512 MUTANT IL-3: A Common Down Regulator for Components of IGE Mediated Signal Transduction Pathway

BACKGROUND: FcepsilonRI mediated signal pathway in basophils and mast cells leads to release of histamine and other mediators. Interestingly, basophils from 10% to 20% of the population do not release histamine and other mediators on activation of the IgE signal transduction pathway and this has been attributed to the absence of tyrosine kinases Lyn and Syk. OBJECTIVE: To investigate the association between histamine releasibility, total serum IgE, expression of IgE receptor and role of IL-3 with reference to non-releaser phenotypes in Indian population. METHODS: Basophils from peripheral blood of healthy adults were purified by density gradient centrifugation and negative immuno-selection. Histamine release assay was performed flourometrically. Total serum IgE was estimated by ELISA and assessment of IgE receptor expression was carried out by flow cytometry. Assessment of Lyn and Syk expression were carried out by flow-cytometry. RESULTS: Histamine release after ConA challenge varied from 0% to 100% in Indian subjects. Eighteen percent subjects showed less than 5% histamine release (non-releasers). Flow-cytometric analysis revealed a significantly reduced expression of FcepsilonRI in non-releaser basophils (P < 0.05). Total serum IgE levels were also significantly low (P < 0.05) in non-releasers. Flow-cytometric analysis revealed a significantly reduced expression of Lyn and Syk kinases in basophils (P < 0.05). Histamine release also significantly correlated with expression of Lyn and Syk kinase (P < 0.05). Non-releasers showed the presence of SNP at +79 (T-C), which leads to the one amino acid change at 8th position in the mature IL-3 from serine to proline. CONCLUSIONS: About 18% of the Indian subjects studied showed non-releaser phenotype and also had reduced serum IgE levels and FcepsilonRI expression reduced Lyn and Syk kinase expression. Non-releasers have shown the presence of less potent isoform of IL-3/P8, which is suspected to be common factor responsible for the non-releaser phenotype. This needs to be extended to a larger sample size and could be a potential target for the development of therapeutics for allergic patients.