DNA sequence of immunoglobulin heavy chain variable region gene in thyroid lymphoma.

Patho-epidemiological studies have shown that thyroid lymphoma (TL) develops in thyroid affected by chronic lymphocytic thyroiditis (CLTH). CLTH is categorized as an organ-specific autoimmune disease, in which activated B-lymphocytes secrete a number of autoantibodies. Because antigenic stimulation might be involved in the pathogenesis of TL, the variable region in heavy chain (V(H)) genes was characterized in 13 cases with TL and 3 with CLTH. Clonal rearrangement of the V(H) gene was found in 11 cases of TL, and cloning study with sequencing of complimentary determining region (CDR) 3 revealed the presence of a major clone in 4. Three of the 4 cases used V(H) 3 gene, with the homologous germline gene of V3-30 in two cases and VH26 in one case. A biased usage of V(H) 3 and V(H) 4 genes with the homologous germline gene of VH26 in V(H) 3 gene was reported previously in cases with CLTH. A high level of somatic mutation (1-21%, average 12%) with non-random distribution of replacement and silent mutations was accumulated in all cases. The frequency of the occurrence of minor clones ranged from 29-44% per case, indicating the presence of on-going mutation. DNA sequencing of immunoglobulin V(H) gene suggests that TL develops among activated lymphoid cells in CLTH at the germinal center stage under antigen selection.