Protein FAM3D is a novel cytokine-like protein that belongs to the FAM3 family. Human FAM3D is synthesized as a 224 amino acid precursor that contains a 25 amino acid signal sequence and a 199 amino acid mature chain. FAM3D is identified based on structural, but not sequence, homology to short chain cytokines including IL-2, IL-4 and GM-CSF. FAM3 proteins are four helix bundle cytokines with four conserved cysteines in all members (FAM3A-D). FAM3B is highly expressed in alpha and beta cells of the pancreas and is being investigated as a potential contributor to beta cell death and development of Type I Diabetes.