[Detection of monoclonal plasma cells in bone marrow and spleen of primary amyloidosis].

A 53-year-old man was diagnosed as primary amyloidosis by biopsy specimens of the mucosa in rectum, spleen and bone marrow (BM). BM examination showed 5.5% of plasma cells with some dysplasia. Immunoglobulin heavy chain gene rearrangement was detected by polymerase chain reaction using third-complementary-determining region (CDR 3) specific primers in BM mononuclear cells and spleen cells embedded in paraffin. The sequence analysis revealed that monoclonal B cells existed in the both, BM and spleen. Flowcytometric analysis using two-color staining showed the phenotype of plasma cells with the expression of CD19+/-, CD27+/-, CD56+/- and CD138+ and CD38++. This phenotype is similar to those of monoclonal gammopathy of undetermined significance (MGUS). Therefore, primary amyloidosis is considered to have two plasma cell populations including normal plasma cells and monoclonal plasma cells in BM. Given that there are two types of plasma cells in patients with primary amyloidosis, amyloid protein is expected to originate from immunoglobulin light chain produced by monoclonal plasma cells.