Neutrophile et immunité : Est-ce inné ou acquis ?

Abstract

Le polynucléaire neutrophile, longtemps considéré comme une simple cellule phagocytaire à durée de vie très courte éliminant les intrus de l’organisme, est, en fait, une cellule dont les diverses facettes fonctionnelles connues en font un acteur indispensable des défenses de première ligne, certes, mais aussi des défenses acquises. À cet aspect multifonctionnel s’associent un retard de sa mort programmée, une plasticité éclairant sa capacité à se transdifférencier en fonction des besoins locaux du processus inflammatoire et infectieux, mais aussi une hétérogénéité de cette cellule constituant des sous-populations variables en fonction des individus. Le neutrophile est certainement la cellule hématopoïétique qui suscite le plus de controverses, dont bien des propriétés restent à découvrir, et dont les secrets fonctionnels cachent sans doute d’étonnantes capacities.

The neutrophil has long been considered a phagocytic cell with a short life-span whose major role is to destroy intruders to the body. Toll receptors and anti-infectious factors such as defensin, perforin and granzymes are newly discovered mechanisms used by neutrophils for the first line of defense against invaders. Moreover, subpopulations of neutrophils share specific functions like the synthesis of certain cytokines and chemokines, as well as the expression of immunoreceptors like the T cell receptor. A primary consequence of inflammation on neutrophils is a delay in their spontaneous programmed cell death. Hence, this multifunctional cell is also a necessary actor of the acquired immune response. Neutrophils have the capacity to degrade and process antigens as well as efficiently present antigenic peptides to lymphocytes. Neutrophil interactions with immune cells, in particular dendritic cells, lead to the formation of IL-12 and TNF-α deviating the immune response towards a Th1 phenotype. Thus, the neutrophil exhibits a cellular plasticity that explains its capacity to transdifferentiate depending on the local requirements of the immune response. The neutrophil is probably the most underappreciated immune cell among hematopoietic leukocytes, and many neutrophil functions remain to be unraveled.