Activation of mouse complement by monoclonal mouse antibodies

Area of Science:

• Immunology
• Complement System
• Antibody Function

Background:

• Antibodies play a crucial role in the immune response by activating the complement system.
• Different antibody isotypes (IgM, IgD, IgG) exhibit distinct effector functions.
• The efficiency of complement activation can vary based on antibody isotype and genetic background.

Purpose of the Study:

• To investigate the complement-activating ability of monoclonal mouse IgM, IgD, and IgG anti-4-hydroxy-3-nitrophenyl)acetyl (NP) antibodies.
• To compare the hemolytic efficiency of different antibody isotypes and IgG subclasses.
• To determine the influence of the H-2 haplotype on complement utilization by IgM and IgG.

Main Methods:

• Hemolytic assays were performed using monoclonal antibodies against NP-conjugated sheep red blood cells.
• Complement activation was assessed by measuring red blood cell lysis.
• Experiments utilized complement from mouse strains with different H-2 haplotypes, specifically H-2k.

Main Results:

• Efficient hemolysis was observed with IgG2a, IgG2b, and IgG3 antibodies, while IgD showed no lysis.
• Some IgG1 antibodies showed weak hemolysis, while others showed none.
• IgM was a potent hemolytic agent, effective at lower concentrations than IgG.
• Under complement-limiting conditions with H-2k haplotype complement, IgG-coated cells were lysed 3-4 times more efficiently than IgM-coated cells.
• This complement utilization discrimination was H-2-linked and not observed with other H-2 alleles (b, d, s).

Conclusions:

• Mouse IgM and specific IgG subclasses (IgG2a, IgG2b, IgG3) effectively activate complement-mediated hemolysis.
• IgM is a more potent activator but less efficient in complement utilization compared to IgG.
• The efficiency of complement utilization by IgM versus IgG is modulated by a gene in the S region of the H-2 complex, particularly evident in the H-2k haplotype.