Dendritic cells: phenotypic and functional heterogeneity

Dendritic cells are specialized to capture antigens, process them and present them to T cells to initiate, regulate and fine tune immune responses towards pathogens and tumours. The story of these cells began more than forty years ago and the interest for them is ever growing because of their central role in immunobiology. Dendritic cells are heterogeneous for origin, anatomical localization, phenotype and function: several subsets of myeloid dendritic cells and plasmacytoid dendritic cells have been recognized until now. Dendritic cells differentiate from haematopoietic stem cells-derived precursors, migrate from sites of antigen uptake to lymphoid organs and during this process mature to antigen presenting cells capable of interacting with lymphocytes and stimulate both immune response and peripheral tolerance to self. Since dendritic cells play crucial roles in infection, cancer, allergy, autoimmunity and graft rejection, thorough knowledge of their subsets and behaviour will open the path to tools allowing better control of many clinical conditions

Exosome-delivered microRNAs promote IFN-α secretion by human plasmacytoid DCs via TLR7

The excessive production of type I IFNs is a hallmark and a main pathogenic mechanism of many autoimmune diseases, including systemic lupus erythematosus (SLE). In these pathologies, the sustained secretion of type I IFNs is dependent on the improper activation of plasmacytoid DCs (pDCs) by self-nucleic acids. However, the nature and origin of pDC-activating self-nucleic acids is still incompletely characterized. Here, we report that exosomes isolated from the plasma of SLE patients can activate the secretion of IFN-α by human blood pDCs in vitro. This activation requires endosomal acidification and is recapitulated by microRNAs isolated from exosomes, suggesting that exosome-delivered microRNAs act as self-ligands of innate single-stranded endosomal RNA sensors. By using synthetic microRNAs, we identified an IFN induction motif that is responsible for the TLR7-dependent activation, maturation, and survival of human pDCs. These findings identify exosome-delivered microRNAs as potentially novel TLR7 endogenous ligands able to induce pDC activation in SLE patients. Therefore, microRNAs may represent novel pathogenic mediators in the onset of autoimmune reactions and potential therapeutic targets in the treatment of type I IFN-mediated diseases

Dexamethasone Induces the Expression and Function of Tryptophan-2-3-dioxygenase in SK-MEL-28 Melanoma Cells

Tryptophan-2,3-dioxygenase (TDO) is one of the key tryptophan-catabolizing enzymes with immunoregulatory properties in cancer. Contrary to expectation, clinical trials showed that inhibitors of the ubiquitously expressed enzyme, indoleamine-2,3-dioxygenase-1 (IDO1), do not provide benefits in melanoma patients. This prompted the hypothesis that TDO may be a more attractive target. Because the promoter of TDO harbors glucocorticoid response elements (GREs), we aimed to assess whether dexamethasone (dex), a commonly used glucocorticoid, modulates TDO expression by means of RT-PCR and immunofluorescence and function by assessing cell proliferation and migration as well as metalloproteinase activity. Our results show that, in SK-Mel-28 melanoma cells, dex up-regulated TDO and its downstream effector aryl hydrocarbon receptor (AHR) but not IDO1. Furthermore, dex stimulated cellular proliferation and migration and poten-tiated MMP2 activity. These effects were inhibited by the selective TDO inhibitor 680C91 and enhanced by IDO1 inhibitors. Taken together, our results demonstrate that the metastatic melanoma cell line SK-Mel-28 possesses a functional TDO which can also modulate cancer cell phenotype di-rectly rather than through immune suppression. Thus, TDO appears to be a promising, tractable target in the management or the treatment of melanoma progression

Effect of cigarette smoke and treatment with relaxin on guinea pig skin

Cigarette smoking causes microvascular dysfunction and skin aging. Relaxin, primarily but not exclusively involved in reproduction, has connective tissue among its targets. Within a project on the interference of relaxin with the effects of smoke on guinea pigs, we examined the skin response to those stimuli. Adult guinea pigs were exposed to cigarette smoke daily for 8 weeks, and some of them were treated also with relaxin, 1 or 10 µg/die. Controls were treated with relaxin vehicle alone. The skin was analyzed by light and electron microscopy and histochemistry for mast cells and the collagen specific chaperonin Hsp47. The epidermis appeared unaffected by any treatment. In the superficial dermis, smoke led to a decrease in mast cell number and intensity of astra blue staining, suggestive of granule discharge. Relaxin caused further significant reduction in mast cell number. In the superficial and deep dermis, the staining intensity of Hsp47 positive cells, assumed as active fibroblasts, increased upon smoke. The staining intensity decreased gradually in the superficial dermis upon relaxin, reaching significance after treatment with 10 µg/die relaxin, while in the deep dermis it decreased significantly upon treatment with 1 µg/die relaxin and underwent further, significant increase with 10 µg/die relaxin. The results suggest that relaxin can enhance skin mast cell secretory response, possibly antagonizing nicotine induced vasoconstriction and, depending on dose and localization of responding cells, can counteract the profibrotic stimulus of smoke on dermal fibroblasts

Age-dependent NK cell dysfunctions in severe COVID-19 patients

Natural Killer (NK) cells are key innate effectors of antiviral immune response, and their activity changes in ageing and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Here, we investigated the age-related changes of NK cell phenotype and function during SARS-CoV-2 infection, by comparing adult and elderly patients both requiring mechanical ventilation. Adult patients had a reduced number of total NK cells, while elderly showed a peculiar skewing of NK cell subsets towards the CD56lowCD16high and CD56neg phenotypes, expressing activation markers and check-point inhibitory receptors. Although NK cell degranulation ability is significantly compromised in both cohorts, IFN-γ production is impaired only in adult patients in a TGF-β-dependent manner. This inhibitory effect was associated with a shorter hospitalization time of adult patients suggesting a role for TGF-β in preventing an excessive NK cell activation and systemic inflammation. Our data highlight an age-dependent role of NK cells in shaping SARS-CoV-2 infection toward a pathophysiological evolution