Western blot analysis probing IL-1β in cell lysates of unstimulated and LPS-stimulated THP-1 cells. An amount of 50 μg/lane of cell lysates obtained from DH-VD₃–pretreated THP-1 cells was blotted and incubated with an anti–IL-1β antibody as described in the Materials and Methods. The left panel represents lysates of unstimulated cells, whereas the right panel depicts lysates of cells stimulated with 100 ng/mL of S minnesota Re 595 LPS. Marked are sizes of the IL-1β precursor protein (33 kD) and the caspase-1 IL-1β cleavage products of 28 kD and 18 kD. The 18-kD fragment represents the mature secretory IL-1β (mIL-1β).