11-8 T-Helper Lymphocytes (Cambridge AS A Level Biology, 9700)

T-helper lymphocytes play a crucial role in the immune system by activating other immune cells through signaling molecules called cytokines. They coordinate responses by stimulating B lymphocytes, T killer lymphocytes, and macrophages to combat pathogens. Without T-helper cells, the immune response weakens, leading to increased susceptibility to infections, as seen in AIDS.