Unravelling immunoregulatory circuits of tissue inflammation

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In the past years we had shown that cell-autonomous Complement is produced both from immune and non-immune cells and delineated the major pathways of their induction, notably LFA-induced signals in T cells and type I interferons in respiratory epithelial cells. These findings were important because they indicated that inflamed tissues, which are unable to access plasma-circulating complement, actually represent a complement-rich environment, the complement here being derived from both immune and non-cells. We thus hypothesized that studying transcriptomes of Complement-activated T cells would reveal the effects of Complement on T cells. We showed that Complement induces a self-contained autocrine/paracrine vitamin D (VitD) system in T cells that is required for appropriate inflammatory T cell shut-down, permitting tissue healing to take place. Briefly, we found that Complement induced a cell-intrinsic VitD system permitting T cells to both activate and respond to VitD. Sensing of active VitD caused genome-wide epigenetic changes that generated new and augmented existing super-enhancers, and recruited key TFs (principally VDR, c-JUN, STAT3 and BACH2) that shaped the VitD response in T cells. We found, as we had done before, that BACH2 was a central TF in these events. T cells of patients with COVID-19 showed Th1 hyper-activation and evidence of dysregulation of this VitD shut-down program, indicating either a lack of substrate (VitD deficiency) and/or abnormal regulation of this system. These data may explain the epidemiologic link between vitamin D insufficiency/deficiency and risk of both developing COVID-19 and suffering mortality after infection. They are also noteworthy because they establish cross-regulation between the two main interests of our lab, Complement and the TF BACH2. We found that this system was operational in psoriatic skin and dysregulated in cells from patients with Job and BRIDA syndromes. As part of a collaboration with colleagues in the UK we also showed that activated Vitamin D represses glycolytic programs in effector CD4+ T cells to repress inflammatory functions. This paper was published in Immunology. Finally, through a collaboration with the Portilla and Lionakis labs, respectively, we also demonstrated that the Complement C5 system is also key to activation of myeloid cells in the kidneys that drive tissue scarring following acute kidney injury (the folic acid model) and that C5 is essential for anti-fungal immunity. Thus, C5 antagonism in humans and mice predisposes to invasive fungal diseases. These patients were published in the American Journal of Physiology and are under review, respectively.