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UM BIOH 370 - Lymphatics and Immune System Day 4
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BIOH 370 1st Edition Lecture 17Outline of Last Lecture Lymphatics and Immunity Day 3I. Inflammation Effects on the Immune ResponseII. Innate Immune Cells That are PhagocytesIII. PAMPs and TLRsIV. Cells Communicate in Two Ways in During Immune Response1. Soluble Mechanisms2. Cell to Cell ContactV. Small Amount of Important Cytokines VI. Two Types of Adaptive Immune Responses1. Cell-mediated Immunity2. Humoral or Antibody- mediated ImmunityOutline of Current Lecture Lymphatics and Immunity Day 4I. T Cells Development and MaturationII. ThymusIII. Thymic SelectionIV. Antigen Presenting Cellsa. Professional APCsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Non-professional APCsV. MHC Synthesis and Antigen Loading in APCsVI. Functions of Secondary Lymphoid OrgansVII. TonsilsCurrent LectureLymphatics and Immunity Day 4I. T Cells Development and Maturationo Size with ageT cells develop in red bone marrow- but don’t mature thereThymus is where T cells mature (thymic selection)In infants, it is found in the inferior neck and extends into the mediastinum, where it partially overlies the heartIncreases in size and is most active during childhood Stops growing during adolescence and then gradually atrophiesII. Thymuso Differs from other lymphoid organs in important waysIt functions strictly in T lymphocyte maturationIt does not directly fight antigenso The stroma of the thymus consists of star-shaped epithelial cells (not reticular fibers)o These thymocytes provide the environment in which T lymphocytes become immunocompetentIII. Thymic Selectiono Positive Selection: only T cells expressing a TCR that can recognize self MHC survive (allows for antigenrecognition presentation later)o Negative selection: T cells with receptors that recognize self-peptide fragments or self antigens are deleted (to prevent auto-immunity)After Thymic Selection, CD4+ and CD8+ T cells that are ‘just right’ but naïve emerge fromthe thymusETP: Early Thymic Progenitors (Pre-T cells)DN: Double Negative Cells (no TCR or CD4 or CD8); rearrangement of TCR genesDeath by Neglect: failure to contact MHC molecules Positive Selection: Cells with TCRs bind to MHCs (MHCI: CD8, MHCII: CD4)Negative Selection: If avidity of binding to MHC-peptide ligands is too high, cells are deleted Mature, but naïve (have never seen antigen) T cell and B cells migrate to secondary lymphatic organs and tissuesIV. Antigen Presenting Cells: Cells that link the innate and adaptive immune systems andare required to activate T cellso Professional APCs= immune cellso Non-professional APCs=non-immune cellsFibroblastsEpithelial CellsEndothelialCellsGlial CellsDendri cCellsB CellsMacrophagesM Cells39V. MHC Synthesis and Antigen Loading in APCso Major Histocompatibility Complex I (MHC Class I, or MHC1)Present at a low level on most nucleated cellsPresent at a higher level on Antigen Presenting Cells (professional)Display internal antigens (self and intracellular pathogens)o Major Histocompatibility Complex II (MHC Class II, or MHC2)Present primarily on immune cells (APCs)Display external antigenso APCs that present Antigen in MHC II can activate CD4+ T Cells(T-helper cells)o CD4+ T helper cells produce cytokines that :1. poison pathogens (ie. IFN-g) and activate inflammation (TH1) -or-2. Act as growth factors to help B cells better produce antibodies (TH2)o TH2 cells help B cells clonally expand after antigen activation primarily through cytokine production (not shown here)o APCs that present antigen on MHCI molecules can activate CD8+ T cells (Cytotoxic T cells)o Activated CD8+ Cytotoxic T cells kill pathogen infected cells VI. Functions of Secondary Lymphoid Organs:o Mounting an appropriate response to pathogen exposure occurs in secondary lymphoid organsFilter lymph—macrophages destroy microorganisms and debrisImmune system—lymphocytes are activated and mount an attack against antigensStore memory lymphocytes that quickly become activated when they see their appropriate antigenVII. Tonsilso Trap digestive and respiratory pathogenso Contain follicles with germinal centers (where B cells divide)o Are not fully encapsulatedo Epithelial tissue overlying tonsil masses invaginates, forming tonsillar cryptso Crypts trap and destroy bacteria and particulate mattero Tonsillectomy:Enlarged tonsils can restrict airwaysCrypts can harbor


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