Human keratinocytes release the endogenous β-galactoside-binding solublelectinimmunoglobulin E (IgE-binding protein) which binds tolangerhans cells where it modulates their binding capacity for IgE glycoforms

Abstract

A better understanding of the pathophysiological role of Langerhans cells (LC) in atopic diseases is dictatedby the characterization of the structures involved in immunoglobulin (IgE)-binding on their cell surface. We previously reported that human LC express the high affinity receptorfor IgE (FcϵRI), as well as the low affinity receptor for IgE (FcϵRII/CD23). In the present study, we document the presence of a third IgE-binding structure on human LC, the IgE-binding protein (ϵBP), an endogenous soluble β-galactosidebinding lectin. Immunohistochemical studies performed on normal human skin revealed an anti-ϵBP reactivity in the cytoplasm of keratinocytes and in that of acinous cells of eccrine sweat glands, ϵBP was also found on the cell surface of LC, as shown by anti-ϵBP/anti-CDla double labeling and flowcytometric analysis. Anti-ϵBP binding to the surface of LC was completely abolished by preincubation with lactose and restored by addition of recombinant human ϵBP, indicating that ϵBP binds to LC surface by virtue of its lectin property. Immunoblot analysis of anti-ϵBP-reactive material in keratinocytes and purified LC disclosed a protein with an apparent molecular weight of 33,000 consistent with ϵBP. Interestingly, mRNA transcripts for ϵBP were detected only in keratinocytes but not in purified LC isolated from normal skin. eBP was found to be released in culture supernatants of keratinocytes. Incubation of LC with these supernatants resulted in ϵBP-bindingto LC surface via proteincarbohydrate interaction. Most importantly, we could show that binding ofhuman myeloma IgE to LC was inhibited by ϵBP. In contrast, neuraminidase-treated human myeloma IgE binds to LC only inthe presence of ϵBP. In situ binding studies revealed that keratinocytes, although containing ϵBP intracytoplasmatically, failed to exhibit any IgE-binding properties. Collectively, our results suggest that human keratinocytes produce the β-galactoside-binding lectinϵBP, which subsequently binds to the surface of LC where it is functional in modulating their binding capacity for IgE glycoforms. © 1993, Rockefeller University Press., All rights reserved.