ABSTRACT
This chapter focuses on vertebrate immune responses and the features that distinguish them from other kinds of cell responses. It begins with innate immune defenses and then discusses the highly specialized properties of the adaptive immune system. Like antibody responses, T-cell-mediated immune responses are exquisitely antigen-specific, and they are at least as important as antibodies in defending vertebrates against infection. Indeed, most adaptive immune responses, including most antibody responses, require helper T cells for their initiation. Most importantly, unlike B cells, T cells can help eliminate pathogens that have entered the interior of host cells, where they are invisible to B cells and antibodies. The chapter concerns how T cells accomplish this feat. Some of the cell-surface proteins discussed in the chapter that belong to the immunoglobulin (Ig) superfamily. There are three main classes of T cells—cytotoxic T cells, helper T cells, and regulatory T cells.
