Evidence of antigen selection in the pathogenesis of primary ocular adnexal lymphoma
Lymphoma, Large B-Cell, Diffuse
Purpose. A comparison of germline and functionally rearranged nucleotide sequences of the immunoglobulin heavy chain expressed by clonal B-cell populations of some lymphomas reveals a pattern typical of the normal B-cell response to antigenic challenge. In view of the putative role of exogenous antigen in other primary extranodal lymphomas, we aimed to determine whether these changes were seen in patients with primary lymphomas of the ocular adnexa. Methods. Genomic DNA and cDNA were prepared from two patients with well characterised primary ocular adnexal lymphoma. Productively rearranged immunoglobulin variable region genes (IgVH) genes were amplified from cDNA by PCR using family-specific 5′ VH primers and a consensus antisense JH primer. DNA sequencing was performed on a total of eight independent plasmid isolates of each amplified gene. These were analyzed in conjunction with the V BASE sequence directory to determine the germline gene from which they were derived. Genomic DNA was then amplified using gene-specific primers and their sequences compared to their functionally rearranged derivatives. Results. Rearranged IgVH genes in both cases exhibited a high number of somatic point mutations. 17 nucleotide differences from that of the germline VH3 gene (94% homology) and 27 nucleotide differences from that of the germline DP-47 gene (27/282 = 90% homology) were observed in these cases. The number of replacement mutations in the regions encoding the antigen binding site were greater than expected by chance alone (p=0.018 and p=0.004 respectively) suggesting that positive antigenic pressure had been applied to these Ig VH gene products. Conclusions. This study suggests that antigen selection may play a role in the pathogenesis of primary ocular adnexal lymphoma.