1 / 56

B lymphocytes

B lymphocytes. J. Ochotná. B- lymphocytes. B- cells recognize native antigen through BCR (B cell receptor)

goldy
Download Presentation

B lymphocytes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. B lymphocytes J. Ochotná

  2. B-lymphocytes • B-cellsrecognizenative antigen throughBCR (B cell receptor) • B-lymphocytewhichbindAgwithBCR are stimulated to proliferateanddifferentiateintoeffectorplasma cellswhichproducelargequantitiesofantibodiesofthesame specificity as the BCR (itisactuallythesame protein in solubleform). Part ofstimulated B-cellsdifferentiate to memorycells. • APC (antigen presenting cell)

  3. Surfacemarkersof B lymphocytes • CD 10 - immature B cells • CD 19 - characteristicsurfacemarkerof B cells • CD 20 - on thesurfaceofIg-positive B cells • IgM, IgD - BCR • MHC gp II - Agpresentingmolecules • CD 40 – costimulating receptor

  4. B cell development • Developmentof B cellstakesplace in the bone marrowandcompletesafteractivationwithAg in secondarylymphoidorgans. Pluripotenthematopoietic stem cell (CD 34)Progenitor B cell - beginrecombinationprocesseswhichlead to a largenumberofclones B lymphocyteswithindividualspecific BCR Pre - B cell - expressionofpre-B receptor (composedof H (m) chainandalternate L chain) Immature - B lymphocyte - expressionofsurfaceIgM (BCR) atthisstageeliminationofautoreactiveclonesMature B lymphocyte -expressionofsurfaceIgMandIgD (BCR)

  5. BCR • BCR iscomposedfromsurfaceimmunoglobulin (IgM, IgD) whichrecognizesAgandassociatedsignalingmoleculesIgaandIGb, which are associatedwiththecytoplasmic protein-tyrosinekinases (PTK) SrcGroup • AfterbindingofAg to 2 or more BCR willapproximate PTK, mutualphosphorylationandphosphorylationofothercytoplasmicproteins, leading to changes in gene transcription, proliferation, differentiationandsecretionofantibodies • Thesignal by bindingAg to the BCR canbeamplified by cooperationwith CR2, whichbinds C3dg (opsonin)

  6. Eliminationofautoreactive B lymphocytes • By randomrearrangementofgenes, connectinginaccuracy, H-L pairingandsomaticmutationsmayalsoariseclonesof B cellsbearingautoreactivereceptorsandproduceautoreactiveantibodies. • Majority ofautoreactive B lymphocytes are eliminated as theimmature B lymphocytes in the bone marrow, ifits BCR bindautoantigenwithsufficientaffinity, receives a signalleading to apoptoticdeath (clonaldeletion). • Ifsomeoftheautoreactiveclonespassthiselimination, theirautoreaktivityusually do not comebecauselackof THlymphocytesfortheiractivation, many autoantigens are cryptic, oroccur in lowconcentrationsand are ignored by theimmunesystem. Tolerance to self-antigensiscritical in preventingautoimmunity in theorganism.

  7. Antigen recognition by B cell in secondarylymphoidorgans

  8. Ontogenesisofantibodies • Synthesisofspecificantibodiesbeginsaroundthe 20.-24. weekofgestation, thetotalconcentrationofIgAandIgMremainsundetectableuntilbirth, IgGbegin to formafterbirth • B lymphocytesrespond to immunizationpredominantly by IgMformation, switching to otherisotypeisslower • SlowgrowthofownIgGdecline in maternalIgG (about 3. to 6.month)

  9. TheIgMconcentrationreachesvaluescomparablewithadults in the 1- 3 yearoflife, IgGandIgAbetween 10.-15. year • Antibody response to polysaccharideantigensappearsaround2. yearoflife • In oldageis a lowerantibody response to newstimuliandincreasedautoantibodiesproduction

