Activation and control of self-reactive gamma delta T cells

Mammalian and avian CD3(+) T cells can be separated into two lymphocyte sub sets bearing heterodimeric T-cell receptors (TCR) composed of either alpha beta or gamma delta chains. Although it is now widely accepted that gamma d elta and alpha beta T cells fulfill mandatory and nonredundant roles, the g enerality of this assumption and the exact functions played by gamma delta T cells remain uncertain. While an early protective role of gamma delta T c ells has long been suspected, recent observations drawn in particular from transgenic models suggest their implication in the homeostatic control of i mmune and nonimmune processes. This hypothesis is also supported by the exi stence of several self-reactive gamma delta T-cell subsets in rodents and h umans, whose specificity and effector properties will be detailed and discu ssed here. The present review will also describe several mechanisms that co uld allow efficient control of these self-reactive subsets while permitting expression of their regulatory and/or protective properties.