Pieter C.M. Res

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-17pos, but no IL-22pos 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-γ (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-17Apos CD4 and CD8 T cell clones, suggesting that in vivo IL-22 single-producers may arise from IL-17Apos 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-17Apos 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 cells.

Composition of Innate Lymphoid Cell Subsets in the Human Skin: Enrichment of NCR+ ILC3 in Lesional Skin and Blood of Psoriasis Patients

Innate lymphoid cells (ILCs) are increasingly appreciated as important regulators of tissue homeostasis and inflammation. However, their role in human skin remains obscure. We found that healthy peripheral blood CD117(+) ILC3, lacking the natural cytotoxicity receptor (NCR) NKp44 (NCR(-) ILC3), CD117(-)NCR(-)CRTH2(-)CD161(+) ILC1, and CRTH2(+) ILC2, express the skin-homing receptor cutaneous lymphocyte antigen (CLA). NCR(+) ILC3 were scarce in peripheral blood. Consistently, we identified in normal skin ILC2 and NCR(-) ILC3, a small proportion of CD161(+) ILC1, and hardly any NCR(+) ILC3, whereas NCR(+) ILC3 were present in cultured dermal explants. The skin ILC2 and NCR(+) ILC3 subsets produced IL-13 and IL-22, respectively, upon cytokine stimulation. Remarkably, dermal NCR(-) ILC3 converted to NCR(+) ILC3 upon culture in IL-1β plus IL-23, cytokines known to be involved in psoriatic inflammation. In line with this observation, significantly increased proportions of NCR(+) ILC3 were present in lesional skin and peripheral blood of psoriasis patients as compared with skin and blood of healthy individuals, respectively, whereas the proportions of ILC2 and CD161(+) ILC1 remained unchanged. NCR(+) ILC3 from skin and blood of psoriasis patients produced IL-22, which is regarded as a key driver of epidermal thickening, suggesting that NCR(+) ILC3 may participate in psoriasis pathology.

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

Abstract:  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‐γ, 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‐γ 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 AD.

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-17A.

Cytokine profiles in interstitial fluid from chronic atopic dermatitis skin

The in vivo levels of inflammatory mediators in chronic atopic dermatitis (AD) skin are not well‐defined due to the lack of a non‐invasive or minimally invasive sampling technique.

Enrichment of the rare CD4+ γδ T-cell subset in patients with atypical CD3δ deficiency

demonstrate the novel finding that human ILC2s highly express the signaling lymphocyte activation molecule family member CD84, although this expression is not selective for ILC2s. Allergen challenge did not increase levels of CD84 expression on ILC2s or CD4 cells. We next assessed the percentage of CRTH21 ILC2s in the peripheral blood of cat-allergic subjects before and 4 hours after nasal cat allergen or diluent challenges (Fig 2). The baseline percentage of CRTH21 cells within the lineage-negative population was 10.7 6 1.9 and 12.0 6 1.3 at the diluent and cat allergen challenge visit, respectively (Fig 2, B). Four hours after diluent challenge, the percentage of CRTH21 cells did not change significantly (9.7 6 1.8) compared with time zero. However, after cat allergen challenge, the percentage of CRTH21 cells nearly doubled to 19.1 6 2.6 compared with baseline (P5 .05) and compared with diluent challenge at 4 hours (P < .05) (Fig 2, B). Thus, nasal cat allergen challenge induced an increased percentage of peripheral blood CRTH21 ILC2s when measured 4 hours after challenge. ILC2s produce large amounts of IL-5 and IL-13 in response to IL-25, IL-33, TSLP, and LTD4 and could initiate and/or propagate allergic airway inflammation. Our studies demonstrate that the percentage of CRTH21 ILC2s in the peripheral blood is rapidly increased (within 4 hours) after allergen challenge. Potential mechanisms for the increase in ILC2s in the peripheral blood may be due to enhanced recruitment of ILC2s from the bone marrow triggered by either humoral (cytokine, chemokine, or mediator production in the nose) and/or cellular mechanisms (cells released from the nasal mucosa trafficking to the bone marrow). The human ILC2 marker CRTH2 is the receptor for prostaglandin D2 (PGD2), a lipid mediator that has a known role in chemotaxis and activation of immune cells. Importantly, a previous study demonstrated that high levels of serum 9a,11b-PGF2, the major PGD2 metabolite, are induced within 5 minutes after airway allergen challenge, suggesting that PGD2 is rapidly available systemically for the recruitment of CRTH21 cells after allergen exposure. We have also recently determined that PGD2 induces chemotaxis of CRTH21 human blood ILC2s in vitro, suggesting that PGD2 may directly regulate the migration of human ILC2s into tissues. The role of increased peripheral blood ILC2 numbers after allergen challenge is unclear. One hypothesis is that greater ILC2 availability in the blood (within 4 hours after challenge) may result in greater numbers of cytokine-producing nasal mucosa ILC2s at later time points, but this would need to be investigated in future studies. Strategies to inhibit the recruitment of ILC2s in allergic individuals may reduce tissue TH2 cytokine levels that contribute to allergic inflammation.

House Dust Mite allergens Der f and Der p induce IL‐31 production by blood derived T cells from Atopic Dermatitis patients

Aero‐allergens, such as house dust mite (HDM), have been suggested to play a role in the initiation of atopic dermatitis (AD)‐related skin inflammation. Here, we analysed the proliferation and the cytokine expression of blood‐derived T cells from AD and healthy individuals upon HDM‐allergen stimulation. The proliferating cells from healthy individuals and AD patients had a significantly different, distinct cytokine profile: in AD blood, we found increased frequencies of HDM‐reactive IL‐31‐producing T cells, as well as a decreased Th1/Th2 and Tc1/Tc2 ratio, suggesting that allergen‐specific T cells in blood of chronic AD patients are subject to pre‐existent Th2‐Tc2 and “Th31‐Tc31” programming.