Serum lectin with known structure activates complement through the classical pathway

Area of Science:

• Immunology
• Biochemistry

Background:

• Mannan-binding protein (MBP) is a lectin that binds mannose and N-acetylglucosamine.
• MBP plays a role in the innate immune system by activating complement.
• Differences in MBP function between serum and liver forms require investigation.

Purpose of the Study:

• To investigate the complement-activating properties of rat serum MBP.
• To compare the functional activity of serum MBP with rat liver MBP.
• To elucidate the mechanism of complement activation by serum MBP.

Main Methods:

• Passive hemolysis assay using mannan-coated sheep erythrocytes.
• Inhibition studies with haptenic sugars.
• Analysis of the N-terminal amino acid sequence of rat serum MBP.

Main Results:

• Rat serum MBP activated the complement system, while rat liver MBP did not.
• Complement activation by serum MBP was sugar-dependent and required C4, indicating classical pathway involvement.
• The N-terminal sequence of rat serum MBP matched MBP-A, confirming their identity.

Conclusions:

• Serum MBP initiates complement activation through its sugar-binding domain via the classical pathway.
• Structural similarities between serum MBP and C1q may inform the mechanism of complement activation.
• Distinct functional properties of serum and liver MBP highlight tissue-specific roles in immunity.