Absence of somatic mutation in the variable region of MPC 11 variants expressing a different heavy chain isotype

Somatic mutation of immunoglobulin variable regions contributes to the diversity of the immune response. Some investigators have postulated that somatic mutation is coupled to isotype switching; others have presented evidence that the two processes are not linked. By using in vitro variants of the MPC 11 mouse myeloma cell line that produce heavy chains of different isotypes, we have examined several V(H) regions at the nucleotide level using a variety of different sequencing procedures. We have found no evidence of somatic mutation and conclude that the processes of somatic mutation and isotype switching may be independent.