Immunomodulation by Paracoccin: mechanisms of protection conferred against experimental paracoccidioidomycosis

Abstract

The thermally dimorphic fungus Paracoccidioides brasiliensis is the causative agent of paracoccidioidomycosis (PCM), endemic in Latin America with the highest prevalence in Brazil, Venezuela and Colombia. The PCM has systemic action and is usually related to granulomatous processes of chronic evolution. During the process of infection by P. brasiliensis antigens found on fungal cell wall are recognized by sentinel cells such as macrophages and dendritic cells. These cells have pattern recognition receptors that interact with highly conserved antigens which are associated with the pathogen. After recognizing the antigen, macrophages and dendritic cells become active in order to eliminate the pathogen and present these antigens to T lymphocytes, initiating an adaptive response. The control of PCM is related to adaptive response Th1, while Th2 response is linked to greater severity of PCM.Lectins are proteins that have the characteristic to bind specifically and reversibly to carbohydrates, some lectins are capable of direct immune response to a specific profile, featuring an immunomodulatory effect. Our group has been working with a lectin of P. brasiliensis, called Paracoccin. This lectin has affinity for N-acetylglucosamine and is distributed on the cell surface of yeast highlighting regions of budding and fungal growth. It is known that Paracoccin induces macrophages to produce pro-inflammatory cytokines such as TNF-± and IL-12 as well as NO.The fact of Paracoccin trigger secretion of IL-12 by macrophages, Th1-related cytokine that participates in the control of PCM, prompted our group to evaluate the prophylactic and therapeutic administration of recombinant Paracoccin (rPCN) in an experimental model of PCM. It was demonstrated protective and immunomodulatory effects when rPCN was administered in vivo by reducing fungal load in the lungs and increased levels of pro-inflammatory cytokines that characterize Th1 profile. In addition, rPCN induced peritoneal macrophages to produce the same cytokine profile as compared to native Paracoccin, as demonstrated by preliminary results. Considering these results, and the effect promoted by the administration of Paracoccin in experimental PCM, the present study aims investigating the effects exerted in vitro by rPCN on murine macrophages and dendritic cells. Therefore, we propose to evaluate: (1) the profile of cytokines secreted in vitro, (2) the expression of innate immunity receptors on the cell surface, (3) the phagocytic activity combined with cell survival, (4) the profile of cytokines in naive mice to which was administered rPCN. Accomplishing these goals will open up possibilities to elucidate the mechanisms responsible for protective immunity conferred by in vivo administration of recombinant form of this fungal component.