: While CD4+ T-cells are traditionally regarded as the main pathogenic T-cell subpopulation in psoriatic arthritis (PsA), the role of circulating CD8+ T-cells remains poorly characterized. We evaluated the differential representation of CD8+ T-cell subpopulations in peripheral blood (PB) of PsA patients.

PATIENTS AND METHODS: CD8+IL-17+, CD8+IFNγ+ and CD8+IL-17-IL-22+ T-cells were evaluated by flow-cytometry in 25 consecutive PsA patients, 7 rheumatoid arthritis (RA) patients, 16 patients with psoriasis, and 26 healthy controls (HC).

RESULTS: We observed a significant expansion of circulating IFN-γ producing CD8+ T-cells in PsA when compared to psoriasis [21.2 (6.9-55.8)% vs. 3.8 (0.7-11.8)%, p < 0.0001] and HC samples [21.2 (6.9-55.8)% vs. 4.05 (0.44-19.8)%, p < 0.0001]. A frequency of circulating IFN-γ producing CD8+T-cells ≥ 9% distinguished PsA from psoriasis patients with a specificity of 84% and a sensitivity of 87.5% [AUC = 0.9 (0.80-0.99), p < 0.0001]. In addition, we found a significant expansion of circulating IL-17 producing CD8+ T cells in RA patients when compared to PsA, psoriasis and HC samples. By contrast, there were no significant between-group differences in the prevalence of circulating IL-22 producing CD8+ T-cells. In PsA patients there was a significant correlation between number of swollen joints and frequency of circulating IFN-γ producing CD8+ T-cells, and between extent and severity of psoriasis and frequency of circulating IL-17 producing CD8+ T-cells.

CONCLUSIONS: Circulating IFNγ-producing CD8+ T-cells are raised in PsA when compared to psoriasis, suggesting a potential pathogenetic involvement of CD8+ T-cells and IFNγ production in chronic joint inflammation and damage. The significant enrichment of circulating IL-17 producing CD8+ T-cells in RA when compared to PsA warrants functional characterization and confirmation in larger studies. We found no significant enrichment of circulating IL-22 producing CD8+ T-cells in PsA, RA and psoriasis.

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