The immunomodulatory effect of propolis on receptors expression, cytokine production and fungicidal activity of human monocytes

OBJECTIVES

Propolis is a beehive product and its immunomodulatory action has been documented; however, little is known concerning its mechanisms of action on human cells. Propolis influence on the initial events of the immune response was assessed, evaluating cell markers, cytokine production and the fungicidal activity of human monocytes.

METHODS

Toll-like receptor (TLR)-2, TLR-4, human leukocyte antigen-DR and cluster of differentiation (CD)80 expression by human monocytes was assessed using a FACSCalibur flow cytometer, cytokine production (tumour necrosis factor (TNF)-α and interleukin (IL)-10) was determined by ELISA and the candidacidal activity was investigated after monocytes incubation with propolis and challenged with Candida albicans. The role of TLR-2 and TLR-4 on propolis action was assessed as well.

KEY FINDINGS

Propolis upregulated TLR-4 and CD80 expression and affected TNF-α and IL-10 production, depending on concentration. Propolis also increased the fungicidal activity of monocytes. Cytokine production was decreased by blocking TLR-4, whereas the fungicidal activity was affected by blocking TLR-2.

CONCLUSIONS

Propolis exerted an immunomodulatory action on cell receptors, cytokine production and fungicidal activity of human monocytes without affecting cell viability and depending on concentration. TLR-2 and TLR-4 may be involved in its mechanism of action.

Paracoccidioides brasiliensis uses endogenous and exogenous arachidonic acid for PGE x production

Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis, the most prevalent deep mycosis in Latin America. Production of eicosanoids during fungal infections plays a critical role on fungal biology as well as on host immune response modulation. The purpose of our study was to assess whether P. brasiliensis strains with different degree of virulence (Pb18, Pb265, Bt79, Pb192) produce prostaglandin E(x) (PGE(x)). Moreover, we asked if P. brasiliensis could use exogenous sources of arachidonic acid (AA), as well as metabolic pathways dependent on cyclooxygenase (COX) enzyme, as reported for mammalian cells. A possible association between this prostanoid and fungus viability was also assessed. Our results showed that all strains, independently of their virulence, produce high PGE(x) levels on 4 h culture that were reduced after 8 h. However, in both culture times, higher prostanoid levels were detected after supplementation of medium with exogenous AA. Treatment with indomethacin, a COX inhibitor, induced a reduction on PGEx, as well as in fungus viability. The data provide evidence that P. brasiliensis produces prostaglandin-like molecules by metabolizing either endogenous or exogenous AA. Moreover, the results suggest the involvement of these mediators on fungal viability.

Inhibition of human neutrophil apoptosis by Paracoccidioides brasiliensis: role of interleukin-8

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by Paracoccidiodes brasiliensis that presents a wide spectrum of clinical manifestations. Because of the great number of neutrophils polymorphonuclear neutrophils (PMN) found in the P. brasiliensis granuloma, studies have been done to evaluate the role of these cells during the development of the infection. This fungus is found intracellularly in PMN and monocytes/macrophages, suggesting that it is capable of evading damage and surviving inside these cells. Thus, in the present study, we investigated whether P. brasiliensis can prolong the lifetime of PMN, and if this process would be related with IL-8 levels. PMN apoptosis and intracellular levels of IL-8 were analysed by flow cytometry and culture supernatants IL-8 levels were evaluated by enzyme-linked immunosorbent assay. We found that coincubation with P. brasiliensis yeast cells results in an inhibition of PMN apoptosis, which was associated with increase in IL-8 production by these cells. Cocultures treatment with monoclonal antibody anti-IL-8 reversed the inhibitory effect of P. brasiliensis on PMN apoptosis, besides to increase spontaneous apoptosis of these cells. These data show that, in contrast to other microbial pathogens that drive phagocytes into apoptosis to escape killing, P. brasiliensis can extend the lifetime of normal human PMN by inducing autocrine IL-8 production.