Myeloperoxidase influences the complement regulatory activity of complement factor H.

Area of Science:

• Immunology
• Complement System Biology
• Pathogenesis of Vasculitis

Background:

• Neutrophil activation and alternative complement pathway are key in ANCA-associated vasculitis (AAV).
• Myeloperoxidase (MPO), released from neutrophils, can activate the alternative complement pathway.

Purpose of the Study:

• Investigate the interaction between MPO and factor H (FH), a crucial regulator of the alternative pathway.
• Determine the effect of MPO on FH's functional activities.

Main Methods:

• Immunostaining of neutrophil extracellular traps (NETs) and kidney biopsies from AAV patients.
• In vitro binding assays (ELISA, surface plasmon resonance) for MPO-FH interaction.
• Functional assays assessing FH's complement regulatory activity.

Main Results:

• FH and MPO co-localized in NETs and kidney biopsies from AAV patients.
• MPO demonstrated nanomolar affinity binding to FH, primarily at SCR1-4.
• MPO inhibited FH's interaction with C3b and its decay-accelerating and cofactor activities.

Conclusions:

• MPO binds to FH and impairs its complement regulatory functions.
• The MPO-FH interaction is implicated in AAV pathogenesis by promoting alternative complement pathway activation.