CELLS OF THE IMMUNE SYSTEM Neutrophils Neutrophils are related to both protective innate immunity and allergic inflammation. They migrate very fast towards the site of infection, fight the pathogens through phagocytosis and extracellular DNA trap (NETosis). Circulating neutrophils are a predominant cell lineage among leukocytes, making up 45–75%, but in healthy children from 4–5-days-old to 4–5 years of age, lymphocytes are prevalent over neutrophils in the bloodstream. The cytoplasm of the cells comprises 200 granules of three types: (i) larger azurophilic containing myeloperoxidase, α defensins, neutrophil elastase, and bactericidal/permeability-increasing protein; (ii) smaller specific granules possessing NADPH oxidase (responsible for reactive oxygen species - ROS), lysozyme, lactoferrin, cathelicidin, and histaminase; and (iii) tertiary granules, which contain metalloproteinases (collagenase and gelatinase). In the last decade, some new neutrophil phenotypes in homeostasis and diseases have been described, including tumors (N1 and N2), but the origin of at least part of the additional blood neutrophil phenotypes remains unestablished. A wide range of cytokines and chemokines regulate the neutrophil activity, including IL-17, IL-8 (CXCL8) and chemokines predominantly of the CXCL subfamily: CXCL1 (GROα), CXCL2 (MIP-2α), CXCL3 (MIP-2β), etc., and use chemokine receptors belonging to G-protein–coupled receptors family. Neutrophils express many cell surface receptors for recognizing the inflammatory environment. Some years ago, a new role of neutrophils in allergy was revised. Neutrophils and allergen-specific T cells accumulate in patients with allergic late-phase reactions, making allergic inflammation more severe, e.g., Th2-low/Th17/neutrophilic endotype in asthma. In the local cytokine environment, neutrophils are converted into functional antigen-presenting cells and activate allergen-specific effector CD4+ T cells. ©V.V.Klimov