FAS and sarcoidosis: Once sarcoidosis-specific biomarker parameters are determined relative to other conditions, flow cytometry of peripheral blood samples could be used to look for a high percentage of TH1 and TH17 CD4+ cells expressing PD-1, high frequency of TH17 and TH17/TH17.1 intermediates, and high levels of Treg with increased CD95/CTLA-4 expression—markers of T-cell dysfunction in sarcoidosis [24,44,48,56].