C1q and mannose-binding lectin binding and complement activation across genetically diverse Mycobacterium...

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Tuberculosis (TB), caused by Mycobacterium tuberculosis complex (MTBC), is a major global health threat.
• Genetic diversity within MTBC influences disease progression and host immune response.
• The complement system, a key innate immunity component, has incompletely understood interactions with MTBC.

Purpose of the Study:

• To investigate the roles of C1q and mannose-binding lectin (MBL) in complement activation against diverse MTBC strains.
• To elucidate the contribution of these pattern recognition molecules (PRMs) in early host-pathogen dynamics during TB infection.

Main Methods:

• Direct binding assays of C1q and MBL to clinical MTBC strains.
• Assessment of complement cascade activation, including C4b/C3b deposition and membrane attack complex (MAC) formation.
• Inhibition experiments using nonimmune serum to determine the primary drivers of complement activation.

Main Results:

• Both C1q and MBL directly bind to MTBC strains in a strain-dependent manner.
• C1q and MBL facilitate complement activation, leading to C4b/C3b deposition and MAC formation.
• C1q is the primary activator in nonimmune serum, with MBL playing a supportive role; MAC formation does not significantly affect MTBC viability.

Conclusions:

• The study reveals a complex interplay between complement system components (C1q, MBL) and MTBC genetic diversity.
• Complement activation, while robust, does not confer direct bacterial killing, highlighting immune evasion mechanisms.
• Understanding MTBC lineage diversity is crucial for comprehending immune responses and developing effective TB therapies.