Immunoglobulins (2 of 2)

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Visit httpsenwikipediaorgwikiImmunoglobulin_heavy_chain for references

Save this image in your brain

Visit httpsenwikipediaorgwikiImmunoglobulin_heavy_chain for references

Generation of antibody diversity

Germline heavy and light

chain gene segments

VDJ or VJ -Recombination -Transcription -Translation

Heavy and light chain

polypeptides

Immunoglobulin assembly

Gene segments will be rearranged during B cell development to assemble a functional gene of either a light or heavy chain

Modified from immunology for medical students 2nd edition

Gene segments

bull L leader

bull V

bull D diversity

bull J joining

bull C

Each gene segment is composed of a set or group of versions of that segment eg Jk (joining kappa) gene set has 5 different versions of Jk

For heavy chain

The variable region

Constant region

4 subtypes of lambda due to 4 different constant region versions

See Kuby immunology for references

Synthesis of light chain L

Leader peptide is removed by proteolytic enzymes after translation

modified

After removal of introns (splicing) from primary RNA transcript

Synthesis of heavy chain

L

L

L

L

L

L

All these steps are before transcription

Then transcription and splicing of the RNA primary transcripthellipand the leader peptide will be removed after translation along with glycosylation

What will happen in splicing

Visit httpsptwikipediaorgwikiRecombinaC3A7C3A3o_V(D)J for referencesmodified

Gene segments

bull L leader

bull V

bull D diversity

bull J joining

bull C

Each gene segment is composed of a set or group of versions of that segment eg Jk (joining kappa) gene set has 5 different versions of Jk

For heavy chain

The variable region

Constant region

4 subtypes of lambda due to 4 different constant region versions

See Kuby immunology for references

Synthesis of light chain L

Leader peptide is removed by proteolytic enzymes after translation

modified

After removal of introns (splicing) from primary RNA transcript

Synthesis of heavy chain

L

L

L

L

L

L

All these steps are before transcription

Then transcription and splicing of the RNA primary transcripthellipand the leader peptide will be removed after translation along with glycosylation

What will happen in splicing

Visit httpsptwikipediaorgwikiRecombinaC3A7C3A3o_V(D)J for referencesmodified

Synthesis of light chain L

Leader peptide is removed by proteolytic enzymes after translation

modified

After removal of introns (splicing) from primary RNA transcript

Synthesis of heavy chain

L

L

L

L

L

L

All these steps are before transcription

Then transcription and splicing of the RNA primary transcripthellipand the leader peptide will be removed after translation along with glycosylation

What will happen in splicing

Visit httpsptwikipediaorgwikiRecombinaC3A7C3A3o_V(D)J for referencesmodified

Synthesis of heavy chain

L

L

L

L

L

L

All these steps are before transcription

Then transcription and splicing of the RNA primary transcripthellipand the leader peptide will be removed after translation along with glycosylation

What will happen in splicing

Visit httpsptwikipediaorgwikiRecombinaC3A7C3A3o_V(D)J for referencesmodified

bull The recombination is somatic (not germline) but when does it occur

Factors of antibody diversity

bull Germline diversityhellipdue to the different versions of each segment

hellip51 VH27 DH 6 JH 40 V kappa 5 J Kappa 30 V lambda and 4 J lambda

bull Combinatorial diversity

hellip51 VH27 DH 6 JH 40 V kappa 5 J Kappa 30 V lambda and 4 J lambda

If we want to synthesize an Ig with kappa light chain for example

Factors of antibody diversity contrsquod

bull Junctional diversity

hellipIn the recombination process we delete some nucleotides and add

others (eg the random addition by TdT enzyme) at junction sites

between the adjoined segments

bull Somatic hypermutationhellipsee next slide

Somatic hypermutation

= affinity maturation

bull Due to very high-rate point mutations in the V regions of heavy and light chains

hellipwill produce antibodies with higher affinity for the antigen

hellipB cells expressing these antibodies are preferentially selected for becoming

plasma cells

Allelic exclusion

bull There is genetic polymorphism in the genes of VH CH VL and CL

hellipwhich means that therersquos difference in each heterozygous individual between the allele from the mother and that from the father

hellipin heterozygotes for these allotypes each B cell either express genes from the mother or from the father (not from both)hellip= allelic exclusion

but the population of B cells in the same person is mixed

Heavy chain isotype switching (Ig class switching)

bull When memory B cells are restimulated they undergo further DNA rearrangement to juxtapose their already-rearranged VDJ gene regions to different heavy chain C region genes

Variable regions are not changed here hellipso the specificity for the antigen is the same

