Adressage et migration : le mouvement perpétuel des lymphocytes.

Abstract

Le contrôle des mouvements continuels des lymphocytes dans l'organisme contribue de façon significative à l'efficacité du système immunitaire en assurant une surveillance permanente de l'ensemble des tissus et en ciblant les leucocytes aux sites d'invasion microbienne ou antigénique. Les études réalisées depuis 20 ans dans ce domaine ont montré que l'adressage des lymphocytes dans un organe est assuré par une cascade d'étapes impliquant des molécules d'adhérence et de signalisation. L'élucidation de ce processus devrait permettre à terme de moduler le ciblage des cellules effectrices notamment lors de syndromes inflammatoires.

The immune system consists of a complex collection of leukocytes and dendritic cells that surveys most tissues in the body for appearance of foreign antigens. For an efficient immune response the interaction and co-localization of antigen-presenting cells, costimulatory helper cells and effector cells are crucial parameters. Therefore the migration routes of antigen presenting cells and of lymphocytes merge in secondary lymphoid organs in order to increase the likelihood and speed of a lymphocyte, finding its cognate antigen. Additionally, antigen primed effector cells are directed to the tissue where they are most likely to encounter their cognate antigen. This highly organized and efficient antigen encounter is based on continuous re-circulation of lymphocytes between blood, peripheral tissues and secondary lymphoid organs. Moreover, the efficacy of the immune system is further increased by the ability of different lymphocyte subsets to recirculate through distinct tissues. The scope of this review is to outline the concept and mechanisms of lymphocyte homing by underlying the molecular function of implicated cell adhesion molecules, chemokines and chemokine receptors, and to propose mechanisms by which homing physiology regulates the homeostasis of immunological resources.