Serial sections of muscle tissue mononuclear cell infiltrate. These sections were taken from a representative anti-Ro52/anti-Ro60-positive patient with polymyositis. They are immunohistochemically stained for B-cell marker CD19 (A) and plasma cell marker CD138 (E). Original magnification, ×25. Details of infiltrate (original magnification, 1.25 × 25) stained for B cell–activating factor of the tumour necrosis factor family receptor (BAFF-R) (B), B cell maturation antigen (BCMA) (C), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) (D), interferon α/β–inducible myxovirus resistance 1 (MX-1) protein (F) and plasmacytoid dendritic cell marker blood dendritic cell antigen 2 (BDCA-2) (G) compared to immunoglobulin G1 isotype control (H). Brown colour indicates positively stained cells, indicated by arrows.