Role of TLR2 and TLR4 in Human Neutrophil Functions AgainstParacoccidioides brasiliensis

Abstract

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.

Fonsecaeapedrosoi Conidia and Hyphae Activate Neutrophils Distinctly: Requirement of TLR-2 and TLR-4 in Neutrophil Effector Functions

“…Using immunofluorescence microscopy, we verified that the absence of TLR-2 and TLR-4 leads to impaired conidial phagocytosis ( Figure 1F and Supplementary Figure 2). Similar results were seen in P. brasiliensis (51,52) and Sporothrix brasiliensis (53,54) infection. In contrast, in C. albicans and A. fumigatus infection, TLR-4 does not play a crucial role in the phagocytic process (55,56).…”

Effect of ArtinM on Human Blood Cells During Infection With Paracoccidioides brasiliensis

“…The increase in phagocytosis promoted by ArtinM may be related to the high production of cytokines, such as TNF-α and IFN-γ by these cells when in the presence of the lectin ( Figures 1 , 2 , 4 , 5 ). In fact, several authors have reported the importance of cytokines in the activation of phagocytic cells and killing of P. brasiliensis yeast ( Cano et al, 1992 ; Moscardi-Bacchi et al, 1994 ; Calvi et al, 2003 ; Carmo et al, 2006 ; Rodrigues et al, 2007 ; Acorci-Valério et al, 2010 ). Similar to ArtinM, a plant lectin, natural components, such as propolis, have been shown to improve the fungicidal activity of macrophages against P. brasiliensis ( Murad et al, 2002 ).…”

Low-level Laser Therapy to the Mouse Femur Enhances the Fungicidal Response of Neutrophils against Paracoccidioides brasiliensis

“…PMN from infected patients may inactivate Pb [ 36 ] and are considered important as immune attack cells that contribute to the host response against this fungal infection, especially in the early stages of PCM [ 37 ]. Nevertheless, neutrophil functions such as fungal killing require activation by cytokines and other elements of the immune system [ 37 ]; IFN-γ, TNF-α, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-15 are some examples of factors that can activate human neutrophils to carry out increased fungicidal activity by a mechanism dependent on production of ROS such as H 2 O 2 and superoxide anion [ 38 , 39 ].…”