Restricted heterogeneity and changing spectrotypes in autoantibodies to La/SS-B

Isoelectric focusing (IEF) spectrotype of specific immunoglobulins has been studied as a marker for B-cell clonality. In the present study, the spectrotype of anti-La antibodies in human autoimmune sera were analyzed by newly developed IEF sandwich assay in which focused total immunoglobulin on filter papers are incubated with crude antigen followed by horse-radish peroxidase-labeled anti-La antibodies. The anti-La spectrotypes contained oligoclonal bands, the positions and patterns of which are different in each patient, suggesting the preferential expansion of limited numbers of anti-La producing B-cell clones unique to individual patients. Furthermore, the bands on anti-La spectrotype in sequentially obtained sera changed continuously, suggesting alteration in the expanding anti-La producing clones. These may reflect affinity maturation and/or diversification of the B-cell epitopes involving somatic mutation.