Interleukin-1 β (IL-1 β) is a pro-inflammatory cytokine that is produced by monocytes, macrophages, and dendritic cells (DCs). IL-1 β signals through the IL-1 receptor, type 1 (IL-1R1) to activate the myeloid differentiation primary response 88 (MYD88) signaling pathway, which contains the cytoplasmic Toll/IL-1 receptor (TIR) domain adapter. IL-1 β and the independently regulated IL-1 α protein have overlapping proinflammatory activities to induce adhesion molecule expression on epithelial cells, control fever induction, initiate rheumatoid arthritis, and promote septic shock.