Interleukin-6(IL-6)isamultifunctionalcytokineinvolvedintheregulationoftheimmuneresponse,hematopoiesisandacutephaseresponse.Ithasbeenrecognizedtobeamemberofthea-helicalcytokinefamily.IL-6exertsitsactionviaacellsurfacereceptorwhichconsistsoftwosubunits,an80kDaligandbindingsubunit(gp80)of468aminoacidsanda130kDasignaltransducingprotein(gp130)of896aminoacidresidues.Bothsubunitsbelongtotherecentlyrecognizedhematopoieticreceptorsuperfamilywhichincludesmanycytokinereceptors.Formanycytokinereceptorssolubleformshavebeendemonstrated.Asolubleformofthehumangp80proteinhasbeendetectedinserumandurinesamples.This55kDaproteinrepresentingtheextracellularportionofgp80isgeneratedbyshedding,aprocessthatseemstobecontrolledbyproteinkinaseC.Itisstillfunctional,indicatingthatsolublegp80playsaBIOLOGicalroleinpromotingIL-6activity.Sofar,thesolubleIL-6receptorisuniqueinactingasanagoNISTtogetherwithitsligand.TheroleofsolubleIL-6RasaMarkerforanumberofpathologicalsituationshasbeendemonstrated.

• HIV:sIL-6Rlevelsareincreasedinpatientswithhumanimmunodeficiencyvirusinfection.
• Multiplemyeloma(MM),monoclonalgammopathyofunderterminedsignificance(MGUS):SerumsolubleIL-6RlevelsaresignificantlyincreasedinindividualswithMGUSandinpatientswithMMascomparedtoage-relatedhealthyindividuals.TheselevelsareindependentofpreviouslyrecognizedprognosticfactorsinMM,especiallyserumIL-6levelsandmyelomacellmass.
• Hodgkin"sDisease(HD):ElevatedlevelsofIL-6receptorexpressioninthemixedcellularitysubtypeofHDhavebeendemonstrated.