These proteins have historically been known under several other names including the "SIS family of cytokines", "SIG family of cytokines", "SCY family of cytokines", "Platelet factor-4 superfamily" or "intercrines". Some chemokines are considered pro-inflammatory and can be induced during an immune response to recruit cells of the immune system to a site of infection, while others are considered homeostatic and are involved in controlling the migration of cells during normal processes of tissue maintenance or development. Chemokines are found in all vertebrates, some viruses and some bacteria, but none have been found in other invertebrates.