Detection of IFN-alpha signature in renal biopsies of patients affected by lupus nephritis. (A-C) Infiltrating plasmacytoid DC in class IV lupus nephritis were characterized with a double staining for MXA (green, A) and BDCA-2 (red, B), a specific plasmacytoid DC marker (C, merge analysis). (D) Type I IFN-induced MXA protein was rarely detectable in class I lupus nephritis; (E) on the contrary, MXA positive tubular epithelial cells and infiltrating leucocytes were detectable in class IV lupus nephritis. (F) PAS staining on a seriate tissue section of the same specimen stained for MXA. (G) Immunohistochemistry analysis for MXA was performed on renal biopsies of eight patients for each group, as described in the Methods section. DC, dendritic cells; PAS, Periodic acid-Schiff.