Basic science for the clinician 33: interleukins of current clinical relevance (part I)

Normal orchestration of wound healing, the protective immune response and inflammation, involve a bewildering array of cells that communicate to each other locally by means of cell-surface receptors and their ligands. For local and middle- to long-distance coordination, some of these same cells make and export soluble messengers that communicate to both immune and nonimmune cells. Although all these messengers have a role in normal immune homeostasis, it is apparent that many are involved in tissue damage in a variety of diseases, eg, rheumatoid arthritis and osteoarthritis. Some of these molecules are known as interleukins. The list of interleukins (IL) is now nearing 30 and, as a result of the molecular biology revolution, we now know the direct clinical relevance of many of them. As benchtop molecular biology matures into therapeutic and diagnostic tools, clinicians must begin to master this disparate group of molecules; making this harder is the fact that unlike acronyms (often impenetrable as they might be), an IL designation does not give a clue as to the source, target, or action of the IL. IL-1 and IL-2 were the first messengers to bear the "interleukin" name 25 years ago; they are well known to rheumatologists by now, so this article deals with some of the characteristics of the other clinically relevant IL molecules starting with IL-3.