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Terminal complement components play a role in the expression of C5a.
Journal of Immunology (Baltimore, Md. : 1950)
|February 1, 1987
Summary
The terminal complement components (C6, C7, C8) are crucial for maximal C5a expression and function. Their presence during C5 cleavage significantly enhances C5a release, impacting the complement cascade.
Area of Science:
- Immunology
- Complement System Biology
Background:
- The complement system is a critical part of innate immunity.
- Complement component C5a is a potent anaphylatoxin and chemoattractant.
- The precise role of terminal complement components in C5a generation is not fully understood.
Purpose of the Study:
- To investigate the role of terminal complement components (C6, C7, C8) in the expression of C5a.
- To determine if these components influence C5a function.
Main Methods:
- Radioimmunoassay (RIA) was used to detect C5a antigenically.
- Polymorphonuclear myeloperoxidase (PMN-MPO) release assay was used to assess C5a function.
- Experiments utilized purified complement components and immunochemically depleted human serum.
Main Results:
- Maximal C5a expression, detected both antigenically and functionally, required the presence of C6, C7, and C8 during C5 cleavage.
- C6 alone did not augment C5a expression.
- C5 cleaved without terminal components, when subsequently incubated with C6 and C7, did not release C5a.
- Freezing/thawing or mild detergent treatment of cleaved C5 did not fully substitute for the terminal components' effect.
Conclusions:
- Terminal complement components (C6-C8) play a significant role in the expression of both C5a antigen and function.
- The mechanism may involve conformational changes in C5 during membrane attack complex formation.
- Further research is needed to elucidate the exact mechanism of terminal component involvement.