<scp>CD19</scp>⁺<scp>IL</scp>‐10⁺ regulatory B cells induced by <scp>IL</scp>‐12p35 regulates functional T‐cell subsets in patients with immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is a condition characterized by immune-mediated platelet loss due to excessive destruction and/or insufficient production. IL-12p35 is involved in autoimmune uveitis; however, its role in ITP remains unknown. In the study, CD19⁺ B and CD4⁺ T cells were isolated from peripheral blood mononuclear cells (PBMCs) of patients with ITP and healthy individuals. CD4⁺CD25^- T cells were cocultured with the CD19⁺ B cells treated with anti-IL-12p35 antibody or IL-12p35 recombinant protein. The impact of IL-12p35 on CD19⁺ B cells was assessed by enzyme-linked immunosorbent assay, Western blotting, quantitative real-time PCR and flow cytometry. PBMCs from patients with ITP showed lower proportions of IL-10⁺CD19⁺ B cells and decreased mRNA levels of IL-12p35-coding gene IL12A than those from healthy individuals. Anti-IL-12p35 antibody-treated CD19⁺ B cells could reduce the population of IL-10⁺ in CD19⁺ B cells and regulate the differentiation of CD4⁺CD25^- T cells, while recombinant IL-12p35 demonstrated the opposite effects. Moreover, the increased IL-10⁺ B-cell population and HIF-1α expression in CD19⁺ B cells induced by recombinant IL-12p35 were reversed by HIF-1α and JAK2/STAT3 inhibitors. In conclusion, CD19⁺IL-10⁺ B cells induced by IL-12p35 regulate CD4⁺ T-cell subsets in patients with ITP via the JAK2/STAT3/HIF-1α signalling pathway.