*2.1.4. Innate lymphoid cells*

In recent years, studies have been published to identify innate lymphoid cells (ILCs), all members of this new family are characterized by a similar lymphocyte morphology, however, lack markers on its surface that identifies them as another immune cell type, because this is defined as lacking cells lineage markers (Lin− ) [39]. The ILCs come from two development pathways: (1) the first called cytotoxic ILCs, integrated by classic NK; (2) on the other hand, we have non-cytotoxical ILCs. The last group is subdivided into three types: ILC1s, ILC2s and ILC3s; they express T-bet, GATA-3 and ROR-γT, respectively, which is the main difference between them. ILCs can directly communicate with several varieties of cells and regulate immunity, inflammation and homeostasis in different tissues [8, 39].

ILC2s plays an important role in the regulation of glucose metabolism, lipid storage and redox balance in lean individuals. It accomplishes these by communicating with other immune cells associated with the type 2 immune axis (i.e. M2, eosinophils and invariant natural killer T) and participates in cross-talk with adipocytes [8, 39]. These cells produce cytokines associated with lymphocyte T-helper 2, cytokines that are required for immunity against helminths, allergic inflammation and tissue repair [8].

In contrast, it was found that cytotoxic ILCs (individuals and mice) and non-cytotoxic ILC1s (mice) are increased in visceral adipose tissue when obesity is present, accompanied by an increase in the production of interferon gamma, the latter contributes to change of the phenotype of macrophages to M1, thus, favours an inflammatory environment and increased recruitment of immune cells type 1 axis [8, 10, 12].
