Innate control of the inflammatory process during fungal infections

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PROJECT SUMMARY The dialogue between innate and adaptive branches of the immune system is a central paradigm of modern immunology and is vital for protection against infections as well as for the pathogenesis of autoimmune, allergic and inflammatory diseases. According to the current model, innate immune sentinels dispersed throughout peripheral tissues sense, via their pattern recognition receptors (PRRs), the presence of microbial clues or endogenous moieties released during an infection, are activated and migrate to the draining lymph node (dLN). This process enables a transfer of “information” from peripheral tissue to the dLN, where the antigen-dependent adaptive immune response against the pathogen is initiated. The dLN also hosts an initial antigen-independent, innate immune response governed by migrating phagocytes that enables expansion of the LN and establishes a pro-inflammatory milieu. These events are required for the development and polarization of the adaptive immune response. Here, we focused our attention on the capacity of ligands derived from the cell wall of Candida (C.) albicans to dictate the LN innate response. Our working hypothesis is that the size and solubility of stimuli that activate the PRRs affect not only the LN innate response itself, but also the final outcome of the immune response. Also, that the LN innate response initiated by soluble fungal ligands can be harnessed to develop a potent and protective adaptive immune response to prevent life-threatening systemic fungal infections. Our preliminary data demonstrate that the physical form of fungal ligands dictates the location where the initial immune response takes place, and thereby determines the activation of adaptive immunity. In particular, we have found that small soluble fungal ligands that are immunosilent in the periphery and do not cause an inflammation in the tissue, become potent immunogens once they reach the dLN. Also, that the LN innate response initiated by these ligands completely bypasses the need of phagocyte migration from the periphery into the dLN and, instead, requires a unique gene signature that is characterized by the production of interferons and that is driven by the activation of the noncanonical NFkB transcription factor RelB in subcapsular sinus macrophages. Notably, Dectins are required for this process but CARD9, the key signaling adaptor downstream of Dectins, is largely dispensable. Plus, the initial innate response to the dLN instructs a potent type 1 adaptive immunity and allows the production of antibodies directed against the most external layer of the fungal cell wall. Fungal diseases are a global health problem and Candida species are the most common cause of invasive fungal infections. We propose to unravel how physical properties of the PAMPs can be harnessed as a therapeutic intervention against systemic fungal infections that are a major medical problem in the US. We anticipate that identifying new features of the immune response that is anatomically restricted to the LN will help with the design of an improved vaccine against poorly controlled pathogens.