Study of phenotype and dynamic of T-cell mediated antifungal immune response in the skin.

BECCACECE I.; BURSTEIN V.L.; GUASCONI L.; ALMEIDA M.; MENA C.; CERVI L.; PRINZ, I.; GRUPPI A.; CHIAPELLO L

Congreso; INFOCUS 2021; 2021

The skin is a physical barrier with a dynamic resident immune system that is crucial tocontrol infection, resolve damage or maintain tissue homeostasis. In the last few yearsit has been discovered that tissue-resident T lymphocytes play a central role in theimmunity against pathogens in barrier organs. Dermatophytes are a highly prevalentcause of human disease worldwide, however, the phenotype and dynamic of skinimmune cell subsets controlling dermatophyte infection remains poorly understood.We have previously demonstrated that IL-17-mediated immunity (IL-17A and IL-17F) isimportant in controlling fungal overgrowth in the skin in an experimental model ofdermatophytosis in C57BL/6 mice (Microsporum canis or Nannizzia gypseaepicutaneous infection). In this study, we aimed to investigate the immune cell subsetsthat produce IL-17A in the skin and the role of tissue-resident cells in the antifungalimmunity during experimental dermatophytosis with N. gypsea.By employing transgenic IL-17A-GFP-reporter mice and flow cytometry (FC) analysis ofepidermal cell suspensions, we observed a significant increase in the frequency of IL-17A-producing CD45+CD3+ T cells at 6 and 8 days of N. gypsea infection in back skin,compared to saline-treated mice (uninfected control, P<0.0001). We demonstrated thatIL-17A in the skin is mainly produced by two distinct populations of leukocytes:conventional βTCR+ and γδTCR-expressing (T) CD3+ T cells.To study the in vivo role of γδT cells in the anti-dermatophytic response we infectedTCRd-GDL transgenic mice, which can be depleted of γδT cells by diphtheria toxintreatment. After N. gypsea infection (8dpi), γδT-depleted mice showed similar levels ofskin fungal burden and IL-17-producing CD45+ skin cell frequency compared to γδT-competent infected controls. In addition, IL-17A production in γδT-depleted animals isproduced not only by CD45+CD3+βTCR+ T lymphocytes but also by CD45+CD3-leukocytes after N. gypsea infection suggesting that, in the abscence of γδT cells, IL-17Aproduction is compensated by different cell populations in the skin.We also investigated the role of skin resident T cells by treating IL-17A-GFP-mice withFingolimod (FTY720, 2μg/g, intraperitoneal daily dose), a drug that prevents the egressof lymphocytes from skin-draining lymph nodes (sdLNs). Flow cytometry analysisrevealed that infected FTY-treated mice showed a diminished number of βTCR+ T cellsinfiltrating the skin compared to infected untreated animals(P<0.05). However, infectedFTY-treated mice maintained a subset of skin resident βTCR+ T and T cells(CD103+CD69+ T cells) that produced IL-17A after infection. Furthermore, nodifferences in the skin fungal burden were observed between FTY-treated vs. untreatedmice, suggesting that skin resident IL-17A-producing βTCR+ T and T cells are sufficientto control dermatophyte infection in a context of impaired influx of T lymphocytes fromsdLNs.Taking together, these data provides new insights about the dynamic of the skin-specificantifungal T cell-mediated response in dermatophytosis showing that IL-17A cytokine isproduced by conventional migratory and resident βTCR+ T and T cell. However, theantifungal immunity in the skin is conserved in the absence of T cell or migratorylymphocytes from skin-draining lymph nodes.