Chemokines and the long trip of leukocytes

Cells from the immune system are involved in a dual function: the survey of invading agents, either infectious or tumoral, and the destruction of such agents. Such a role requires a constant traffic of immune cells in the body. This migration process is highly regulated. There is a spontaneous traffic of immune cells, observed in healthy individuals, allowing the detection of foreign agents, and requiring the migration of leukocytes to lymphoid and non-lymphoid organs. In addition, inflammatory processes induced by the intrusion a foreign agent into the body lead to the massive recruitment of immune cells at this site of invasion. The leukocyte migration events are highly regulated, through the production by tissues of cytokines with chemoattractant properties, the chemokines, and through the regulation of expression of chemokine receptors by leukocytes. The type of chemokines produced by a tissular compartment varies according to its location and to its basal or inflammatory status. The chemokine receptors expressed by a leukocyte depends on the type of this cell, its revel of maturation and of activation. This combined regulation orchestrates the migration of leukocytes, allowing each immune cell td reach the good site at the good moment, so that it can perform its specific function of survey or of fight against an invading agent.