Linear α-(1 → 6)-d-glucan from Bifidobacterium bifidum BIM В-733D is low molecular mass biopolymer with unique immunochemical properties.

Role of microorganisms in induction of/protection from autoimmune diseases is proven though molecular mechanisms and bacterial/viral/yeast biopolymers responsible for these effects are in the research stage. Autoantobodies (AAbs) to thyroid peroxidase (anti-TPO) and thyroglobulin (anti-Tg) as well as AAbs to transglutaminase 2 (anti-TG2) and antibodies to gliadins (anti-gliadins) are serological markers of autoimmune thyroid disease and celiac disease, respectively, and players in pathogenesis of these autoimmune diseases. In current study, biopolymer of Bifidobacterium bifidum BIM В-733D that interacts selectively with anti-gliadins (Bb-Ganti-gliadins ) was isolated by affinity chromatography with anti-gliadins, purified by size exclusion chromatography on TSK 40 gel and identified by NMR as linear α-(1 → 6)-d-glucan with molecular mass about 5000 Da. It was proven that compounds Bb-Ganti-gliadins and Bb-Ganti-TPO /Bb-Ganti-Tg isolated early from the same strain [Kiseleva, E. P. et al., Benef Microbes.2013, 4, 375 -391] are the same substance designated GBb . Its unique immunochemical property is the ability to interact selectively with anti-TPO, anti-Tg, anti-TG2 and anti-gliadins in presence of no less than 10-fold excess of total immunoglobulins of class G (tIgG), as it was proven by ELISA. Synthesis of GBb -bovine serum albumin (GBb -BSA) conjugate is an example of increasing the reliability and reproducibility of ELISA results by mediated immobilization of a polysaccharide covalently attached to a well-adsorbed protein. Taking into account that there are population of bispecific anti-gliadins (anti-gliadins and anti-TG2 simultaneously) we regard our data as first argument in favor of hypothesis that GBb differentiates between human AAbs per se and other human Ig (e.g. antibodies to antigens of infectious agents) due to its binding with a yet unidentified site which is present in the molecules of all AAbs (independently on their specificity) and absent in other human Igs.