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The cytokine IL-9, derived primarily from T-helper (Th)-9 lymphocytes, promotes expansion of the Th2 subset and is implicated in the mechanisms of allergic asthma. We hypothesize that IL-9 also plays a role in human allergic contact dermatitis (ACD). To investigate this hypothesis, skin biopsy specimens of positive patch test sites from non-atopic patients were assayed using qPCR and immunohistochemistry. Along with Th2 associated cytokines, IFN-γ, IL-4, and IL-17A, expression of IL-9, and PU.1, a Th9-associated transcription factor, were elevated when compared to paired normal skin. Immunohistochemistry on ACD skin biopsies identified PU.1+CD3+, and PU.1+CD4+ cells, consistent with Th9 lymphocytes, in the inflammatory infiltrate. PBMC from nickel-allergic patients, but not non-allergic controls, show significant IL-9 production in response to nickel. Blocking studies with monoclonal antibodies to HLA-DR (but not HLA-A, B, C) or chloroquine significantly reduced this nickel-specific IL-9 production. Additionally, blockade of IL-9 or IL-4 enhanced allergen-specific IFN-γ production. A contact hypersensitivity model using IL-9−/− mice, shows enhanced Th1 lymphocyte immune responses, when compared to WT mice, consistent with our human in vitro data. This study demonstrates that IL-9, through its direct effects on Th1 and ability to promote IL-4 secretion, has a regulatory role for Th1 lymphocytes in ACD.

Dear Editor,Recent articles have drawn the attention to the different types of cutaneous manifestations associated to COVID-19. 1 Notwithstanding, there is a dearth of works focusing on signs involving the nails, whose inspection should be a fundamental component of an adequate dermatological examination.We report the case of an 89-year-old woman in a nursing home who amid an outbreak of coronavirus disease 2019 (COVID-19) presented cough and asthenia. A diagnosis of COVID-19 was made after PCR of a nasopharyngeal swab specimen tested negative to SARS-CoV-2 infection. After 16 weeks from the event, she developed orange discolorations at the end of the nail beds of her fingers (Figure 1). When the ungual lesions were brought to medical attention, a blood test highlighted the presence of IgG against SARS-CoV-2 and ferropenic anemia. The patient also developed sarcopenia, as part of a post-COVID-19 syndrome. Notably, the lesions remained unaltered and had the same features at follow-up a month later.Nails, like the skin, can provide important information regarding the presence and nature of systemic diseases. As a matter of fact, compelling evidence indicates that nails may presumptively be affected by or give clues about COVID-19 as much as the rest of the body. 2,3 In our patient, the shape of the proximal border of discoloration followed the shape of the lunula, indicating a systemic cause.Neri et al 2 reported the case of a COVID-19 patient who developed the "red half-moon" sign, which consists in "distally convex halfmoon-shaped red bands surrounding the distal margin of the lunula".Interestingly, this novel finding has been corroborated by a recent article by Méndes-Flores et al 3 Of note, both case reports involved patients of female sex. However, unlike the evidence that we found in the literature, the nail lesions of our patient were located distally in the nails. Interestingly, similar findings have been documented in patients affected by Kawasaki disease, a disease with a vascular etiology. 4 Recently, transverse leukonychia has been described in a COVID-19 patient. 5

