Intracellular staining for IFN-γ in stimulated BAL T cells. Representative experiments are shown for the flow cytometric analysis of BAL cells from a patient with sarcoidosis (a) or CBD (b) stimulated with either medium alone, SEB, or BeSO₄ and subsequently stained for surface CD4 and intracellular IFN-γ expression. The number in the upper right quadrant of each density plot indicates the percentage of CD4⁺ T cells expressing IFN-γ. (c) Representative flow cytometric staining of BAL cells from two CBD patients shows concordance of expression of the activation marker CD69 with IFN-γ after stimulation with BeSO₄.