Immunostimulatory probiotic Lactobacillus rhamnosus HN001 and Bifidobacterium lactis HN019 do not induce pathological inflammation in mouse model of experimental autoimmune thyroiditis

The possibility that intestinal microflora contribute to the pathogenesis of autoimmune diseases has raised issues regarding the safety of probiotic organisms, especially those with immunostimulating properties, in individuals with such immune dysfunctions. In this study, the effect of consumption of probiotic lactic acid bacteria (LAB) strains Lactobacillus rhamnosus HN001(HN001) and Bifidobacterium lactis HN019 (HN019) on the induction and progression of experimental autoimmune thyroiditis (EAT) was investigated in CBA/CaH (H-2 k) mice. HN001 or HN019 in skim milk were fed to mice daily (1–1.5×10 8 cfu/mouse/day) for 5 to 9 weeks. A mild form of EAT was induced by subcutaneous injection of mouse thyroglobulin (MTg) with either Freund's adjuvant (complete and incomplete, CFA and IFA) or lipopolysaccharide (LPS). The proliferative responses of spleen lymphocyte to MTg stimulation in vitro and the presence (and degree) of mononuclear cell infiltration in thyroid gland tissues were examined to assess the development and severity of EAT. The levels of serum anti-MTg antibodies (IgG1 and IgG2a) and spleen weight index were determined to detect the presence of autoimmune responses of mice receiving MTg. Results showed that 8 weeks after immunization, 16.67–50% of the mice developed mild EAT with lymphocyte infiltration in the thyroid glands. Probiotic feeding did not induce full-blown EAT. There were no differences in spleen weight index or the proliferative spleenocytes in response to PMA between mice that received MTg alone and mice that received MTg and probiotic LAB strains.