CD4 cells are a type of white blood cell. They belong to the immunoglobulin superfamily and are also called helper T cells or CD4 T lymphocytes. 

CD4 cells are responsible for triggering the immune system and coordinating an immune response to destroy infection-causing viruses, bacteria and other germs. They do this by stimulating other immune cells such as B lymphocytes (B cells), CD8 T lymphocytes (CD8 cells), and macrophages to combat pathogens.