14. Macrophages, their ontogenesis and function.

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• 14. Macrophages, their ontogenesis and function.
• 15. T-lymphocytes, ontogenesis, surface markers.
  Subpopulations of T-lymphocytes and their
  functions.
• 16. The role of thymus. Positive and negative
  selection of T-lymphocytes.
• 17. B-lymphocytes - ontogenesis, surface markers,
  function.
• 18. Primary immune organs and their role in the
  immune system.
• 19. Secondary immune organs - structure and
  function of lymphatic node and spleen.
• 20. Mucosal immune system.
• 
  

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Macrophages- ontogenesis

• are a tissue- based phagocytic cells, derived
  from blood monocytes
• play important roles in innate and adaptive
  immune responses
• their development courses in the bone marrow
• an undifferentiated stem cell gives rise to the
  myeloid and lymphoid progenitor
• myeloid progenitor cells differentiate into the
  erythrocytic, granulocytic and monocytic cell
  lines and megakaryocytes

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Conversion

• of the myeloid precursor cells into monocytes and
  macrophages is affected by
• GM-CSF granulocyte-monocyte colony stimulating
  factor bone marrow (BM)stromal cells,
  lymphocytes- production of monocytes from BM
• M-CSF monocyte colony stimulating factor-
  stromal cells, lymphocytes, endothelial cells,
  epithelial cells- production and maturation of
  monocytes
• IL-3 lymphocytes- production of monocytes
  (other blood cells) from BM

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Macrophages- development

• Monocytes- in the blood
• Macrophages - in tissues

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Macrophages - terminology
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histiocytes
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Macrophages

• a monocyte enter damaged tissue through the
  endothelium of a blood vessel
• a monocyte is attracted to damaged site by
  chemokines, triggered by stimuli including
  damaged cells, pathogens and cytokines released
  by macrophages
• after migration of monocytes to the tissues they
  differentiate into different form of macrophages
• macrophages survive several months

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Macrophage surface molecules

• MHC gp class I, II assist in the presentation of
  epitopes to T lymphocytes
• CD 35 - complement receptor 1 (CR 1), binds
  complement C3b
• Receptor for the Fc portion of IgG

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Function of macrophages

• Phagocytosis
• Production of monokines
• Presentation of epitops with MHC class II
• Presentation of epitops with MHC class I

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Phagocytosis

• a foreign substances are ingested
• a living organisms are killed and digested
• follows sparing of antigenic epitopes and their
  distribution on the cell membrane

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Presentation epitopes with MHC gp class II

• After endocytosis and degradation of the antigen,
  preservation of its epitopes follows
• epitope is coupled with the MHC gp class II-
  moved to the cell surface and contact the T-cell
  receptor
• MHC (major histocompatibility complex) complex
  of genes that governs the production of the major
  histocompatibility antigens - in humans are
  termed HLAs (human leukocyte antigens)

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Presentation epitopes with MHC gp class I

• intracelular parasites are degradeted in
  proteasomes of macrophages
• their peptides are coupled to TAP (transporters
  associated with antigen processing molecules 1,2)
  that carry the epitope and MHC gp class I to the
  cell surface- protect epitopes from phagocytic
  destruction

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Monokines cytokines produced by macrophages

• IL- 1 a, ß- stimulate both T and B cells, IG
  synthesis, activation of other macrophages,
  sensitizing cells to IL-2 and IFN
• TNF- a - similar in function to IL-1
• IL- 8 - secreted by activated macrophages
• - chemokine for neutrophils, T cells
• IL-12 - promotes induction of Th1 cells, inhibits
  Th2 cells
• IFN- a- activates host cells to induce enzymes
  that inhibit protein synthesis needed for viral
  replication increases expression of MHC gp I
  class on host cells activates NK cells, T cells,
  other macrophages

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Macrophage - functions

• Macrophages provide line of defense against tumor
  cells and body cells infected with fungus or
  parasites.
• a T- cell becomes an activated effector cell
  after recognition of an antigen on the surface of
  the APC, releases chemical mediators that
  stimulate macrophages into a more aggressive form

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15. T-lymphocytes, ontogenesis, surface markers.
Subpopulations of T-lymphocytes and their
functions.
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T lymphocytes- ontogenesis

