Autoimmune antibody positivity Anti-ribosomal P protein antibody positivity The presence of an antibody in the blood circulation that is directed against ribosomal P protein. Anti-ribosomal P protein antibodies (anti-ribo P) have been reported as one of the specific autoantibodies in patients with systemic lupus erythematosus (SLE) and has been demonstrated to bind and activate macrophages in vitro. Anti-ribosomal P protein antibodies (Abs) recognize three specific ribosomal proteins located in the large ribosome's subunit. The term anti-ribosomal P protein Abs, often shortened in anti-P Abs, is due to the fact that these three proteins, P0, P1 and P2, of 38, 19 and 17 Kd molecular weight, respectively, are phosphorylated. One of the major points of interest of these autoAbs derives from their high specificity for systemic lupus erythematosus (SLE), their description in other connective tissue diseases (CTDs) being only occasional.