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

Factors of antibody diversity

bull Germline diversityhellipdue to the different versions of each segment

hellip51 VH27 DH 6 JH 40 V kappa 5 J Kappa 30 V lambda and 4 J lambda

bull Combinatorial diversity

hellip51 VH27 DH 6 JH 40 V kappa 5 J Kappa 30 V lambda and 4 J lambda

If we want to synthesize an Ig with kappa light chain for example

Factors of antibody diversity contrsquod

bull Junctional diversity

hellipIn the recombination process we delete some nucleotides and add

others (eg the random addition by TdT enzyme) at junction sites

between the adjoined segments

bull Somatic hypermutationhellipsee next slide

Somatic hypermutation

= affinity maturation

bull Due to very high-rate point mutations in the V regions of heavy and light chains

hellipwill produce antibodies with higher affinity for the antigen

hellipB cells expressing these antibodies are preferentially selected for becoming

plasma cells

Allelic exclusion

bull There is genetic polymorphism in the genes of VH CH VL and CL

hellipwhich means that therersquos difference in each heterozygous individual between the allele from the mother and that from the father

hellipin heterozygotes for these allotypes each B cell either express genes from the mother or from the father (not from both)hellip= allelic exclusion

but the population of B cells in the same person is mixed

Heavy chain isotype switching (Ig class switching)

bull When memory B cells are restimulated they undergo further DNA rearrangement to juxtapose their already-rearranged VDJ gene regions to different heavy chain C region genes

Variable regions are not changed here hellipso the specificity for the antigen is the same

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

Factors of antibody diversity contrsquod

bull Junctional diversity

hellipIn the recombination process we delete some nucleotides and add

others (eg the random addition by TdT enzyme) at junction sites

between the adjoined segments

bull Somatic hypermutationhellipsee next slide

Somatic hypermutation

= affinity maturation

bull Due to very high-rate point mutations in the V regions of heavy and light chains

hellipwill produce antibodies with higher affinity for the antigen

hellipB cells expressing these antibodies are preferentially selected for becoming

plasma cells

Allelic exclusion

bull There is genetic polymorphism in the genes of VH CH VL and CL

hellipwhich means that therersquos difference in each heterozygous individual between the allele from the mother and that from the father

hellipin heterozygotes for these allotypes each B cell either express genes from the mother or from the father (not from both)hellip= allelic exclusion

but the population of B cells in the same person is mixed

Heavy chain isotype switching (Ig class switching)

bull When memory B cells are restimulated they undergo further DNA rearrangement to juxtapose their already-rearranged VDJ gene regions to different heavy chain C region genes

Variable regions are not changed here hellipso the specificity for the antigen is the same

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

Somatic hypermutation

= affinity maturation

bull Due to very high-rate point mutations in the V regions of heavy and light chains

hellipwill produce antibodies with higher affinity for the antigen

hellipB cells expressing these antibodies are preferentially selected for becoming

plasma cells

Allelic exclusion

bull There is genetic polymorphism in the genes of VH CH VL and CL

hellipwhich means that therersquos difference in each heterozygous individual between the allele from the mother and that from the father

hellipin heterozygotes for these allotypes each B cell either express genes from the mother or from the father (not from both)hellip= allelic exclusion

but the population of B cells in the same person is mixed

Heavy chain isotype switching (Ig class switching)

bull When memory B cells are restimulated they undergo further DNA rearrangement to juxtapose their already-rearranged VDJ gene regions to different heavy chain C region genes

Variable regions are not changed here hellipso the specificity for the antigen is the same

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

Allelic exclusion

bull There is genetic polymorphism in the genes of VH CH VL and CL

hellipwhich means that therersquos difference in each heterozygous individual between the allele from the mother and that from the father

hellipin heterozygotes for these allotypes each B cell either express genes from the mother or from the father (not from both)hellip= allelic exclusion

but the population of B cells in the same person is mixed

Heavy chain isotype switching (Ig class switching)

bull When memory B cells are restimulated they undergo further DNA rearrangement to juxtapose their already-rearranged VDJ gene regions to different heavy chain C region genes

Variable regions are not changed here hellipso the specificity for the antigen is the same

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

Heavy chain isotype switching (Ig class switching)

bull When memory B cells are restimulated they undergo further DNA rearrangement to juxtapose their already-rearranged VDJ gene regions to different heavy chain C region genes

Variable regions are not changed here hellipso the specificity for the antigen is the same

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

Heavy chain isotype switching (Ig class switching)

Variable region is the same Visit httpwwwpinsdaddycomimmunoglobulin-gene-

rearrangement_fmB1dEpw71srNWRpFMIiGXeqLxSN4Et9LeFQHwkL98ZmahBBbQF4HLmEJIuNvLm9l7CnIebWb2sdAlSyRfYNiQ2 for referencesmodified

This sequence

is important

Lippincottrsquos illustrated reviews immunology 2nd editionmodified

How does the unstimulated B cell express both IgM and IgD

Important enzymes

bull V(D)J recombinases

-For cleaving and rejoining DNA segments

-RAG-1 and RAG-2 only found in lymphocytes (if absent problem in lymphocyte development)

= recombination activating gene

bull Terminal deoxynucleotidyl transferase (TdT)

hellipadds nucleotides

How does the unstimulated B cell express both IgM and IgD

Important enzymes

bull V(D)J recombinases

-For cleaving and rejoining DNA segments

-RAG-1 and RAG-2 only found in lymphocytes (if absent problem in lymphocyte development)

= recombination activating gene

bull Terminal deoxynucleotidyl transferase (TdT)

hellipadds nucleotides

Important enzymes

bull V(D)J recombinases

-For cleaving and rejoining DNA segments

-RAG-1 and RAG-2 only found in lymphocytes (if absent problem in lymphocyte development)

= recombination activating gene

bull Terminal deoxynucleotidyl transferase (TdT)

hellipadds nucleotides