Serum and plasma fibronectin binds to complement reacted immune complexes primarily via Clq

Area of Science:

• Immunology
• Biochemistry

Background:

• Immune complexes (IC) play a role in various immune responses.
• Fibronectin is a protein involved in cell adhesion and immune modulation.
• The interaction between fibronectin and complement components on IC is not fully understood.

Purpose of the Study:

• To investigate the binding mechanisms of fibronectin to human complement components (Clq, C3b) and complement-reacted immune complexes (IC).
• To determine the primary complement component responsible for fibronectin binding to IC.

Main Methods:

• Enzyme-linked immunosorbent assays (ELISA) were used to quantify binding.
• Microplates were coated with BSA and specific antibodies to form IC.
• Complement components (Clq, C3b) and fibronectin binding were assessed under various conditions, including the use of EDTA and different antibody fragments.

Main Results:

• Fibronectin binding to IC was predominantly mediated by Clq, with minimal binding observed via C3b.
• EDTA inhibited C3b binding but not Clq binding, while F(ab')2 fragments blocked Clq binding but not C3b binding.
• Fibronectin showed dose-dependent binding to IC pretreated with Clq, confirming Clq as the main binding partner.

Conclusions:

• Fibronectin's primary interaction with complement-reacted immune complexes is through the Clq component.
• Understanding this interaction is vital for elucidating fibronectin's role in immune complex clearance and inflammatory processes.