Isolation and molecular characterization of the B cells producing the paraprotein in a case of benign monoclonal gammapathy in C57BL mice.

Benign monoclonal gammapathy (BMG) is defined as a benign monoclonal B cell proliferative disorder characterized by the presence of a persisting component of homogenous immunoglobulins (H-Ig) in the serum. A possible role of antigenic stimulation in the development of BMG has been suggested. From a C57BL mouse, a murine model for BMG, we have isolated clonally related B cells in order to investigate the occurrence of somatic mutations in the variable heavy chain (VH) region of the genes of H-Ig-producing B cell clones. Therefore, B cells were immortalized by hybridoma technology. The hybridomas were screened for resemblance of the serum H-Ig component by Wieme agar electrophoresis, followed by immunoblotting and isoelectrofocusing. Clonal relationship was investigated by Southern blot analysis using a JH probe. In this way we isolated five hybridomas producing an IgG2a, kappa that was identical to the original serum H-Ig component according to testing with anti-idiotypic antisera. mRNA sequencing of four hybridomas showed only one base pair difference in the VH genes. This particular gene belonged to the J558 VH gene family. When compared to the most closely related known VH sequence, three base pair differences were found. The almost complete absence of base pair differences in the VH genes of the four sequenced hybridomas, compared with an independently derived hybridoma, suggests that the same germ-line VH gene has been used and that somatic mutations were infrequent in our BMG clone.