Characterization of a New Ex Vivo Model for the Study of Psoriasis Immunopathology

Psoriasis is an inflammatory immune-mediated skin disease that usually occurs in individuals with genetic susceptibility in conjunction with environmental triggers. Circulating effector memory skin-tropic CLA+ T cells have been shown to participate in the development of several immune cell-mediated cutaneous diseases, due to its selective recruitment into the skin and the subsequent rapid effector response upon cognate antigen recognition. Several studies point to the capacity of recirculation of CLA+ T cells between skin and blood, which suggests that in skin diseases implying chronicity, such as psoriasis, the study of circulating CLA+ T cells could constitute peripheral cellular biomarkers and thus providing a tool for translational evaluation of current pathology status. In this regard, we proposed an ex vivo model that uses isolated memory CLA+ T cells from patient’s blood and then are cultured together with autologous epidermal cells, in order to match more accurately a proper intercellular interaction in the cutaneous context of skin lesions. Once established the cellular basis, this experimental approach is completed by the activation with a clinical relevant trigger, the Streptococcus pyogenes. Based on this antigen-specific innate stimulus, the study of the circulating memory CLA+ T-cell subset as a potential carrier of disease-associated information, has allowed the characterization of different aspects of psoriasis disease. Such activation induces, among others, high levels of IL-17 response by CLA+ T cells, which is predominant in case of guttate psoriasis, and correlates with IL-17-regulated transcripts levels in keratinocytes as well, resembling a psoriatic-associated gene expression pattern. Interestingly, IL-17A have been shown to be the key disease-associated cytokine responsible of psoriasis severity in patients. Therefore, the finding of a CLA+ T-cell-selective production of IL-9, which in turn is necessary for optimal production of IL-17A from CLA+ T cells, upon activation with S. pyogenes, suggests a significant Th17-supportive role from other less-characterized skin-homing T-cell lineages in psoriasis. Additionally, we have found a synchronicity in guttate psoriasis-derived CLA+T-cell ex vivo responses to S. pyogenes, the rate of streptococcal exposure (ASO) and disease severity (PASI), thereby supporting that clinical outcomes can be reflected by peripheral CLA+ T cells following encounter of an antigen that initially triggered the disease. However, the assessment of the relation of S. pyogenes-exerted effector function in plaque psoriasis-derived samples with their clinic status, has still to be elucidated. Finally, the early determination of the IL-17-targeted gene ZC3H12A, which encodes for the ribonuclease MCPIP1, in keratinocytes, through strep-induced production of IL-17A by the CLA+/Epi coculture, led to the succeeding characterization of its aberrant, and rapid IL-17A-induced, expression in psoriatic lesions and epidermal cells, respectively, where its ribonuclease activity could be modulating other altered-expressed genes. Overall, psoriatic-associated events can be reproduced ex vivo in a CLA- and SE-dependent manner and provides a tool to expand knowledge and understanding of immune responses in psoriasis.La mayoría de los avances en psoriasis han tenido lugar a través de investigación traslacional. Los linfocitos T circulantes con tropismo cutáneo (CLA+) constituyen biomarcadores celulares para el estudio de enfermedades cutáneas mediadas por células T. El estudio de dichas células periféricas puede aportar información traslacional relevante, por ejemplo, a través del análisis de sus respuestas al ser activadas con desencadenantes asociados a la enfermedad, como el Streptococcus pypogenes, la faringitis por el cual está asociada a la aparición de psoriasis en gotas, y al empeoramiento de la psoriasis en placa. Las células T circulantes CLA+ de pacientes con psoriasis en gotas, en presencia de células epidérmicas autólogas y de un extracto de S. pyogenes (SE), producen una respuesta efectora predominante de tipo Th17 (IL-17A). Otros mediadores relevantes, como el IFN-gamma y la IL-9, también son producidos en este modelo. Curiosamente, se ha observado un pico temporal común entre los niveles de ASO en sangre, de PASI (severidad), y la cantidad de citoquinas producidas por los linfocitos T CLA+. El cocultivo de células T CLA+ y células epidérmicas (CLA+/Epi), provenientes de pacientes con psoriasis en placa, también responden al SE, y producen IL-17A, IFN-gamma e IL-9, ésta última siendo necesaria para la producción óptima de los niveles de IL-17A, tanto en gotas como en placas. Sin embargo, todavía queda por dilucidar qué tipo de relación existe entre la respuesta efectora ex vivo y los aspectos clínicos de estos pacientes. Finalmente, debido a que la IL-17A en psoriasis constituye la citoquina clave responsable de la severidad en la enfermedad, es importante estudiar genes en células cutáneas cuya expresión esté regulada por IL-17A. Así mismo, hemos determinado que la expresión del gen ZC3H12A es inducida en queratinocitos por la IL-17A, y que su producto proteico, la ribonucleasa MCPIP1, se localiza de forma anormal en la epidermis de las lesiones psoriáticas, donde probablemente podría afectar la expresión de otros genes. En conjunto, se han podido estudiar diferentes aspectos de la psoriasis a través del estudio de las células T CLA+ circulantes en respuesta a un estímulo asociado a la enfermedad