Carbohydrate antibodies

 Polysaccharides and carbohydrates can be classified on the basis of their monomer composition.

It is so usual to distinguish between homo and hetero polysaccharides, depending on whether they have one or more monosaccharide units. 

Glucans are polymers of D-glucose (a.k.a. dextrans), galactans are polymers of D-galactose and xylans of D-xylose polymers. Chitosans are polymers of D-glucosamine.

Heteropolysaccharides are classified according to the nature of the main saccharide units that compose them. For instance, the araboxylans are mixed polymers of arabinose and xylose. The same principle applies to classify galactoarabans, galactomannans, etc.

We can also classify polysaccharides according to their biological functions. 

The main reserve polysaccharides are, in bacteria, fungi and in animal cells glycogen, and in plants, starch, a mixture of amylose and amylopectin. These macromolecules are α1 4 / α1 6-homoglucans, with the exception of amylose which is not or very little branched. Other reserve polysaccharides, less widespread than the previous ones, are fructans (inulin, levans), present only in certain plants (artichoke, dahlia and some grasses). Galactomannans are reserves in mushrooms and plants, and laminarins (β1 3 / β1 6-homoglucans) exist only in algae of the genus Laminaria. The main structural polysaccharides are cellulose plant walls (β1 4-homoglucan), chitin constituting the arthropod cuticle (β1 4-chitosan), hemicelluloses and pectins (complex heteropolysaccharides). Other less common structural polysaccharides are agarose and agaropectin agar and carrageenates extracted from algae.

Antibodies to carbohydrate antigens are crucial for: 

• the study of bacteria, tumors, blood groups, and cell-cell adhesion interactions
• the analysis of viral, hormone, and toxin receptors
• the analysis of the glycosylation of recombinant proteins.

However, antibodies to carbohydrate compounds are very tricky to generate because of the T-cell-independent response to carbohydrates. The outcome is low affinity and difficult to work with IgM antibodies. Screening technologies that include IgM antibodies can cause selections of antibodies with low-affinity binding sites because of the net avidity enhancement. Unfortunately, the low-affinity binding site can also have a similar affinity for unwanted structures.