• The undifferentiated stem cell in BM gives rise
  to the lymphoid precursor cell which matures into
  3 types of lymphocytes
• T lymphocytes
• B lymphocytes
• Natural killer (NK) cell
• Pro-thymocytes come to the thymus where continue
  the maturation into T lymphocytes
• Maturation of B lymphocytes continue in BM

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Surface markers of T cells

• CD (cluster of differentiation) proteins-
  molecules on the cells membrane, allow the
  identification of cells
• TCR- receptor for antigen
• MHC gp I or II class

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CD proteins

• allow an identification of T-cell subsets
• CD 2 adhesion molecule
• CD 3 important in intracellular signaling to
  initiate an immune response closely associated
  with TCR
• CD 5,7
• CD 4,8 are expresed on subclasses of mature T
  cells CD4 reacts with MHC gp II.class),CD8
  reacts with MHC gp I. class on macrophages
• CD 28- receptor for costimulator molecules CD80
  and 86

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Maturation of T lymphocytes

• Consist of three types of processes
• Proliferation of immature cells
• Expression of antigen receptors genes
• Selection of lymphocytes that express useful
  antigen receptor (TCR)

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TCR

• Antigen receptors are encoded by several gene
  segments that recombine during lymphocyte
  maturation
• Heterodimer consisting of 2 nonidentical
  polypeptide chains linked together by disulfide
  bonds
• gt 95 T cells express the aß heterodimer, 5 ?d
• TCR heterodimer is noncovalently associated with
  the ?,d,e chains of the CD3 molecule
• COMPLEX TCR- CD3 makes contact with both the Ag
  and MHC gp

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Subpopulation of T cells

• Subpopulation of T cells have been defined
  according to their particular function and their
  CD membrane markers
• Cytotoxic T lymphocytes TcCD8
• - recognize the foreign epitope in
  association
• with class I MHC molecules
• Helper T-lymphocytes Th CD4
• - recognize the epitopes in association with
  
• class II MHC molecules

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Cytotoxic T lymphocytes (TcCD8)

• cause lysis of target cells are active against
  tumors, virus-infected cells, transplanted
  allogenetic tissue
• release TNF- depresses proteosynthesis
• recognize the foreign epitope in association with
  class I MHC molecules
• destroy their target cells by releasing perforin
  (create poresin the cell membrane and cytoplasm
  escapes) and granzymes (degrading essential
  macromolecules)

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Helper T-lymphocytes(Th CD4)

• recognize the epitopes in association with II MHC
  p II.class
• help B cells to produce antibodies and help
  phagocytes to destroy ingested microbes
• subsets of Th cells Th1, Th2 cells

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Th1 cells

• secrete
• INF-? (gamma interferon) activates macrophages
  to become more effective at killing phagocytosed
  microbes, supresses the development of Th2 cells
• IL- 2 stimulates survival and proliferation of
  T cells, called T-cell growth factor
• TNF (tumor necrosis factor)- stimulates the
  recruitment of neutrophils and monocytes to sites
  of infection, activates these cells to eradicate
  microbes
• IL-3 promotes expansion of immature marrow
  progenitors of all blood cells
• GM-CSF acts on progenitors in the bone marrow
  to increase production of neutrophils and
  monocytes

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Th2 cells

• secrete
• IL-4 induces differentiation of Th2 cells from
  naive CD4 precursors, stimulation of IgE
  production by B cells
• IL-5 activates mast cells
• IL-6 stimulates the synthesis of acute phase
  proteins by hepatocytes
• IL-10 inhibits activated macrophages, supresses
  Th1 production
• IL-3, GM-CSF

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Regulatory T cells

• Express CD4, CD25, FoxP3
• Regulate the activation or effector function of
  other T cells
• Are necessary to maintain tolerance to self
  antigens

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16. The role of thymus. Positive and
negative selection of T lymphocytes.
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The role of thymus

• In the two thymic lobes, lymphocyte precursors
  from the bone-marrow become thymocytes, and
  subsequently mature into T cells
• Once mature, T cells emigrate from the thymus and
  constitute the peripheral T cell repertoire
  responsible for directing many facets of the
  specific immune system

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Phases of thymocyte maturation

• A rare population of hematopoietic progenitors
  enters the thymus from the blood, and expands by
  cell division to generate a large population of
  immature thymocytes
• Immature thymocytes each make distinct T cell
  receptors by a process of gene rearrangement.
• This process is error-prone, and some thymocytes
  fail to make functional T cell receptors, whereas
  other thymocytes make T cell receptors that are
  autoreactive

