Individual variation of anti-Sm autoantibodies in the MRL/MP-lpr/lpr mouse: age-related increase in diversity.

The prevalence and diversity of anti-Sm antibodies (which are a marker of human lupus) were investigated in MRL/MP-lpr/lpr mice. The low prevalence of anti-Sm reported by other workers was confirmed. Anti-Sm antibodies bound to either the 28 kD or both 28 and 16 kD polypeptides on immunoblots. Antibodies to the 16 kD polypeptide, detected on spectrotyping blots, were not detected on immunoblots probed with sera from three mice, suggesting that these antibodies were binding only to an additional conformational epitope. Isoelectric focusing of the sera showed that the anti-Sm antibodies were restricted in clonal diversity and in some cases resembled the pattern of a monoclonal antibody. A longitudinal increase in antibody titre was correlated in some mice with an increase in the diversity of clones expressing anti-Sm antibody. Anti-nRNP antibodies were also detected in the mouse serum but had a lower prevalence than anti-Sm antibodies.