Complement activity is associated with disease severity in multifocal motor neuropathy

Area of Science:

• Immunology
• Neurology
• Complement System

Background:

• Multifocal motor neuropathy (MMN) is a rare autoimmune disorder affecting peripheral nerves.
• The role of the complement system, particularly innate pathways, in MMN pathogenesis is not fully understood.
• Anti-GM1 antibodies are implicated in MMN, but their complement-activating capacity and correlation with disease severity require further investigation.

Purpose of the Study:

• To determine if high innate activity of the classical and lectin complement pathways is associated with MMN.
• To investigate the correlation between innate complement activity, anti-GM1 antibody complement-activating potential, and MMN disease severity.

Main Methods:

• A case-control study involving 79 MMN patients and 79 healthy controls.
• Assessment of muscle weakness (Medical Research Council scale) and axonal loss (nerve conduction studies).
• Measurement of classical and lectin complement pathway activity, serum mannose-binding lectin (MBL) levels, and MBL gene polymorphisms (MBL2).
• Quantification of complement-activating properties of anti-GM1 IgM antibodies.

Main Results:

• No significant differences in classical or lectin pathway activity, MBL levels, or MBL2 genotypes between patients and controls.
• Complement activation by anti-GM1 IgM antibodies was solely via the classical pathway and correlated with antibody titers.
• High innate classical pathway activity and potent complement-activating anti-GM1 IgM antibodies were significantly associated with increased muscle weakness and axonal loss.

Conclusions:

• High innate classical complement pathway activity and efficient complement-activating anti-GM1 IgM antibodies are key determinants of MMN disease severity.
• These findings emphasize the critical role of anti-GM1 antibody-mediated complement activation in MMN pathogenesis and clinical progression.