CD4 T cells are a type of white blood cell that play a crucial role in the immune system. They help coordinate the body's response to infections by signaling other immune cells, such as B cells and CD8 T cells, to take action against pathogens. These cells are also known as helper T cells because they assist in activating and regulating immune responses. A healthy count of CD4 T cells is essential for maintaining a strong immune system, and their levels are often monitored in individuals with HIV/AIDS to assess immune function.