Sublethal DNA damage switches off B cell effector programs in an RA-FLS-PBMC co-culture.

Rheumatoid arthritis (RA) features lymphocyte-driven inflammation, in which B cells, alongside T cells, play key effector roles (e.g., autoantibody production, antigen presentation, cytokine or chemokine production). Within activated B cells, during normal diversification, activation-induced cytidine deaminase (AID) introduces targeted DNA lesions in immunoglobulin loci (class-switch recombination/somatic hypermutation), creating a potential vulnerability to sublethal genotoxic stress. T cells also contribute to RA pathogenesis through cytokine production and cell-mediated responses, and are exposed to similar genotoxic stressors in the inflamed joint environment. Given this, we asked whether a single dose/concentration of sublethal genomic damage can modulate lymphocyte effector function without overt cytotoxicity. Peripheral blood mononuclear cells from healthy donors were co-cultured with RA fibroblast-like synoviocytes and exposed once to an IC₂₀ or IC₅₀ dose/concentration of γ-irradiation (γ-IR), hydrogen peroxide (H₂O₂), or the oxazaphosphorine metabolite 4-hydroperoxyifosfamide (4-OOH IFA). Viability, γ-H2AX kinetics, cell cycle status, cytokine and immunoglobulin secretion, and a 28-gene damage response/differentiation panel were quantified at either 24 hours or 5 days post-treatment. Together, the data indicate that a single, carefully titrated low-concentration genotoxic hit might selectively suppress lymphocyte effector programs, with B cells being more durably affected than T cells. At 2 Gy, overall cell viability remained above 80%, whereas IL-10 expression declined by approximately 70%, indicating functional silencing in the absence of substantial cytotoxicity. Conceptually, targeting this vulnerability might help to dampen B cell activity in RA while largely preserving overall immune viability and T cell competence.