Interferon and heparan sulphate.

In 1954, substances that protected cells from viral infection were discovered and named IFN (interferon). This family of cytokines, which were the first to be used in clinical therapy, is classified into type I and II IFNs. Type I mainly consists of IFNalpha and IFNbeta subtypes, which are structurally related and bind to a common receptor. IFNgamma, the sole type II IFN, is structurally unrelated, binds to a different receptor and, as a dimer, strongly interacts with HS (heparan sulphate). In addition to its antiviral activity, it modulates nearly all phases of immune and inflammatory responses. IFNgamma binding to HS controls the blood clearance, the subsequent tissue targeting and the local accumulation of the cytokine. It also regulates IFNgamma activity by a unique mechanism involving a controlled processing of the C-terminal peptide. The binding site encompasses an N-acetylated glucosamine-rich domain separating two highly sulphated sequences that each binds to one IFNgamma monomer. Based on this template, a set of glycoconjugate mimetics that would mimic the IFNgamma binding site has been synthesized. One of these molecules displays high affinity for the cytokine and inhibits binding to both HS and IFNgammaR (IFNgamma receptor), the cell-surface receptor. These results validate the HS structural determinants for IFNgamma recognition, and provide a new strategy to inhibit IFNgamma in a number of diseases in which the cytokine has been identified as a target.