Beryllium-stimulated apoptosis in macrophage cell lines

Abstract

In vitro stimulation of bronchoalveolar lavage cells from patients with chronic beryllium disease (CBD) induces the production of TNF-α. We tested the hypothesis that beryllium (Be)-stimulated TNF-α might induce apoptosis in mouse and human macrophage cell lines. These cell lines were selected because they produce a range of Be-stimulated TNF-α. The mouse macrophage cell line H36.12j produces high levels of Be-stimulated TNF-α. The mouse macrophage cell line P388D.1 produces low, constitutive, levels of TNF-α and does not up-regulate Be-stimulated TNF-α production. The DEOHS-1 human CBD macrophage cell line does not produce constitutive or Be-stimulated TNF-α. Apoptosis was determined by microscopic observation of propidium iodide stained fragmented nuclei in unstimulated and BeSO 4-stimulated macrophage cell lines. BeSO 4 induced apoptosis in all macrophage cell lines tested. Beryllium-stimulated apoptosis was dose-responsive and maximal after 24 h of exposure to 100 μM BeSO 4. In contrast, unstimulated and Al 2(SO 4) 3-stimulated macrophage cell lines did not undergo apoptosis. The general caspase inhibitor BD-fmk inhibited Be-stimulated macrophage cell line apoptosis at concentrations above 50 μM. Our data show that Be-stimulated macrophage cell line apoptosis was caspase-dependent and not solely dependent on Be-stimulated TNF-α levels. We speculate that the release of Be-antigen from apoptotic macrophages may serve to re-introduce Be material back into the lung microenvironment, make it available for uptake by new macrophages, and thereby amplify Be-stimulated cytokine production, promoting ongoing inflammation and granuloma maintenance in CBD.