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The glycoprotein gp43 is an immunodominant antigen secreted by Paracoccidioides brasiliensis, the agent of paracoccidioidomycosis. The present study evaluated whether gp43 can interact with toll-like (TLR2, TLR4) and mannose (MR) receptors on the surface of human monocytes, and how that affects their expression and cytokine production. Monocytes were incubated with or without monoclonal antibodies anti-TLR2, anti-TLR4, or anti-MR, individually or in combination, prior to the addition of gp43. The gp43 binding to monocyte surface, as well as expression of TLR2, TLR4, and MRs were analyzed by flow cytometry, while production of TNF-α and IL-10 was monitored by ELISA. The results suggested that gp43 binds to TLR2, TLR4, and MR receptors, with TLR2 and MR having the strongest effect. All three receptors influenced the production of IL-10, while TNF-α production was associated with expression of TLR4 and MR. The modulatory effect of gp43 was demonstrated by high levels of TLR4 expression associated with increased production of TNF-α after 4 h of culture. Alternatively, high levels of TLR2 expression, and elevated production of IL-10, were detected after 18 h. We showed that interaction between gp43 and monocytes may affect the innate immune response by modulating the expression of the pattern recognition receptors TLR2, TLR4 and MR, as well as production of pro- and anti-inflammatory cytokines.

In paracoccidioidomycosis, a systemic mycosis caused by the fungus Paracoccidioides brasiliensis (Pb), studies have focused on the role of neutrophils that are involved in primary response to the fungus. Neutrophil functions are regulated by pro‐ and anti‐inflammatory cytokines. The molecular mechanisms involved in this process are not fully understood, but there are strong evidences about the involvement of toll‐like receptors (TLR). We aimed at evaluating TLR2 and TLR4 expression on human neutrophils activated with GM‐CSF, IL‐15, TNF‐α or IFN‐γ and challenged with a virulent strain of P. brasiliensis (Pb18). Moreover, we asked if these receptors have a role on fungicidal activity, H2O2 and IL‐6, IL‐8, TNF‐α and IL‐10 production by activated and challenged cells. All cytokines increased TLR2 and TLR4 expression. Pb18 also increased TLR2 expression inducing an additional effect to that of cytokines. On the contrary, it inhibited TLR4 expression. All cytokines increased neutrophil fungicidal activity and H2O2 production, but this process was not associated with TLR2 or TLR4. Neutrophils activation with GM‐CSF and TNF‐α resulted in a significative increase in IL‐8 production, while IL‐15 and IFN‐γ have no effect. Pb18 alone also increased IL‐8 production. None of the cytokines activated neutrophils for IL‐10 release. This cytokine was only detected after Pb18 challenge. Interestingly, IL‐8 and IL‐10 production involved TLR2 and mainly TLR4 modulation. Our data suggest that Pb18 uses TLR4 to gain access to human neutrophils. This interaction results in IL‐8 and IL‐10 production that may be considered as a pathogenic mechanism in paracoccidioidomycosis.

Silibinin is a chemically defined flavonoid and the main active component of silymarin, a polyphenolic complex from Silybum marianum, which has anti-inflammatory, hepatoprotective and anticarcinogenic properties. Monocytes obtained from healthy individuals were incubated with silibinin to evaluate cell viability, hydrogen peroxide (H(2)O(2)) release and tumour necrosis factor-alpha (TNF-α) production by these cells. The duration of treatment and different silibinin concentrations had no significant effect on cell viability. Monocytes showed a dose-dependent inhibitory effect on H(2)O(2) release by phorbol myristate acetate-stimulated monocytes in silibinin concentrations ranging from 6.25 to 50 µg mL(-1). Significant inhibition of TNF-α production by lipopolysaccharide-stimulated monocytes was observed at concentrations of 12.5, 50 and 100 µg mL(-1) of silibinin. These results suggest that silibinin exerts antioxidant and anti-inflammatory properties on human monocytes through an inhibitory effect on H(2)O(2) release and on TNF-α production, respectively.