Heavy and light chain utilization in autoantibodies of elderly patients with systemic lupus erythematosus

To determine whether age-related changes in immune function affect patterns of autoantibody production, we have examined the isotype and light chain utilization in autoantibodies of elderly patients with systemic lupus erythematosus (SLE). Enzyme-linked immunosorbent assays (ELISA) were used to determine the frequencies of IgG and IgM antibodies to single-stranded DNA (ssDNA), Sm, and the 70K protein component of RNP in the sera of 53 patients with SLE older than age 60. The IgG subclass distributions and kappa/lambda ratios for each of these autoantibodies were also determined and compared to measurements performed on the sera of 53 young adult patients with SLE. The frequencies of autoantibodies of each specificity, except IgM anti-ss DNA antibodies, were higher among the young adult patients, although the magnitudes of the responses were similar in both age groups. IgG anti-Sm antibodies were composed of both IgG1 and IgG2 subclasses, while IgG anti-70K RNP and IgG anti-ssDNA were predominantly of the IgG1 subclass. There were no differences in the IgG subclass distributions of any of the three autoantibodies between the elderly and young adult patient sera. The kappa/lambda ratios for each of the three autoantibodies were similar to that present in total serum immunoglobulins, and kappa/lambda ratios of autoantibodies, standardized to the kappa/lambda ratios of serum, were not different between elderly and young adult groups. Few patient sera of either age group (9 elderly, 7 young adult) demonstrated even midly skewed light chain ratios in their autoantibody responses. Thus, despite developing in an immunological environment that may have altered the clonality and isotype distribution of their responses, the autoantibodies produced by elderly patients with SLE were qualitatively similar to autoantibodies of younger patients.