Enhanced survival and multiple gene expression in human eosinphils exposed to soluble secretory IgA

Abstract

6 O A Enhanced Survival and Multiple Gene Expression in Human ~,F-Ir Eosinphils Exposed to Soluble Secretory IgA Kathleen R Bartemes, Kate Cooper, Hirohito Kita Mayo Clinic, Rochester, MN In humans, eosinophils are tissue-resident cells with >99% residing in tissues, especially in the mucosal tissues; many eosinophils are found in the intestine of normal individuals. Secretory IgA (S-IgA) is the main antibody secreted by the mucosa of the airways and gastrointestinal tract and is considered to provide protective mucosal immunity. Because of this common spatial distribution of eosinophils and S-IgA in mucosa, we speculated that S-IgA may have more profound effects than previously appreciated on homeostasis, gene expression, or effector functions of human eosinophils. In this study, we addressed this question by using two different forms of SIgA, namely S-IgA immobilized onto polystyrene beads (immobilized SIgA) and S-IgA kept in solution (soluble S-IgA) to mimic in vivo environment. We found that eosinophils incubated with immobilized S-IgA showed marked degranulation, as detected by the release of eosinophilderived neurotoxin (EDN), and superoxide production, compared to unstimulated eosinophils or to eosinophils incubated with uncoated beads. Immobilized S-IgA did not affect eosinophil viability as examined by exclusion of propidium iodide after 48 hours of incubation. In contrast, soluble S-IgA showed minimal effects on eosinophil degranulation and superoxide production. Furthermore, soluble S-IgA did inhibit eosinophil apoptosis and markedly enhanced 48-hour survival, suggesting that soluble SIgA does not affect release of mediators by eosinophils, but does affect cell survival and perhaps gene expression. Indeed, messenger RNA microarray analyses using Affymetrix Human Genome U95A Array showed that more than 120 genes are upregulated >2-fold in human eosinophils incubated with soluble S-IgA (7 ktg/ml) for 6 hours compared to those incubated with soluble IgG (7 Bg/ml) or medium alone. An example of upregulated genes includes those for signal transduction molecules (e.g. Act-2, pim-l, NF~b), cytokines/chemokines (e.g. IL113, IL-8, TNF-tx), and cell surface molecules (e.g. CD44, [32 integrin otD). Furthermore, the production of several representative proteins (e.g. IL-8) was also confirmed by immunoassays. These findings suggest that S-IgA may have pivotal effects on human eosinophils; an immobilized form is associated with effector functions and a soluble form is associated with survival and gene expression. Furthermore, eosinophils interacting with S-IgA in mucosal tissues or the lumen may express sets of genes which may be unique compared to those expressed by peripheral blood eosinophils.