Modulation of classical C3 convertase of complement by tear lactoferrin

Area of Science:

• Immunology
• Biochemistry

Background:

• The complement system is crucial for innate immunity.
• Lactoferrin is an iron-binding protein found in various bodily secretions.
• Dysregulation of complement activation is implicated in inflammatory diseases.

Purpose of the Study:

• To investigate the anti-complementary effects of lactoferrin.
• To elucidate the mechanism by which lactoferrin modulates complement activation.
• To explore the potential anti-inflammatory role of lactoferrin.

Main Methods:

• Isolation of lactoferrin from human tears.
• Assays to measure complement-mediated lysis of antibody-coated red blood cells.
• Investigation of lactoferrin's effect on complement component assembly (C1, C4, C2, C3).
• Determination of the role of divalent cations (Fe3+, Mg++, Ca++) in lactoferrin's activity.

Main Results:

• Lactoferrin inhibited complement-mediated lysis.
• The inhibitory effect was reversed by Fe3+ but not Mg++ or Ca++.
• Lactoferrin blocked the assembly of the C42 enzyme (C3 convertase) but did not affect its function once formed.
• Inhibition occurred when lactoferrin and C2 were incubated with EAC14 cells.

Conclusions:

• Lactoferrin modulates complement activation by inhibiting C3 convertase formation.
• Lactoferrin may exert anti-inflammatory effects by regulating the complement system.
• Iron binding is critical for lactoferrin's anti-complementary activity.