Characterization of the Innate Immune Response to Crystalline Silica

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DESCRIPTION (provided by applicant): Silica is the most abundant mineral in the earth's crust account for prevalent exposure to respirable silicates in many occupations in both affluent and developing nations. Besides smoking, this is the major preventable cause of chronic obstructive pulmonary disease, with silica the causing a particularly devastating set of diseases known as pulmonary silicoses. Careful studies in both human samples and animal models have determined that crystalline forms silica (i.e., SiO2) is the cause of pulmonary inflammation that culminates in the manifestations of COPD. Moreover, these studies have implicated activation of the innate immune system, including macrophage dependent secretion of TNF and IL-1? in the pathophysiology of pulmonary silicosis. The mechanism by which crystalline silica stimulates these acute inflammatory responses remains controversial, however. Several studies have implicated members of the scavenger receptor family in promoting uptake of particulates, including crystalline silica. However, these receptors also appear to promote the uptake of noncrystalline silicates and missing signaling the motifs that would be necessary to stimulate the intracellular inflammatory responses uniquely associated with exposure to crystalline silica. Other studies have ascribed this inflammatory activity to the potential for silicate particulates to stimulate oxidant stress and promote cell death. However, these models fail to account for the unique structural features of those silica crystals that stimulate inflammation. They are further undermined by the poor correlations between oxidant stress, macrophage death and the inflammatory response exhibited by macrophages exposed to crystalline silica. Intriguingly, two pro-inflammatory crystals monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD), have recently been shown to mediate their potent biological activity through Nalp3/CIAS, a cytosolic Pattern Recognition Receptors (c-PRR). This raises the possibility that PRRs, which evolved to recognize repeating molecular patterns associated with microbes, may also recognize the repetitive pattern biologically active crystals present to the environment. Specifically, we propose to: 1. Do scavenger receptors contribute to the inflammatory response associated with crystalline silica? 2. Do PRRs from the TLR, NDB or C-type lectin receptor families direct the unique and specific inflammatory response to crystalline silica? PUBLIC HEALTH RELEVANCE The inhalation of crystalline silicates is a common occupational hazard and represents an important cause of several destructive pulmonary inflammatory diseases. However, the mechanism by which silica crystals stimulate this potent innate immune response has not been elucidated. Based on intriguing preliminary studies, we propose to investigate the role receptors from the innate immune system play in mediating the specific and destructive inflammatory response to crystalline silica.