Killing of human melanoma cells by the membrane attack complex of human complement as a function of its molecular
Abstract:
The efficiency of the membrane attack complex (MAC) in killing M21 melanoma cells was determined varying the molar ratio of cell-bound C9:C8. It was found that C5b-8 produced functional channels as evidenced by 86Rb release and propidium iodide uptake; cell killing occurred in the absence of C9 with greater than 5 X 10(5) C5b-8/cell; the maximal molar ratio of C9:C8 was 6.6:1; using nonlytic numbers of C5b-8 (4.7 X 10(5)/cell), greater than 90% killing ensued at a C9:C8 molar ratio of 2.8:1 at which approximately 9,000 poly C9/cell were formed, and 50% killing at a ratio of 1:1; (e) when the MAC was assembled on cells at 0 degree C, consisting of C5b-8(1)9(1), and unbound C9 was removed before incubation at 37 degrees C, killing was similar to that observed when poly C9 formation was allowed to occur. Thus, MAC lytic efficiency toward M21 cells may be enhanced by but does not depend on poly C9 formation.
Insights
The membrane attack complex (MAC) efficiently kills melanoma cells. Poly C9 formation enhances MAC lytic efficiency but is not essential for cell death, revealing key insights into complement system function.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- The membrane attack complex (MAC) is a key effector of the complement system, crucial for eliminating pathogens and altered self-cells.
- Understanding MAC's lytic efficiency is vital for developing targeted immunotherapies, particularly for cancers like melanoma.
Purpose of the Study:
- To investigate the role of C9 polymerization in the lytic efficiency of the MAC against M21 melanoma cells.
- To determine the optimal molar ratios of C9 to C5b-8 for effective cell killing.
Main Methods:
- Quantifying cell-bound C5b-8 and C9 using varying molar ratios.
- Assessing membrane channel formation via 86Rb release and propidium iodide uptake.
- Measuring M21 melanoma cell killing efficacy at different C9:C8 ratios and poly C9 formation levels.
Main Results:
- C5b-8 alone formed functional channels and induced cell killing at high concentrations (>5 X 10^5 C5b-8/cell).
- Maximal C9:C8 molar ratio observed was 6.6:1.
- Significant melanoma cell killing (>90%) occurred at a C9:C8 ratio of 2.8:1, with ~9,000 poly C9/cell formed.
- 50% cell killing was achieved at a C9:C8 ratio of 1:1.
- Cell killing was comparable whether poly C9 formation was allowed or prevented after initial MAC assembly.
Conclusions:
- MAC-mediated lysis of M21 melanoma cells is enhanced by poly C9 formation.
- However, poly C9 formation is not strictly required for MAC-induced cell death.
- These findings highlight the complex mechanisms governing MAC function and its potential as a therapeutic target.
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