CD5-positive B-cell malignancies frequently express cross-reactive idiotypes associated with IgM autoantibodies

Using monoclonal antibodies (MAb) specific for cross-reactive idiotypes (CRIs) associated with human monoclonal IgM autoantibodies, we examined 57 biopsy specimens that previously had been noted to have immunohistologic features of CD5-positive B-cell small lymphocytic (SL) non-Hodgkin's lymphoma (NHL). Twenty-five lymphoma specimens were noted to be from patients with chronic lymphocytic leukemia (CLL). Eight of thirty-four (24%) immunoglobulin (Ig) kappa light-chain expressing lymphomas reacted with 17.109, a MAb specific for a major CRI encoded by a conserved Ig kappa variable region gene (V_k gene) of the V_kIIIb sub-subgroup. All 17.109-reactive tissues and two 17.109-negative specimens were recognized by another MAb specific for V_kIIIb framework determinant(s). Seven of all fifty-six (13%) Ig-expressing tumors bound G6, a MAb specific for an autoantibody heavy-chain-associated CRI that is encoded by a conserved antibody heavy chain variable region gene(s) (V_Hgene) of the V_H1 subgroup. All seven Go-positive lymphomas and two Go-negative tumors reacted with Cc1, another MAb specific for a rheumatoid factor heavy-chain-associated CRI. A third autoantibody-heavy-chain-associated CRI, termed Lc1, was expressed by seven (13%) other lymphomas. Finally, a fourth MAb specific for RF heavy-chain-associated CRI, named B6, detected two additional tumors. The expression frequencies of autoantibody-associated CRIs among SL NHL patients without peripheral lymphocytosis did not differ from those noted among patients with CLL but were significantly higher than those observed among patients with NHL of follicular center-cell origin. These data imply that the malignant B cells of patients with either CD5-positive B cell SL NHL or CLL express a restricted set of Ig V genes that have not substantially diversified from the germline DNA.