Extensive plasma cell infiltration with crystal IgG inclusions and mutated IgV(H) gene in an osteoarthritis patient with lymphoplasmacellular synovitis. A case report

Immunoglobulin Crystals in Reactive Plasma Cells in a Dog

Intracellular crystalline deposits of immunoglobulin are occasionally seen in human B-cell lymphoproliferative disorders such as multiple myeloma, chronic lymphocytic leukemia, and various forms of lymphoma. Even more uncommon is the occurrence of immunoglobulin crystals in benign plasma cells or reactive lymphocytes. Here we describe the histologic, immunohistochemical, and ultrastructural features of intracellular immunoglobulin crystals in nonneoplastic plasma cells in a chronic inflammatory lesion in a dog. Microscopically, the intracellular, nonbirefringent eosinophilic crystals were square to rectangular, 2–20 μgm long, and caused nuclear displacement to the periphery. The crystal-containing cells, as well as some of the crystals themselves, were positive for lambda light chain. Ultrastructural findings were consistent with a lattice network of protein-molecule alignment. The cause and significance of the crystals is unknown.

B Cell Clonal Expansion and Somatic Hypermutation of Ig Variable Heavy Chain Genes in the Synovial Membrane of Patients with Osteoarthritis

Inflammatory mediators have been explored as possible factors in the initiation and/or progression of osteoarthritis (OA). This study shows that synovial infiltration by B lymphocytes is present in almost half of the knee OA cases. The degree of B lymphocyte infiltration is associated with more pronounced synovial inflammation and with the presence of plasma cells and lymphoid follicles in more severe cases. To examine whether these B cells are merely bystanders or could be involved in the pathogenesis of OA, we analyzed the Ig H chain variable region (V(H)) genes of B cells recovered from the synovial membrane of five OA patients with marked B cell infiltration. Sequence analysis of CDR3 regions of rearranged VDJ genes revealed clonal or oligoclonal B cell expansions in all cases. Expanded B cell clones in four of five OA patients showed clustered somatic mutations, occurring mainly in the CDRs and with a high replacement-to-silent ratio (>2.9), indicating that these cells are postgerminal center B cells that had been positively selected through their Ag receptor. These data demonstrate the presence in inflamed knee OA synovium of clonally expanded, Ag-driven B cells that may contribute to the development or progression of the disease.

Crystalline plasma cell inclusions in helicobacter-associated gastritis

BACKGROUND

Crystalline cytoplasmic inclusions are well documented in B cell lymphomas but have rarely been described in reactive plasmacytic infiltrates.

AIM

Three cases of Lelicobacter-associated gastritis are described in which plasma cells focally contained rhomboid and needle-shaped crystalline inclusions.

METHODS

Crystalline inclusions were identified in the gastric biopsy specimens from three patients undergoing routine upper gastrointestinal endoscopy. The cells were characterised immunohistochemically using the following antisera: cytokeratin, leucocyte common antigen, desmin, CD20, CD68, CD79a, CD138, immunoglobulin (Ig)G, IgA and IgM heavy chains, and kappa and lambda Ig light chains. Clinical follow-up data were obtained.

RESULTS

All biopsies showed a Lelicobacter-associated active chronic gastritis. Variable numbers of plasma cells with intracytoplasmic crystalline inclusions in the superficial lamina propria were seen. The crystals were not stained with any of the antisera tested, but the cells containing the crystals expressed CD79a and CD138 and, in the two assessable cases, showed IgA and lambda light chain immunoreactivity. The more numerous morphologically normal plasma cells in each patient were polytypic, and there were no histological features to suggest lymphoma. Crystals were not identified in the plasma cells in mucosal biopsy specimens from other sites in any of the patients.

CONCLUSIONS

Crystalline inclusions in plasma cells can occur in association with Lelicobacter gastritis. Although light chain restriction was shown in two patients, the overall histological and clinical findings indicated a reactive process. The presence of plasma cell crystals in isolation should not be considered to be diagnostic of lymphoma.

Roles of B cells in rheumatoid arthritis

B lymphocytes play several critical roles in the pathogenesis of rheumatoid arthritis. They are the source of the rheumatoid factors and anticitrullinated protein antibodies, which contribute to immune complex formation and complement activation in the joints. B cells are also very efficient antigen-presenting cells, and can contribute to T cell activation through expression of costimulatory molecules. B cells both respond to and produce the chemokines and cytokines that promote leukocyte infiltration into the joints, formation of ectopic lymphoid structures, angiogenesis, and synovial hyperplasia. The success of B cell depletion therapy in rheumatoid arthritis may depend on disruption of all these diverse functions.