Class switching is primarily induced by cytokines secreted by T helper cells. Different cytokines promote switching to different immunoglobulin classes. For instance, Interleukin-4 (IL-4) typically induces switching to IgE and IgG1, while Transforming growth factor-beta (TGF-β) promotes switching to IgA. Additionally, CD40-CD40L interaction is crucial for the initiation of CSR.