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Anti-myeloperoxidase autoantibodies react with native but not denatured myeloperoxidase
Abstract:
We wondered whether anti-myeloperoxidase (MPO) autoantibodies (MPO-ANCA) found in patients with systemic vasculitis react with a conformational epitope or epitopes on the MPO molecule. Sera from 15 human MPO-ANCA, and a polyclonal and a monoclonal anti-MPO antibodies were reacted with MPO in native and denatured states. Human MPO-ANCA and mouse monoclonal anti-MPO reacted with native MPO, and a 120-kD band representing the MPO hologenzyme, but not with denatured MPO fragments; however, MPO-ANCA and mouse anti-MPO did not demonstrate competitive inhibition of binding to MPO. Polyclonal rabbit anti-MPO reacted with both native and denatured MPO. All MPO-ANCA tested showed the same patterns of reactivity with native and denatured MPO in dot blot and Western blot analyses. Both polyclonal and monoclonal anti-MPO antibodies inhibited MPO's protein iodination by over 90%, whereas MPO-ANCA IgGs, normal IgGs and disease control IgGs did not. These data suggest that (i) MPO-ANCA interact with a conformational epitope on the MPO molecule; and (ii) MPO-ANCA from different patients have similar reactivity with native versus denatured MPO.
Insights
Autoantibodies against myeloperoxidase (MPO-ANCA) in vasculitis patients target specific MPO shapes, not broken fragments. This suggests a consistent binding pattern across patients for these critical MPO-ANCA.
Area of Science:
- Immunology
- Autoimmunity
- Protein Chemistry
Background:
- Systemic vasculitis often involves anti-myeloperoxidase (MPO) autoantibodies (MPO-ANCA).
- The specific epitopes targeted by MPO-ANCA on the MPO molecule remain incompletely understood.
- Understanding MPO-ANCA binding is crucial for diagnosing and potentially treating MPO-associated vasculitis.
Purpose of the Study:
- To determine if human MPO-ANCA react with conformational or linear epitopes on the myeloperoxidase (MPO) molecule.
- To compare the reactivity of MPO-ANCA with native and denatured MPO.
- To investigate the functional consequences of MPO-ANCA binding.
Main Methods:
- Sera from 15 MPO-ANCA patients, a polyclonal anti-MPO antibody, and a monoclonal anti-MPO antibody were used.
- Reactions were tested against MPO in both native (intact) and denatured (fragmented) states using dot blot and Western blot analyses.
- Competitive inhibition assays and MPO protein iodination inhibition assays were performed.
Main Results:
- Human MPO-ANCA and monoclonal anti-MPO bound to native MPO (hologenenzyme) but not denatured MPO fragments.
- Polyclonal anti-MPO reacted with both native and denatured MPO.
- MPO-ANCA did not inhibit MPO's protein iodination, unlike polyclonal and monoclonal anti-MPO antibodies.
Conclusions:
- MPO-ANCA primarily interact with conformational epitopes on the native MPO molecule.
- Reactivity patterns of MPO-ANCA against native versus denatured MPO are consistent across different patients.
- MPO-ANCA binding does not appear to inhibit the enzymatic activity of MPO, unlike specific anti-MPO antibodies.