Chemokines: coded messages for T-cell missions.

Chemokines and their receptors control leukocyte migration and homing throughout the body in both physiological and pathological conditions. In the context of the adaptive immune system, which requires high efficiency and control, chemokines and chemokine receptors represent a versatile code that orchestrates the "who, where and when" of the immune response by providing the spatio-temporal guidance for T-cell development, priming and effector functions. In addition to their chemotactic properties, chemokines can directly modulate T-cell responses by amplifying signals at the immune synapse and tuning Th1/Th2 polarization. In this review we will discuss the role of chemokines in T-cell biology, following an ideal pilgrimage that spans the key steps of the T-cell life.