Metal nanoparticles and immune cell heterogeneityCurrently, various metal NPs are used for diagnostics and therapy. The metal component can be represented by Ag, Au, Pt, rare earth metals, oxides of iron, nickel, copper, and others. These NPs can interact with the immune cells depending on the delivery root (local or systemic, intravenous or dietary or intranasal) [1,2]. Metal nanoparticles and inborn immunityOnce NPs enter the body, they encounter circulating monocytes or tissue resident macrophages that actively engulf and transfer NPs to different sites. NPs can polarize macrophages towards pro-(M1) or anti-inflammatory (M2) profile with respect to microenvironment and the type of metal [3]. M1 and M2 macrophages release a variety of cytokines which, in turn, recruit other immune cells that suppress (regulatory T cells) or prolong (cytotoxic T cells, T helpers, B lymphocytes) inflammation and the immune reaction triggered by NPs. Simultaneously with macrophages, NPs target neutrophils, the innate immune cells that fight against pathogens via extracellular trap formation and subsequent specific cell death termed netoptosis, for pathogen restriction and killing. A number of metal NPs up-regulate neutrophil extracellular trap activity and stimulate antimicrobial potential [4,5]. In some cases, nanosilver can also cause non-classical activation of neutrophils with IL8 release but not netoptosis, and the effect depends on NP size [6,7].