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Membrane cofactor protein (MCP; CD46). Isoforms differ in protection against the classical pathway of complement
1Division of Rheumatology, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
Journal of Immunology (Baltimore, Md. : 1950)
|June 1, 1996
Summary
Membrane cofactor protein (MCP; CD46) isoforms BC offer superior protection against complement activation via the classical pathway. These findings highlight the biological significance of MCP isoform variation and its therapeutic potential.
Area of Science:
- Immunology
- Molecular Biology
Background:
- Membrane cofactor protein (MCP; CD46) is a key regulator of complement activation on host cells.
- MCP exists as four main isoforms generated by alternative splicing, differing in O-glycosylation domains and cytoplasmic tails.
Purpose of the Study:
- To characterize the complement inhibitory profiles of the four common MCP isoforms.
- To determine the functional significance of isoform-specific differences in O-glycosylation and cytoplasmic tails.
Main Methods:
- Comparison of C4b binding affinities across MCP isoforms.
- Cytoprotection assays using transfected isoforms with equivalent copy numbers.
- Assessment of C4b cleavage efficiency by individual MCP isoforms.
Main Results:
- MCP isoforms (BC) with larger O-glycosylation domains exhibited higher C4b binding efficiency compared to smaller, less glycosylated C isoforms.
- BC isoforms provided enhanced cytoprotection in classical pathway-mediated complement activation.
- BC isoforms demonstrated more efficient cleavage of cell-bound C4b than C isoforms.
Conclusions:
- MCP BC isoforms preferentially inhibit the classical pathway of complement activation.
- Isoform variation in MCP plays a significant physiological role in complement regulation.
- MCP isoforms hold therapeutic potential as complement inhibitors, particularly in xenotransplantation.