Fig. 1

a In a normal tissue microenvironment, the diverse populations of cells are healthy. b In response to different stressors, some cells undergo irreversible growth arrest and acquire a senescent phenotype. Senescent cells have an effect on the innate immune system by secreting inflammatory factors that are part of the SASP. The SASP generally promotes the proliferation and polarization of M1 macrophages and the suppression of M2 macrophages. c In response to the amplified inflammatory signals, NK cells are recruited to site(s) containing senescent cells, which express NK activating ligands on their surface. These NKG2D ligands bind to NKG2D receptors present on NK cells leading to the death of senescent cells. d However, some senescent cells have strategies to avoid elimination. For example, they can express inhibitory ligands that bind to NKG2A receptors on NK cells, blocking their killing. The immune evasion of senescent cells can lead to their accumulation in tissues over time and causes age-associated diseases