Repetitive usage of immunoglobulin VH and D gene segments in CD5+ Ly-1 B clones of (NZB x NZW)F1 mice.

The usually small Ly-1 B cell population is markedly increased in older mice by expansion of certain clones. This results in a cellular picture very similar to human B chronic lymphocytic leukemia. Here we report a molecular analysis of the immunoglobulin gene rearrangements of the Ly-1 B cell populations in (NZB x NZW)F1 females. We find that (i) the number of clones found in the peritoneum (a major tissue source of Ly-1 B cells) decreases with age till mono- or biclonality is common by approximately 6 months, (ii) many clones from different mice show the same size rearrangements at both the Ig heavy and light chain loci and (iii) the IgH rearrangements found in a clone isolated from the spleen of one mouse are a subset of those found in the peritoneum of the same mouse, implying migration occurs from the peritoneum to the spleen. Molecular cloning and sequencing of the IgH rearrangements from the peritoneal clones of one B/W mouse revealed that all productive rearrangements used the identical unmutated VH and D elements joined to different JHS. Indeed, two VDJH4 rearrangements were recovered which were identical but for six junctional (N region) nucleotides. The conservation of VH and D segment usage in the rearrangements of these Ly-1 B cell clones could indicate some strong selective pressure for clonal expansion (for example antigen selection) operates via the immunoglobulin molecules of these cells. Southern analyses of other (NZB x NZW)F1 mice with this cloned VH and the usage of the same or similar VH genes among a number of Ly-1 B origin tumors in other mouse strains indicate the generality of this repetitive VH gene usage in individual mice.