IL-5 inhibits caspase processing in the spontaneous apoptosis of peripheral blood eosinophils.
Peripheral blood eosinophils were cultured in the presence or absence of IL-5 (10−10 M) or STS (10−5 M) and analyzed at the times shown for processing of caspase-3 (A), -6 (B), -7 (C), and -8 (D) by immunoblotting. Jurkat T cells treated with or without etoposide (50 μM) for 4 hours were used as controls. The proforms and processed subunits are indicated. Apoptosis was assessed by annexin V binding to determine percentage cells with externalized PS and apoptotic morphology after Kimura stain, as described in “Materials and methods.” Eosinophils constitutively expressed caspase-3, -6, -7, and -8. Culturing in the absence of IL-5 and treatment with STS resulted in activation of all of the caspases. IL-5 prevented caspase activation over the 24-hour culture period. Longer exposure of the caspase-3 (A) blot revealed the presence of p20 and p19 subunits after 6 hours in untreated eosinophils. Shorter exposure of the caspase-8 (D) blot revealed the proform to be a doublet of 53 and 55 kd. Results are representative of 3 separate experiments.
