Multiple routes of complement activation by Mycobacterium bovis BCG

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Mycobacterium tuberculosis is a leading global infectious disease.
• Intracellular survival within macrophages is a key immune evasion strategy.
• Complement-mediated opsonization may facilitate macrophage entry.

Purpose of the Study:

• To elucidate the mechanisms of complement activation by Mycobacterium bovis BCG.
• To investigate the roles of classical, lectin, and alternative pathways in M. bovis BCG-complement interactions.

Main Methods:

• Utilized Mycobacterium bovis BCG as a model organism.
• Assessed complement activation pathways (classical, lectin, alternative) using human serum.
• Investigated direct binding of complement components (C1q, MBL, L-ficolin, Factor H) to mycobacteria.
• Examined the influence of antibodies and bacterial proteases.

Main Results:

• M. bovis BCG directly activates classical, lectin, and alternative complement pathways.
• Classical pathway activation is both antibody-independent (C1q binding) and antibody-dependent (IgG, IgM enhancement).
• Alternative pathway activation is antibody-independent, with Factor H binding suggesting regulation.
• Lectin pathway activation involves MBL and L-ficolin binding, leading to MASP2 activation.

Conclusions:

• M. bovis BCG extensively interacts with the human complement system.
• The bacterium activates all three complement pathways through direct molecular interactions.
• Understanding these interactions provides insights into mycobacterial pathogenesis and immune evasion.