Interleukins are a group of cytokines that are expressed by white blood cells (leukocytes, hence the -leukin) as a means of communication (inter-). The function of the immune system depends in a large part on interleukins, and rare deficiencies of a number of them have been described, all featuring autoimmune diseases or immune deficiency.

A list of interleukins with function:

• IL-1: secreted by macrophages, induces acute phase reaction
• IL-2: secreted by T cells, stimulates growth and differentiation of T cell response. Can be used in immunotherapy to treat cancer.
• IL-3: secreted by T cells, stimulates bone marrow stem cells.
• IL-4: involved in proliferation of B cells, and the development of T cells and mast cells. Important role in allergic responses.
• IL-5: role in stimulation of B cells, eosinophil production, IgA production
• IL-6: secreted by macrophages, induces acute phase reaction
• IL-7: involved in B, T and NK cell survival, development and homeostasis
• IL-8: Neutrophil chemotaxis
• IL-9: stimulates mast cells
• IL-10: inhibits Th1 cytokine production
• IL-11: acute phase protein production
• IL-12: NK cell stimulation, Th1 cells induction