Polysaccharide epitopes recognized by human α-L-Rha antibodies

Area of Science:

• Immunology
• Glycobiology
• Microbiology

Background:

• Anti-glycan antibodies are abundant in human blood, with anti-rhamnose (anti-Rha) antibodies being the most prevalent.
• These anti-Rha antibodies are found in all individuals, indicating a natural, non-adaptive origin.
• Rhamnose is a component of bacterial and plant polysaccharides, but the specific epitopes recognized by human antibodies remain unclear.

Purpose of the Study:

• To identify the specific rhamnose-containing epitopes recognized by human anti-Rha antibodies.
• To investigate the binding characteristics of naturally occurring anti-Rha antibodies from human immunoglobulin preparations.
• To understand the in vivo recognition patterns of these antibodies.

Main Methods:

• Antibodies (IgG, IgM, IgA) were isolated from human immunoglobulin preparations using an alpha-L-rhamnose (α-L-Rha)-Sepharose affinity adsorbent.
• Isolated antibodies were analyzed against a large array of approximately 1000 bacterial and plant polysaccharides, with over 240 containing rhamnose.
• Binding specificity was assessed based on the location and linkage of rhamnose residues within the polysaccharide structures.

Main Results:

• Anti-α-L-Rha antibodies bound to polysaccharides with terminal or pendant rhamnose (α1-2, 1-3, 1-4 linkages) but not internal positions.
• Recognition occurred for both bacterial O-antigens and plant polysaccharides.
• A high proportion of IgM and IgA antibodies suggested polyvalence, with a narrow epitope specificity for the monosaccharide.

Conclusions:

• Human polyclonal anti-α-L-Rha antibodies possess a defined epitope specificity, primarily recognizing terminal or pendant rhamnose.
• The polyvalent nature of these antibodies, particularly IgM and IgA, suggests efficient recognition of natural targets.
• In vivo, anti-Rha antibodies likely target patterns of densely packed polysaccharides like lipopolysaccharides or plant cell walls rather than single repetitive epitopes.