  10. Humoralimmune response

  11. Humoral response induced by • T-independent antigens • Cause predominantlyIgMproduction • Bacterialpolysaccharides, lipopolysaccharides, andpolymericformsof protein • T-dependentantigens • Reaction to these Agoccurs in twophases - primaryandsecondary • Initiatethedevelopmentofmemorycellsandformationofhigh-affinityantibodiesanddifferentisotypes

  12. T-independent andT-dependentimmune response

  13. Antibodyresponsesinducedby T-dependent antigen Primaryphaseofantibody response • ThefirstcontactwithAg • Takesplace in secondarylymphoidorgans • Stimulationof B cells by Agbinding to BCR • Agabsorption by APCanditspresentation via MHC gpclass II to precursorsof TH cell → formationofcloneof antigen-specific TH2 cells, whichprovideassistance to competentB cells, leading to theirproliferation, differentiationinto plasma (produceAb) andmemorycells

  14. Plasma cells are spread by bloodstreamintotheorganism (particularly bone marrow) • Antibodiesproduced in theprimarystage (3-4 days) are IgMandhave a lowaffinityforAg, createwithAgimmunecomplexes • Immunecomplexes are captured in thesecondarylymphoidorgans on thesurfaceof FDC (folliculardendriticcells) - Agpresentingcells to B lymphocytes

  15. Secondaryphaseofantibodies response • RecognitionofAg on FDC (Ifissufficientamountofimmunecomplexes on FDCs) • Germinal center reaction: underthe influence ofsignalsfromthe FDC (Ag) and TH2 cells (CD40L, cytokines) isagainstartedtheproliferationanddifferentiationofB cellsaccompaniedwithsomaticmutations → formationofclonesof B cellswithnew BCR → surviveonly B cellswith a BCR withthehighestaffinityforAg = affinitymaturationofantibodies • Thereisalsoisotypeswitching, whichisotypesarisedeterminescytokineenvironment

  16. In thesecondaryphaseoftheimmune response generateantibodieswithhigheraffinityto Agandothereffectorcharacteristicsdependent on isotype, alsoformed a memorycellsfornext meeting withtheAg • Antibodies in the body persistfor a longtimeafterprimaryinfection • ContactbetweenCD40 (B lymphocytes) andCD40L (TH2 lymphocytes) isessentialfortheinitiationofsomaticmutations, isotypeswitchingandformationofmemorycells

  17. B cell activation

  18. Primaryandsecondaryimmuneresponse • Primaryimmuneresponse – occursafterthefirsthexposure to antigen • Secondaryimmuneresponse –occursaftersubsequent encounter with the same antigen and is more rapid leading to the activation of previously generated memory cells

  19. Primaryandsecondaryimmuneresponse

  20. Immunoglobulins (Antibodies)

  21. Immunoglobulinstructure • 2 heavy (H) chainscovalentlylinked by disulfide bonds, each H chainisconnected to a light (L) chain by disulfide bonds • H chainconsistsof 4 to 5 domains(1 variable, 3-4 constant) • L chainconsistsof 2 immunoglobulindomains(1 variable, 1 constant) • Typesof L chains - k, l • Typesof H chains - m, d, g (g1-4), a(a1, a2), e

  22. Variabledomainsof L and H chainformthebindingsiteforAg • Hinge region wheretheheavychainlinked by disulfide bonds • Immunoglobulins are glykoproteins (glycosilatedFc part) • J chain • Secretorycomponent

  23. Immunoglobulinstructure

  24. Immunoglobulins functions • Antigen neutralization • Antigen agglutination • Complementactivation (IgM, IgG) • Opsonization (IgA, IgG) • Mast cell activationusingIgE • ADCC

  25. Classesofimmunoglobulinsandtheirfunctions • Distinguished by theconstant part of H chain toIgM, IgD, IgG (IgG1 - IgG4), IgA (IgA1, IgA2), IgE • IgM • as a monomer form BCR • secreted as pentamer (10 bindingsites) • firstisotypethatformsafterthe meeting withAg • Agneutralization, activatescomplement, do not bind to Fcreceptors on phagocytes • (concentrationof 0.9 to 2.5 g / l; biol. half-life 6 days)

