University:
American Career College
Course:
NURS115 | Intermediate Medical
Academic year:

2021
Views:

32

Pages:

61
Author:

Kelsey Zavala

Outline • Classification and discrimination of the innate & adaptive immune system cells • Anatomy and main functions of lymphoid tissues • The cells of the innate and adaptive immune system are normally present as circulating cells in the blood and lymph, in lymphoid organs, and as scattered cells in virtually all tissues. Principal mechanisms of innate and adaptive immunity Origin of leucocytes • Leucocytes and other blood cells differentiate from HSCs. • Heamatopoiesis, at the first trimester, take place in yolk sac of embryo & paraaortic mesenchyme (mesoblastic phase) • Then this development follows liver and spleen (hepatic phase) • After birth bone marrow is the main place of heamatopoiesis (medulary phase) Development of various cell types from pluripotent BM stem cells Leucocytes are found in various tissues Blood smear is a an easy method for observation of blood components Neutrophil Eosinophil Neutrophil Lymphocyte Basophil Monocyte Geimsa staining A normal count and morphology in CBC is usually a reflection of normal immune system Is this a lymphocyte? Lymphocyte Cellular markers May receive a CD name Cell Differentiation markers are a reflection of cell lineage & its differentiation status CD • The cluster of differentiation (CD) nomenclature is a widely adopted uniform method for naming cell surface molecules that are characteristic of a particular cell lineage or differentiation stage, have a defined structure, and are recognized by a group (cluster) of monoclonal antibodies Hematopoietic stem cells • HSCs are pluripotent, self-renewing, CD34+ cells which may differentiate into progenitor cells • Progenitor cells have some commitment to develop myeloid or lymphoid cell line Major cells of the innate immune system Major cells of the specific immune system Phagocytosis is a main mechanism of innate immunity Neutrophils or polymorphonuclear (PMNs) leukocytes are the most abundant circulating white blood cells, mediate earliest phases of inflammatory reactions, and their life span is 2-3 days. • Neutrophils mainly use cytoskeletal rearrangements and enzyme assembly to mount rapid, transient responses • whereas macrophages rely mostly on new gene transcription. • These functions of phagocytes are important in innate immunity • Mononuclear phagocytes (Monocyte / Macrophages), recognize and engulf microbes and dead cells and present their contents (Ag) to T lymphocytes. • They also produce cytokines and help in repair of damaged tissues Dendritic Cells (DC) • Engulf small particles by Pinocytosis or Endocytosis and eventually present antigens. • Have long “dendrites”, high amount of costimulatory and MHC class II molecules • Professional antigen presenting cells (APC) Langerhans cells, • They are a type of DC found in the epithelial layer of skin, develop from embryonic precursors in the yolk sac or fetal liver, early during the development of the organism, and take up residence in the skin prior to birth. All DCs express both class I and class II major histocompatibility complex (MHC) molecules Plasmacytoid DC • Plasmacytoid DCs produce the antiviral cytokine type I interferon (IFN) in response to viruses and may capture blood-borne microbes and carry their antigens to the spleen for presentation to T cells • They resemble plasma cells morphologically. They develop in the bone marrow • Found in the blood and in small numbers in lymphoid organs Follicular dendritic cells (FDCs) • Another population of cells called follicular dendritic cells (FDCs) • They are not derived from bone marrow precursors and do not present protein antigens to T cells, but rather they are involved in B cell activation in lymphoid organs Antigen-Presenting Cells Capture Ags, display to lymphocytes, and stimulate their proliferation and differentiation Dendritic Cells: Myeloid DC (Interstitial, Interdigitating, Langerhans); lymphoid DC, follicular DC Main APCs for activating Naive T cells Link innate and adaptive immune responses B lymphocytes and Activated Macrophages MQ are APC for Effector T Lymphocytes Follicular DC help in development of memory Found in germinal centers, present Ags to follicular B cells to help them to develop to memory cells, they also help lymphoid organ development. All nucleated cells are potentially APCs for CTLs Maturation of mononuclear phagocytes and dendritic cells Mast Cells, Basophils, Eosinophils Mast Cells Bone marrow-derived cells Present in the skin and mucosal epithelium Contain abundant cytoplasmic granules filled with cytokines histamine, and