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| Author(s): |
Flávio Vieira Loures
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI) |
| Defense date: | 2010-03-08 |
| Examining board members: |
Vera Lucia Garcia Calich;
Maria Heloisa Souza Lima Blotta;
Ana Campa;
Antonio Condino Neto;
Lourdes Isaac
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| Advisor: | Vera Lucia Garcia Calich |
| Abstract | |
The immunological mechanisms that govern the interaction between hosts and the dimorphic fungus Paracoccidioides brasiliensis have been scarcely studied. Both, fungal and phagocyte receptors involved in this interaction are poorly understood. Based on these facts, the aim of our study was to characterize in vitro and in vivo the role played by Toll Like Receptor-2 (TLR-2) and the adaptor protein MyD88 (myeloid differentiation primary response gene 88) in murine pulmonary paracoccidioidomycosis. The TLR-2 is a receptor of innate immunity involved in the recognition of PAMPs (pathogen associated molecular patterns), whereas MyD88 is a molecule involved in cell signaling induced by many TLRs . TLR-mediated activation results in the production of several nuclear transcription factors, including NFB, which activate important genes of the inflammatory response. Wild-type (WT) besides TLR- 2- and MyD88-deficient C57Bl/6 mice were used in our investigation. We showed that, compared to control animals, TLR2-/- mice developed a less severe pulmonary infection associated with reduced synthesis of nitric oxide (NO). Equivalent results were obtained with in vitro infected peritoneal and alveolar macrophages. Unexpectedly, despite the differences in fungal loads, TLR-2-/- and WT mice showed equivalent survival times and pulmonary lesions. Studies with lung infiltrating leukocytes revealed an increase of polymorphonuclear neutrophil leukocytes (PMNs) in TLR-2-/- mice associated with a low number of activated T CD4 and T CD8+ lymphocytes. Compared with WT mice, the TLR-2-deficient mice showed slight differences in the production of pulmonary Th1 and Th2 cytokines, but presented higher levels of KC, a CXC chemokine involved in neutrophil chemotaxis, besides increased levels of Th17 cytokines ( IL-6, IL-17, IL-23 and TGF-). Furthermore, the prevalent Th17 immune response developed by TLR-2-/- mice was associated with lower expansion of regulatory T cells CD4+CD25+FoxP3+. Thus, TLR-2 controls the innate and adaptive immunity against the P. brasiliensis infection and negatively regulates Th17 immune response and pulmonary pathology. Studies with MyD88-deficient mice showed an impaired production of NO in vivo and in vitro, and a deficient in vivo production of Th1, Th2 and Th17 cytokines. In addition, infected MyD88-deficient mice developed an impaired immune response, evidenced by poorly activated macrophages, as well as by an inefficient adaptive immunity mediated by a diminished influx of activated CD4+ T cells to the lungs. These events led to increased fungal loads in the lungs of MyD88-deficient mice and allowed a marked dissemination of the fungus to other organs such as liver and spleen, which presented severe lesions composed by coalescent granulomas containing high numbers of fungal cells. As consequence, MyD88-deficient mice were unable to control fungal growth and presented a decreased survival time. Our findings demonstrate that MyD88 signaling is important to the activation of fungicidal mechanisms and to the induction of the innate and adaptive immunity against P. brasiliensis. Altogether, our work shows that both TLR-2 and the adapter molecule MyD88, play an important role in controlling of P. brasiliensis infection, as well as in the induction of immune responses against this primary fungal pathogen. (AU) | |