Le polynucléaire éosinophile : nouveautés en physiologie et implications diagnostiques

The eosinophil is a leukocyte that has long been neglected. It is now known to have a broad spectrum of contrasting functions. It can act as both an effector cell and a regulatory cell, involved in the progression or resolution phases of the inflammatory response. Its properties mean that it can be both beneficial and detrimental to the host. These findings have chiefly been acquired from the study of particular pathological contexts mainly associated with allergies and parasitic diseases. The impact of eosinophils on other disorders and in particular on certain homeostatic processes is now attracting increasing interest. Despite the development of high-performance analytical techniques, it can often be challenging to determine precisely the physiopathological role of eosinophils in a given pathological context. In recent years, the characterisation of certain regulatory mechanisms of blood and tissue hypereosinophilia (HEs) has been one of the most promising innovative findings. The same can be said of the growing awareness of its involvement in the innate and adaptive immune responses. Based on these aspects, which are dealt with in the first part of this review (“Nouveautés en physiologie”), we will present a “physiopathological” classification of HEs in the second part (“Implications diagnostiques”), and place particular emphasis on the fact that no HE should be ignored. Thanks to these various contributions, we are now in a position to offer patients more appropriate diagnosis and treatment.