In vitro activation of complement by isolated human heart subcellular membranes

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• The complement system is a crucial part of innate immunity.
• Mitochondrial damage is implicated in various inflammatory conditions.
• Understanding complement activation by cellular components is vital for autoimmune disease research.

Purpose of the Study:

• To investigate the in vitro activation of the human complement system by mitochondrial membranes from normal human heart tissue.
• To elucidate the specific pathways involved in complement activation mediated by these membranes.
• To determine the interaction of mitochondrial membranes with key complement components.

Main Methods:

• Incubation of isolated heart mitochondrial membranes with normal human serum.
• Assessing complement activation via C3 depletion.
• Utilizing various complement inhibition strategies (EGTA, C2-deficient serum, C1-depleted serum, heat inactivation, EDTA).
• Analyzing Factor B conversion.
• Investigating the binding and activation of C1 and C4 to mitochondrial membranes.

Main Results:

• Mitochondrial membranes induced complement activation, evidenced by C3 depletion.
• Activation involved both classical and alternative complement pathways, as indicated by inhibition studies.
• Mitochondrial membranes bound and activated C1, and subsequently C4, but did not directly convert C3.
• Factor B conversion occurred in normal and EGTA-treated serum but not in EDTA-treated serum.

Conclusions:

• Heart mitochondrial membranes activate the human complement system via both classical and alternative pathways.
• Mitochondrial membranes form stable complexes with C1 and C4.
• These membranes lack inherent enzymatic activity to directly cause C3 conversion, suggesting indirect mechanisms initiate downstream complement cascade.