Dectin-1 Activation Exacerbates Obesity and Insulin Resistance in the Absence of MyD88

This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, grant numbers 11/15682-4, 12/02270-2, 15/18121-4), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Regenera INCT Process Grant 465656/2014-5). JL is funded by the NIH/NIDDK R01DK106210. GDB is funded by the Wellcome Trust and the MRC Centre for Medical Mycology. Open access journalPeer reviewedPublisher PD

Regulatory T cells in paracoccidioidomycosis

This review addresses the role of regulatory T cells (Tregs), which are essential for maintaining peripheral tolerance and controlling pathogen immunity, in the host response against Paracoccidioides brasiliensis, a primary fungal pathogen. A brief introduction on the general features of Treg cells summarizes their main functions, subpopulations, mechanisms of suppression and plasticity. The main aspects of immunity in the diverse forms of the P. brasiliensis infection are presented, as are the few extant studies on the relevance of Treg cells in the control of severity of the human disease. Finally, the influence of Toll-like receptors, Dectin-1, NOD-like receptor P3 (NLRP3), Myeloid differentiation factor-88 (MyD88), as well as the enzyme indoleamine 2,3 dioxygenase (IDO) on the expansion and function of Treg cells in a murine model of pulmonary paracoccidioidomycosis (PCM) is also discussed. It is demonstrated that some of these components are involved in the negative control of Treg cell expansion, whereas others positively trigger the proliferation and activity of these cells. Finally, the studies here summarized highlight the dual role of Treg cells in PCM, which can be protective by controlling excessive immunity and tissue pathology but also deleterious by inhibiting the anti-fungal immunity necessary to control fungal growth and dissemination

CD28 Exerts Protective and Detrimental Effects in a Pulmonary Model of Paracoccidioidomycosis▿

T-cell immunity has been claimed as the main immunoprotective mechanism against Paracoccidioides brasiliensis infection, the most important fungal infection in Latin America. As the initial events that control T-cell activation in paracoccidioidomycosis (PCM) are not well established, we decided to investigate the role of CD28, an important costimulatory molecule for the activation of effector and regulatory T cells, in the immunity against this pulmonary pathogen. Using CD28-deficient (CD28−/−) and normal wild-type (WT) C57BL/6 mice, we were able to demonstrate that CD28 costimulation determines in pulmonary paracoccidioidomycosis an early immunoprotection but a late deleterious effect associated with impaired immunity and uncontrolled fungal growth. Up to week 10 postinfection, CD28−/− mice presented increased pulmonary and hepatic fungal loads allied with diminished production of antibodies and pro- and anti-inflammatory cytokines besides impaired activation and migration of effector and regulatory T (Treg) cells to the lungs. Unexpectedly, CD28-sufficient mice progressively lost the control of fungal growth, resulting in an increased mortality associated with persistent presence of Treg cells, deactivation of inflammatory macrophages and T cells, prevalent presence of anti-inflammatory cytokines, elevated fungal burdens, and extensive hepatic lesions. As a whole, our findings suggest that CD28 is required for the early protective T-cell responses to P. brasiliensis infection, but it also induces the expansion of regulatory circuits that lately impair adaptive immunity, allowing uncontrolled fungal growth and overwhelming infection, which leads to precocious mortality of mice

Toll-Like Receptor 4 Signaling Leads to Severe Fungal Infection Associated with Enhanced Proinflammatory Immunity and Impaired Expansion of Regulatory T Cells▿

Toll-like receptors (TLRs) present in innate immune cells recognize pathogen molecular patterns and influence immunity to control the host-parasite interaction. The objective of this study was to characterize the involvement of TLR4 in the innate and adaptive immunity to Paracoccidioides brasiliensis, the most important primary fungal pathogen of Latin America. We compared the responses of C3H/HeJ mice, which are naturally defective in TLR4 signaling, with those of C3H/HePas mice, which express functional receptors, after in vitro and in vivo infection with P. brasiliensis. Unexpectedly, we verified that TLR4-defective macrophages infected in vitro with P. brasiliensis presented decreased fungal loads associated with impaired synthesis of nitric oxide, interleukin-12 (IL-12), and macrophage chemotactic protein 1 (MCP-1). After intratracheal infection with 1 million yeasts, TLR4-defective mice developed reduced fungal burdens and decreased levels of pulmonary nitric oxide, proinflammatory cytokines, and antibodies. TLR4-competent mice produced elevated levels of IL-12 and tumor necrosis factor alpha (TNF-α), besides cytokines of the Th17 pattern, indicating a proinflammatory role for TLR4 signaling. The more severe infection of TLR4-normal mice resulted in increased influx of activated macrophages and T cells to the lungs and progressive control of fungal burdens but impaired expansion of regulatory T cells (Treg cells). In contrast, TLR4-defective mice were not able to clear their diminished fungal burdens totally, a defect associated with deficient activation of T-cell immunity and enhanced development of Treg cells. These divergent patterns of immunity, however, resulted in equivalent mortality rates, indicating that control of elevated fungal growth mediated by vigorous inflammatory reactions is as deleterious to the hosts as low fungal loads inefficiently controlled by limited inflammatory reactions

Indoleamine 2,3-dioxygenase controls fungal loads and immunity in Paracoccidioidomicosis but is more important to susceptible than resistant hosts.

