Hashimoto's Thyroiditis Rewires T Cell Sugar Coat in Opposite Directions

**Why this matters:** The sugar molecules coating immune cells are not mere decoration—they directly regulate receptor clustering, T cell activation thresholds, and self-tolerance. Alterations in N-glycosylation have been linked to autoimmune diseases including ulcerative colitis and rheumatoid arthritis, yet almost nothing was known about glycome changes on helper T cell subsets in Hashimoto's thyroiditis (HT), the most common organ-specific autoimmune disease worldwide.

**What was studied:** Investigators recruited 158 adult women across three groups: healthy controls (CTR, n=53), early-stage HT patients with elevated anti-TPO and/or anti-Tg antibodies but normal TSH (HT1, n=45), and treated hypothyroid HT patients with normalized TSH on L-thyroxine replacement (HT2, n=60). From peripheral blood, CD4+CD25- (non-activated helper T) and CD4+CD25+ (late-activated/regulatory T) cells were magnetically sorted. N-glycans were released enzymatically with PNGase F, labeled with 2-aminobenzoic acid (2-AA), and profiled by MALDI-ToF mass spectrometry. Expression of key glycosidases (MAN1A1, MAN1A2, MAN1B1, MAN1C1, MAN2A1, MAN2A2) and glycosyltransferases (MGAT1, MGAT2, MGAT3, MGAT4A, MGAT4B, MGAT5, ST3GAL3, ST6GAL1, B4GALT1, FUT8) was assessed by RT-qPCR.

**Key results:** In healthy controls, CD4+CD25- cells are dominated by complex-type N-glycans, while CD4+CD25+ cells show a prevalence of high-mannose (oligomannose) structures—an intrinsic glycomic difference between these two T cell pools not previously described. In HT1 (active autoimmunity, intact thyroid function), CD4+CD25- cells undergo a dramatic shift toward oligomannose-type glycans, while CD4+CD25+ cells paradoxically increase complex-type glycans—essentially mirroring each other's baseline profile. In HT2 (treated, euthyroid patients), both subsets largely revert toward the glycan distribution seen in healthy controls, suggesting metabolic normalization via L-thyroxine influences glycosylation machinery. RT-qPCR confirmed partial correlates at the transcript level, including changes in alpha-mannosidase and MGAT family gene expression consistent with the glycomic shifts observed.

**Implications:** These findings identify N-glycosylation remodeling as a dynamic, disease-stage-dependent feature of CD4+ T cell biology in HT. The opposing glycome shifts in the two T cell subsets during active autoimmunity may reflect differential regulation of receptor signaling, immune synapse formation, or Treg suppressive function. The restoration of glycan profiles under L-thyroxine therapy raises the possibility that thyroid hormone levels directly or indirectly regulate T cell glycosylation enzymes, opening new research avenues into glycan-targeted immunomodulation.

**Caveats:** The study is cross-sectional and entirely female, limiting causal inference and generalizability. CD25 alone does not cleanly distinguish regulatory T cells (Tregs) from recently activated effector T cells, so the functional identity of the CD4+CD25+ pool remains ambiguous. Glycan profiling was performed on bulk cell lysates rather than specific surface receptors, so it is unclear which individual glycoproteins drive the observed shifts.