Activated Effector T cells can be placed into three functioning classes, detecting peptide antigens originating from various types of pathogen: The first class being 1) Cytotoxic T cells, which kill infected target cells by apoptosis without using cytokines, 2) TH1 cells, which primarily function to activate macrophages, and 3) TH2 cells, which primarily function to stimulate B cells into producing antibodies.