Isolation and structural identification of glycopolymers of Bifidobacterium bifidum BIM B-733D as putative players in pathogenesis of autoimmune thyroid diseases

• Bifidobacterium bifidum 791 (commercially available as B. bifidum BIM B-733D) cell-surface biopolymers (BPs) interact selectively with human serum thyroid peroxidase (TPO) and thyroglobulin (Tg) autoantibodies (anti-TPO and anti-Tg, respectively). BPanti-TPO and BPanti-Tg were isolated from the soluble fraction of B. bifidum BIM B-733D by affinity chromatography with anti-TPO or anti-Tg, respectively. Homogeneity of affinity eluates (AE(anti-TPO) and AE(anti-Tg)) was tested by size exclusion chromatography. For each AE, the elution profiles generated on the basis of absorbance at 280 nm do not conform to ELISA data for functional activity characteristic of BPs. Moreover, high functional activity was detected in chromatographic fractions that had significantly different molecular weights and no absorbance at 280 nm, which suggests a non-protein (carbohydrate) nature of BPanti-TPO and BPanti-Tg. The semi-preparative size exclusion chromatography of AE(anti-TPO) and AE(anti-Tg) with detection by refractometer gave 5,000-7,000 Da fractions containing substances that interact selectively with either anti-TPO (BPanti-TPO) or anti-Tg (BPanti-Tg) according to ELISA data. Analysis by two-dimensional NMR spectroscopy including a H-1, C-13-heteronuclear single-quantum coherence experiment indicated that both substances are linear alpha-1,6-glucans. For the first time, an immunological similarity (molecular mimicry) of glycopolymers of B. bifidum BIM B-733D and human thyroid proteins, TPO and Tg, was shown. On the whole, our data point to a possible role of bifidobacteria in the pathogenesis of autoimmune thyroid diseases (ATD). The main requirements for triggering/acceleration or prevention/abrogation of ATD by bifidobacteria through molecular mimicry mechanism are hypothesised to be (1) genetic predisposition to ATD and (2) intestinal epithelium penetration by alpha-1,6-glucan.

Subject headings

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Keyword

molecular mimicry

6-glucan

alpha-1

autoantibodies

Publication and Content Type

art (subject category)

ref (subject category)