On-chip complement activation is a suitable technique for the simultaneous detection of the presence and complement activating properties of autoantibodies

Krisztián Papp, József Prechl, Zsuzsanna Szekeres, Anna Erdei

Molecular Immunology 44 (2007) 3953

The complement system plays important role in several diseases, but still its responsibility is not appreciated in many cases. In clinical diagnosis usually the overall functionality of complement is measured but the antigen specific effects in particular disease are not quantified because of the lack of an appropriate method. Our group worked out an improved protein chip technology for serum profiling which, after these appropriate modifications, measures antigen specific complement activation, giving an extra dimension to conventional antigen arrays.
DNA was used as model antigen for testing the effectiveness of our technique. Antibodies against DNA are present in the sera of patents suffering from SLE; this being important criterion for the diagnosis of the disease. We tested the complement activating properties of anti-DNA monoclonal antibodies of different isotypes. The binding of these antibodies to dsDNA, ssDNA and plasmid DNA, and complement activation were measured simultaneously. Our results confirm that complement activation does not correlate with the number of bound antibody molecules, but it is rather affected by the density of epitopes.
The ability to activate the complement system influences the pathogenicity of autoantibodies. To test the presence of anti-dsDNA antibodies with strong complement activating properties in murine model of systemic lupus erythematosus, serum immune profile of normal and severely ill MLR/lpr mice was determined. As expected, autoantibodies against dsDNA with complement activating properties were detected in autoimmune animals. Currently we are testing sera derived from patients with autoimmune diseases and determining the incidence and complement activation properties of anti-DNA antibodies with different isotypes.
Our results suggest that on-chip complement activation is suitable for the multiplex detection of complement fixing autoantibodies in an antigen specific manner.