HUMAN EOSINOPHILS EXPRESS MESSENGER-RNA ENCODING RANTES AND STORE ANDRELEASE BIOLOGICALLY-ACTIVE RANTES PROTEIN

Eosinophils synthesize and store various cytokines with potential auto crine activity. We hypothesized that eosinophils synthesize and store RANTES, a CC chemokine with potent eosinophil chemotactic activity. Ex pression of RANTES mRNA in highly purified eosinophil populations was detected by reverse transcription followed by polymerase chain reactio n analysis. In situ hybridization (ISH) with S-35-labeled RANTES-speci fic riboprobes showed that 6.8-10% of peripheral blood eosinophils obt ained from atopic subjects expressed RANTES mRNA, increasing to 25% af ter incubation (16 h) with interferon(IFN)-gamma, but not ionomycin in vitro. Peripheral blood eosinophils also showed specific immunoreacti vity with an anti-RANTES monoclonal antibody, consistent with translat ion of the mRNA. By enzyme-linked immunosorbent assay, blood eosinophi ls were shown to contain a median of 7300 pg (range 5200-8800) RANTES per 10(6) cells, of which a mean of 24% was released into culture supe rnatants after stimulation of the cells with serum-coated particles in vitro. These culture supernatants exhibited eosinophil chemotactic ac tivity which was inhibited (mean 68%) by a specific anti-RANTES antibo dy. Sequential immunocytochemistry and ISH on biopsies obtained from a llergen-induced late-phase cutaneous reactions showed that 55-75% of t he infiltrating RANTES mRNA(-) cells were EG2(-) eosinophils. Allergen , but not diluent challenge, was also associated with a time-dependent increase in the number of cells showing RANTES immunoreactivity. Of t hese cells, 55% were identified as eosinophils by morphological criter ia. Thus, human eosinophils have the capacity to synthesize, store and secrete physiologically relevant quantities of RANTES, and may theref ore be an important source of this chemokine in allergic inflammation.