Differential expression and function of IgA receptors (CD89 and CD71) during maturation of dendritic cells.

Dendritic cells (DC) are the most efficient antigen-presenting cells residing in mainly peripheral tissues. Antigen uptake by DC is particularly efficient, being mediated by various receptors such as lectin, scavenger receptors, and Fc receptors (FcRs). Immunoglobulin A (IgA) is part of the first-line immune barrier in mucosae, where DC are numerous. A member of the FcR family, FcalphaRI, is expressed on interstitial DC. We report here that monocyte-derived DC (Mo-DC) express another IgA receptor (IgA-R), the transferrin receptor (TfR), even in the absence of DC proliferation in vitro. Upon incubation with inflammatory cytokines such as tumor necrosis factor alpha and interleukin (IL)-1beta or maturating agents (lipopolysaccharide, CD40 ligand), FcalphaRI and TfR expression on Mo-DC was specifically up-regulated, whereas FcgammaRs and FcepsilonRI expression was down-regulated. Both IgA-Rs were functional, being able to mediate endocytosis by immature and activated Mo-DC. Although FcalphaRI internalized IgA complexes on both types of DC, TfR was only able to mediate IgA complex internalization by immature cells. Cross-linking of FcalphaRI but not of TfR resulted in up-regulation of major histocompatibility complex (MHC) class II/CD86 expression and secretion of IL-10 and IL-12 by immature Mo-DC. Moreover, in activated Mo-DC, cross-linking of FcalphaRI could up-regulated MHC class II/CD86 and triggered IL-10 secretion. Our findings led us to propose that FcalphaRI expressed by interstitial-type DC could play a critical role to sample IgA-recognized antigens and also during DC activation.