Paracoccidioidomycosis, a primary fungal infection restricted to Latin America, is acquired by inhalation of fungal particles. The immunoregulatory mechanisms that control the severe and mild forms of paracoccidioidomycosis are still unclear. Indoleamine 2,3-dioxygenase (IDO), an IFN-γ induced enzyme that catalyzes tryptophan metabolism, can control host-pathogen interaction by inhibiting pathogen growth, T cell immunity and tissue inflammation.In this study, we investigated the role of IDO in pulmonary paracoccidioidomycosis of susceptible and resistant mice. IDO was blocked by 1-methyl-dl-tryptophan (1MT), and fungal infection studied in vitro and in vivo. Paracoccidioides brasiliensis infection was more severe in 1MT treated than untreated macrophages of resistant and susceptible mice, concurrently with decreased production of kynurenines and IDO mRNA. Similar results were observed in the pulmonary infection. Independent of the host genetic pattern, IDO inhibition reduced fungal clearance but enhanced T cell immunity. The early IDO inhibition resulted in increased differentiation of dendritic and Th17 cells, accompanied by reduced responses of Th1 and Treg cells. Despite these equivalent biological effects, only in susceptible mice the temporary IDO blockade caused sustained fungal growth, increased tissue pathology and mortality rates. In contrast, resistant mice were able to recover the transitory IDO blockade by the late control of fungal burdens without enhanced tissue pathology.Our studies demonstrate for the first time that in pulmonary paracoccidioidomycosis, IDO is an important immunoregulatory enzyme that promotes fungal clearance and inhibits T cell immunity and inflammation, with prominent importance to susceptible hosts. In fact, only in the susceptible background IDO inhibition resulted in uncontrolled tissue pathology and mortality rates. Our findings open new perspectives to understand the immunopathology of paracoccidioidomycosis, and suggest that an insufficient IDO activity could be associated with the severe cases of human PCM characterized by inefficient fungal clearance and excessive inflammation

Loss- and Gain-of-Function Approaches Indicate a Dual Role Exerted by Regulatory T Cells in Pulmonary Paracoccidioidomycosis.

Paracoccidioidomycosis (PCM), is a pulmonary fungal disease whose severity depends on the adequate development of T cell immunity. Although regulatory T (Treg) cells were shown to control immunity against PCM, deleterious or protective effects were described in different experimental settings. To clarify the function of Treg cells in pulmonary PCM, loss-and gain-of-function approaches were performed with Foxp3GFP knock-in mice and immunodeficient Rag1-/- mice, respectively, which were intratracheally infected with 106 yeast cells. The activity of Foxp3-expressing Treg cells in pulmonary PCM was determined in Foxp3GFP transgenic mice. First, it was verified that natural Treg cells migrate to the lungs of infected mice, where they become activated. Depletion of Treg cells led to reduced fungal load, diminished pathogen dissemination and increased Th1/Th2/Th17 immunity. Further, adoptive transfer of diverse T cell subsets to Rag1-/- mice subsequently infected by the pulmonary route demonstrated that isolated CD4+Foxp3+ Treg cells were able to confer some degree of immunoprotection and that CD4+Foxp3- T cells alone reduced fungal growth and enhanced T cell immunity, but induced vigorous inflammatory reactions in the lungs. Nevertheless, transfer of Treg cells combined with CD4+Foxp3- T cells generated more efficient and balanced immune Th1/Th2/Th17 responses able to limit pathogen growth and excessive tissue inflammation, leading to regressive disease and increased survival rates. Altogether, these loss- and gain-of-function approaches allow us to clearly demonstrate the dual role of Treg cells in pulmonary PCM, their deleterious effects by impairing T cell immunity and pathogen eradication, and their protective role by suppressing exacerbated tissue inflammation

MR signaling controls the different patterns of cytokines produced by A/J and B10.A macrophages.

<p>Macrophages from A/J and B10.A mice were treated by anti-MR antibodies (20 µg/mL) for 30 min. After, some cultures were challenged with viable <i>P. brasiliensis</i> yeasts (1∶25, fungus:macrophages ratio) for 48 h. Supernatants were removed and used for cytokines measurements by ELISA. Data are means ± SEM of triplicate samples from two experiment determinations. (*P<0.05, **P<0.01 and ***P<0.001).</p

TLR4 and CR3 blockade by anti-TLR4 and anti-CD11b antibodies modulated the cytokines production of <i>P. brasiliensis</i> infected A/J and B10.A macrophages.

<p>Macrophages from A/J and B10.A mice were untreated or treated with anti-TLR4 and anti-CD11b antibodies (10 µg/ml) for 30 min., infected or not with <i>P. brasiliensis</i> yeasts cells, and then cultivated for 48 h. The levels of cytokines were assessed by ELISA in the cell supernatants. Data are means ± SEM of triplicate samples from two experiment determinations. (*P<0.05, **P<0.01 and ***P<0.001).</p