Lymphocyte Development PDF

Lymphocytes  Lymphocytes are the cells that specifically recognize and respond to foreign antigens and are therefore the mediators of humoral and cellular immunity. Classes of Lymphocytes Roles Neutra...

Lymphocytes  Lymphocytes are the cells that specifically recognize and respond to foreign antigens and are therefore the mediators of humoral and cellular immunity. Classes of Lymphocytes Roles Neutralization of microbe, phagocytosis, B Lymphocyte complement activation Activation of macrophages Helper T Lymphocyte Inflammation T-CD4 Activation of (proliferation and differentiation) of T and B lymphocytes Cytotoxic T Lymphocyte T-CD8 Killing of infected cell Regulatory T Lymphocyte Suppression of immune response T-Reg Natural Killer (NK ) Cells Killing of infected cell 3 Sequential Events for Lymphocyte Development 1 2 3 4 5 5  Sequential Events for Lymphocyte Development Commitment of progenitor cells to the B lymphoid or T lymphoid lineage. Proliferation of progenitors and immature committed cells at specific early stages of development, providing a large pool of cells that can generate useful lymphocytes. The sequential and ordered rearrangement of antigen receptor genes and the expression of antigen receptor proteins. (The terms rearrangement and recombination are used interchangeably.) Selection events that preserve cells that have produced functional antigen receptor proteins and eliminate potentially dangerous cells that strongly recognize self antigens. Differentiation of B and T cells into functionally and phenotypically distinct subpopulations. B cells develop into follicular, marginal zone, and B-1 cells; and T cells develop into CD4+ and CD8+ αβ T lymphocytes, natural killer T (NKT) cells, MAIT 6 B Lymphocyte B cells have only one role: to make antibodies. They can produce a nearly limitless array of different antibody specificities, but the body does not stockpile all the cells needed to do this. Instead, it maintains a small number (only billions!) of B cells of these many specificities (while continuing to introduce new ones), and it expands and contracts specific subpopulations as needed. This system is fueled by hematopoietic stem cells in the bone marrow, which produce over 60 billion new B cells each day. 7  Multipotent stem Hematopoietic cells give rise to stem cells distinct B and T lineages The EBF, E2A, and Pax-5 transcription factors induce the expression of genes required for B cell development: Rag-1 and Rag-2 proteins Pre-B and the B cell receptor IgM Down stream signaling proteins IgD Follicular B cells Marginal zone 8 Epigenetic mechanisms that regulate Lymphocyte Development the methylation of DNA on certain cytosine residues that generally silences genes.  Posttranslational modifications of the histone tails of nucleosomes (e.g., acetylation, methylation, and ubiquitination) that may render genes either active or inactive depending on the histone modified and the nature of the modification. Active remodeling of chromatin by protein machines called remodeling complexes that can also either enhance or suppress gene expression; The silencing of gene expression by noncoding RNAs. 9 Epigenetic Changes in Lymphocyte Development Nat Struct Mol Biol. 2013 Mar; 20(3):274-81 10  Histones Post-translational Modifications  Histone modifications in antigen receptor gene loci are required for recruitment of proteins that mediate gene recombination to form functional antigen receptor genes. Perla Cota, et al. (2013). ISBN: 978-953-51-1192-4, InTech, DOI: 10.5772/55983. 11  MicroRNAs in Lymphocyte Development  Gene ablation studies have revealed that many specific miRNAs are involved in lymphocyte development  Deletion of Dicer, a key enzyme in miRNA generation in the B lineage results in a block at the pro-B to pre-B cell transition, primarily by being permissive for the apoptosis of pre-B cells Temo Barwar, et al. VOL. 68, NO. 23, 2016 12 AMERICAN COLLEGE OF CARDIOLOGY  Selection Processes That Shape the B Lymphocyte Repertoires The process of lymphocyte development contains numerous steps, called checkpoints, at which the developing cells are tested and continue to mature only if a preceding step in the process has been successfully completed. 1.) the successful production of one of the polypeptide chains and 2.) the assembly of a complete receptor. Pre-antigen receptors and antigen receptors deliver signals to developing lymphocytes that are required for the survival of these cells and for their proliferation and continued maturation. The pre- antigen receptor is the first checkpoint during lymphocyte development. In the next step of maturation, developing B and T cells express complete antigen receptors and the cells are selected for survival based on what these receptors recognize. Cells that express useful antigen receptors may be preserved, and potentially harmful cells that strongly recognize self structures may be eliminated. 13 Stimulation of B Cell Development 14 Checkpoints in Lymphocyte Maturation  Positive selection preserves receptor-expressing cells and is coupled to the generation of different B cell subsets  Negative selection is the process that eliminates developing lymphocytes whose antigen receptors bind strongly to self- antigens present in the generative lymphoid organs. Apoptosis Apoptosis 15 Stages of B Lymphocyte Maturation 16 Immunoglobulin Expression during B Lymphocyte Maturation 17 Adaptive defenses Humoral immunity Antigen-binding site Immunoglobulin H ea vy ch ai n Li gh tc ha in Hinge region Stem region Heavy chain Light chain variable region variable region Heavy chain Light chain constant region constant region Disulfide bond 19 Domains of Immunoglobulin Proteins variable domains constant domains CDRs : Complementary Determining regions 20 Germline Organization of Human Immunoglobulin Loci 21 Human Immunoglobulin Repertoire 22 Transcriptional Regulation of Immunoglobulin Genes 23 Immunoglobulin Gene Recombination and Expression 24 Co-expression of IgM an IgD 25 B Lymphocytes Subset 26  Stages of T Cell Maturation During T cell maturation, there is a precise order in which TCR genes are rearranged and in which the TCR and CD4 and CD8 coreceptors are expressed 27 Monoclonal Antibodies in Clinical Use 28 Monoclonal Antibodies in Clinical Use 29