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

The mechanism of enhanced presentation of ovalbumin (OVA) internalized as immunoglobulin A (IgA)-OVA via the IgA Fc receptor (Fc alphaR) was analyzed by focusing on the role of the Fc alphaR-associated gamma chain. Comparison of B-cell transfectants expressing Fc alphaR plus wild-type (WT) gamma chain or gamma chain in which the immunoreceptor tyrosine-based activation motif (ITAM) was altered by tyrosine mutation or substitution with the ITAM of Fc gamma RIIA showed that signaling-competent ITAM was not required for endocytosis of IgA-OVA, However, antigen presentation was impaired by ITAM changes. Signaling-competent gamma -chain ITAM appeared necessary for transport of ligated Fc alphaR to a lamp-1(+) late endocytic compartment for remodeling and/or activation of that compartment and also for efficient degradation of IgA complexes. Moreover, Fc alphaR ligation also activated efficient processing of nonreceptor-targeted antigen. The results suggest that gamma -chain signaling activates the antigen processing compartment (C) 2001 by The American Society of Hematology.