In vitro Functional Activity of IgG1 and IgG3 Polyclonal and Monoclonal anti-D

• Published in: Vox sanguinis 1997-01, Vol.72 (1), p.45-51
• Main Author: Kumpel, B. M.
• Format: Article
• Language: English
• Subjects: Antibodies, Monoclonal; Biological and medical sciences; Cells, Cultured; Hematology; Hemolysis - immunology; Humans; Immunoglobulin G - immunology; Investigative techniques, diagnostic techniques (general aspects); Isoantibodies - immunology; Killer Cells, Natural - immunology; Medical sciences; Monocytes - immunology; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Rh-Hr Blood-Group System - immunology; Rho(D) Immune Globulin
• ISSN: 0042-9007; 1423-0410
• DOI: 10.1046/j.1423-0410.1997.00045.x

Background and objectives: IgG anti‐D is generally restricted to IgG1 and IgG3; it mediates red cell destruction through interactions with IgG Fc receptors (FcγR) on effector cells. The relative ability of these two IgG subclasses of anti‐D to mediate haemolysis in vitro by monocytes and K cells was investigated. Materials and methods: Anti‐D was affinity purified from 5 preparations of prophylactic anti‐D immunoglobulin, and IgG subclasses quantified by ELISA; mean levels were 86.5% IgG1, 1.4% IgG2, 11.6% IgG3 and 0.4% IgG4. IgG1 and IgG3 polyclonal anti‐D were further purified separately from some of the anti‐D by removal of either IgG3 using magnetic beads coated with anti‐IgG3, or of IgG1 using protein A. These preparations were compared with monoclonal anti‐D (BRAD‐3 and BRAD‐5) for their ability to lyse red cells in antibody‐dependent cell‐mediated cytotoxicity (ADCC) assays. Results: Monocyte‐mediated lysis of red cells coated with IgG3 anti‐D was approximately twice that of cells coated with IgG1 anti‐D at similar sensitization levels, and anti‐D preparations containing 10% or more IgG3 gave similar lysis. By contrast, in the K cell ADCC, IgG1 anti‐D was 2–4 times more haemolytic than IgG3 anti‐D. Polyclonal IgG1 and IgG3 anti‐D promoted about 20% more lysis than BRAD‐5 (IgG1) and BRAD‐3 (IgG3), respectively, in the K cell ADCC, although no difference was observed between polyclonal and monoclonal anti‐D in the monocyte ADCC. Conclusions: These experiments demonstrated a functional dichotomy between these two subclasses of anti‐D; IgG3‐coated red cells were lysed preferentially by monocytes mediated predominantly through FcγRI interactions, whereas haemolysis of IgG1‐sensitized cells was mediated mainly by FcγRIII on K cells.