Background Leprosy is a chronic infectious disease caused by Mycobacterium leprae. Patients have distinct clinical forms, and the host´s immunological response regulate those manifestations. In this work, the presence of the myeloid-derived suppressor cell and the regulatory protein annexin A1 is described in patients with multibacillary leprosy and with type 1 and 2 reactions. Methods Patients were submitted to skin biopsy for histopathological analysis to obtain a bacilloscopic index. Immunofluorescence was used to detect myeloid-derived suppressor cells and annexin A1. Results The data demonstrated that the presence of granulocytic and monocytic myeloid-derived suppressor cells in leprosy patients. A high number of monocytic myeloid-derived suppressor cells were observed in lepromatous leprosy and type 2 reactional patients. The presence of annexin A1 was observed in all myeloid-derived suppressor cells. In particular, the monocytic myeloid-derived suppressor cell in the lepromatous patients has higher levels of this protein when compared to the reactional patients. This data suggest that the higher expression of this protein may be related to regulatory response against a severe infection, contributing to anergic response. In type 1 reactional patients, the expression of annexin A1 was reduced. Conclusions Myeloid-derived suppressor cell are present in leprosy patients and annexin A1 might be regulated the host response against Mycobacterium leprae.

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Background: Leprosy is a chronic infectious disease caused by Mycobacterium leprae. Patients have distinct clinical forms, and host´s immunological response regulate those manifestations. In this work, the presence of the myeloid-derived suppressor cell and the regulatory protein annexin A1 is described in patients with multibacillary leprosy and with type 1 and 2 reactions. Methods: Patients were submitted to skin biopsy for histopathological analysis to obtain bacilloscopic index. Immunofluorescence was used to detect myeloid-derived suppressor cells and annexin A1.Results: The data demonstrated that the presence of granulocytic and monocytic myeloid-derived suppressor cells in leprosy patients. The high number of monocytic myeloid-derived suppressor cells were observed in lepromatous leprosy and type 2 reactional patients with Bacillus Calmette–Guérin (BCG) vaccination scar. The presence of annexin A1 was observed in all myeloid-derived suppressor cells. In particularly, the monocytic myeloid-derived suppressor cell in the lepromatous patients has higher levels of this protein when compared to the reactional patients. This data suggest that the higher expression of this protein may be related to regulatory response against a severe infection, contributing to anergic response. In type 1 reactional patients, the expression of annexin A1 was reduced. Conclusions: Myeloid-derived suppressor cell are present in leprosy patients and annexin A1 might be regulated the host response against Mycobacterium leprae.