Homologies between proteins of Borrelia burgdorferi and thyroid autoantigens

Area of Science:

• Immunology
• Microbiology
• Genetics

Background:

• Autoimmune thyroid diseases (AITD) like Graves' disease and Hashimoto's thyroiditis have genetic links to HLA loci.
• Molecular mimicry, where microbial antigens resemble self-antigens, is a proposed mechanism for AITD development.
• Previous studies suggested Yersinia enterocolitica (YE) as a potential trigger due to antibody cross-reactivity with the human TSH receptor (hTSH-R).

Purpose of the Study:

• To investigate the molecular homology between the human TSH receptor (hTSH-R) and antigens from Yersinia enterocolitica (YE) and Borrelia burgdorferi (Bb).
• To further explore the potential role of YE and Borrelia burgdorferi (Bb) as environmental triggers for AITD via molecular mimicry.

Main Methods:

• Utilized the Basic Local Alignment Search Tool (BLAST) to identify sequence homology between hTSH-R and proteins from YE and Bb.
• Analyzed sequence identity and similarity percentages for matched regions.
• Correlated identified homologous regions with known human T-cell epitopes within the hTSH-R.

Main Results:

• Identified four homologous regions between hTSH-R and YE proteins (YopM, Ysp, exopolygalacturonase, SpyA) with 23-31% identity and 40-48% similarity.
• Found five homologous regions between hTSH-R and Bb proteins (OspA, FlaA, BBG02, BBJ08, hypothetical protein) with 27-50% identity and 40-75% similarity.
• Observed overlap between homologous regions and known hTSH-R T-cell epitopes.

Conclusions:

• The findings support the hypothesis that Borrelia burgdorferi (Bb) and Yersinia enterocolitica (YE) can act as environmental triggers for AITD.
• Molecular mimicry between these microbes and hTSH-R is a plausible mechanism in genetically predisposed individuals.
• This study strengthens the link between specific microbial exposures and the development of autoimmune thyroid diseases.