Immunomodulatory Effects of Lactobacillus brevis NES-428 in a Hyperthyroidism Mouse Model: Potential Applications for Graves’ Disease

<b>Background:</b> Safe, microbiome-based interventions for autoimmune hyperthyroidism are lacking. We isolated the lactic acid bacterium NES-428 from kimchi and previously demonstrated that it shares 99% 16S-rRNA identity with <i>Lactobacillus brevis</i> reference strains, confirming NES-428 as a novel strain. Here we evaluated its immunomodulatory and anti-thyroid activity in cellular and murine models. <b>Methods:</b> Jurkat T cells (5 × 10⁶) were incubated with heat-killed NES-428 for 24 h and subsequently stimulated with phorbol 12-myristate 13-acetate/ionomycin (50 ng mL^-1/1 µg mL^-1) for 6 h; cytokine transcripts were quantified by qRT-PCR. Hyperthyroidism was induced in female BALB/c mice by three intramuscular injections of adenovirus-encoding human TSH receptor (Ad-TSHR). Mice received a daily oral dose of NES-428 (1 × 10⁹ CFU) for 15 weeks. Serum thyroxine (T₄) levels, splenocyte cytokine secretion, and thyroid histopathology were assessed. Statistical analyses employed one-way ANOVA with Tukey post hoc or log-rank tests (α = 0.05). <b>Results:</b> NES-428 pre-conditioning of Jurkat cells significantly down-regulated <i>IL-2</i> and <i>IFN-γ</i> transcripts (-48% and -43%, respectively; <i>p</i> < 0.01) compared with stimulated controls while modestly increasing <i>IL-4</i> (+26%). In Ad-TSHR mice, daily NES-428 reduced mean serum T₄ from 11.2 ± 2.1 to 5.8 ± 1.4 µg dL^-1 (<i>p</i> < 0.001), restored body weight gain, and normalized follicular architecture relative to untreated hyperthyroid animals. NES-428 supplementation also lowered splenocyte IFN-γ secretion by 58% and raised IL-4 by 41% (<i>p</i> < 0.05). <b>Conclusions:</b> The kimchi-derived strain NES-428 attenuates Th1-skewed cytokine responses and ameliorates experimental hyperthyroidism in vivo. These findings support further investigation of NES-428 as a probiotic candidate for immune modulation in Graves' disease.