Interleukin 9 is a cytokine classically considered to be associated with the Th2 lymphocyte subset; however, an IL-9 producing T-cell subset, Th9, has recently been recognized and implicated in the pathogenesis of allergic inflammation. 1,2 Despite the known role of this cytokine in various forms of allergic inflammation, the role of IL-9 specifically in allergic contact dermatitis (ACD) has not been fully established. A recent collaborative study conducted by the Departments of Dermatology at the University of Maryland School of Medicine and the University of Rome has contributed to our evolving understanding of the role of IL-9 in ACD by demonstrating that IL-9 serves a regulatory role by modulating allergen-specific IFN-F production by Th1 cells. In the study, a 5-fold increase in gene expression of IL-9 as well as a 2-to 3-fold increase in the Th9 transcription factor PU.1 was present in skin biopsies from 7 patients with positive patch test results to nickel. Furthermore, approximately 4% of the infiltrating CD3 + /CD4 + T cells in positive patch test biopsies from 5 patients with ACD to different allergens were found to be Th9 cells. A robust, dose-dependent production of IL-9 in vitro by peripheral blood mononuclear cells derived from 7 nickel-allergic patients was observed in response to increasing doses of nickel. It was also demonstrated that IL-9 acts to regulate allergen-specific Th1 lymphocyte responses indirectly by enhancing IL-4 production by Th2 lymphocytes. These in vitro data were confirmed in a contact hypersensitivity model using IL-9 j / j mice, which demonstrated enhanced Th1 lymphocyte immune responses when compared with wildtype mice. Surprisingly, irritant contact dermatitis was impaired in IL-9 j/j mice compared with wild-type mice, suggesting a role for IL-9 in promoting an inflammatory response during contact dermatitis. 3 This prompted us to study IL-9 production in extreme cases of ACD at the protein level (ex vivo).We studied 5 extreme bullous patch test reactions (3+) elicited by patch testing with paraphenylenediamine in highly allergic patients. Blister fluid was aspirated at the 48-or 72-hour readings and studied for IL-9 content using an IL-9Yspecific enzyme linked immunosorbent assay. 3 High levels of IL-9 were identified in all 5 ACD specimens (1589 T 459 pg/mL; n = 5). In addition, we measured IL-9 levels in 3 normal human serum controls and blister fluid from 3 different control blistering skin diseases: an ischemic blister, an edema blister, and bullous pyoderma gangrenosum (PG). Interleukin 9 levels were undetectable in all of these samples with the exception of PG, in which IL-9 was mildly elevated (199 pg/mL) (Fig. 1).Significantly elevated levels of IL-9 in extreme patch test reactions suggest that IL-9 may serve as an inflammatory mediator in ACD. The cellular source of IL-9 in the blister fluid is currently unknown, possibly T cells, mast cells, or another cell type. Although further studies are necessary to clarify the role of IL-9 as an inflammatory mediator in AC...

Imiquimod is a TLR7/8 agonist that has anti-cancer therapeutic efficacy in the treatment of pre-cancerous skin lesions and certain non-melanoma skin cancers. To test our hypothesis that imiquimod enhances DNA repair as a mechanism for its anticancer activity, the nucleotide excision repair genes were studied in bone marrow derived cells. Imiquimod enhanced the expression of XPA and other DNA repair genes (qPCR analysis), and resulted in an increased nuclear localization of the DNA repair enzyme XPA. This was dependent on MyD88, as bone marrow derived cells from MyD88−/− mice did not increase XPA gene expression, and did not enhance the survival of MyD88−/− derived bone marrow derived cells after UVB exposure as was observed in bone marrow derived cells from MyD88+/+ mice. Imiquimod also enhanced DNA repair of UVL irradiated gene expression constructs, and accelerated the resolution of cyclobutane pyrimidine dimers (CBPD) after UVL exposures in P388 and XS52. Lastly, topical treatment of mouse skin with 5% imiquimod cream prior to UVL irradiation resulted in a decrease in the number of cyclobutane pyridimine dimer positive, APC that were found in local lymph nodes 24 hours after UVL irradiation in both wild type and IL-12 gene targeted mice. In total, these data support the idea that TLR7 agonists such as imiquimod enhance DNA repair in bone marrow derived cells. This property is likely to be an important mechanism for its anti-cancer effects, because it protects cutaneous APC from the deleterious effects of UVL.

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patients who had COVID-19 and got vaccinated against the SARS-CoV-2 infection is still evolving.Further studies to elucidate the mild to moderate cutaneous reactions to vaccines are warranted.

In general, the use of reflectance confocal microscopy in diseases of the dermis is hampered because of the laser depth penetration limits (~250 µm). 5 In our case, it allowed the detection in the upper dermis of bright structures of different sizes corresponding to the dense lymphohistiocytic infiltrate: the small pinpoint particles likely correlate with lymphocytes, whereas the larger pleomorphic cells with epithelioid histiocytes. Although the dermal infiltrate of epithelioid histiocytes is not specific of CGPD, it is highly suggestive of a granulomatous disease. In conclusion, we have reported the dermoscopy and reflectance confocal microscopy features of CGPD. These techniques, combined with the clinical features, may be useful to narrow down the differential diagnosis, possibly limiting, in selected cases, the need for skin biopsy. Childhood granulomatous periorificial dermatitis is a benign and self-limiting condition, and a prompt diagnosis is important to avoid overtreatment.