Light chains in Mediterranean lymphoma.

Four cases of Mediterranean lymphoma, in two of which serum alpha chains had been identified, were investigated with immunohistochemical techniques. In addition to alpha chains of alpha 1, subclass, monotypic light chains were identified in infiltrating tumour cells in all four patients and in plasma cells in two. The pattern of staining was in keeping with loss of light chain occurring with plasma cell differentiation and strongly suggested that the plasma cells and tumour cells shared a common clonal origin. In two patients concentrations of dendritic reticulum cells were identified in the tumour. These results support the suggestion that Mediterranean lymphoma is a tumour of follicle centre cells which undergoes plasma cell differentiation as a result of exposure to lumenal antigen.