In the human body, several factors play immunological roles. The molecular mechanisms of functions of these factors have been investigated extensively in the past. Interleukin 1 (IL-1) is a secreted protein and performs a central part in inflammatory responses. IL-1 binds to cell surface specific receptors and activates transcription factors through cytoplasmic mediators such as Myeloid differentiation factor 88 (MyD88), IL-1 receptor-associated kinase (IRAK) and TNF receptor-associated factor 6 (TRAF6). These are responsible for the induction of target genes, which are able to orchestrate or suppress the immune response. This review summarizes the available information to date on the signal transduction of IL-1.