Anna von Mikecz

Characterization of Eukaryotic Protein L7 as a Novel Autoantigen Which Frequently Elicits an Immune Response in Patients Suffering from Systemic Autoimmune Disease

Autoantibodies targeted against cellular proteins and nucleic acids are a common feature of autoimmune diseases. In this study, we show that ribosomal protein L7 is a novel autoantigen in patients suffering from systemic lupus erythematosus (SLE) and other connective tissue diseases. From 24 patients diagnosed as having SLE, 18 produce antibodies which precipitate in vitro translated L7 protein. The anti-L7 titer appears to correlate with the active state of the disease. Anti-L7 autoantibodies were also detected in 7 of 13 patients with mixed connective tissue disease (MCTD), 2 of 7 patients with rheumatoid arthritis (RA), 1 of 4 patients with Sjögrens syndrome (SS) and in 1 patient with progressive systemic sclerosis (PSS). Anti-L7 autoantibodies belong to the IgG-class and detect specifically at least two epitopes on the L7 molecule, as shown by immunoprecipitation and immunoblotting. The epitope(s) of the highly conserved C-terminal region are preferentially recognized. Utilizing rabbit anti-L7 serum, autoimmune sera and affinity-purified anti-L7 autoantibodies in immunoblotting, and rabbit and chicken anti-L7 antibodies in indirect immunofluorescence, we detect L7 protein in the nuclei and in the cytoplasm of various cell-lines. Yet unlike most integral structural components of ribosomes, L7 is absent from nucleoli.

PML promotes MHC class II gene expression by stabilizing the class II transactivator

Promyelocytic leukemia (PML) protein binds to and stabilizes CIITA at PML nuclear bodies, which promotes expression of the MHC class II gene locus in response to interferon-γ exposure.

Correlation between chlamydial infection and autoimmune response: molecular mimicry between RNA polymerase major σ subunit fromChlamydia trachomatis and human L7

L7 is one of the ribosomal proteins frequently targeted by autoantibodies in rheumatic autoimmune diseases. A computer search revealed a region within the immunodominant epitope of L7 (peptide II) that is highly homologous to amino acid sequence 264 – 286 of the RNA polymerase major σ factor of the eubacterium Chlamydia trachomatis. Anti‐L7 autoantibodies affinity purified from the immunodominant epitope were able to recognize this sequence as they reacted with purified recombinant σ factor. Immunofluorescence labeling experiments on C. trachomatis lysates revealed a punctate staining pattern of numerous spots when incubated with the affinity‐purified anti‐peptide II autoantibodies. Binding of autoantibodies to peptide II was inhibited by the homologous σ peptide. This is the first demonstration of epitope mimicry between a human and a chlamydial protein on the level of B cells. Antibody screening revealed a significant correlation between the presence of anti‐L7 autoantibodies and C. trachomatis infection in patients with systemic lupus erythematosus and mixed connective tissue disease. Our results suggest that molecular mimicry is involved in the initiation of anti‐L7 autoantibody response and may represent a first glance into the immunopathology of Chlamydia with respect to systemic rheumatic diseases.

Antinuclear Autoantibodies: Fluorescent Highlights on Structure and Function in the Nucleus

The eukaryotic nucleus is dynamically organized with respect to particular activities, such as RNA transcription, RNA processing or DNA replication. The spatial separation of metabolic activities is best reflected by the identification of functionally related proteins, in particular substructures of the nucleus. In a variety of human diseases, the integrity of such structures can be compromised, thus underlining the importance of a proper nuclear architecture for cell viability. Besides their clinical relevance, antinuclear autoantibodies (ANAs) have contributed to a large extent to the identification of subnuclear compartments, the isolation and cloning of their components (the autoantigens), as well a the characterization of their function. Although sophisticated techniques, such as confocal laser scanning microscopy (CLSM), fluorescence resonance energy transfer (FRET) and in vivo observation of cellular events have recently been established as valuable tools to study subnuclear architecture and function, cell biologists will continue to appreciate the specificity and power of ANAs for their research.