CD28 and infection: The most significant protective effect was observed in CD25 on CD28+ CD4+ cells, a subset that plays a key role in regulating and maintaining immune system balance.[15] CD4+ T cells are central to the immune system, responsible for coordinating immune responses, including activating other immune cells such as B cells and macrophages, as well as directly killing infected cells.[16] CD25 (IL-2 receptor α chain) is highly expressed on activated T cells, enhancing their proliferation and survival, thus boosting infection resistance.[17]