Isotype switching and titer variation of anti-Ro/SSA antibodies over time in 100 patients with undifferentiated connective tissue disease (UCTD)

Objective. To correlate the clinical course of the disease with the titer, the isotype profile and the switch of the anti-Ro/SSA antibodies in a cohort of patients affected by UCTD. Methods. One hundred selected patients with anti-Ro/SSA antibodies detected by counterimmunoelectrophoresis (CIE), and affected by UCTD with a mean follow-up of 7.6 years (SD 4.8 yrs.), were studied. The titer of IgA, IgG and IgM anti-Ro/SSA antibodies was determined in two different sera, obtained at the time of diagnosis and at the last visit, by ELISA with Ro/SSA recombinant proteins as substrate. Results. Thirty-five patients evolved from UCTD to a different connective tissue disease, while 65 showed a stable disease. Anti-Ro/SSA antibodies were detected in 91% and 97% of the patients, at baseline and during follow-up, respectively. IgG dominates the anti-Ro response. The titer of IgA, IgM and IgG anti-Ro/SSA did not differ significantly between the two groups of patients with UCTD. An increasing trend of IgG and IgA anti-Ro/SSA titer could be detected in patients evolving in primary Sjögren's Syndrome (pSS), but only the increase of IgG anti-Ro/SSA was significant (p = 0.0235). Conclusion. IgG dominates the anti-Ro/SSA response in patients with UCTD. No substantial change of the antibody isotype against Ro/SSA peptides could be observed during follow-up. The titer of IgG anti-Ro/ SSA significantly raised in the group of patients evolving in pSS.