Overview of the lives of lymphocytes

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A partial overview of the development and maturation of lymphocytes for undergraduate pathology in medical school.

A partial overview of the development and maturation of lymphocytes for undergraduate pathology in medical school.

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  • 1. C.Riedinger The lives of lymphocytes B-cell T-cellGeneration Bone marrow Bone marrowMaturation Bone marrow ThymusGenerearrangement Bone marrow Thymusof receptor Bone marrow ThymusSelection -ve selection only +ve (cortical epithelial cells) and –ve Leave marrow as naïve (but mature) Leave thymus as naïve (but mature)Result B-cells T-cells, either CD8+ or CD4+ Lymph nodes: • B-cell arrives from periphery either naïve or having encountered Lymph nodes: AG, which it has internalised and (paracortex) displayed via MHCII (1st signal) 1. TCR engagement: • B-cell meets T-cell = mutual TCR/CD4 - MHCII** activation: 2. Engagement of co-stim molecules: MHCII - TCR CD28 - B7.1/2 (CD80/86)Activation B7.1/2 - CD28 CD40L - CD40 CD40 - CD40L • In germinal centre: B-cell binds AG presented on follicular dendritic cell* • This contact with the AG allows affinity maturationResult Activated B-cell Activated CD4 TH0 cell Proliferation • Can now give help to CD8 cytotoxic and somatic hypermutation / T-cell affinity maturation Class-switching • Abundant AG • Little AG • High affinity • Weak affinity AG AG binding binding • IL-12 • IL-4Downstreamfunctions anddifferentiation Differentiation to plasma cell, TH1-cell TH2-cell memory B-cell… • Cell-mediated • Humoral response response • EC pathogen • IC pathogen • IL10 • IFNγ, TNFβ *Follicular dendritic cell: • NOT derived from bone marrow haematopoetic stem cells, but mesenchymal precursors • LACK MHC class II and express FEW pattern-recognising receptors • Do express complement receptors and FcγRIIb • They trap antigen opsonised by complement or antibodies and hold it at their surface in the form of an AG/AB/C3d complex • Enable activated B-cells to form germinal centres ** any professional antigen-presenting cell