Interleukin-1 (IL-1) is a cytokine primarily produced by macrophages that plays a major role in acute inflammation. By promoting vasodilation, capillary permeability, and activation of endothelial cells, IL-1 stimulates inflammation, which creates a hostile environment for pathogens and helps white blood cells reach sites of infection. IL-1 also acts indirectly on the hypothalamus to cause fever. Lastly, IL-1 promotes bone resorption by osteoclast activation, which plays an important role in the pathogenesis of osteolytic lesions in cancer.

Key Points

  • IL-1 (interleukin-1)
    • Secreted by Macrophages
      • Also by cancer/neoplastic and some epithelial cells
    • Actions
      • Fever (pyrogen)
        • Via production of PGE2, which acts on hypothalamic nuclei
      • Stimulates inflammation
        • Promotes vasodilation and capillary permeability
        • Activates endothelium to express adhesion molecules
        • Induces chemokine secretion to recruit WBCs
      • Osteoclast-activating factor
        • IL-1 promotes bone resorption leading to osteopenia
        • Tumor production of IL-1 plays a role in creation of lytic (hole-punch) bone lesions in cancer