MAST-CELLS ENHANCE EOSINOPHIL SURVIVAL IN-VITRO - ROLE OF TNF-ALPHA AND GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR

Mast cell-eosinophil interactions in allergy have not Set been complet ely defined, To determine whether mast cells influence eosinophil surv ival, human peripheral blood eosinophils were incubated with rat perit oneal mast cell sonicate, After 3 days, viable eosinophils in medium w ere 21.3% compared with 44% with mast cell sonicate. Like sonicate, su pernatants of compound 48/80-activated mast cells enhanced eosinophil survival, demonstrating that the factor(s) involved is stored preforme d and rapidly released. Increased eosinophil survival was due to an in hibition of apoptosis (morphologic analysis; annexin V/PI). Neutralizi ng Abs to granulocyte-macrophage CSF (GM-CSF), hut not to IL-3 or IL-5 , decreased by 61.7% the enhancing effect on eosinophil viability, Eos inophils are the source of GM-CSF since its release in the culture med ium was inhibited by their incubation with the mast cell sonicate toge ther with dexamethasone. In addition, eosinophils incubated with the s onicate expressed mRNA for GMCSF, To partially characterize the mast c ell-derived factor(s) increasing eosinophil survival, the sonicate was heated (56 degrees C/30 min or 100 degrees C/10 min) or preincubated with antihistamines or with anti-TNF-alpha-neutralizing Abs, Most of t he activity was heat labile. TNF-alpha was found to be predominantly ( 70%) responsible, while histamine had no role, Mast cell sonicate also caused eosinophils to release eosinophil peroxidase and to display mo rphologic signs of activation, In conclusion, we have demonstrated tha t mast cells enhance eosinophil survival in part through their activat ion to produce and release the autocrine survival cytokine GM-CSF.