J chain dictates the recognition of IgA by FcRL4

Abstract

Fc-receptor-like 4 (FcRL4) selectively recognizes systemic IgA. The cryo-electron microscopy structure of the FcRL4–Fcα (IgA-Fc)–Joining (J) chain complex reveals that FcRL4 interacts with Fcα–J in a 1:1 stoichiometry, with FcRL4 primarily interacting with the J chain. The binding of Fcα–J to FcRL4 would hinder the binding of pIgR, but not FcαRI. These findings provide new insights into IgA and emphasize significant differences between various IgA receptors.