Pulmonary paracoccidioidomycosis in AhR deficient hosts is severe and associated with defective Treg and Th22 responses

Abstract

AhR is a ligand-activated transcription factor that plays an important role in the innate and adaptive immune responses. In infection models, it has been associated with host responses that promote or inhibit disease progression. In pulmonary paracoccidioidomycosis, a primary fungal infection endemic in Latin America, immune protection is mediated by Th1/Th17 cells and disease severity with predominant Th2/Th9/Treg responses. Because of its important role at epithelial barriers, we evaluate the role of AhR in the outcome of a pulmonary model of paracoccidioidomycosis. AhR −/− mice show increased fungal burdens, enhanced tissue pathology and mortality. During the infection, AhR −/− mice have more pulmonary myeloid cells with activated phenotype and reduced numbers expressing indoleamine 2,3 dioxygenase 1. AhR-deficient lungs have altered production of cytokines and reduced numbers of innate lymphoid cells (NK, ILC3 and NCR IL-22). The lungs of AhR −/− mice showed increased presence Th17 cells concomitant with reduced numbers of Th1, Th22 and Foxp3 + Treg cells. Furthermore, treatment of infected WT mice with an AhR-specific antagonist (CH223191) reproduced the main findings obtained in AhR −/− mice. Collectively our data demonstrate that in pulmonary paracoccidioidomycosis AhR controls fungal burden and excessive tissue inflammation and is a possible target for antifungal therapy. AhR is a ligand-activated cytosolic transcription factor with known involvement in the metabolism of xenobiotic compounds. It mediates the toxic effects of man-made aryl hydrocarbons including 2,3,7,8-tetrachlorodibenzenop-dioxin (also known as TCDD or Dioxin) 1 but can also be activated by a diverse set of endogenous and exogenous ligands 2. In steady state, AhR remains in the cytoplasm as part of an inactive complex composed of several chaperone proteins 3. Upon ligand binding, AhR is released, translocate to the nucleus and heterodimerizes with its partner AhR Nuclear Translocator (ARNT). The heterodimer can bind genomic regions containing its binding motif, thereby inducing the transcription of target genes including detoxifying enzymes of the cytochrome P 450 family 4 and the AhR repressor that disrupts the AhR/ARNT complex and attenuates AhR signaling. In the nucleus, AhR can interact with several transcription factors that regulate its activity 3. The degree of AhR activation may dependent on the structure and receptor affinity of the ligand. Several tryptophan (Trp) degradation products such as Kynurenine (Kyn), produced by the enzymatic action of indoleamine 2,3 dioxygenase (IDO-1) and 6-formylindolo[3,2-b] carbazole (FICZ), a tryptophan condensation product, are well known AhR ligands 5,6. AhR is expressed by cells of the innate and adaptive immune system and participates in the control of cell proliferation, differentiation and cytokine secretion 6-10. In 2008, different laboratories showed that AhR contributes to the differentiation of Th17 and regulatory T cells (Treg) 8-10. Interestingly, two different AhR ligands (TCDD and...

AhR Ligands Modulate the Differentiation of Innate Lymphoid Cells and T Helper Cell Subsets That Control the Severity of a Pulmonary Fungal Infection

“…CH223191 treatment reduced the number of IDO+ CD11c+ cells and increased the number of viable P. brasiliensis yeasts present in the lungs at both time points studied. This agrees with our previous reports demonstrating the increased P. brasiliensis growth when IDO is metabolically inhibited or genetically ablated, possibly by the increased TRP availability for fungal metabolism (34)(35)(36)(37), The reduction in IDO was concomitant with that of AhR, the two components that are mutually controlled (14). Contrasting the treatments with FICZ and L-Kyn, CH223191 caused a large increase in the number of CD11c+ myeloid cells expressing activation molecules, intracellular TNF-a and a preferential expansion of myeloid DCs.…”

“…This transcription factor is expressed by epithelial and immune cells, is involved in mucous secretion (59) and the balanced immune response in the lung (49). In accordance, our studies have demonstrated the important participation of AhR in the control of disease severity and immune response in pulmonary PCM (34)(35)(36)(37)46). The present study allowed us to demonstrate that this fungal infection can be modulated by AhR ligands in opposed directions as previously demonstrated in other experimental models (10,11,45), suggesting their therapeutic use in different forms of the disease.…”

“…TRP shortage leads to reduced fungal growth and diminished infection of DCs and macrophages. The enhanced L-Kyn synthesis, via AhR activation, increases the expansion of Treg cells that control excessive Th17-mediated tissue pathology (34)(35)(36)(37)46). Our studies also demonstrated an important interconnection between IDO and AhR expression, where a balanced activation of these mediators proved to be fundamental for the control of fungal immunity and disease tolerance (34)(35)(36)(37)46).…”

“…In susceptible (B10.A) mice, IDO is induced by IFN-g and exhibits a prevalent enzymatic activity whereas in resistant (A/J) mice IDO is TGF-b induced and behaves as a signaling molecule (34)(35)(36). Our studies have also demonstrated that IDO and AhR are mutually regulated and control the number of ILCs and the Th17/Treg balance (34)(35)(36)(37). Altogether, our findings defined the important regulatory role of the IDO/AhR axis in the immunity and severity of pulmonary PCM leading us to better evaluate the role of AhR in pulmonary PCM.…”

“…RNA isolation from lung macerates of AhR ligand-treated and untreated mice was performed as previously described (37). A NanoDrop ND-1000 spectrophotometer was used to determine RNA purity and concentration.…”