CELLSANDTISSUESOFTHEIMMUNESYSTEMWhiteBloodCellsOVERVIEWOFTHEIMMUNESYSTEMCells:lymphocytes,macrophages&monocytes,dendriticcells,granulocytes.Allarisefrompluripotenthematopoieticstemcellsinbonemarrow.Organs:lymphnodes(foundinvariouslocations),thymus,spleen-theseconstitutethelymphoidorgansThymusandbursa(bonemarrow)arecalledcentrallymphoidorgansPeripheralLymphoidOrgans:Exceptlymphnodes,spleen,andtonsils,liver,intestineandskinarealsoarealsoimportantpartsoftheimmunesystem.LymphocytesJacquesMillerfoundthatremovalofthymus(thymectomy)fromneonatalmiceresultedinfewerlymphocytesandnoantibodytosheepredbloodcells(1962).Lateron,inthymectomizedanimals,theabilitytorejectallograftsandtomountdelayedhypersensitivityresponseswasdrasticallyreduced.Bythemid-1960s,immunologistswereconvincedthattherewereindeedtwoseparatearmsoftheimmunesystem:onedealingexclusivelywiththeproductionofcirculatingantibodies(humoralimmunity),andanotherthatisinvolvedinthedelayedhypersensitivity-typereactionsandgraftrejections(cell-mediatedimmunity).Tohaveagoodimmuneresponse,bothhavetoexist.ATCell?ABCell?ImmuneCellsCanBeAnalyzedbyFlowCytometryAnti-CD3TvsBCellsClassIMHCexpression–OnallcellsClassIIMHCexpression-OnBcells,monos/macs&DCsandactivatedhumanTcellsLOCATIONOFMAJORLYMPHOIDORGANSTHROUGHOUTTHEBODYMONOCYTESANDMACROPHAGES*ExpressCD14,areceptorforawidevarietyofbacterialenvelopemolecules:LPS,componentsofbacterialcellwalls.LigationofCD14leadstomacrophageactivation.*AreactivatedbyTcellderivedcytokinessuchasinterferons:leadingtoincreasedphagocytosisandmicrobicidalactivity(increasedactivityofdegradativeenzymes,nitrogenandoxygenfreeradicalproductionandprostaglandinsetc.).*ExpressreceptorsforAb(FcR)andcomplement.*Actasscavengersforapoptoticcells,celldebrisandsenescentcells(e.g.,Kupffercellsintheliverbind"old"erythrocytes).DENDRITICCELLSTHEDENDRITICCELLTHAT’SNOTADENDRITICCELLGRANULOCYTESBASOPHILSANDMASTCELLSEOSINOPHILSORGANSOFTHEIMMUNESYSTEMPRIMARYLYMPHOIDORGANSPRIMARYLYMPHOIDORGANS:T