TLR9 activation dampens the early inflammatory response to Paracoccidioides brasiliensis, impacting host survival.
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.


RESULTS
We 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
Our 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.
Life and Health Sciences Research Institute, ICVS, School of Health Sciences, University of Minho, Braga, Portugal.
João Filipe
JF
Menino
Margarida
M
Saraiva
Ana G
AG
Gomes-Alves
Diogo
D
Lobo-Silva
Mark
M
Sturme
Jéssica
J
Gomes-Rezende
Ana Laura
AL
Saraiva
Gustavo H
GH
Goldman
Cristina
C
Cunha
Agostinho
A
Carvalho
Luigina
L
Romani
Jorge
J
Pedrosa
António Gil
AG
Castro
Fernando
F
Rodrigues
D000818:Animals; D004195:Disease Models, Animal; D006651:Histocytochemistry; D007249:Inflammation / Q000473:pathology*; D008099:Liver / Q000473:pathology; D008264:Macrophages / Q000276:immunology / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010228:Paracoccidioides / Q000276:immunology*; D010229:Paracoccidioidomycosis / Q000276:immunology* / Q000473:pathology*; D016019:Survival Analysis; D051217:Toll-Like Receptor 9 / Q000276:immunology*
C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9