other mediators Basophils Blood granulocytes with many structural and functional similarities to mast cells Eosinophils Blood granulocytes that express cytoplasmic granules containing enzymes that are harmful to the cell walls of parasites but can also damage host tissues Classification of cells based on their functionality Lymphocytes • The only cells in the body that express clonally distributed antigen receptors, each specific for a different antigenic determinant. • Each clone of T and B lymphocytes expresses antigen receptors with a single specificity, which is different from the specificities of the receptors in all other clones Subsets of T Lymphocytes • They express antigen receptors called αβ T cell receptors (TCRs)4+ helper T lymphocytes and CD8+ CTLs • CD4+ helper T cells secrete cytokines that act on various other cells, including other T lymphocytes, B cells, and macrophages • CD8+ CTLs recognize and kill cells infected with viruses as well as other microbes that can live inside host cells, and also kill cancer cells. • CD4+ regulatory T cells have αβ receptors; their function is to inhibit immune responses • Natural killer T (NKT) cells, mucosa associated invariant T (MAIT) cells • γδ T cells are three numerically smaller subsets of T cells that express TCRs with limited diversity • The total number of lymphocytes in a healthy adult is approximately 5 × 1011 • ~2% are in the blood, • ~4% in the skin • ~10% in the bone marrow • ~15% in the mucosal lymphoid tissues of the gastrointestinal and respiratory tracts • ~65% in lymphoid organs (mainly the spleen and lymph nodes) Natural Killer Cells • Belong to innate immune cells and lack specific Ag receptors • Lack T and B cell markers • Kill virus infected & tumor cells of the host • Express Ig receptors and are involved in Ab-dependent cellmediated cytotoxicity (ADCC) Subset of B cells • Follicular B cells, marginal zone B cells, and B-1 cells, • Each of which is found in distinct anatomic locations within lymphoid tissues. Folicular B cells • They are found in lymphoid tissues and blood • Follicular B cells give rise to most of the high-affinity antibodies and memory B cells that protect people from repeat infections by the same microbes. B1 and marginal zone B cells • B-1 cells are found mainly in mucosal tissues and the peritoneal and pleural cavities • Marginal zone B cells are present mainly in the spleen. Stages in the life history of lymphocytes Stages in the life history of lymphocytes Functions of lymphocytes Hemostasis Hematopoiesis Organs of the immune system Functional classification of the organs and tissues of the immune system Leukocyte production & maturation Ag encounterance & specific Immune response starts Ag entrs & Immune response occurs Lymphoid linage originating organs Major lymphoid organs in the Adult human Bone marrow is the central site of B-cell origination and development Thymus • A central lymphoid organ • Lobular organization • Epithelial reticular cells • Hassal’s corpuscles (flattened epithelial reticular cells) Thymus lobe lobules Thymus Thymus and Immune Function • DiGeorge’s syndrome: a congenital (partial) defect (human) • Nude mice: A certain mice in which the thymus fails to develop – Absence of circulating T cells – Absence of cell-mediated immunity – Increase of infectious disease Thymus decrease in size and cellularity after puberty The Lymphatic System • Lymphatic system consists of specialized vessels that drain fluid from tissues into and out of lymph nodes and then into blood, is essential for tissue fluid homeostasis and immune responses • Lymphatic system collects microbial antigens from their portals of entry and delivers them to lymph nodes, where they can stimulate adaptive immune responses Lymphatic System What is the use of lymphatic system organization? Lymphatic vessels • Resemble veins • One-way valves opened by pressure of interstitial fluid • Found throughout body except: – – – – Avascular tissues Central nervous system Spleenic pulp Bone marrow Anatomic segregation of T and B cells Spleen • A part of the circulatory system with immune system function • Functions – Blood filtration: selectively removes aged or antibody coated RBCs from the circulation. – Blood storage : 1/3 of the total platelet mass is here, and it is in dynamic equilibrium with the circulating pool. About 5% of total red blood cell mass is here. Spleen Red pulp: Network of sinusoids populated by macrophages and numerous RBCs and few lymphocytes White Pulp: Nodular lymphoid structures of spleen that surround central arteries, forming periarteriolar lymphoid sheath (PALS) populated mainly by T lymphocytes Spleen Spleen