Temperature-sensitive binding of solid phase C1q to aggregated human immunoglobulin G

Area of Science:

• Immunology
• Biochemistry

Background:

• The first component of complement (C1q) plays a crucial role in the innate immune system by initiating the classical complement pathway.
• C1q recognizes and binds to aggregated immunoglobulins and immune complexes, initiating downstream complement activation.
• Understanding the factors influencing C1q binding is essential for comprehending immune complex clearance and inflammatory processes.

Purpose of the Study:

• To investigate the effect of temperature on the binding activity of solid-phase immobilized C1q to aggregated human gamma-globulin and immune complexes.
• To determine the reversibility of C1q binding and explore potential conformational changes induced by immobilization and temperature.

Main Methods:

• Covalent coupling of purified C1q to Sepharose beads using cyanogen bromide activation.
• Assessing the binding of aggregated human gamma-globulin and immune complexes to immobilized C1q at different temperatures (4°C, 23°C, and 42°C).
• Investigating the reversibility of binding by temperature manipulation and eluting bound complexes.

Main Results:

• Solid-phase C1q exhibited significantly reduced binding to aggregated gamma-globulin and immune complexes at room temperature (23°C) compared to 4°C.
• Binding was nearly complete at 4°C, and the temperature-sensitive binding was reversible.
• Elution of bound complexes was achieved by increasing the temperature from 4°C to 23°C.
• Free C1q or C1q adsorbed onto polystyrene demonstrated binding activity at both 23°C and 4°C, suggesting immobilization-induced conformational changes.

Conclusions:

• Immobilization of C1q onto a solid support, such as Sepharose, induces temperature-dependent binding activity.
• Conformational restraints imposed by covalent coupling to a solid support may limit C1q's functional activity at elevated temperatures.
• These findings highlight the importance of temperature and immobilization conditions in studying C1q-ligand interactions.