Immunofluorescence experiments were done as reported before (10 (link)). The technique is based on the ability of biotinylated TG2, followed by labeled streptavidin, to selectively bind TG2-specific antibody deposits inside of plasma cells. Briefly, biopsy specimens stored at -70°C were thawed and rinsed with PBS. Primary reagents were incubated in 1.2% BSA in PBS, for 45 min at RT. Sections were extensively rinsed with PBS, and secondary reagents were incubated in 12% BSA in PBS, for 30 min at RT. Sections were rinsed with PBS and mounted. The following antibodies and reagents were used: mouse anti-CD138 (1:25, AbD Serotec), recombinant human TG2 produced in E. coli and biotinylated as reported before (10 (link)) (5 μg/ml), mouse anti-TG2 mAb CUB7402 (1:1000, Neomarkers), anti-TACI (1:200, sc-7332 N-19), anti-BCMA (1:200, sc-11743 N-16), anti-BAFF-R (1:150, eBioscience 8A7) primary antibodies. Secondary antibodies were used as follows: Alexa Fluor 546/488/649-conjugated anti-goat, anti-mouse and anti-rabbit pAbs (1:1000, LifeTechnologies), streptavidin-cy2 (1:1000, Amersham Biosciences), streptavidin-cy3 (1:2000, Amersham Biosciences), anti-mouse-cy3 (1:1500, Southern Biotech), anti-IgA-FITC (1:40, Dako). DAPI was used to counterstain nuclei.