γδ T Cells: First Line of Defense and Beyond

gamma delta T cells, alpha beta T cells, and B cells are present together in all but the most primitive vertebrates, suggesting that each population contributes to host immune competence uniquely and that all three are necessary for maintaining immune competence. Functional and molecular analyses indicate that in infections, gamma delta T cells respond earlier than alpha beta T cells do and that they emerge late after pathogen numbers start to decline. Thus, these cells may be involved in both establishing and regulating the inflammatory response. Moreover, gamma delta T cells and alpha beta T cells are clearly distinct in their antigen recognition and activation requirements as well as in the development of their antigen-specific repertoire and effector function. These aspects allow gamma delta T cells to occupy unique temporal and functional niches in host immune defense. We review these and other advances in gamma delta T cell biology in the context of their being the major initial IL-17 producers in acute infection.