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Positive and negative selection

• Immature thymocytes undergo a process of
  selection, based on the specificity of their T
  cell receptors.
• This involves selection of T cells that are
  functional (positive selection), and elimination
  of T cells that are autoreactive (negative
  selection)

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Thymus positive selection of T - cells

• precursor T cells enter thymus from the blood
• they are presented with self-antigens complexed
  with MHC molecules on the surface of cortical
  epithelial cells
• only those thymocytes which bind the MHC/antigen
  complex with adequate affinity will receive a
  vital "survival signal"
• the other thymocytes die (gt95)

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Thymus negative selection of T - cells

• thymocytes that survive positive selection
  migrate towards the boundary of the thymic cortex
  and thymic medulla
• they are again presented with self-antigen in
  complex with MHC molecules on antigen-presenting
  cells
• thymocytes that interact too strongly with the
  antigen receive an signal for apoptosis

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17. B-lymphocytes - ontogenesis, surface markers,
function.
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B-lymphocytes

• are an essential component of the innate immune
  system
• Maturation of B cells course in the BM
• B cells ordinate from stem cells and need to be
  in touch with the stromal cells in the bone
  marrow
• Stromal cells produce SCF (stem cell factor)
  needed for development at early period, IL-7
  needed at later period of maturation
• Ig gene rearrangements and the appearance of
  surface markers identify the stage of B-cell
  development

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Development of B lymphocytes

• Lymphoid progenitor gives rise to precursors of B
  cells pro- B cells
• During maturation from the pro-B cells into the
  pre-B cells Ig genes of the heavy chain
  recombine pre-B cells express pre-BCR
• During maturation from the pre-B cells into the
• B cells Ig genes of the light chain
  recombine
• Immature B cells express membrane IgM
• Mature B cells express membrane IgM and IgD BCR
  and are able to respond to antigen in peripheral
  lymphoid tissues

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Negative selection

• If an immature B cell binds an antigen in the
  bone marrow with high affinity- further
  maturation is stopped and B cell dies by
  apoptosis
• Negative selection eliminates potentially
  dangerous cells that can recognize and react
  against self antigens
• B cells that survive this selection process leave
  the bone marrow through efferent blood vessels

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B-lymphocytes surface markers

• CD 10 - immature B cells, malignant cells
• CD 35 - receptor for the C3b of the complement
• CD 19 - a characteristic marker of B cells
• CD 20 - a typical surface antigen of Ig-positive
  B lymphocytes
• IgM, IgD - antigen receptors BCR
• MHC class II - antigen-presenting molecules

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B-lymphocytes functions

• After stimulation B lymfocytes convert into the
  plasma cells and produce antibodies against
  soluble antigens
• Other functions are
• antigen presentation
• cooperation with complement

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18. Primary immune organs and their role in the
immune system.
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Primary immune organs

• Bone marrow
• Thymus
• are places of development, differenciation and
  maturation of immunocompetent cells and
  elimination of autoreactive cells
• T and B lymphocytes mature and become competent
  to respond to antigens in PIOs

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Bone marrow

• is the central cavity of bone that is the site of
  generation of all circulating blood cells in the
  adult, including immature lymphocytes, and the
  site of B-cell maturation.
• The pluripotent stem cell gives rise to the
  progenitor of all immune cells
• Production of cells course in the places divided
  by vascullar sinuses
• Endothelial cells of the sinuses produce
  cytokines
• Sinuses are borded by reticular cells

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Differentiation in the BM

• Differentiation from the stem cell is influenced
  by
• membrane interaction between the stem
• cells and the stromal cells
• cytokines (CSF, IL-3, trombopoetin,
• erytropoetin)

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Thymus

• is located between the sternum and the major
  vessel trunks
• It consist of two lobes
• Each lobe is surrounded by a capsule and is
  divided into lobules, which are separated from
  each other by strands of connective tissue
  trabeculae

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Structure of the thymus

• Each lobule is organized into two compartments
• the cortex (outer compartment) contains
  lymphocytes that proliferate
• the medulla (inner compartment)- mature
  lymphocytes, Hassalls bodies

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Thymus - morphology

• stromal cells composed of
• thymic epithelial cells produce thymulin,
  thymopoetin, thymosin that influence the
  maturation of T cells
• dendritic cells
• macrophages
• The thymus contain a large number of blood
  vessels and efferent lymphoid vessels that drain
  into the mediastinal lymph nodes

