Binding of Submaximal C1q Promotes Complement-Dependent Cytotoxicity (CDC) of B Cells Opsonized with Anti-CD20 mAbs Ofatumumab (OFA) or Rituximab (RTX): Considerably Higher Levels of CDC Are Induced by OFA than by RTX
Autor: | Paul V. Beum, Paul W. H. I. Parren, Frank J. Beurskens, Ronald P. Taylor, Margaret A. Lindorfer, Jan G. J. van de Winkel, Andrew W. Pawluczkowycz |
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Rok vydání: | 2009 |
Předmět: |
Immunology
B-Lymphocyte Subsets Dose-Response Relationship Immunologic chemical and pharmacologic phenomena Antibodies Monoclonal Humanized Antibodies Monoclonal Murine-Derived Classical complement pathway immune system diseases Cell Line Tumor medicine Humans Immunology and Allergy Complement Pathway Classical Opsonin B cell CD20 biology Chemistry Complement C1q Antibodies Monoclonal Opsonin Proteins Antigens CD20 Cytotoxicity Tests Immunologic Virology Molecular biology Complement-dependent cytotoxicity Complement system medicine.anatomical_structure Complement C3b biology.protein Antibody Rituximab Complement membrane attack complex Protein Binding |
Zdroj: | The Journal of Immunology. 183:749-758 |
ISSN: | 1550-6606 0022-1767 |
Popis: | The CD20 mAb ofatumumab (OFA) is more effective than rituximab (RTX) in promoting complement-dependent cytotoxicity (CDC) of B cells via the classical pathway (CP) of complement. CP activation is initiated by C1q binding to cell-bound IgG. Therefore, we examined the role of C1q in the dynamics of complement activation and CDC of B cell lines and primary cells from patients with chronic lymphocytic leukemia, reacted with OFA or RTX. C1q binding, complement activation, and colocalization of C1q with cell-bound mAbs were determined by flow cytometry and high-resolution digital imaging. C1q binds avidly to OFA-opsonized Raji and Daudi cells (KD = 12–16 nM) and colocalizes substantially with cell-bound OFA. Cells opsonized with OFA undergo high levels of complement activation and CDC in C1q-depleted serum supplemented with low concentrations of C1q. Under comparable conditions, RTX-opsonized cells bind less C1q; in addition, even when higher concentrations of C1q are used to achieve comparable C1q binding to RTX-opsonized cells, less complement activation and CDC are observed. Greater CDC induced by OFA may occur because C1q is bound in close proximity and with high avidity to OFA, resulting in effective CP activation. Moreover, OFA binds to the small, extracellular CD20 loop, placing the mAb considerably closer to the cell membrane than does RTX. This may facilitate effective capture and concentration of activated complement components closer to the cell membrane, potentially shielding them from inactivation by fluid phase agents and promoting efficient generation of the membrane attack complex. |
Databáze: | OpenAIRE |
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