B Cell Development PDF

WELCOME! BMS 545 IMMUNOLOGY OCTOBER 25, 2024  OBJECTIVES  List the 6 phases of functional B cell development, what occurs during each phase, and where the phases occur  List & describe the stages of B cell receptor development (this is within Phase 1), their terminology (e.g. stem cell, e...

WELCOME! BMS 545 IMMUNOLOGY OCTOBER 25, 2024  OBJECTIVES  List the 6 phases of functional B cell development, what occurs during each phase, and where the phases occur  List & describe the stages of B cell receptor development (this is within Phase 1), their terminology (e.g. stem cell, early pro B, etc.) and what occurs at each stage (e.g. heavy or light chain rearrangement, & Ig status)  Define & provide examples of different B cell markers (genes or proteins, etc.) that allow us to differentiate stages of development (e.g. CD markers, FLT3, RAG, BTK, etc.)  Describe how early B cells are dependent on bone marrow stromal cells, including key adhesion markers  Compare and contrast B1 & B2 lineages, their roles, functions, locations, etc.  Compare and contrast T cells and B cells in terms of development, roles, activation, etc. Figure 6.1 The development of B cells can be divided into six functionally different phases Bone Marrow Secondary Lymphoid Tissue  First three phases (yellow boxes) correspond to development in the bone marrow  Last three phases (pink boxes) correspond to development in the secondary lymphoid tissues  *Notice how positive & negative selection are a little different here than T cells  Today we’ll be going through everything that happens during Phase 1  The development of B cells in the bone marrow 6-1 B-cell development in the bone marrow proceeds through several stages (Part of Phase 1) Figure 6.3 Pro-B cells develop from the pluripotent hematopoietic stem cell  Cells at different stages of development are identified by different combinations of CD proteins on their surface  CD34- vascular addressin that is expressed on endothelial venules in lymph nodes and is involved in the extravasation of white blood cells  CD10- might have a role in inactivating regulatory peptides favoring differentiation events.  In normal lymphoid ontogeny, CD10 is expressed on pro-B cells and also on mature germinal center B cells.  CD127- the α chain of the receptor for interleukin-7  CD19- a subunit of the B-cell co-receptor, which cooperates with the antigen receptor to produce activating signals when antigen is bound Figure 6.4 The development of B cells in the bone marrow proceeds through stages defined by the rearrangement and expression of the immunoglobulin genes  In stem cells, immunoglobulin (Ig) genes are in the germline configuration  The first rearrangements are of the heavy-chain (H-chain) genes  Joining DH to JH defines early pro-B cell, which becomes a late pro-B cell on joining VH to DJH  Expression of a functional μ chain defines large pre-B cell  Large pre-B cells proliferate, producing small pre-B cells in which rearrangement of light-chain (L-chain) gene occurs  Successful light-chain gene rearrangement & expression of IgM on the cell surface define immature B cell  The development of B cells in the bone marrow 6-7 A program of protein expression underlies the stages of B-cell development Figure 6.11 Timing of the production of proteins involved in immunoglobulin gene rearrangement and expression during B-cell development  Rearrangement of Ig genes & expression of pre-BCR & cell-surface IgM require specialized proteins at different times during development:  FLT3 (Fms-like tyrosine kinase 3)- protein kinase & a cell-surface receptor on stem cells that, on binding to cytokine FLT3 ligand produced by bone marrow stromal cells, receives signals that cause stem cell to differentiate into CLP & B cell progenitor  Kit- acts as a receptor for the signaling molecule "stem cell factor (SCF)“  IL-7R- Receptor for IL-7 (IL-7 next slide)  RAG proteins- essential for gene rearrangement & are selectively expressed at the 2 stages where gene rearrangements are made  TdT- inserts N nucleotides  VpreB & λ5 polypeptides- make up surrogate light chain  Igα & Igβ (aka CD79a & CD79b)- Have long cytoplasmic tails with ITAMs that interact with intracellular signaling proteins; have binding sites for immunoglobulin C region on extracellular portions. Complex of BCR with Igα & Igβ serves as the functional B-cell receptor complex  CD19 (slide 6 above)  Bruton’s Tyrosine Kinase (BTK)- a kinase & crucial mediator of B cell receptor signaling  Pax-5- nuclear transcription factor & B cell specific activator protein  The development of B cells in the bone marrow 6-2 B-cell development is stimulated by bone marrow stromal cells Figure 6.5 The early stages of B-cell development are dependent on bone marrow stromal cells  Interactions of bone marrow stromal cells with developing B cells at successive stages are shown here  Stem cells & early pro-B cells use integrin VLA-4 (Very Late Antigen 4) to bind to adhesion molecule VCAM-1 (vascular cell adhesion molecule 1) on stromal cells  + interactions of other cell-adhesion molecules (CAMs) promote binding of Kit on B cell to stem-cell factor (SCF) on stromal cell  Activation of Kit causes B cell to proliferate  Interleukin-7 (IL-7) plays crucial role in early development of B cells, primarily by promoting proliferation & survival of B cell progenitors during their transition from pro-B to pre-B cell stage.  The development of B cells in the bone marrow 6-3 Rearrangement of the immunoglobulin heavy-chain genes occurs in pro-B cells Figure 6.6 Rearrangement of immunoglobulin heavy-chain genes in pro-B cells gives rise to productive and nonproductive rearrangements A productive rearrangement enables B cell to proceed to next stage of development Rearrangements can occur successively at H-chain genes on both chromosomes, & if neither is successful = cell dies  The development of B cells in the bone marrow 6-4 The pre-B-cell receptor monitors the quality of immunoglobulin heavy chains Figure 6.7 The pre-B-cell receptor resembles the B-cell receptor  pre-B-cell receptor is distinguished from B-cell receptor by absence of a κ or λ immunoglobulin light chain & the presence instead of a surrogate light chain composed of VpreB & λ5 polypeptides  Surrogate light chain- protein that mimics an immunoglobulin light chain & is an essential factor in immunoglobulin biosynthesis. Made up of two subunits,:VpreB & λ5, & is produced by pro-B cells, but forms the pre-B cell receptor with a heavy chain in pre- B cells  pre-B-cell receptor is in low abundance at cell surface & is largely retained inside cell in membrane-enclosed vesicles, where it generates signals that lead to cessation of heavy-chain gene rearrangements  In addition to forming 2 Ig-like domains of surrogate light chain, VpreB & λ5 have extensions that cause oligomerization of pre-B-cell receptors & transduction of signals necessary for pre-B-cell survival  The development of B cells in the bone marrow 6-5 Rearrangement of the light-chain loci occurs in pre-B cells Figure 6.8 The organization of the light-chain loci allows nonproductive rearrangements to be followed by a productive rearrangement Several attempts to rearrange the same light chain gene can be made by using V & J segments not involved in previous rearrangements  In the first rearrangement,Vκ1 is joined to Jκ2, with excision of first joint & Jκ1  This rearrangement is nonproductive, due to loss of correct reading frame  In the second rearrangement,Vκ2 is joined to Jκ4, with excision of first joint and Vκ3, & is also nonproductive  In the third rearrangement, in which Vκ3 is joined to Jκ5 with excision of second joint, is productive & leads to transcription & translation of a functional κ light *κ light-chain locus is illustrated here chain Figure 6.9 Rearrangement of the immunoglobulin light-chain genes in pre-B cells leads to the expression of cell- surface IgM *small pre-B  The development of B cells in the bone marrow 6-6 B cells encounter two checkpoints during their development in the bone marrow Figure 6.10 Two checkpoints determine the fate of B cells during their development in the bone marrow  First checkpoint- when heavy-chain genes have rearranged & pro-B cells are making a μ chain  If the μ chain is able to bind the surrogate light chain & form a pre- B-cell receptor, the pro-B cell will receive survival signals that allow it to continue along the developmental pathway  Second checkpoint- when light-chain genes have rearranged & pre-B cells are making a light chain  If the light chain is able to bind the μ chain & assemble a B-cell receptor, the pre-B cell will receive survival signals that allow it to continue along the developmental pathway  ALSO A SCIENTIST- Prodhi Manisha He/Him- Pansexual/Transgender man Postgraduate student (MSc) at UPV/EHU in Molecular Biology & Biomedicine Cancer Immunology researcher Grew up in a war-torn country and fled because he wanted to express who he was, queer and interested in science, without fear of being slain. Even after fleeing, he faced many barriers-