Impaired Function of CTLA-4 in the Lungs of Patients with Chronic Beryllium Disease Contributes to Persistent Inflammation

Abstract

Chronic beryllium disease (CBD) is an occupational lung disorder characterized by granulomatous inflammation and the accumulation of beryllium-responsive CD4+ T cells in the lung. These differentiated effector memory T cells secrete IL-2, IFN-γ, and TNF-α upon in vitro activation. Beryllium-responsive CD4+ T cells in the lung are CD28 independent and have increased expression of the coinhibitory receptor, programmed death 1, resulting in Ag-specific T cells that proliferate poorly yet retain the ability to express Th1-type cytokines. To further investigate the role of coinhibitory receptors in the beryllium-induced immune response, we examined the expression of CTLA-4 in blood and bronchoalveolar lavage cells from subjects with CBD. CTLA-4 expression was elevated on CD4+ T cells from the lungs of study subjects compared with blood. Furthermore, CTLA-4 expression was greatest in the beryllium-responsive subset of CD4+ T cells that retained the ability to proliferate and express IL-2. Functional assays show that the induction of CTLA-4 signaling in blood cells inhibited beryllium-induced T cell proliferation while having no effect on the proliferative capacity of beryllium-responsive CD4+ T cells in the lung. Collectively, our findings suggest a dysfunctional CTLA-4 pathway in the lung and its potential contribution to the persistent inflammatory response that characterizes CBD.