• Animals
• Autoantibodies/immunology
• Humans
• Lupus Erythematosus, Systemic/immunology
• Lupus Nephritis
• Lupus Vasculitis, Central Nervous System
• Mice
• Ribosomal Proteins/immunology

IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory disease with multiple organ disorders. Recently, in IgG4-RD, increased circulating plasmablasts have been found. The subsets of plasmablasts are negative for RP105 (CD180). A large population of B cells lacking RP105 (RP105-negative B cells) are found in patients with active with systemic lupus erythematosus and other systemic autoimmune diseases, including dermatomyositis, and Sjögren’s syndrome. In other conditions, such as neuromyelitis optica, Kawasaki’s disease, primary biliary cirrhosis and aging, RP105 expression on B cells and monocytes also alters. We review the basic science and clinical significance of RP105-negative B cells including plasmablasts in various immune-based diseases. RP105-negative B cells, especially plasmablasts, play crucial roles in both systemic and organ-specific autoimmune and inflammatory disorders.

• Plasmablast
• CD180
• IgG4-related disease
• Autoimmune disease

• Antibodies, Antinuclear/blood
• Autoantigens/blood
• Autoimmune Diseases/blood
• Autoimmune Diseases/diagnosis
• Autoimmune Diseases/immunology
• Automation, Laboratory/instrumentation
• Automation, Laboratory/standards
• Cell Line
• Diagnostic Errors/prevention & control
• Fluorescent Antibody Technique, Indirect/standards
• Fluorescent Antibody Technique, Indirect/trends
• Forecasting
• Humans
• Sensitivity and Specificity

Autoantibodies to the ribosomal P proteins represent a highly specific marker for the diagnosis of systemic lupus erythematosus, where they have been associated with certain clinical manifestations. Historically, autoantibodies against ribosomal P proteins have been detected by indirect immunofluorescence, immunodiffusion, immunoblot, and other immunoassays. More recently, enzyme-linked immunosorbent assays and line and addressable laser bead immunoassays have become more widely used. The primary goal of this study was to determine the sensitivity of indirect immunofluorescence using conventional HEp-2 substrates in the detection of sera with ribosomal P antibodies as detected by other immunoassays.

Anti-ribosomal P-positive sera (n = 345) as detected by an addressable laser bead immunoassay were collected between 2003 and 2007 and analysed by indirect immunofluorescence. Furthermore, 51 anti-ribosomal P-positive samples from an unselected systemic lupus erythematosus cohort (n = 100) and the Centers for Disease Control and Prevention (CDC) anti-nuclear antibody (ANA) reference sera were tested for anti-ribosomal P reactivity.

In the cohort of 345 anti-ribosomal P-positive samples identified by addressable laser bead immunoassay, a low sensitivity (<30%) of indirect immunofluorescence on HEp-2 cell substrates was observed. Although the degree of sensitivity varied among different manufacturers, all immunofluorescence substrates exhibited limited sensitivity and false-negative results were not restricted to samples with low anti-ribosomal P titers. Even the anti-ribosomal P reactivity of CDC ANA reference serum number 12 was not clearly predictable by indirect immunofluorescence. Comparison of five different methods for the detection of anti-ribosomal P found moderate qualitative agreements.

Based on our data, we conclude that indirect immunofluorescence on HEp-2 cells is not a reliable screening test for the prediction of ribosomal P antibodies. As this method is widely used as a first-line screening test for anti-nuclear and other autoantibodies, special considerations for the detection of ribosomal P antibodies are needed. As with many other autoantibodies, further effort is required for the standardisation of ribosomal P immunoassays.