The
monoclonal antibody (MoAb) 17.109 recognizes a cross-reactive idiotype (CRI) associated with the light chains of Waldenstrom's
macroglobulins with
rheumatoid factor (RF) activity. The MoAb also reacts with a proportion of
IgM-RF molecules from the sera of
rheumatoid arthritis and primary
Sjogren's syndrome patients, and from the sera of seropositive normal human subjects. In the present experiments, we used affinity chromatography to purify the 17.109 CRI-positive
immunoglobulin from serum and have analyzed the isolated material by Western blotting. The purified 17.109 CRI-positive material from the sera of
rheumatoid arthritis patients,
Sjogren's syndrome patients, and normal subjects contained exclusively kappa light chains, and had demonstrated RF activity. In every case the 17.109 CRI-positive isolates reacted with
antibodies against synthetic
peptides corresponding to both the conserved second and
third complementarity-determining regions (CDR) of the monoclonal kappa
IgM-RF
paraprotein Sie. The binding was inhibited specifically by the free
peptides in
solution. The antipeptide
antibodies did not react appreciably with unfractionated human
immunoglobulin. The data establish that the 17.109 CRI-positive
immunoglobulin from diverse human sera have similar or identical second and third light chain CDR. These results suggest i) that the MoAb 17.109 identifies the
protein product of a single or a very few V kappa genes, ii) that the ability to make kappa light chains with the 17.109-associated variable region is widespread in the human population, and iii) that the 17.109-defined kappa variable region segment is associated with
IgM-RF
autoantibodies.