Chronic beryllium disease (CBD) is a granulomatous lung disorder caused by beryllium exposure in the workplace and is characterized by the accumulation of beryllium-specific CD4+ T cells in the lung. Due to its unique chemical and physical properties, beryllium continues to be utilized in high-technology industries. Thus, CBD remains an important public health concern with more than 1,000,000 US workers having been exposed to beryllium and at risk for disease development. With the presence of a known antigen and an accessible target organ, CBD is an important model of immune-mediated, organ destruction. We and others have shown that the most important HLA molecule for beryllium presentation is HLA-DP. Using fibroblasts expressing mutated HLA-DP2 molecules, beryllium recognition was dependent on the glutamic acid residue at position 69 (2Glu69) of the HLA-DP 2-chain. In addition, T cell recognition of beryllium occurred in the absence of antigen processing, and nuclear magnetic resonance definitively showed that soluble HLA-DP2 directly bound beryllium. The goals of the studies in the current application are to elucidate the mechanism by which beryllium-specific CD4+ T cells recognize beryllium in the context of HLA-DP2 and to demonstrate the stability of the beryllium-specific memory T cell pool. The most likely possibilities of how 2Glu69 influences beryllium recognition are that 1) beryllium directly binds to the carboxylate of 2Glu69 in HLA-DP2 molecules, with peptide(s) only required to complete the 12TCR ligand or that 2) the effect of 2Glu69 on beryllium presentation is indirect through its influence on the repertoire of peptides that can bind to DP2, among which are peptides that can present beryllium. Our preliminary data favor the first hypothesis and suggest that we can study beryllium binding to HLA-DP2 prior to knowing which peptides are important for T cell recognition of the DP2- peptide/Be2+ complex. The first specific aim will provide definitive proof of beryllium binding with x-ray crystallography of HLA-DP2 with and without beryllium. The generation of HLA-DP2 mutants in the second aim will serve as a functional correlate to the structural studies in Aim #1.
The third aim will delineate which peptides are required to complete the 12TCR ligand while the final specific aim will determine whether progression from beryllium sensitization to disease is associated with an increased frequency of beryllium- specific CD4+ T cells in blood. Together, these studies will strengthen our understanding of how antigens cause granulomatous inflammation and specifically how metal antigens trigger an immune response. In addition, they will potentially allow the development of biomarkers to predict disease progression in high-risk subjects.
This translational study will utilize blood and lung specimens from human subjects with an occupational lung disorder to further our understanding of the beryllium-induced immune mechanisms that lead to disabling lung dysfunction. In a disease characterized by progressive loss of lung function, the identification of potential biomarkers of disease progression will greatly advance the welfare of this patient population.
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