C1q binding and C1 activation by various isolated cellular membranes

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• The complement system is crucial for innate immunity.
• C1q is the initiating component of the classical complement pathway.
• Cellular membranes play roles in various biological processes.

Purpose of the Study:

• To investigate the interaction between human C1q and cellular/subcellular membranes.
• To determine if this interaction leads to complement activation.
• To explore the potential role of this interaction in inflammation.

Main Methods:

• Binding assays using radioiodinated human C1q and membrane preparations from various tissues and species.
• C1 activation assays measuring the conversion of 125I-C1s.
• Competition assays with excess C1q to identify binding sites.

Main Results:

• Cellular and subcellular membranes from multiple species (human, baboon, bovine, rabbit, rat) bound human C1q with high affinity.
• Most membrane preparations activated the C1 complex.
• Baboon heart mitochondrial membranes activated C1, dependent on C1q binding, suggesting an integral membrane binding site for C1q's globular regions.

Conclusions:

• Cellular and subcellular membranes can bind and activate the C1 complex via C1q.
• The interaction of C1q with mitochondrial membranes may involve its globular heads.
• This binding and activation process could contribute to initiating or amplifying inflammation after tissue damage.