  26. IgG • isotypes IgG1-IgG4 differentabilityofcomplementactivationandbindingto Fcreceptorson phagocytes(opsonization) • neutralization, opsonization, complementactivation • passesthe placenta (protectionof fetus in utero) • predominantlyformedin secondaryimmuneresponse • (concentrationof 8 to 18 g / l; biol. half-lifeof 21 days)

  27. SecretoryIgA • dimer withsecretorycomponent • protectionofmucousmembranes • neutralization, opsonization, do not activatecomplement • saliva, tears, breastmilk • SerumIgA • monomer, dimer ortrimer • (0.9 to 3.5 g / l; biol. half-lifeof 6 days)

  28. IgD • monomer form a BCR • in serumis in a verylowconcentration • (0.1 g / l; biol. half-life 3 days) • IgE • applies in defense againstmulticellularparasites • isthemain cause ofallergicreactions • ( 3x10-4 g / l; biol. half-life 2 days)

  29. The genetic basis for the development of immunoglobulin

  30. Thegenetic basis oftheimmunoglobulinsdevelopment • Gene segmentsfor H chains – on chromosome 14 V (variable) D (Diversity) J (joining) Cconstantdomainsof H chain • Gene segmentsfor L chains - k on chromosome 2                                          - l on chromosome 22 V (variable) J (joining) Cconstantdomainof L chain • Attheendsof V, D, J segmentsthat are signalsequenceswhich are recognized enzyme VDJ recombinasethatcarryouttherearrangementof these genes • On thesidesof C segments are so-calledswitchsequences, which are recognized by enzyme recombinasethatcarryoutisotypeswitching

  31. Therearrangementofgenescoding H chain 1) DJ rearrangement- excision a sectionIgHbetweenDandJ segment (runs on bothchromosomes) 2) VD rearrangement- excisionsectionbetweensomeV segment and DJ, ifisrearrangement on some chromosome successfull, stopstheregrouping on thesecond chromosome – itiscalledallelicexclusion(thisisalsotruefor L chain) TranscriptofrearrangedIgH gene intomRNA , splicingoftheprimarytranscript. Thefirstform H chainm. Ifrearrangementisunsuccessful, B lymphocytedie.

  32. Therearrangementofgenescoding L chain 1)First, rearrangethegenesencodingthe L chaink, thereisexcisionofsectionsbetween a VandJ segment (simultaneously on bothchromosomes), iftherearrangementissuccessful on onechromosomes, regrouping on thesecond chromosome stops – itiscalledallelicexclusion. 2) Ifregroupingofthekgenesisunsuccessful, start theregroupinggenesl. 3) Not all H and L chaincanformtogether a stabledimmers. Ifregroupingisunsuccessful, B lymphocytedie.

  33. Isotype (class) switching • Occursduringtheterminaldifferentiationof B lymphocyteafteractivationwithAg on thesurfaceofFDC and TH2 (requirecostimulatingsignalthrough CD40) • Enzymesrecombinasesrecognizetheswitchsequenceslocated on thesidesof C segmentsandexcise gene segments • Switchsequenceis not between Cmand Cdsegments - B cell canproducebeforeisotypeclassswitchingIgMandIgDsimultaneously • Aftereliminationofthe C domain part istranscribedintomRNAthat segment, whichistheclosest to VDJ segment andaftersplicingandtranslationarisecorrespondingisotypeofthe H chain

  34. Isotype switching

  35. Isotype switching • Cytokinesregulatewhichisotypeoccurs: IL-4stimulatesswitching to IgEandIgG4 TGFbstimulatesswitching to IgG2 andIgA

  36. Anti-idiotypicantibodies • IDIOTOP= summaryofantigenicdeterminant (epitopes) ofthevariablepart ofantibody • Idiotypicstructuresof 1st generationantibodiescanberecognized by some B cells as antigensandcaninduceproductionofanti-idiotypicantibodies(2nd generationantibodies; somebindingsitesmayremindAg, whichcausedformationof 1st generationantibodies) • Againstthe 2nd generationantibodiesformateantibodiesof 3rd generation(anti-antiidiotypicantibodies) • Theidiotypic network may play a role in regulationofantibodyresponse

