Transient Foxp3(+) regulatory T-cell depletion enhances protective Th1/Th17 immune response in murine sporotrichosis caused by Sporothrix schenckii

Selective depletion of regulatory T cells enhances the immunogenicity of a recombinant-based vaccine against Sporothrix spp

Introduction

Regulatory T cells (Tregs) have been shown to limit the protective immune response against pathogenic species of the fungus Sporothrix spp, the causal agent of sporotrichosis. However, the specific function of Tregs during vaccination against these fungi is known.

Methods

We evaluated the effect of Tregs depletion on the immunogenicity of an experimental recombinant anti-Sporothrix vaccine, using the DEREG mice. In this model, only Foxp3(+) Tregs express eGFP and diphtheria toxin (DT) receptors, and transient Tregs depletion is achieved by DT administration.

Results

Tregs depletion enhanced the frequency of specific IFNγ+ T cells (Th1 lymphocytes) and cytokine production after either the first or second vaccine dose. However, depletion of Tregs during the second dose caused greater stimulation of specific Th1 lymphocytes than depletion during the first dose. Similarly, the highest production of IgG, IgG1, and IgG2a anti rSsEno antibody was detected after Tregs depletion during boost immunization compared to the other immunized groups. Importantly, vaccine immunogenicity improvement after Tregs depletion also had an impact on the more efficient reduction of fungal load in the skin and liver after the challenge with S. brasiliensis in an experimental infection model. Interestingly, the reduction in fungal load was greatest in the Tregs depleted group during boosting.

Discussion

Our results illustrate that Tregs restrict vaccine-induced immune response and their transient depletion could enhance anti-Sporothrix vaccine immunogenicity. Further studies are required to elucidate whether Tregs depletion may be a way to improve the efficacy of vaccination against Sporothrix spp.

Sporothrix schenckii regulates macrophage inflammatory responses via the c-JUN-induced Dab2 transcription

Macrophages, which serve as a bridge between innate and adaptive immunity, play an important role in sporotrichosis. Sporothrix schenckii infections can produce immune responses such as macrophage polarization and inflammatory factor secretion. In the early stages of inflammation, the expression of DAB2 in macrophages is increased, which controls the secretion of inflammatory factors and affects the polarization of macrophages. However, the expressions and mechanisms of DAB2 in sporotrichosis are not clear. In this study, we examined the expression of DAB2 and its regulation of inflammatory factors under conditions of Sporothrix schenckii infection. Our results indicated that the Sporothrix schenckii infection increased the expression of DAB2 and revealed a mixed M1/M2-like type of gene expression in BMDMs with the inhibited Il6, Il1β and Arg1, and induced Tnfα, Il10 and Mgl1. The deficiency of Dab2 gene suspended the changes of cytokines. In addition, JNK activity in BMDMs was inhibited by Sporothrix schenckii infection, leading to an increase in c-JUN. We also identified c-JUN as a transcription factor for Dab2 through chromatin immunoprecipitation and luciferase reporter assays. In an in vivo mouse model, sporotrichosis induced skin lesions were accompanied with an upregulation of c-JUN and inhibition of JNK activity, which were in accord with findings from in vitro experiments. Taken together, these findings indicate that in the early stages of Sporothrix schenckii infection there is a promotion of DAB2 expression through the JNK/c-JUN pathway, effects which can then control the expression of inflammatory factors.

Current Models to Study the Sporothrix-Host Interaction

Sporotrichosis is a worldwide distributed subcutaneous mycosis that affects mammals, including human beings. The infection is caused by members of the Sporothrix pathogenic clade, which includes Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa. The fungus can be acquired through traumatic inoculation of conidia growing in vegetal debris or by zoonotic transmission from sick animals. Although is not considered a life-threatening disease, it is an emergent health problem that affects mostly immunocompromised patients. The sporotrichosis causative agents differ in their virulence, host range, and sensitivity to antifungal drugs; therefore, it is relevant to understand the molecular bases of their pathogenesis, interaction with immune effectors, and mechanisms to acquired resistance to antifungal compounds. Murine models are considered the gold standard to address these questions; however, some alternative hosts offer numerous advantages over mammalian models, such as invertebrates like Galleria mellonella and Tenebrio molitor, or ex vivo models, which are useful tools to approach questions beyond virulence, without the ethical or budgetary features associated with the use of animal models. In this review, we analyze the different models currently used to study the host-Sporothrix interaction.

Chitin-rich heteroglycan from Sporothrix schenckii sensu stricto potentiates fungal clearance in a mouse model of sporotrichosis and promotes macrophages phagocytosis

Background

Fungal cell wall polysaccharides maintain the integrity of fungi and interact with host immune cells. The immunomodulation of fungal polysaccharides has been demonstrated in previous studies. However, the effect of chitin-rich heteroglycan extracted from Sporothrix schenckiisensu stricto on the immune response has not been investigated.

