Paracoccidioidomycosis (PCM) is a systemic mycosis, endemic in most Latin American countries, especially in Brazil. It is caused by the thermo-dimorphic fungus of the genus Paracoccidioides (Paracoccidioides brasiliensis and Paracoccidioides lutzii). Innate immune response plays a crucial role in host defense against fungal infections, and neutrophils (PMNs) are able to combat microorganisms with three different mechanisms: phagocytosis, secretion of granular proteins, which have antimicrobial properties, and the most recent described mechanism called NETosis. This new process is characterized by the release of net-like structures called Neutrophil Extracellular Traps (NETs), which is composed of nuclear (decondensed DNA and histones) and granular material such as elastase. Several microorganisms have the ability of inducing NETs formation, including gram-positive and gram-negative bacteria, viruses and some fungi. We proposed to identify NETs in tegumentary lesions of patients with PCM and to analyze the interaction between two strains of P. brasiliensis and human PMNs by NETs formation in vitro. In this context, the presence of NETs in vivo was evidenced in tegumentary lesions of patients with PCM by confocal spectrum analyzer. Furthermore, we showed that the high virulent P. brasiliensis strain 18 (Pb18) and the lower virulent strain Pb265 are able to induce different patterns of NETs formation in vitro. The quantification of extracellular DNA corroborates the idea of the ability of P. brasiliensis in inducing NETs release. In conclusion, our data show for the first time the identification of NETs in lesions of patients with PCM and demonstrate distinct patterns of NETs in cultures challenged with fungi in vitro. The presence of NETs components both in vivo and in vitro open new possibilities for the detailed investigation of immunity in PCM.

Fungal recognition by Dectin-1 receptor triggers a series of cellular mechanisms involved in a protective activation of the immune system. In this study, we aimed to evaluate the participation of Dectin-1 receptor in the induction of IL-8, TNF-α, IL-12, IL-10 and IL-17A secretion by human monocytes activated with different cytokines, and challenged in vitro with Paracoccidioides brasiliensis (P. brasiliensis). Our results show that monocytes challenged with P. brasiliensis (Pb265) are able to produce IL-12, IL-8, IL-17, IL-10 and TNF-α. Dectin-1 receptor blockage decreased the IL-12, IL-17, IL-10 and TNF-α levels indicating the participation of such receptor in the induction of these cytokines. Only IL-8 production was not affected by the blockage. Cells activation with different cytokines showed that GM-CSF was able to induce secretion of all cytokines and the receptor blockage prior to the challenge also decreased the cytokine secretion, except IL-8. Monocytes activated with TNF-α promoted IL-8, IL-10 and TNF-α production, whereas stimulation with IFN-γ promoted mainly IL-12 and TNF-α. Thus, these findings bring new and important knowledge about Dectin-1 participation in cytokines production by monocytes challenged with Pb265.

Paracoccidioidomycosis (PCM), a systemic mycosis endemic in Latin America, occurs after inhalation of mycelial components of Paracoccidioides spp. When the fungus reaches the lungs and interacts with the alveolar macrophages and other cells, phagocytic cells such as neutrophils and monocytes are immediately recruited to the injured site. The interaction between surface molecules of pathogens and homologous receptors, present on the surface membrane of phagocytes, modulates the innate immune cell activation. Studies have shown the importance of fungal recognition by the Dectin-1 receptor, which can induce a series of cellular protective responses against fungi. The objective of the present study was to evaluate Dectin-1 receptor expression and the effector mechanisms of human monocytes and neutrophils activated or not with different cytokines, such as IFN-γ, TNF-α, and GM-CSF, followed by the challenge with Paracoccidioides brasiliensis (P. brasiliensis or Pb265). Therefore, analysis of Dectin-1 receptor expression was done by flow cytometry whereas the effector mechanisms were evaluated by fungal recovery by colony-forming unit (CFU) counting and hydrogen peroxide (H2O2) production. Our results showed that, after treatment with IFN-γ, TNF-α, and GM-CSF and challenge with Pb265, cells, especially monocytes, demonstrated an increase in Dectin-1 expression. Both types of cells treated with the cytokines exhibited a decreased fungal recovery and, conversely, an increased production of H2O2. However, when cultures were treated with an anti-Dectin-1 monoclonal antibody, to block the P. brasiliensis binding, a decrease in H2O2 production and an increase in fungal recovery were detected. This effect was observed in all cultures treated with the specific monoclonal antibody. These results show the involvement of the Dectin-1 receptor in fungal recognition and its consequent participation in the induction of the killing mechanisms against P. brasiliensis.