To study the expression of OX40 on T follicular helper (Tfh) cells and the ligand OX40L on antigen-presenting cells (APCs) in peripheral blood of patients with type 1 diabetes mellitus (T1DM) and the role of OX40 signaling in promoting Tfh cells to assist B-cell differentiation. The gene discussed is TNFSF4; the disease is diabetes mellitus.