HUMAN BLOOD EOSINOPHILS PRODUCE AND SECRETE INTERLEUKIN-4

Interleukin 4 (Il-4) is an immunoregulatory cytokine which induces T-c ell proliferation and differentiation into a Th-2 phenotype, and is of particular importance for the induction of IgE synthesis. In the pres ent study, the capability of human peripheral blood eosinophils from a llergic and non-allergic donors to produce Il-4 was examined. Using re verse transcribed polymerase chain reaction (RT-PCR), it was shown tha t highly purified eosinophils from allergic patients express mRNA for Il-4. Resting eosinophils also gave specific immunoreactivity with ant i-Il-4 antibodies, consistent with translation of Il-4 mRNA. Light and electron microscopic immunocytochemistry revealed that Il-4 was prest ored in the eosinophilic granules. These results were confirmed by Il- 4 specific ELISA which showed that Il-4 production could be upregulate d in the eosinophils and released from the eosinophils following stimu lation with the calcium ionophore A23187. These data indicate that eos inophils may be an important source of Il-4 at sites of allergic infla mmation. Thus, eosinophils may act as immunomodulatory cells enhancing the allergic response through formation of Th-2-cells and inducing th e isotype switching to IgE in human B-cells.