Active Human Complement Reduces the Zika Virus Load via Formation of the Membrane-Attack Complex

Area of Science:

• Virology
• Immunology
• Infectious Diseases

Background:

• Zika virus (ZIKV) gained prominence due to its association with microcephaly and Guillain-Barré Syndrome.
• Limited research exists on ZIKV interactions with the human complement system.
• Understanding ZIKV's susceptibility to complement is crucial for developing antiviral strategies.

Purpose of the Study:

• To investigate the stability of Zika virus (ZIKV) in human complement.
• To identify the mechanisms of ZIKV inactivation by complement.
• To determine the role of different complement pathways in ZIKV neutralization.

Main Methods:

• ZIKV was incubated with varying concentrations of human serum (10% and 50%) at 37°C.
• Viral titers were measured to assess infectivity.
• Complement activation pathways, antibody involvement (IgM), C1q binding, and Membrane Attack Complex (MAC) formation were analyzed.

Main Results:

• ZIKV showed relative stability at low complement concentrations (10%).
• High complement concentrations (50%) significantly reduced ZIKV titers within minutes.
• The classical complement pathway, initiated by IgM antibodies, was identified as the primary mechanism.
• Direct binding of C1q to ZIKV envelope and NS1 proteins was observed.
• Formation of the MAC on the viral surface was essential for viral inactivation, suggesting complement-mediated lysis, not opsonization, is critical.

Conclusions:

• Zika virus (ZIKV) is susceptible to inactivation by the human complement system, particularly at higher concentrations.
• The classical complement pathway and subsequent MAC formation are crucial for ZIKV neutralization.
• These findings highlight the importance of complement-mediated lysis in controlling ZIKV infection and inform potential therapeutic interventions.