Autoantibodies to the ribosomal phosphoproteins (Rib-P) are a serological feature of patients with systemic lupus erythematosus (SLE). The reported prevalence of anti-Rib-P antibodies in SLE ranges from 10 to 40%, being higher in Asian patients. The variation in the observed frequency may be related to a number of factors but is dependent in large part on the test system used to detect the autoantibodies. An association of anti-Rib-P with central nervous system involvement and neuropsychiatric manifestations of SLE has been controversial. In the present international multicenter study, we evaluated the clinical accuracy of a new sensitive Rib-Pspecific enzyme-linked immunosorbent assay based on recombinant Rib-P polypeptides. The results showed that 21.3% of 947 SLE patients, but only 0.7% of 1,113 control patients, had a positive test result (P < 0.0001). The sensitivity, specificity, positive and negative predictive values, and diagnostic efficiency were determined to be 21.3%, 99.3%, 95.6%, 62.2%, and 65.3%, respectively. When evaluated in the context of participating centers, the prevalence of anti-Rib-P antibodies was found in descending frequency, as follows: China (35%) > Poland (34%) > Japan (28%) > United States (26%) > Germany (Freiburg; 23.3%) > Denmark (20.5%) > Germany (Berlin; 19%) > Mexico (15.7%) > Israel (11.7%) > Brazil (10%) > Canada (8%). The substantial data from this study indicate that the prevalence of anti-Rib-P antibodies may not be restricted to the genetic background of the patients or to the detection system but may depend on regional practice differences and patient selection. We confirm previously reported associations of antiribosomal antibodies with clinical symptoms and serological findings. Remarkably, we found a lower occurrence of serositis in Rib-P-positive lupus patients.Autoantibodies to the ribosomal phosphoproteins (Rib-P) are a serological feature of patients with systemic lupus erythematosus (SLE) (4,8,9). The Rib-P autoantigen(s) consists of three protein components of the 60S ribosomal subunit, designated P0 (38 kDa), P1 (19 kDa), and P2 (17 kDa) (8, 12). A pentameric complex composed of one copy of P0 and two copies each of P1 and P2 interacts with the 28S rRNA molecule to form a GTPase domain, which is active during the elongation step of protein translation (8). The major immunoreactive epitope of this ribosomal autoantigen has been localized to the carboxy-terminal domain, which is highly conserved in all three proteins and contains two phosphorylated serine residues (e.g., Ser 102 and Ser 105 of human P2) (8,16,17). Several studies have shown that both the acidic and hydrophobic clusters, but not the phosphorylation of the P proteins, are critical for autoantibody binding (8,16,23). Furthermore, epitope mapping studies have shown that the major epitope domain is located within the last six C-terminal amino acids (GFGLFD) (8,16,23).The reported prevalence of anti-Rib-P antibodies in SLE ranges from 10 to 40%, being higher in Asian patients and at a relatively low...