Results

In this study, chitin-rich heteroglycan was extracted from S. schenckiisensu stricto, and immunomodulation was investigated via histopathological analysis of skin lesions in a mouse model of sporotrichosis and evaluation of the phagocytic function and cytokine secretion of macrophages in vitro. The results showed that the skin lesions regressed and granulomatous inflammation was reduced in infected mice within 5 weeks. Moreover, heteroglycan promoted the fungal phagocytosis by macrophages and modulated the cytokine secretion. Heteroglycan upregulated TNF-α expression early at 24 h and IL-12 expression late at 72 h after incubation, which might result from moderate activation of macrophages and contribute to the subsequent adaptive immune response.

Conclusions

Chitin-rich heteroglycan extracted from S. schenckiisensu stricto potentiated fungal clearance in a mouse model of sporotrichosis. Moreover, chitin-rich heteroglycan promoted fungus phagocytosis by macrophages and modulated cytokines secretion. These results might indicate that chitin-rich heteroglycan could be considered as an immunomodulator used in the treatment of sporotrichosis.

Foxp3 Silencing with Antisense Oligonucleotide Improves Immunogenicity of an Adjuvanted Recombinant Vaccine against Sporothrix schenckii

Background: In recent years, there has been great interest in developing molecular adjuvants based on antisense oligonucleotides (ASOs) targeting immunosuppressor pathways with inhibitory effects on regulatory T cells (Tregs) to improve immunogenicity and vaccine efficacy. We aim to evaluate the immunostimulating effect of 2′OMe phosphorothioated Foxp3-targeted ASO in an antifungal adjuvanted recombinant vaccine. Methods: The uptake kinetics of Foxp3 ASO, its cytotoxicity and its ability to deplete Tregs were evaluated in murine splenocytes in vitro. Groups of mice were vaccinated with recombinant enolase (Eno) of Sporothix schenckii in Montanide Gel 01 adjuvant alone or in combination with either 1 µg or 8 µg of Foxp3 ASO. The titers of antigen-specific antibody in serum samples from vaccinated mice (male C57BL/6) were determined by ELISA (enzyme-linked immunosorbent assay). Cultured splenocytes from each group were activated in vitro with Eno and the levels of IFN-γ and IL-12 were also measured by ELISA. The results showed that the anti-Eno antibody titer was significantly higher upon addition of 8 µM Foxp3 ASO in the vaccine formulation compared to the standard vaccine without ASO. In vitro and in vivo experiments suggest that Foxp3 ASO enhances specific immune responses by means of Treg depletion during vaccination. Conclusion: Foxp3 ASO significantly enhances immune responses against co-delivered adjuvanted recombinant Eno vaccine and it has the potential to improve vaccine immunogenicity.

Paracoccidioidomycosis Protective Immunity

Protective immunity against Paracoccidioides consists of a stepwise activation of numerous effector mechanisms that comprise many cellular and soluble components. At the initial phase of non-specific innate immunity, resistance against Paracoccidioides comes from phagocytic polymorphonuclear neutrophils, natural killer (NK) cells and monocytes, supplemented by soluble factors such as cytokines and complement system components. Invariant receptors (Toll-like receptors (TLRs), Dectins) which are present in cells of the immune system, detect patterns present in Paracoccidioides (but not in the host) informing the hosts cells that there is an infection in progress, and that the acquired immunity must be activated. The role of components involved in the innate immunity of paracoccidioidomycosis is herein presented. Humoral immunity, represented by specific antibodies which control the fungi in the blood and body fluids, and its role in paracoccidioidomycosis (which was previously considered controversial) is also discussed. The protective mechanisms (involving various components) of cellular immunity are also discussed, covering topics such as: lysis by activated macrophages and cytotoxic T lymphocytes, the participation of lytic products, and the role of cytokines secreted by T helper lymphocytes in increasing the efficiency of Paracoccidioides, lysis.

Th2 Biased Immunity With Altered B Cell Profiles in Circulation of Patients With Sporotrichosis Caused by Sporothrix globosa

Sporotrichosis is a subcutaneous mycotic infection, and Sporothrixglobosa is one of the causative agents with a worldwide distribution, notably in Asia. However, the immune profile in human sporotrichosis caused by S. globosa still remains obscure. Here, we demonstrated enhanced Th2 response in circulation with significant increases in Th2 frequency, Th2/Tregs as well as IL-4 seretion in patients. Elevated IL-17A⁺Th17 percentage was accompanied with reduced IL-17A level in serum, which may imply a dysfunction of this CD4⁺T subset in S. globosa infection. In addition, Th2 percentage, the ratios of Th2/Tregs and Th17/Tregs were all raised in patients with fixed cutaneous form, while only Th2/Tregs displayed increment in lymphocutaneous form. Meanwhile, the percentage of double negative B cells was significantly increased and positively correlated with Th2 and Tregs in whole patients. Except naïve B cells, all memory B cells together with Th2 cells increased in patients with short duration (less than 6 months), which may suggest a collaboration of T cells with altered B cell profile in human sporotrichosis caused by S. globosa. In consistent with the changes of IFN-γ⁺Th1, IL-4⁺Th2 and IL-17A⁺Th17 in patients with short duration, the percentages of these effector T cells all expanded when cocultured with S. globosa yeast cells in vitro. These data shed light on the potential involvement of peripheral T and B cell immunity against this mycotic infection and indicated that different immune responses existed in different stages of sporotrichosis; meanwhile different immune profile may contribute to different clinical manifestations of this disease.