As a zoonotic disease that has already spread globally to several million human beings and possibly to domestic and wild animals

The pandemic of coronavirus disease 2019 (COVID‐19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), has caused an unprecedented global social and economic impact, and high numbers of deaths. Many risk factors have been identified in the progression of COVID‐19 into a severe and critical stage, including old age, male gender, underlying comorbidities such as hypertension, diabetes, obesity, chronic lung diseases, heart, liver and kidney diseases, tumors, clinically apparent immunodeficiencies, local immunodeficiencies, such as early type I interferon secretion capacity, and pregnancy. Possible complications include acute kidney injury, coagulation disorders, thoromboembolism. The development of lymphopenia and eosinopenia are laboratory indicators of COVID‐19. Laboratory parameters to monitor disease progression include lactate dehydrogenase, procalcitonin, high‐sensitivity C‐reactive protein, proinflammatory cytokines such as interleukin (IL)‐6, IL‐1β, Krebs von den Lungen‐6 (KL‐6), and ferritin. The development of a cytokine storm and extensive chest computed tomography imaging patterns are indicators of a severe disease. In addition, socioeconomic status, diet, lifestyle, geographical differences, ethnicity, exposed viral load, day of initiation of treatment, and quality of health care have been reported to influence individual outcomes. In this review, we highlight the scientific evidence on the risk factors of severity of COVID‐19.

CD4+CD25+ regulatory T cells (Treg) can inhibit a variety of autoimmune and inflammatory diseases, but their involvement in regulating virus-induced immunopathology is not known. We have evaluated the role of Treg in viral immunopathological lesion stromal keratitis. This frequent cause of human blindness results from a T cell-mediated immunoinflammatory response to HSV in the corneal stroma. The results show that lesions were significantly more severe if mice were depleted of Treg before infection. The Treg was also shown to modulate lesion expression induced by adoptive transfer of pathogenic CD4+ T cells in infected SCID recipients. The mechanism of Treg control of stromal keratitis involved suppressed antiviral immunity and impaired expression of the molecule required for T cell migration to lesion sites. Interestingly, Treg isolated from ocular lesions in nondepleted mice showed in vitro inhibitory effects involving IL-10, but were not very effective in established lesions. Our results decipher the in vivo role of Treg in a virus-induced immunopathology and imply that manipulation of regulatory cell function represents a useful approach to control viral-induced immunoinflammatory disease.

Allergy is a Th2-mediated disease that involves the formation of specific IgE antibodies against innocuous environmental substances. The prevalence of allergic diseases has dramatically increased over the past decades, affecting up to 30% of the population in industrialized countries. The understanding of mechanisms underlying allergic diseases as well as those operating in non-allergic healthy responses and allergen-specific immunotherapy has experienced exciting advances over the past 15 years. Studies in healthy non-atopic individuals and several clinical trials of allergen-specific immunotherapy have demonstrated that the induction of a tolerant state in peripheral T cells represent a key step in healthy immune responses to allergens. Both naturally occurring thymus-derived CD4 1 CD25 1 FOXP3 1 Treg and inducible type 1 Treg inhibit the development of allergy via several mechanisms, including suppression of other effector Th1, Th2, Th17 cells; suppression of eosinophils, mast cells and basophils; Ab isotype change from IgE to IgG4; suppression of inflammatory DC; and suppression of inflammatory cell migration to tissues. The identification of the molecules involved in these processes will contribute to the development of more efficient and safer treatment modalities.Key words: Allergy . Allergen-specific immunotherapy . Tolerance . Treg IntroductionThe immune system is a complex interactive network with the capacity to protect the host from a broad range of pathogens while keeping a state of tolerance to self and innocuous non-self antigens. Immune tolerance-related diseases such as allergy, autoimmunity, tumor tolerance and rejection of organ transplants arise as a direct consequence of dysregulated immune responses. The main clinical manifestations of allergy encompass allergic rhinitis, allergic asthma, food allergy, atopic eczema/ dermatitis and anaphylaxis. Currently, allergen-specific immunotherapy (allergen-SIT) by administration of increasing doses of allergen extracts remains as the single curative treatment of allergic diseases with the potential to modify the course of the disease [1].Adoptive transfer experiments in mouse models of allergy and asthmatic inflammation have shown that Treg are essential for the induction and maintenance of immune tolerance to allergens [2]. In humans, studies on immune responses to allergens in healthy individuals have demonstrated the existence of dominant Treg subsets specific to common environmental allergens [3]. In addition, allergen-SIT represents the only clinically established treatment that induces antigen-specific Treg and peripheral tolerance with the capacity to restore homeostasis in human subjects [3][4][5][6][7][8]. Accordingly, active immune regulation through allergen-specific Treg emerges as a potential therapeutic option 1232Review in the prevention and cure of allergic diseases. The aim of this review is to discuss the immune regulation mechanisms operating in allergic diseases with a focus on the role of Treg in the generation of tolerance agai...