  37. Mucosal and skin immune system

  38. Function and structureofthemucosal and skin immunesystemMucousmembranes and skin are in constantcontactwiththeoutsideenvironment, thereisconcentratedabout80% ofimmunocompetentcells.Skin - barrieragainstmechanical, physical and chemicaldamage, and againstthepenetrationofmicroorganisms, humanssurfaceabout1,5 m2Mucosalimmunesystem - preventsthepenetrationofpathogenicmicroorganisms, preventsthedevelopmentofself-harminflammatoryimmuneresponsesagainstpathogens and harmlessantigensfromtheexternalenvironment, mucosalsurfaceabout 400 m2

  39. Barrier functions of the human body and defence mechanismsMechanical bariers – intact skin and mucus, movement of cilia, coughing, sneezing,the flow of air and fluids, vomiting, diarheaChemical inhibitors- secrets of exocrine glands with bactericidal effects (fatty acids , lysozyme, pepsin, defensins, acidic pH of the stomach and urine)Other factors – body temperature (37OC), tissue oxygen tension, age, stress Physiological microflora

  40. Structure of mucosal immune systemMALT (mucous associated lymphoid tissue) BALT (bronchus associated lymphoid tissue)GALT (gut associated lymphoid tissue)NALT (nasal associated lymphoid tissue) o-MALT (organized) – consists of lymphoid follicles in the mucous membrane, tonsil and adenoids, appendix, Peyer patches d-MALT (diffuse) – consist of leukocytes diffusely distributed in the lamina propria (T and B lymphocytes, macrophages, neutrophils, eosinophils and mast cells)

  41. HumoralimmunemechanismsofthemucoussystemsIgA*(secretoryimmunoglobulin A)* most significantmucosalimmunoglobulin*transcytosis - IgAistransportedacrosstheepitheliumusingtransport Fc receptor (polymeric-Igreceptor), on luminal sideisIgA split offwiththe part ofthe receptor calledsecretorycomponent, whichprotectsIgagainstintestinalproteases*neutralizeantigens on mucosalsurfaces, don´t activatecomplement, bindsto Fcreceptors on phagocytes, in PeyerśpatchesmaybeimmunecomplexeswithIgAcapturedand caninduceimmune response

  42. sIgM* secretory immunoglobulin M* applied in newborns and in selective IgA deficiency* more prone to intestinal protease degradation* neutralize antigens on mucosal surfacesIgG*get on the mucous membrane by diffusion* applies particularly in the lower airways

  43. Inductionofmucosalimmune responseInductionofmucosalimmune response* M cells - specializedenterocytesthatprovide transport ofAg (endocyteAgfromthesurroundings) - are in closecontactwithlymphocytesand APC*mucosalimmunizationleads to stimulationof TH2 and TH3 lymphocytesandIgAproductionOral tolerance* majority ofantigensgivenorallycausessuppressionofspecificimmunity(criticalisalsothesizeofthentigenicparticles)*Trlymphocytes (regulatory) - productionof IL-10

  44. Immune mechanisms of inflammation (local and systemic reactions)

  45. Inflammation • Is a physiologicalresponse to breachthe integrity oftheorganism, leading to localizationofdamage, protectionagainstinfectionofdamagedsitesandhealing.

  46. Causesofinflammation • Physicalinjury • Infection by pathogens • Damagecaused by chemicals • Cancer • Alergicdisease • Autoimmunedisease

  47. Inflammationacute(physiologicaldefensivereactions, usuallysubsidewithoutconsequences, damagedtissuehealscompletely)chronic(usuallypathologicalreactions, occurspartialdestructionoftissueandcompensationwithfibroustissue) Response oftheorganismlocalsystemic

  48. Local body's response to inflammationManifestations- pain (dolor), heat (calor), redness (rubor), swelling (tumor) and loss of function (funkcio laesa)

More Related