STAT3 (Signal transducer and activator of transduction 3) is a transcription factor that binds to the interleukin-6 responsive elements located in the promoter regions of various acute-phase protein genes. STAT3 is activated by IL-31 receptor pathway. Active STAT3 consists in homodimers or heterodimers with family member STAT1 and serine phosphorylation is important for DNA-binding and transcriptional activities. Defects in STAT3 are the cause of hyperimmunoglobulin E recurrent infection syndrome (Job syndrome).