LOW-MOLECULAR-WEIGHT IGM IN PRIMARY SJOGRENS-SYNDROME

Low molecular weight IgM (LMW IgM), the monomeric subunit of pentameri c IgM, was measured in the serum of 27 patients with primary Sjogren's syndrome. LMW IgM was also measured in a control group consisting of 24 patients with psoriatic arthritis (PA) and 8 patients with active r heumatoid arthritis (RA). LMW IgM was found in the majority of patient s with primary SS (63%) and those patients had a longer disease durati on than those without SS (80.7 +/-43.9 months vs 37+/-18.3, p = 001). Although the differences were not significant, SS patients with LMW Ig M showed higher rates of: seropositive disease (71% vs 50%), anti-Ro ( 59% vs 30%) and anti-La antibodies (12% vs 0%), extraglandular involve ment (76% vs 60%) and raised gammaglobulins levels (47% vs 30%) compar ed to those without LMW IgM. Our only two patients with active RA and vasculitis had LMW IgM. None of the patients with PA showed LMW IgM, r egardless of their Kammer subgroup classification, disease activity or radiological evidence of erosions. The presence of LMW IgM in a high percentage of patients with primary SS appears to be the expression of a dysregulation of B cell state that may predispose these patients to developing malignant lympoproliferation.