Intranodal expansion of follicular T helper cells in patients with multiple sclerosis.

The efficacy of anti-CD20 therapies places B cells and their interaction with T cells at the center of attention for multiple sclerosis (MS) pathogenesis. Follicular T helper cells (Tfh), which guide B cell maturation in germinal centers within lymph nodes (LNs), are elevated in the circulation and cerebrospinal fluid of patients with MS (pwMS). However, the LN spatial landscape has remained largely without investigation for pwMS. Using cyclic immunofluorescence, we assessed cell abundance and spatial connections in FFPE LNs of 33 pwMS and 35 non-MS controls. The presence of EBV was analyzed through EBER immunostaining and multiplex quantitative PCR. Our analysis showed that Tfh cells were expanded in LNs of pwMS and accumulated especially in the mantle zone and B cell follicles compared with controls. The Tfh/T follicular regulator ratio was increased in pwMS, while B cell ratios were similar between the cohorts. The interaction of Tfh cells with follicular B cells was higher in pwMS. Interestingly, Tfh accumulation was also observed in 5 prediagnostic MS cases. No signs of EBV latency were detected in either group. These findings highlight LNs as a site of early and persistent immune activation in pwMS, with therapeutic implications to be further addressed.