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Interferons: Type II and III

Ellen Margaret Moran, Charles Institute of Dermatology, University College Dublin, Ireland

Interferons were first described in the late 1950s by two scientists – Isaacs and Lindenmann – who assigned an antiviral factor the name ‘interferon’. This was due to the molecule’s ability to ‘interfere’ with the growth of the influenza virus. In the subsequent twenty years, the type I interferon family – comprising key members such as IFN-α and IFN-β – was well characterised. The type I interferons are considered the first line of defence against numerous viral infections in humans.

Two additional interferon subtypes have also been identified as being biologically significant: type II interferon or IFN-γ and the type III interferons IFN-λ1, IFN-λ2 and IFN-λ3. IFN-γ is secreted by natural killer (NK) cells, T cells and antigen presenting cells (monocytes, macrophages and dendritic cells) whereas to date the only source of type III interferons identified is plasmacytoid dendritic cells (DCs).

IFN-γ was initially described as an antiviral factor, however, it has since been demonstrated to contribute to a much wider range of biological activities. Binding of IFN-γ to its receptors promotes cellular immune responses; activation of macrophages and NK cells; upregulation of MHC expression and promoting leucocyte migration. IFN-γ is also considered the key cytokine in the Th1 immune response.

Type III interferons are co-expressed with type I interferons by virally infected cells and both contribute to the early antiviral response. In addition, type III IFNs are capable of modulating the adaptive immune response. IFN-λ increases MHC I and II expression on DCs as well as levels of CCR7, the chemokine receptor crucial for DC migration to lymph nodes.

The broad functions of the interferon family are evidenced by the treatments currently in use and/or in development that modulate the various members for the treatment of diseases such as chronic hepatitis C infection and multiple sclerosis.

  Members Cellular source Functions
Type II IFN-γ NK cells,T cells,


Antigen Presenting Cells

–          Activates macrophages and NK cells-          Upregulation of MHC expression


–          Drives leucocyte migration

–          Mediator of Th1 immune response

Type III IFN- λ1, IFN-λ2, IFN-λ3 Plasmacytoid DCs –          Upregulation of DC MHC I and II expression-          Modulation of CCR7 mediated DC migration