Summary The presence of immunoglobulin crystal inclusions in plasma cells from plasmacytomas and B-NHLs (linked to overstimulation and overproduction) has been fre- quently reported. Our case describes a lymphoplasma- cellular synovitis in a patient with osteoarthritis (OA) showing an unusually high plasma cell infiltration and for the first time crystals in plasma cells. Using im- munohistochemistry, these crystals were identified as being IgG with a balanced lambda/kappa ratio. IgV H gene analysis (n = 5 clones) showed that they were somatically mutated (R/S of CDR > 3); in one case, an insertion of 9 nucleotides on the CDR2 region was observed. High R/S values in the CDR indicated antigen selectivity and affinity (4/5). Since no germinal centers could be detected and the analyzed B cells showed antigen selectivity, it may be concluded that already antigenically activated B cells migrated into the synovium and locally differentiated into plasma cells, leading to the extensive infiltration observed. Rheumatoid fibroblasts were shown to support termi- nal B cell differentiation. Our data suggests that the abil- ity of fibroblasts to activate B cells is not only restricted Teaching Case Extensive Plasma Cell Infiltration with Crystal IgG Inclusions and Mutated IgV H Gene in an Osteoarthritis Patient with Lymphoplasmacellular Synovitis. A Case Report* Raquel Magalhães 1 , Thorsten Gehrke 2 , Maria M. Souto-Carneiro 3 , Jörg Kriegsmann 4 , Veit Krenn 1 1 Institute of Pathology, Charité, Humboldt University Berlin, 2 ENDO-Klinik, Hamburg, 3 National Institute of Arthritis Musculoskeletal and Skin Diseases, NIH Bethesda; 4 Gemeinschaftspraxis für Pathologie, Trier Pathol. Res. Pract. 198: 45–50 (2002) 0344-0338/02/198/1-45 $15.00/0 PATHOLOGY RESEARCH AND PRACTICE © Urban & Fischer Verlag http://www.urbanfischer.de/journals/prp to RA, but also occurs in OA. The intense plasma cell infiltration contributed to further cartilage damage by altering the microenvironment of the nourishing syn- ovial tissue or by the local production of pathogenic au- toantibodies. Key words: Plasma cells – Osteoarthritis – Crystal in- clusions – IgV H genes Abbreviations: B-NHL = B lymphocyte non Hodgkin lym- phoma; IgVH = immunoglobulin variable heavy chain; R/S, replacement to silent mutation ratio; CDR = complementarity determining region; FR = framework region; RA = rheumatoid arthritis Introduction Accumulation of plasma cells and B-lymphocytes is a constant phenomenon of long standing synovitis in au- toimmune (rheumatoid arthritis, reactive arthritis, psori- atic arthritis) and degenerative joint diseases [11, 18, 27]. Address for correspondence: Veit Krenn, Institute for Pathology of Charité, Humboldt University Berlin, Schu- mannstr. 20–21, 10115 Berlin, Germany. Tel.: +49 (0)30/45053-6134, Fax: +49 (0)30/45053-6907. E-mail: veit.krenn@charite.de * The present work was supported by the SFB 421(Protektive und pathologische Folgen der Antigenverarbeitung)