Abstract
IL-16 is a pleiotropic, pro-inflammatory cytokine that induces regulatory CD4+ T cells to migrate to a site of inflammation or tissue damage. IL-16 is a ligand for CD4 and binds at the proximal, D4 region well outside of the binding site for MHC class II. The sequence and structure of IL-16 is highly conserved among disparate vertebrates but CD4 is less well conserved and is highly variable at the distal, D1 region that binds to MHC class II during T-cell activation and effector function. Conversely, the D4 region, like its ligand, is very highly conserved. This conservation of sequence and structure suggests that the role of CD4 as a receptor for IL-16 has been retained throughout vertebrate phylogeny. Because of the conservation of this receptor: ligand pair, we set out to demonstrate that recombinant human IL-16 (rhIL-16) can elicit the same effects on lymphocytes from the amphibian Xenopus laevis as it would on human lymphocytes. Our data suggest that rhIL-16 attracts a population of CD4+ lymphocytes with a regulatory phenotype.
Keywords
CD4, IL-16, CTLA-4, CD28, Xenopus