UPDATE ON GENE COMPLETIONS AND ANNOTATIONS Evolutionary divergence and functions of the human interleukin (IL) gene family Chad Brocker,1 David Thompson,2 Akiko Matsumoto,1 Daniel W. Nebert3* and Vasilis Vasiliou1 1Molecular Toxicology and Environmental Health Sciences Program, Department of Pharmaceutical Sciences, University of Colorado Denver, Aurora, CO 80045, USA 2Department of Clinical Pharmacy, University of Colorado Denver, Aurora, CO 80045, USA 3Department of Environmental Health and Center for Environmental Genetics (CEG), University of Cincinnati Medical Center, Cincinnati, OH 45267–0056, USA *Correspondence to: Tel: þ1 513 821 4664; Fax: þ1 513 558 0925; E-mail:
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[email protected] Date received (in revised form): 22nd September 2010 Abstract Cytokines play a very important role in nearly all aspects of inflammation and immunity. The term ‘interleukin’ (IL) has been used to describe a group of cytokines with complex immunomodulatory functions — including cell proliferation, maturation, migration and adhesion. These cytokines also play an important role in immune cell differentiation and activation. Determining the exact function of a particular cytokine is complicated by the influence of the producing cell type, the responding cell type and the phase of the immune response. ILs can also have pro- and anti-inflammatory effects, further complicating their characterisation. These molecules are under constant pressure to evolve due to continual competition between the host’s immune system and infecting organisms; as such, ILs have undergone significant evolution. This has resulted in little amino acid conservation between orthologous proteins, which further complicates the gene family organisation. Within the literature there are a number of overlapping nomenclature and classification systems derived from biological function, receptor-binding properties and originating cell type.