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19. Secondary immune organs - structure and
function of lymphatic node and spleen.
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Secondary immune organs

• consist of the spleen, the lymph nodes, the
  mucosal and cutaneous immune system
• are organized to optimize interactions of
  antigens, APCs and lymphocytes
• are places of the development of adaptive immune
  responses

lymphatic nodes
Peyers patches
tonsils
spleen
appendix
MALT
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Lymphatic node

• are nodular aggregates of lymphoid tissues
  located along lymphatic channels throughout the
  body
• Lymph comes from tissues and most parenchymal
  organs to the lymph nodes
• Lymph contains a mixture of substances absorbed
  from epithelia and tissues
• as the lymph passes through lymph nodes, APCs in
  the LN are able to sample the antigens of
  microbes that may enter through epithelia into
  tissues

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Lymphatic node

• lymph circulates to the lymph node via afferent
  lymphatic vessels and drains into the node just
  beneath the capsule in a space called the
  subcapsular sinus
• the subcapsular sinus drains into trabecular
  sinuses and finally into medullary sinuses
• the sinus space is criss-crossed by the
  pseudopods of macrophages which act to trap
  foreign particles and filter the lymph
• the medullary sinuses converge at the hilum and
  lymph then leaves the lymph node via the efferent
  lymphatic vessel

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Lymphatic node- medulla

• The medullary cords are cords of lymphatic
  tissue, and include plasma cells and T cells
• The medullary sinuses are vessel-like
  spaces separating the medullary cords
  contain histiocytes ( immobile macrophages) and
  reticular cells.
• Lymph flows to the medullary sinuses from
  cortical sinuses, and into efferent lymphatic
  vessels

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Lymphatic node- cortex
Contains lymphoid folicles acumulation of
B-lymphocytes and folicular dentritic cells When
a lymphocyte recognizes an antigen, B cells
become activated and migrate to germinal centers
to the secondary nodule
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Spleen

• is a secondary lymphoid organ positioned high in
  the left abdominal cavity
• is surrounded by a capsule, which sends
  trabeculae into the interior to form a
  compartmentalized structure
• there are two types of compartments -red pulp and
  white pulp with a marginal zone in between
• is NOT supplied by afferent lymphatics

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Spleen

• Red pulp place of mechanical filtration and
  elimination of senescent red and white blood
  cells and microbes
• White pulp T lymphocytes CD4,CD8 are around
  arterioles (periarteriolar lymphoid sheaths), B
  lymphocytes are in the folicles final maturation
  of B lymphocytes course in germinal center of
  secondary folicles

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Mucosal immune system

• MALT mucosal-associated lymphoid tissue
• GALT gut-associated lymphoid tissue
• BALT bronchus-associated lymphoid tissue
• digestive, respiratory, and urogenital systems
  are lined by mucous membranes
• includes loose clusters of lymphoid cells in
  lamina propria of intestinal villi
• contains a very large population of plasma cells
  that synthetize IgA antibodies

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M cells

• are epithelial cells that are specialized for the
  transport antigen from the lumen of the
  respiratory, digestive, and urogenital tracts to
  the underlying MALT
• contain a characteristic pocket filled with B
  cells, T cells, and macrophages
• are found at inductive sites that overlie
  organized lymphoid follicles in the lamina
  propria
• antigens are endocytosed and transported within
  vesicles from the luminal membrane to the pocket
  membrane, where the vesicles fuse and deliver
  their contents to antigen-presenting cells

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DC dendritic cells, IEC intestinal epithelial
cell (Nu-nucleus), MC M cell, IEL intra
epithelial lymphocytes, PP Peyers patches, MØ
macrophages
Pv particulate Ag in pinocytic vesicle of M cell
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Secretory IgA

• daily production of secretory IgA into mucous
  secretions exceeds that of any other class of
  immunoglobulin (5-15 g each day)
• is an important line of defense for mucosal
  surfaces against bacteria
• binding of secretory IgA to bacteria and viruses
  also prevents attachment to mucosal epithelial
  cells, thereby inhibiting infection and
  colonization

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Cutaneous immune system

• Epidermis contains keratin cells that produce
  IL-1, 6 and TNF during inflamation and IL-10,
  TGF-ß during healing
• Dermis contains fibroblasts that produce
  collagen, remove apoptotic cells
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