Credit: La Jolla Institute for Allergy and Immunology
Based on cell surface markers known as CD4 and CD8, T cells generally fall into two broad categories: CD4–positive helper T cells, which¬ help activate other immune cells and CD8-positive cytotoxic T cells, which kill cells that are cancerous or infected with viruses. Under certain circumstances, however, a portion of helper T cells turns into cytotoxic T cells (CD4-CTLs).