Natural antibodies against a polysaccharide (Bo) from sugar cane mediate its complement-activating effect

Area of Science:

• Immunology
• Biochemistry

Background:

• The complement system is a crucial part of innate immunity.
• Glucans are polysaccharides that can interact with the immune system.
• Understanding these interactions is key to developing new immunotherapies.

Purpose of the Study:

• To investigate the interaction between a sugarcane-derived glucan (Bo) and human immunoglobulins.
• To elucidate the mechanism by which Bo activates the complement system.

Main Methods:

• Precipitation assays using human serum IgG.
• Complement activation assays via the classical pathway.
• Binding studies using IgG-Sepharose chromatography.
• Analysis of C1 fixation and inhibition.

Main Results:

• Bo specifically precipitates a fraction of human IgG.
• Bo-IgG complexes activate complement via the classical pathway by fixing C1.
• Bo binds to the F(ab) region of specific IgG antibodies.
• Bo does not inhibit C1 binding to aggregated IgG, unlike protein A.

Conclusions:

• Human serum contains natural antibodies against Bo.
• These antibodies form immune complexes with Bo, activating complement through the classical pathway.
• The interaction involves the F(ab) region of the antibodies, not Fc-mediated binding.