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These tertiary-level lecture notes by Dr Samuel Munjita provide a detailed examination of lymphocyte development, a core topic for students pursuing diplomas, degrees, or professional programmes in immunology, biomedical sciences, or medicine. The material comprehensively covers the development of both B and T lymphocytes from hematopoietic stem cells. It outlines the stages of B-cell development within the bone marrow, dependent on stromal cells and growth factors like IL-7, and describes the critical process of gene rearrangement for the B-cell receptor. The notes also detail T-cell development within the thymus, explaining the progression from double-negative to double-positive and finally to single-positive CD4 or CD8 T cells, including the crucial processes of positive and negative selection. Key surface markers for identifying different developmental stages, such as CD45R, CD19, CD4, CD8, and CD25, are clearly explained. This structured content is designed to build a deep understanding of adaptive immune cell ontogeny, making it an essential revision resource for university students preparing for examinations in immunology and related fields. The notes offer clear explanations of cellular interactions, selection mechanisms, and functional outcomes. Download this resource to strengthen your grasp of lymphocyte differentiation and maturation for academic success.
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Lymphocyte Development Dr Samuel Munjita Lecture objectives At the end of this lecture, you should be able to Provide an overview of B and T cell development List the markers for specific stages of B and T cell development Explain the role of specific molecules in T and B-cell growth and development Compare and contrast the development of T and B lymphocytes and phagocytic cells Introduction Hematopoietic stem cell (HSC) HSCs give rise to two cell populations: The common myeloid progenitor (CMP) The common lymphocyte progenitor (CLP). CMP differentiation results in the production of: neutrophils, basophils, eosinophils, monocyte, macrophages, erythrocytes and dendritic cells. The CLP is responsible for the production of B lymphocytes, T lymphocytes, and natural killer cells Introduction In this lecture, we shall carefully study the development of B and T lymphocytes B and T lymphocytes are the major cells of the adaptive immune responses When activated, B lymphocytes differentiate into plasma cells to produce antibodies. B cells are a key component of the humoral immune responses. T lymphocytes are part of the cell mediated immune system Development of B cells B cells develop in the bone marrow with the help of stromal cells and achieve maturity in secondary lymphoid organs, in this case, the spleen B-cell development is dependent on the non-lymphoid stromal cells of the bone marrow Stem cells isolated from the bone marrow and grown in culture fail to differentiate into B cells unless bone marrow stromal cells are also present. The stroma, whose name derives from the Greek word for a mattress, provides a necessary support for B-cell development. Development of B cells The contribution of the stromal cells to B cell development is twofold: First, they form specific adhesive contacts with the developing B-lineage cells through interactions between cell-adhesion molecules and their ligands. Second, they provide growth factors that stimulate B cell lymphocyte differentiation and proliferation (Fig. 1). Development of B cells Figure 1: The early stages of B-cell development are dependent on bone marrow stromal cells Lymphoid progenitor cells and early pro-B cells bind to the adhesion molecule VCAM-1 on stromal cells through the integrin VLA-4 and also interact through other cell-adhesion molecules (CAMs). These adhesive interactions promote the binding of the receptor tyrosine kinase (Kit) found on the surface of the pro-B cell to stem-cell factor (SCF) on the stromal cell, resulting in activation of the kinase and induction of the growth/proliferation of the B-cell progenitors. Late pro-B cell and Pre-B cell require interleukin-7 (IL-7) for proliferation and further development. Development of B cells As B-lineage cells mature, they migrate within the marrow, remaining in contact with the stromal cells. The earliest stem cells ( early pro-B cells) lie in a region called the sub-endosteum, which is adjacent to the inner bone surface. Pro-B stage is marked by cells expressing an enzyme called terminal deoxynucleotidyl transferase (TdT) As maturation proceeds, B-lineage cells move toward the central axis of the marrow cavity ready for export. Development of B cells Later stages of maturation become less dependent on contact with stromal cells, and the final stages of development of immature B cells into mature B cells occur in peripheral lymphoid organs, in this case, its the spleen. Stages in B-cell development Stages in B-cell development are distinguished by the expression of immunoglobulin chains and particular cell-surface proteins The stages in B-cell development are defined by the sequential rearrangement and expression of heavy- and light-chain immunoglobulin genes (Fig. 2). However, the stem cells in the germline configuration are not linked to rearrangement of their immunoglobulin (Ig) gene segments Stages in B-cell development Antibody structure: The left-hand image shows a schematic of a B-cell receptor/antibody. VL-variable region of light chain; VH-variable region of heavy chain; CL-constant region of light chain; CH-constant region of heavy chain. The right-hand image is a 3D structure of an IgG antibody (Lauren M.F. Merlo, Laura Mandik-Nayak, 2013) Stages in B-cell Development GENE REARANGEMENT The portion of the B-cell receptor (BCR) that recognizes antigens is made up of three disparate genetic regions, termed V, D, and J, that are spliced and recombined at the genetic level in a combinatorial process unique to the immune system. Multiple genes encoding each of these …
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