IFN-gamma,alsocalledTypeIIIinterferon,isahomodimericglycoproteincontainingapproximately21to24kDsubunits.IncontrasttoIFN-alphaandIFN-betasynthesis,whichcanoccurinanycell,productionofIFN-gammaisafunctionofTcellsandNKcells.AllIFN-gammainducersactivateTcellseitherinapolyclonal(mitogensorantibodies)orinaclonallyrestricted,antigen-specific,manner.IFN-gammaisproducedduringinfectionbyTcellsofthecytotoxic/suppressorphenotype(CD8)andbyasubtypeofhelperTcells,theTh1cells.Th1cellssecreteIL-2,IL-3,TNF-betaandIFN-gamma,whereasTh4cellsmainlyproduceIL-3,IL-4,IL-5,andIL-10,butlittleornoIFN-gamma.IFN-gammapreferentiallyinhibitstheproliferationofTh4butnotTh1cells,indicatingthatthepresenceofIFN-gammaduringanimmuneresponsewillresultinthepreferentialproliferationofTh1cells.
TypeIIIFNorIFN-gammaisalymphokinethatdisplaysnomolecularhomologywithtypeIIFN,butsharessomeimportant
BIOLOGicactivities.Specifically,IFN-gammainducesananti-viralstateandisantiproliferative.Inaddition,IFN-gammahasseveralpropertiesrelatedtoimmunoregulation.
(1)IFN-gammaisapotentactivatorofmononuclearphagocytes,augmentsendocytosisandphagocytosisbymonocytes,andactivatesmacrophagestokilltumorcellsbyreleasingreactiveoxygenintermediatesandTNF-alpha.
(2)IFN-gammainducesoraugmentstheexpressionofMHCantigensonmacrophages,TandBcellsandsometumorcelllines.
(3)OnTandBcellsIFN-gammapromotesdifferentiation.
(4)Finally,IFN-gammaactivatesneutrophils,NKcellsandvascularendothelialcells.
Synonyms:Immuneinterferon,IFG
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