Interleukin-1 (IL-1) is produced by ameboid microglia in the central nervous system (CNS). This study shows that ameboid microglia, when activated, release significant quantities of IL-1, which stimulates astroglial proliferation. IL-1 is a peptide growth factor released by many cell types, particularly by activated mononuclear phagocytes in response to endotoxin or following phagocytosis of bacteria or inert particles. IL-1 is thought to mediate tissue damage during inflammation by stimulating T cell function, inducing prostaglandin and protease release, and stimulating fibroblast proliferation. IL-1 has been isolated from traumatized mammalian brain and shown to be a potent astroglial growth factor. The cellular sources of brain IL-1 remain uncertain, but the study shows that ameboid microglia are a major source of IL-1 in vitro. Astroglia proliferate in the brain during embryonic development and after injury. Specific peptide growth factors have been isolated from the brain during these periods and have been implicated as regulators of gliogenesis. The study shows that one factor released by ameboid microglia is an 18 kD peptide that stimulates the growth of astroglia. By using copurification techniques, antibody neutralization, and two different types of IL-1 assays, the study shows that this factor is IL-1. The study also shows that microglial IL-1 stimulates astroglial proliferation in vitro. The effect of IL-1 upon astroglia is further supported by recent work showing that recombinant IL-1 is a mitogen for both brain astroglia and the astrocytoma cell line, U373. The study concludes that ameboid microglia are the major producers of brain IL-1 in vitro. The study also suggests that ameboid cells are the more likely source of IL-1 during acute phases of brain injury. The study highlights the role of IL-1 in regulating astroglial proliferation and its potential as a therapeutic target in CNS injury and disease.Interleukin-1 (IL-1) is produced by ameboid microglia in the central nervous system (CNS). This study shows that ameboid microglia, when activated, release significant quantities of IL-1, which stimulates astroglial proliferation. IL-1 is a peptide growth factor released by many cell types, particularly by activated mononuclear phagocytes in response to endotoxin or following phagocytosis of bacteria or inert particles. IL-1 is thought to mediate tissue damage during inflammation by stimulating T cell function, inducing prostaglandin and protease release, and stimulating fibroblast proliferation. IL-1 has been isolated from traumatized mammalian brain and shown to be a potent astroglial growth factor. The cellular sources of brain IL-1 remain uncertain, but the study shows that ameboid microglia are a major source of IL-1 in vitro. Astroglia proliferate in the brain during embryonic development and after injury. Specific peptide growth factors have been isolated from the brain during these periods and have been implicated as regulators of gliogenesis. The study shows that one factor released by ameboid microglia is an 18 kD peptide that stimulates the growth of astroglia. By using copurification techniques, antibody neutralization, and two different types of IL-1 assays, the study shows that this factor is IL-1. The study also shows that microglial IL-1 stimulates astroglial proliferation in vitro. The effect of IL-1 upon astroglia is further supported by recent work showing that recombinant IL-1 is a mitogen for both brain astroglia and the astrocytoma cell line, U373. The study concludes that ameboid microglia are the major producers of brain IL-1 in vitro. The study also suggests that ameboid cells are the more likely source of IL-1 during acute phases of brain injury. The study highlights the role of IL-1 in regulating astroglial proliferation and its potential as a therapeutic target in CNS injury and disease.