Inflammasome Inhibition by RTD-1 Treatment. (A) Caspase-1 activity was determined in THP-1 macrophages stimulated with LPS (100 ng/mL) and RTD-1 (7.14 μg/mL) or azithromycin (50 μg/mL) for 6 h; ATP (5 mM) was added for an additional 45 min. Cells were labelled with FLICA caspase-1 specific monoclonal antibodies and fluorescence was measured. (B) Representative confocal images of inflammasome activation are shown. (C) The direct effect of RTD-1 on caspase-1 activity using an enzymatic inhibition assay (* p ≤ 0.01, ** p ≤ 0.001). FLICA caspase-1 specific monoclonal antibody (green), Hoechst 33,342 nuclear stain (blue). ATP, adenosine triphosphate; AZM, azithromycin; LPS, lipopolysaccharide.