Natural killer (NK) cells are lymphocytes involved in cytotoxic response by the innate immune system to viral infections and to the development of tumor cells. NK cells are typically identified by the absence of TCR and the presence of adhesion molecules (CD56). The majority of circulating NK cells express low CD56 and CD16 levels and are considered mature NK cells. On the one hand, NKs have a direct cytotoxic function by activating their lytic program mediated by the binding of their receptors to IgG by opsonization and, on the other hand, they have a secondary function mediated by the production of soluble factors that promote the innate response mediated by cytokines, chemokines, and other regulators.
Natural killer cell deficiency is part of a heterogeneous group of primary immunodeficiencies. Disorders in this group have a diverse etiology: genetic defects in various genes encoding NK receptors, proteins involved in degranulation pathways of granzymes and other cytotoxic products, and genes of the development and differentiation of the lymphoid lineage, which lead to the development of combined immunodeficiencies, among others.
