Senescent Fibroblasts Impair B Cell Proliferation via Cell-Cell Contact.

Ageing profoundly impairs vaccine efficacy, leaving older individuals highly susceptible to infectious diseases despite vaccination. Although B cells retain the intrinsic capacity to generate germinal centre (GC) responses in older people, age-associated defects in T cells, dendritic cells and follicular dendritic cells (FDCs) limit the development of high-affinity, class-switched antibody responses. Here, we hypothesised that senescent fibroblasts disrupt B cell activation and expansion, thus contributing to the diminution of the humoral response in ageing. To test this hypothesis, we established an in vitro system in which human tonsil-derived YK6 fibroblasts expressing CD40L are co-cultured with PBMC-derived B cells. B cell activation, proliferation, and phenotype in response to low- and high-stimulation conditions was determined in co-culture with control or bleomycin-treated YK6 fibroblasts. Control YK6 fibroblasts promoted B-cell activation and proliferation in both 2D and 3D cultures, whereas bleomycin-treated fibroblasts robustly inhibited B-cell proliferation without impairing early activation. Conditioned media from bleomycin-treated fibroblasts partially reduced B cell proliferation, although to a lesser extent than direct co-culture, suggesting cell-cell contact was key to inhibiting B cell proliferation. Bleomycin-treated YK6 fibroblasts upregulated genes associated with impaired lymphocyte responses, such as PDCD1LG2, which may impact B cell activation. Indeed, B cells co-cultured with bleomycin-treated fibroblasts failed to fully initiate glycolysis and were essentially unable to synthesise new protein. Together, these findings suggest that senescence-like changes in fibroblasts could restrict B-cell proliferative capacity, which may contribute to impaired B cell responses in ageing.