U1 and systemic lupus erythematosus: The samples from patients with confirmed SLE (n = 114) consisted of sera that had been judged to be either anti-U1-RNP positive (n = 53) or anti-U1-RNP negative (n = 61) in the clinical routine (using the addressable laser bead immunoassay (ALBIA) and/or EUROLINE immunoblot) (Figure 1).