Human Mannose-binding Lectin in Immunity: Friend, Foe, or Both?

Area of Science:

• Immunology
• Microbiology
• Genetics

Background:

• Human mannose-binding lectin (MBL) is a crucial pattern recognition molecule in the innate immune system.
• MBL initiates the lectin pathway of complement activation, a primitive defense mechanism against pathogens.
• A significant portion of the human population (approximately 5%) possesses genetic variations leading to a lack of functional serum MBL.

Purpose of the Study:

• To investigate the immunological significance of human mannose-binding lectin (MBL).
• To determine if the absence of functional MBL impacts susceptibility to infections.
• To evaluate the evolutionary role of MBL in human populations.

Main Methods:

• Review of prospective studies on individuals with and without functional MBL.
• Analysis of infection rates and severity in different MBL genotypes.
• Comparative analysis of immune responses in MBL-deficient versus MBL-sufficient individuals.

Main Results:

• Individuals lacking functional serum MBL do not exhibit increased susceptibility to severe infections.
• Prospective studies have not identified a significant clinical disadvantage for MBL-deficient individuals.
• These findings challenge the presumed essential role of MBL in protective immunity.

Conclusions:

• Human MBL appears to be largely redundant for effective protective immunity against common infections.
• The lack of a clear disadvantage in MBL-deficient individuals suggests MBL may not be under strong positive selection for pathogen defense.
• There is a possibility that MBL has been subject to counter-selection due to potential deleterious effects.