Modulation of immunoglobulin G oligomerization by variable domain glycans: A mechanism to regulate complement...

Area of Science:

• Immunology
• Glycobiology
• Structural Biology

Background:

• Immunoglobulin G (IgG) possesses conserved fragment crystallizable (Fc) domain glycans, but variable domain glycans (VDGs) can also be expressed.
• Elevated VDGs are characteristic of rheumatoid arthritis autoantibodies and linked to other autoimmune diseases.
• The functional impact of VDGs on IgG remains largely unknown.

Purpose of the Study:

• To investigate how VDGs influence the capacity of IgG antibodies to activate the complement system.
• To elucidate the structural and functional mechanisms by which VDGs affect complement activation.

Main Methods:

• Complement activation assays using IgG with varying VDG levels.
• Structure-function analyses to determine the impact of VDGs on IgG.
• Cryoelectron tomography to visualize IgG-C1q complexes on antigen-coated vesicles.

Main Results:

• VDGs on IgG were found to inhibit the initiation of the classical complement pathway.
• VDGs reduce complement activation by hindering IgG oligomer formation on antigen surfaces.
• Impaired IgG oligomerization leads to reduced C1q binding and lower complement activation potential.

Conclusions:

• VDGs represent a novel regulatory mechanism modulating IgG's ability to activate the complement system.
• This finding expands our understanding of IgG functional diversity and immune effector mechanisms.
• The study identifies VDGs as key players in controlling antibody-mediated complement activation.