Immunopathologie de l'asthme sévère

Severe asthma represents a heterogeneous entity for which the immunopathology is poorly understood, in part because of the difficulty of obtaining material in situ material from patients. There are two types of severe asthma, depending on the presence or absence of eosinophils. The pathophysiology of severe asthma of early onset with eosinophilia is similar to that of less severe asthma, with infiltration of Th2 lymphocytes; such cases are more likely to have exacerbations. When the onset occurs later, asthma is much more like the hypereosinophilic syndromes. Severe asthma without eosinophilia is more often accompanied by neutrophil infiltration; this type of asthma responds poorly to corticoids. Induced sputum can be used for non-invasive longitudinal follow-up of bronchial inflammation in severe asthma, allowing evaluation of cellular activation during and between exacerbations. The ISEA study (Induced Sputum in Exacerbations of Asthma) revealed that simultaneous activation of Th1 and Th2 lymphocytes and a greater deficiency of T regulatory lymphocytes occur during the course of exacerbations. This type of approach is indispensable for the identification of relevant therapeutic targets, and ultimately for the identification of early markers that are predictive of exacerbations.