Effect of neonatal BCG vaccination on the evolution of Hashimoto’s Thyroiditis

Background Hashimoto’s thyroiditis (HT) involves the autoimmune destruction of thyrocytes with the presence of anti-thyroid peroxidase (TPO) and/or anti-thyroglobulin (TG) antibodies. In autoimmune diseases, an immunomodulatory role of Bacillus Calmette-Guerin (BCG) vaccination has been reported with decreased autoantibody production and induction of regulatory T cells. We hypothesize that a decline in the efficacy of BCG might be associated with the appearance of HT during adulthood. Methods Adult subjects with subclinical HT (HT-SCH) (n=39) and non-autoimmune subclinical hypothyroidism (NA-SCH) (n=25) were enrolled along with euthyroid healthy controls (HC) (n=20). The BCG-specific immune responses were determined by the Mantoux test and BCG-induced in-vitro proliferation of peripheral blood mononuclear cells (PBMC). Anti-thyroid cellular immune responses were assessed in subjects with human leukocyte antigen (HLA)-A*02 and HLA-A*24 alleles by determining the frequency of CD8+ T cells recognizing major histocompatibility complex (MHC) dextramers (DMR) carrying TPO-derived peptides, by flow cytometry. Results The HT-SCH group had a lower rate of Mantoux test reactivity (38.5%) as compared to NA-SCH (64%) and HC subjects (65%) (p=0.047). However, the BCG-induced in-vitro proliferation of PBMC was similar in HT-SCH, NA-SCH, and HC groups. Further, the BCG-vaccinated SCH subjects had lower levels of thyroid stimulating hormone (TSH) (p=0.026). Next, the SCH subjects had higher frequencies of peripheral DMR+ CD8+ T cells as compared to HC subjects (p=0.001). Interestingly, the frequency of peripheral DMR+ CD8+ T cells was significantly higher in HT-SCH than HC subjects (p=0.045). Finally, we observed a positive correlation between the frequency of DMR+CD8+ T cells and TSH levels (r = +0.620, p=0.006). Conclusions Collectively, our results highlight a complex relationship of neonatal BCG vaccination with the genesis of HT, via modulation of autoimmune responses directed towards thyroid autoantigens. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research did not receive any specific grant from any funding agency in public, commercial or not-for-profit sector. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved by the institutional ethics committee of Post Graduate Institute of Medical Education and Research (PGIMER) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors