Overrepresentation of IL-17A and IL-22 Producing CD8 T Cells in Lesional Skin Suggests Their Involvement in the Pathogenesis of Psoriasis

Background: Although recent studies indicate a crucial role for IL-17A and IL-22 producing T cells in the pathogenesis of psoriasis, limited information is available on their frequency and heterogeneity and their distribution in skin in situ. Methodology/Principal Findings: By spectral imaging analysis of double-stained skin sections we demonstrated that IL-17 was mainly expressed by mast cells and neutrophils and IL-22 by macrophages and dendritic cells. Only an occasional IL-17(pos), but no IL-22(pos) T cell could be detected in psoriatic skin, whereas neither of these cytokines was expressed by T cells in normal skin. However, examination of in vitro-activated T cells by flow cytometry revealed that substantial percentages of skin-derived CD4 and CD8 T cells were able to produce IL-17A alone or together with IL-22 (i.e. Th17 and Tc17, respectively) or to produce IL-22 in absence of IL-17A and IFN-gamma (i.e. Th22 and Tc22, respectively). Remarkably, a significant proportional rise in Tc17 and Tc22 cells, but not in Th17 and Th22 cells, was found in T cells isolated from psoriatic versus normal skin. Interestingly, we found IL-22 single-producers in many skin-derived IL-17A(pos) CD4 and CD8 T cell clones, suggesting that in vivo IL-22 single-producers may arise from IL-17A(pos) T cells as well. Conclusions/Significance: The increased presence of Tc17 and Tc22 cells in lesional psoriatic skin suggests that these types of CD8 T cells play a significant role in the pathogenesis of psoriasis. As part of the skin-derived IL-17A(pos) CD4 and CD8 T clones developed into IL-22 single-producers, this demonstrates plasticity in their cytokine production profile and suggests a developmental relationship between Th17 and Th22 cells and between Tc17 and Tc22 cell

Increased frequencies of IL-31-producing T cells are found in chronic atopic dermatitis skin

Interleukin (IL)-31 has been associated with pruritus, a characteristic feature of atopic dermatitis (AD). Local T cell responses may be responsible for the increased level of IL-31 mRNA observed in AD. We investigated the frequency of IL-31-producing T cells in AD lesions, as well as their cytokine profile. T cells were isolated from chronic AD lesions, autologous blood and healthy donor skin. Intracellular expression of IL-31, IFN-?, IL-13, IL-17 and IL-22 was measured using flow cytometry. T cells from AD lesions contained significantly higher percentages of IL-31-producing T cells compared to autologous blood and donor skin. Many IL-31-producing T cells co-produced IL-13 and to lesser extent IL-22, but rarely IFN-? or IL-17. A substantial part of the IL-31-producing T cells did not co-produce any of the other cytokines and could therefore not be linked to any of the known functionally different T cell subsets. The T cell infiltrates were also relatively enriched for Th2/Tc2 and Th22/Tc22 cells, while frequencies of Th1/Tc1 and Th17 cells were decreased. This is the first report describing the detection of IL-31 at protein level in skin-infiltrating T cells. We show here that T cells in chronic AD skin produce IL-31 and that AD lesions contain increased levels of these IL-31-producing T cells. This suggests that a substantial part of previously reported increased IL-31 mRNA levels in AD skin is T cell derived and that these cells may be involved in the pathogenesis of A

The IL-17A-producing CD8+ T-cell population in psoriatic lesional skin comprises mucosa-associated invariant T cells and conventional T cells

IL-17A is pivotal in the etiology of psoriasis, and CD8(+) T cells with the ability to produce this cytokine (Tc17 cells) are over-represented in psoriatic lesions. Here we demonstrate that the frequency of Tc17 cells in peripheral blood of psoriasis patients correlated with the clinical severity of the disease. Analysis of cutaneous-associated lymphocyte antigen expression showed that the blood Tc17 population contains a significantly higher proportion of cells with skin-homing potential compared with the CD8(+) T-cell population lacking IL-17A/IL-22 expression. IL-17A-producing CD8(+) T cells in blood have previously been reported to belong mainly to the mucosa-associated invariant T-cell (MAIT cell) lineage characterized by TCR Vα7.2 chain, CD161, IL-18Rα, and multidrug transporter ABCB1 expression. We demonstrate the presence of CD8(+) MAIT cells in the dermis and epidermis of psoriatic plaques, as well as healthy skin; however, IL-17A-producing CD8(+) MAIT cells were predominantly found in psoriatic skin. Notably, we observed IL-17A production in a large proportion of psoriatic plaque-derived CD8(+) T cells devoid of MAIT cell characteristics, likely representing conventional CD8(+) T cells. In conclusion, we provide supporting evidence that implicates Tc17 cells in the pathogenesis of psoriasis and describe the presence of innate CD8(+) MAIT cells in psoriatic lesions as an alternative source of IL-17

Cytokine profiles of dermis-derived CD4 and CD8 bulk T cell populations.

<p>Relative contribution of T cells with different expression profiles of IL-17A, IL-22 and IFN-γ production among <i>in vitro</i> activated dermal CD4 T cells (a) and CD8 T (b) from psoriatic skin (closed symbols) versus normal skin (open symbols). Each series of a particular symbol represents data from one individual. Specifically T cells with the ability to produce IL-17A and/or IL-22 are present in increased percentages of the CD8 T cell population in lesional skin compared to normal skin. *P<0.05; **P<0.01 Depicted data show the results obtained by six color flow cytometry of the eight independent experiments.</p

Cytokine profile of psoriatic skin derived Th17 and Tc17 clones.

<p>IL-17A^pos CD4 and CD8 T cell clones (Th17 and Tc17, respectively) from psoriatic skin have the ability to give rise to a proportion of IL-22 producing cells that lack IL-17A and IFN-γ expression (the putative Th22 and Tc22, respectively). IL-17A^pos CD4 dermal T cells and CD8 epidermal T cells derived from psoriatic skin were cloned and subsequently assayed for intracellular IL-17A, IL-22, and IFN-γ after PMA ionomycin stimulation. Representative examples of CD4 and CD8 T cell clones are given. Part of the cells within the CD4 Th17 clone expressed IL-22, but lacked both IL-17A (right-bottom quadrant in the upper dot-plot) and IFN-γ expression (associated histogram indicated by arrow), a cytokine pattern typical of Th22 cells. Likewise, part of the cells of the CD8 Tc17 clone (bottom dot-plot) lacked IL-17A and IFN-γ expression, which is a Tc22 cytokine profile.</p

Cytokine expression in skin derived dermal T cells after in vitro stimulation.

<p>T cells with the ability to produce IL-17A and/or IL-22 and/or IFN-γ are present in the dermis of both psoriatic and normal skin. Bulk T cells derived from the dermis were stimulated with PMA and ionomycin and stained for cell surface expression of CD3, CD4 and CD8 and intracellular expression of IL-17A, IL-22 and IFN-γ. Dot-plots contain the CD3 cells within the lymphocyte gate. This analysis shows the presence among dermal CD3 T cells of both normal and psoriatic skin of single and double producers of IL-17A, IL-22 and IFN-γ. Results are representative for eight independent experiments.</p