Immunoglobulin class switching

[1] During this process, the constant-region portion of the antibody heavy chain is changed, but the variable region of the heavy chain stays the same (the terms variable and constant refer to changes or lack thereof between antibodies that target different epitopes).[2] Naïve mature B cells produce both IgM and IgD, which are the first two heavy chain segments in the immunoglobulin locus.This allows AP-endonucleases to cut the newly-formed abasic site, creating the initial SSBs that spontaneously form DSBs.[7] The intervening DNA between the S-regions is subsequently deleted from the chromosome, removing unwanted μ or δ heavy chain constant region exons and allowing substitution of a γ, α or ε constant region gene segment.[9] With the exception of the μ and δ genes, only one antibody class is expressed by a B cell at any point in time.
Mechanism of class-switch recombination that allows isotype switching in activated B cells.
B cellimmunoglobulinisotypeheavy chainepitopesaffinityeffectorB cell receptorV(D)J recombinationheavy chainsT helper cellsantibodychromosomenucleotidenickedenzymesactivation-induced (cytidine) deaminaseuracilDNA glycosylaseapyrimidic/apurinic (AP)-endonucleasesnon-homologous end joininglocus suicide recombinationImmune checkpointImmunogeneticsJournal of Medical VirologyPLoS BiologyBibcodeInternational ImmunologyBanchereau JMedical Subject HeadingsLymphocyticadaptive immune systemcomplementAntigenSuperantigenAllergenAntigenic variationHaptenEpitopeLinearConformationalMimotopeAntigen presentationprofessional APCsDendritic cellMacrophageImmunogenMonoclonal antibodiesPolyclonal antibodiesAutoantibodyMicroantibodyPolyclonal B cell responseAllotypeIdiotypeImmune complexParatopeImmunityAutoimmunityAlloimmunityAllergyHypersensitivityInflammationCross-reactivityCo-stimulationToleranceCentralPeripheralClonal anergyClonal deletionTolerance in pregnancyImmunodeficiencyImmune privilegeAffinity maturationSomatic hypermutationClonal selectionJunctional diversityLymphocytesCellularT cellHumoralNK cellCytokinesOpsoninCytolysin