Association of active human herpesvirus-6 (HHV-6) infection with autoimmune thyroid gland diseases

Viral infections frequently have been cited as important environmental factors implicated in the onset of autoimmune thyroiditis (AIT). The aim of this study was to determine the involvement of HHV-6 infection in the development of autoimmune thyroiditis.

This study included 45 patients (42 female and 3 male; median age 47.00 IQR 38.50-57.00) with histologically, laboratory, and clinically confirmed autoimmune thyroiditis, as well as 30 autopsied subjects (26 female and 4 male; median age 58.50, IQR 51.50-67.00) without thyroid pathologies and 30 healthy blood donors (25 female and 5 male; median age 33.50, IQR 27.75-44.25) as controls. Results were obtained by applying molecular virology and immunohistochemistry techniques.

The presence of persistent HHV-6 infection in AIT patients was significantly higher (p 0.0058) than in the control group (44/45 (98%) vs. 23/30 (77%), respectively). Also, a significantly higher frequency of HHV-6 activation marker (U79/80 mRNA) was found in patients' thyroid gland tissue samples with AIT in comparison with the control group (18/44 (41%) vs. 1/17 (6%), respectively; p 0.0118). The median HHV-6 load was found to be higher in patients with active viral infection than in patients without it (2147, IQR 971-4188 vs. 551, IQR 145-1589 copies/1×10⁶ cells; p 0.003). The presence of HHV-6 antigen expression was demonstrated in intrafollicular cellular clusters and immunohistochemistry indicated thyrocytes in the follicle wall.

These findings provide evidence of strong HHV-6 infection association with AIT development.