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Expression of functional cell surface C1-inactivator by U937 cells
B P Randazzo1, H B Fleit, A P Kaplan
1Department of Medicine, State University of New York, Stony Brook 11794.
Clinical Immunology and Immunopathology
|December 1, 1988
Summary
Human U937 cells express active C1-inhibitor (C1-INA) on their surface, potentially protecting them from complement-mediated lysis. This cell-surface C1-INA activity was confirmed and characterized.
Area of Science:
- Immunology
- Cell Biology
Background:
- The human monocyte-like cell line U937 synthesizes and expresses C1-inhibitor (C1-INA) on its surface.
- Previous findings established the synthesis and surface expression of C1-INA by U937 cells.
Purpose of the Study:
- To provide evidence for the functional activity of cell surface-expressed C1-INA on U937 cells.
- To characterize the molecular nature of surface-expressed C1-INA and investigate factors influencing its expression.
Main Methods:
- Hemolytic assay using intact U937 cells to assess C1-INA activity.
- Inhibition studies using monospecific antibody to C1-INA.
- SDS-PAGE and Western blotting of radiolabeled cell surface proteins after anti-C1-INA affinity chromatography.
- Phorbol ester treatment to modulate C1-INA expression.
Main Results:
- Intact U937 cells exhibited functional C1-INA activity in a hemolytic assay, which was blocked by anti-C1-INA antibody.
- SDS-PAGE revealed two surface proteins with affinity for C1-INA: a 105 kDa protein identical to plasma C1-INA and a 200 kDa protein of undetermined identity.
- Phorbol ester treatment increased the percentage of U937 cells expressing surface C1-INA.
Conclusions:
- U937 cells express functional cell surface C1-INA.
- The 200 kDa protein may represent a C1-INA receptor, a dimer, or an unrelated binding protein.
- Surface C1-INA on U937 cells may protect these human tumor cells from host complement-mediated lysis in vivo.