Interleukins (IL) are a type of cytokine first thought to be expressed by leukocytes alone but have later been found to be produced by many other body cells. They play essential roles in the activation and differentiation of immune cells, as well as proliferation, maturation, migration, and adhesion. They also have pro-inflammatory and anti-inflammatory properties. The primary function of interleukins is, therefore, to modulate growth, differentiation, and activation during inflammatory and immune responses. Interleukins consist of a large group of proteins that can elicit many reactions in cells and tissues by binding to high-affinity receptors in cell surfaces. Il-38 acts on T cells and inhibits the synthesis of IL-17 and IL-22. The placenta, tonsil's B lymphocytes, spleen, skin, and thymus widely express IL-38. [1] Reference 1. Justiz Vaillant AA, Qurie A. Interleukin. In:StatPearls. Treasure Island (FL): StatPearls Publishing; June 12, 2019.