Difference in antigenic determinant profiles between human and rat myeloperoxidase

Area of Science:

• Immunology
• Biochemistry
• Evolutionary Biology

Background:

• Myeloperoxidase (MPO) is a key enzyme implicated in autoimmune diseases, particularly those associated with anti-neutrophil cytoplasmic antibodies (ANCA).
• Understanding the antigenic determinants of MPO is crucial for developing accurate diagnostic tools and effective animal models for research.

Purpose of the Study:

• To investigate the cross-reactivity of human MPO-ANCA with rat MPO.
• To compare the antigenic epitopes of human and rat MPO.
• To evaluate the suitability of human MPO as an antigen in animal models for generating ANCA.

Main Methods:

• Enzyme-linked immunosorbent assay (ELISA) was employed using purified rat and human MPO.
• Human MPO-ANCA positive sera and monoclonal antibodies (mouse anti-rat MPO, mouse anti-human MPO) were utilized.
• Cross-inhibition studies were performed by preincubation with human MPO or irrelevant antigen.

Main Results:

• Only one out of 36 human MPO-ANCA positive sera showed significant binding to rat MPO, with poor inhibition by human MPO.
• Three out of four mouse anti-human MPO monoclonal antibodies did not recognize rat MPO; one IgA antibody showed weak binding.
• The mouse anti-rat MPO monoclonal antibody did not bind human MPO, indicating distinct epitopes between species.

Conclusions:

• Human MPO-ANCA predominantly recognize epitopes absent in rat MPO, suggesting recent evolutionary divergence.
• Rat MPO contains unique epitopes altered during evolution, and human MPO may not be optimal for raising ANCA in rodent models.
• Comparative amino acid sequence analysis of rat and human MPO is recommended to identify key antigenic epitopes.