TLR9 Activation Dampens the Early Inflammatory Response to Paracoccidioides brasiliensis, Impacting Host Survival

Abstract

Background Paracoccidioides brasiliensis causes paracoccidioidomycosis, one of the most prevalent systemic mycosis in Latin America. Thus, understanding the characteristics of the protective immune response to P. brasiliensis is of interest, as it may reveal targets for disease control. The initiation of the immune response relies on the activation of pattern recognition receptors, among which are TLRs. Both TLR2 and TLR4 have been implicated in the recognition of P. brasiliensis and regulation of the immune response. However, the role of TLR9 during the infection by this fungus remains unclear.Methodology/Principal findingsWe used in vitro and in vivo models of infection by P. brasiliensis, comparing wild type and TLR9 deficient (−/−) mice, to assess the contribution of TLR9 on cytokine induction, phagocytosis and outcome of infection. We show that TLR9 recognizes either the yeast form or DNA from P. brasiliensis by stimulating the expression/production of pro-inflammatory cytokines by bone marrow derived macrophages, also increasing their phagocytic ability. We further show that TLR9 plays a protective role early after intravenous infection with P. brasiliensis, as infected TLR9−/− mice died at higher rate during the first 48 hours post infection than wild type mice. Moreover, TLR9−/− mice presented tissue damage and increased expression of several cytokines, such as TNF-α and IL-6. The increased pattern of cytokine expression was also observed during intraperitoneal infection of TLR9−/− mice, with enhanced recruitment of neutrophils. The phenotype of TLR9−/− hosts observed during the early stages of P. brasiliensis infection was reverted upon a transient, 48 hours post-infection, neutrophil depletion.Conclusions/SignificanceOur results suggest that TLR9 activation plays an early protective role against P. brasiliensis, by avoiding a deregulated type of inflammatory response associated to neutrophils that may lead to tissue damage. Thus modulation of TLR9 may be of interest to potentiate the host response against this pathogen.

CD103+ Conventional Dendritic Cells Are Critical for TLR7/9-Dependent Host Defense against Histoplasma capsulatum, an Endemic Fungal Pathogen of Humans

“…TLR7 and/or TLR9 are essential for the induction of IFN-I in response to other fungal pathogens such as Paracoccidioides brasiliensis , Candida albicans , Aspergillus fumigatus , and Cryptococcus neoformans [ 5 , 7 , 9 , 42 – 46 ], but little is known about which cells are responsible for producing IFN-I in vivo during infections with these fungi. Our in vitro differentiated BMDCs most closely resemble CD11b + cDCs, and these cells were clearly capable of a robust IFN-I response to Histoplasma infection.…”

Dectin-1 Controls TLR9 Trafficking to Phagosomes Containing β-1,3 Glucan

“…The specificity of TLR9 is not only restricted to microbial DNA but can also directly bind malarial hemozoin resulting in TLR9 conformational changes (58). For fungal organisms, TLR9 can be triggered by fungal DNA (7, 59, 60). TLR9 can recognize fungal species of various groups including C. albicans, A. fumigatus, Cryptococcus neoformans, Saccharomyces cerevisiae, Paracocci brasiliensis, and Malassezia furfur (12, 13, 59).…”

“…For fungal organisms, TLR9 can be triggered by fungal DNA (7, 59, 60). TLR9 can recognize fungal species of various groups including C. albicans, A. fumigatus, Cryptococcus neoformans, Saccharomyces cerevisiae, Paracocci brasiliensis, and Malassezia furfur (12, 13, 59). TLR9 plays an essential and protective role in P. brasiliensis infection as TLR9 −/− mice succumb to death yet had higher TNFα and IL-6 expression (59).…”

“…TLR9 can recognize fungal species of various groups including C. albicans, A. fumigatus, Cryptococcus neoformans, Saccharomyces cerevisiae, Paracocci brasiliensis, and Malassezia furfur (12, 13, 59). TLR9 plays an essential and protective role in P. brasiliensis infection as TLR9 −/− mice succumb to death yet had higher TNFα and IL-6 expression (59). In contrast, TLR9 −/− mice had a survival advantage compared to wild-type mice when challenged with C. albicans and A. fumigatus (6).…”

New insights into a complex fungal pathogen: the case of Paracoccidioides spp.

“…More recently, knockout mice have allowed the role of several molecules that participate in host– Paracoccidiioides interactions to be elucidated. These include interleukin (IL)‐10, IL‐12, IL‐18 (Costa et al ., ; Livonesi et al ., ; Ketelut‐Carneiro et al ., ), nitric oxide (Bernardino et al ., ), dectin‐1 (Loures et al ., ); MyD88, Toll‐like receptor (TLR)‐2, TLR‐4, TLR‐9 (González et al ., ; Loures et al ., , ; Menino et al , ), CCR‐5 (Moreira et al ., , ) and caspase‐1 (Ketelut‐Carneiro et al ., ).…”