Eosinophil: a central player in modulating pathological complexity in asthma

Eosinophils are the major inflammatory cells which play a crucial role in the development of allergic and non-allergic asthma phenotypes. Eosinophilic asthma is the most heterogeneous phenotype where activated eosinophils are reported to be significantly associated with asthma severity. Activated eosinophils display an array of cell adhesion molecules that not only act as an activation marker, suitable for assessing severity, but also secrete several tissue factors, cytokines and chemokines which modulate the clinical severity. Eosinophil activations are also strictly associated with activation of other hetero cellular populations like neutrophils, macrophages, mast cells, and platelets which culminate in the onset and progression of abnormal phenotypes such as bronchoconstriction, allergic response, fibrosis instigated by tissue inflammation, epithelial injury, and oxidative stress. During the activated state, eosinophils release several potent toxic signaling molecules such as major basic proteins, eosinophil peroxidase, eosinophil cationic protein (ECP), and lipid mediators, rendering tissue damage and subsequently leading to allergic manifestation. The tissue mediators render a more complex manifestation of a severe phenotype by activating prominent signaling cross-talk. Here, in the current review with the help of search engines of PubMed, Medline, etc, we have tried to shed light and explore some of the potent determinants regulating eosinophil activation leading to asthma phenotype.