TRANSFORMING GROWTH-FACTOR-BETA ABROGATES THE EFFECTS OF HEMATOPOIETINS ON EOSINOPHILS AND INDUCES THEIR APOPTOSIS

Hematopoietins, interleukin (IL)-3, IL-5, and granulocyte/macsophage c olony-stimulating factor (GM-CSF) have previously been shown to prolon g eosinophil survival and abrogate apoptosis. The objective of this st udy was to investigate the effect of transforming growth factor beta ( TGF-beta) on eosinophil survival and apoptosis. Eosinophils from perip heral blood of mildly eosinophilic donors were isolated to >97% purity using discontinuous Percoll density gradient. Eosinophils were cultur ed with hematopoietins with or without TGF-beta for 4 d and their viab ility was assessed. We confirmed previous observations that hematopoie tins prolonged eosinophil survival and inhibited apoptosis. TGF-beta a t concentrations greater than or equal to 10(-12) M abrogated the surv ival-prolonging effects of hematopoietins in a dose-dependent manner a nd induced apoptosis as determined by DNA fragmentation in agarose gel s. The effect of TGF-beta was blocked by an anti-TGF-beta antibody. Th e anti-TGF-beta antibody also prolonged eosinophil survival on its own . The culture of eosinophils with IL-3 and GM-CSF stimulated the synth esis of GM-CSF and IL-5, respectively, suggesting an autocrine mechani sm of growth factor production. TGF-beta inhibited the synthesis of GM -CSF and IL-5 by eosinophils. TGF-beta did not have any effect on the expression of GM-CSF receptors on eosinophils. We also studied the eff ect of TGF-beta on eosinophil function and found that TGF-beta inhibit ed the release of eosinophil peroxidase. Thus, TGF-beta seems to inhib it eosinophil survival and function. The inhibition of endogenous synt hesis of hematopoietins may be one mechanism by which TGF-beta blocks eosinophil survival and induces apoptosis.