Disease activity and functional ability measures. Course of the erythrocyte sedimentation rate (ESR), the 28-joint count Disease Activity Score (DAS28) and the Health Assessment Questionnaire (HAQ) over 3 years. (a) All patients. (b) IgG-class antibodies against cyclic citrullinated peptides (IgG anti-CCP)-positive RA patients. (c) 20 IgA-class antibodies against cyclic citrullinated peptides (IgA anti-CCP)-positive patients and 20 IgA anti-CCP-negative patients, with pairwise comparable IgG levels. *P < 0.05.