Highlevelsoflowmolecularweight(LMW)IgMincertaindiseasesareassociatedwithclinicalandlaboratoryindiceswhichreflecttheseverityofthedisease.TheseassociationssuggestthatLMWIgMmayplayanimportantroleintheimmunopathogenesisofthesediseases.TofurtherapproachthequestionconcerningthefunctionalactivityofLMWIgMindisease,apanelofLMWIgMandhighmolecularweight(HMW)IgMpreparationswithorwithoutrheumatoidfactor(RF)activitywereusedtoinvestigatetheirantibodybindingactivityandtheireffectorfunction.ItwasfoundthatLMWIgM-RFandHMWIgM-RFhadasimilarbindingcapacitytoFcfragmentastherewasnosignificantdifferenceintheaffinityindexbetweenthem.ItfurthershowedthattherateofactivationandtotalamountofutilizationofcomplementbyLMWIgMandHMWIgMwassimilar,althoughthemeanfluorescenceofC3depositionbyIgM-RFandHMWIgM-RFwasslightlyhigherthanthatofLMWIgM-RFandothercontrolRFantibodies.However,thecurrentstudydemonstratedthatLMWIgMhadstrongneutrophilactivatingpropertieswhencomparedwithHMWIgM.ThesefindingssuggestthatonemechanismofLMWIgMcontributingtotheimmunopathogenesisofRAmaybeduetotheformationofcirculatingimmunecomplex(CIC)byLMWIgMwithsubsequentactivationofneutrophils.WhetherLMWIgMhasotherfunctionalactivityindiseaseisunclearandneedsfurtherinvestigation.
