Recombinant HLA-DP2 binds beryllium and tolerizes beryllium-specific pathogenic CD4⁺ T cells

Chronic beryllium disease is a lung disorder caused by beryllium exposure in the workplace and is characterized by granulomatous inflammation and the accumulation of beryllium-specific, HLA-DP2-restricted CD4⁺ T lymphocytes in the lung that proliferate and secrete Th1-type cytokines. To characterize the interaction among HLA-DP2, beryllium, and CD4⁺ T cells, we constructed rHLA-DP2 and rHLA-DP4 molecules consisting of the α-1 and β-1 domains of the HLA-DP molecules genetically linked into single polypeptide chains. Peptide binding to rHLA-DP2 and rHLA-DP4 was consistent with previously published peptide-binding motifs for these MHC class II molecules, with peptide binding dominated by aromatic residues in the P1 pocket. ⁹Be nuclear magnetic resonance spectroscopy showed that beryllium binds to the HLA-DP2-derived molecule, with no binding to the HLA-DP4 molecule that differs from DP2 by four amino acid residues. Using beryllium-specific CD4⁺ T cell lines derived from the lungs of chronic beryllium disease patients, beryllium presentation to those cells was independent of Ag processing because fixed APCs were capable of presenting BeSO₄ and inducing T cell proliferation. Exposure of beryllium-specific CD4⁺ T cells to BeSO₄-pulsed, plate-bound rHLA-DP2 molecules induced IFN-γ secretion. In addition, pretreatmeat of beryllium-specific CD4⁺ T cells with BeSO ₄-pulsed, plate-bound HLA-DP2 blocked proliferation and EL-2 secretion upon re-exposure to beryllium presented by APCs. Thus, the rHLA-DP2 molecules described herein provide a template for engineering variants that retain the ability to tolerize pathogenic CD4⁺ T cells, but do so in the absence of the beryllium Ag.