Presentation of ovalbumin internalized via the immunoglobulin-A Fc receptor is enhanced through Fc receptor γ-chain signaling

Abstract

Abstract The mechanism of enhanced presentation of ovalbumin (OVA) internalized as immunoglobulin A (IgA)–OVA via the IgA Fc receptor (FcαR) was analyzed by focusing on the role of the FcαR-associated γ chain. Comparison of B-cell transfectants expressing FcαR plus wild-type (WT) γ chain or γ chain in which the immunoreceptor tyrosine-based activation motif (ITAM) was altered by tyrosine mutation or substitution with the ITAM of FcγRIIA showed that signaling-competent ITAM was not required for endocytosis of IgA-OVA. However, antigen presentation was impaired by ITAM changes. Signaling-competent γ-chain ITAM appeared necessary for transport of ligated FcαR to a lamp-1+ late endocytic compartment for remodeling and/or activation of that compartment and also for efficient degradation of IgA complexes. Moreover, FcαR ligation also activated efficient processing of nonreceptor-targeted antigen. The results suggest that γ-chain signaling activates the antigen processing compartment.