CD4 T Cell Help

Abstract

The two main branches of the adaptive immune system that directly fight infections are the CTL and the antibodies. The adaptive immune system, however, contains another branch: the CD4 T helper cells. Just as the CTL, they bear a T cell receptor that can specifically recognize antigen. Instead of the CD8 surface receptor that is found on CTL, the helper cells bear the CD4 receptor. Upon antigenic stimulation, the helper cells become activated, undergo clonal expansion, and differentiate into memory cells. While it has been documented that CD4 T cells can have direct antiviral activity [Doherty et al. (1997)], this is thought to be not their main function. As their name implies, their prevalent function is to help the CTL and antibody responses to develop and to fight the infection. This chapter investigates the dynamics of CD4 T cell help in the context of CTL responses.