4 Anatomy of the Immune System II Immunology

#4 Anatomy of the Immune System II Immunology 297 July 28, 2015 Ikuo Tsunoda, MD, Ph. D. Associate Professor Department of Microbiology and Immunology LSUHSC Homepage: http: //tsunodalaboratory. web. fc 2. com/ E-mail: itsunoda@hotmail. com

Lymphoid organs • Primary (central) • Secondary (peripheral)

• Primary lymphoid tissues • Lymphocytes are generated and differentiate into mature lymphocytes • Bone marrow for B cells • Thymus for T cells • Secondary lymphoid tissues • Tissues in which lymphocytes are brought with antigen and adaptive immune responses are initiated • Lymph nodes, spleen, Peyer’s patches

Adaptive immunity

The adaptive responses are divided into humoral vs. cellmediated immunity CD 4 CD 8 (Th cell) (CTL) Figure 1 -2: Types of adaptive immunity. In humoral immunity, B lymphocytes secrete antibodies that prevent infections and eliminate extracellular microbes. In cell -mediated immunity, helper T lymphocytes activate macrophages to kill phagocytosed microbes, or cytotoxic T lymphocytes directly destroy infected cells.

CD: cluster of differentiation • The basis of a system for identifying cell surface molecules of immune cells • Each molecule is given a specific number prefixed by CD • Each molecules is usually recognized by a group (=cluster) of monoclonal antibodies • Used to classify cells • CD 3; T cell • CD 4; helper T (Th) cell • CD 8; cytotoxic T cell or lymphocyte (CTL) • CD 20; B cell

The key stages of lymphocyte differentiation (naïve, effector and memory cells) naïve lymphocytes are called small “resting” cells B lymphocytes T lymphocytes naive naïve B cells naïve CD 4 T cells naïve CD 8 T cells effector plasma cells helper T cells cytotoxic T cells (Th 1, Th 2) (CTL) memory B cells memory CD 4 T cells memory CD 8 T cells

Naïve lymphocytes re-circulate until they encounter their specific antigen Figure 2 -5: Maturation of lymphocytes. Lymphocytes develop from bone marrow stem cells, mature in the generative lymphoid organs (bone marrow and thymus for B and T cells, respectively), and then circulate through the blood to secondary lymphoid organs (lymph nodes, spleen, regional lymphoid tissues such as mucosa-associated lymphoid tissues). Fully mature T cells leave thymus, but immature B cells leave the bone marrow and complete their maturation in secondary lymphoid organs. Naive lymphocytes may respond to foreign antigens in these secondary lymphoid tissues or return by lymphatic drainage to the blood and recirculate through other secondary lymphoid organs.

Naïve B cells that encounter antigen differentiate into effector B cells (plasma cells) that secrete antibodies to protect against infection or memory B cells

Lymphocyte Plasma cell

Three classes of effector T cells to deal with multiple types of pathogens Stimulate macrophages to kill intracellular pathogens. Kill infected cells displaying foreign antigen, typically virus infected cells. Stimulate antibody production to facilitate elimination of extracellular pathogens.

1 -5 Major Histocompatibility Complex (MHC) Molecules and the Detection of Infection • T cells do not interact directly with intact antigen • T cells recognize fragments of antigen carried to the cell surface by MHC molecule • Two classes of MHC

T cell responses initiate from interaction with antigen + MHC molecules MHC class I Tissue Distribution • Most cells MHC class II Tissue Distribution • APCs • • • Macrophages Dendritic cells B cells • Thymic epithelium Function • Antigen presentation to CD 8 + T cells • Intracellular (cytoplasmic) antigen Function • Antigen presentation to CD 4+ T cells • Extracellular (internalized) antigen MHC = major histocompatibility complex

Antigen presenting cells (APCs) APCs present antigen to CD 4+ T cells on MHC class II molecules

T cell responses initiate from interaction with antigen + MHC molecules

Recognition of viral antigen and MHC class I molecules by CD 8+ cytotoxic T cells

Recognition of internalized bacterial antigen and MHC class II molecules on APCs by CD 4+ T cells

• CD 4+ helper T (Th)1 cells recognize fragments of bacteria internalized by macrophages • Th 1 cells activate macrophage to destroy the internalized bacteria • CD 4+ Th 2 cells recognize antigen fragments internalized by B cells • Th 2 cells activate B cell to proliferate and differentiate into an antibody-secreting plasma cells

Two waves of the immune response The innate immune response participates in activation of the adaptive immune response

The innate immune response and the adaptive immune response meet in the secondary lymphoid organs The innate immune response participates in activation of the adaptive immune response

The production of T-cell immune effector responses requires the cooperative function of both secondary and tertiary lymphoid sites Fundamental Immunology 4 th edition chapter 10 Fig. 10

Initiation of adaptive immunity The entire process is initiated by the capture of antigen by APC, and the subsequent presentation of the antigen (on MHC molecules) to T cells

Naïve lymphocyte: • mature T or B cells that have never encountered foreign antigen • die after 1 to 3 months if they do not recognize antigens • Lymphocytes mature in the bone marrow (B cells) and thymus (T cells) and enter secondary lymphoid organs as naive lymphocytes • Antigens are captured by dendritic cells and concentrated in lymph nodes, where they activate naïve lymphocytes • Effector T cells develop in the lymph nodes, enter the circulation, and migrate to peripheral tissues

IV_8_2_Dendritic_Migration-H 264 Janeway’s Immnobiology

Secondary lymphoid organs Peripheral Lymph Nodes (500 -600 in humans) Ø connected to lymphatic network Ø drain peripheral tissues – migration of antigen / APCs into LNs Ø compartments optimize antigen / lymphocyte interactions

The lymphatic system collects extracellular fluid from tissues and returns it to the blood. The fluid is continuously produced by filtration from the blood. It passes through the lymph nodes, drains into the thoracic duct and is then returned to the blood.

The lymphatic system Peripheral LNs are located at the points of convergence of lymphatic vessels. Afferent lymphatic vessels drain fluid from the tissues into the LN. Activated lymphocytes leave the LNs in the lymph fluid, which exits via the efferent lymphatic vessels to return to the blood.

Antigens are captured from a site of infection, and transported to the draining lymph node, where the immune response is initiated Figure 2 -11: The lymphatic system. The major lymphatic vessels, which drain into the inferior vena cava (and superior vena cava, not shown), and collections of lymph nodes are illustrated. Antigens are captured from a site of infection and the draining lymph node to which these antigens are transported and where the immune response is initiated.

http: //study. com/academy/lesson/functions-of-the-lymphatic-system. html

In tissues, dendritic cells pick up antigen, then migrate to regional lymph nodes via lymphatics.

The lymph nodes are the sites where the lymph and blood circulatory pathways come together

Peripheral lymph node structure cortex medulla LNs are highly organized structures that are specialized to trap APCs for presentation of antigen to circulating lymphocytes. B cells are organized in follicles (some are germinal centers). T cell are diffusely distributed in the paracortical areas – T cell zones.

Lymphocytes move from circulation into the lymph node via extravasation in the post-capillary venules

Lymphocytes move from circulation into the lymph node via extravasation in the post-capillary venules The venules located in lymphoid organs are lined with specialized endothelial cells. Thus the vessels are termed “high endothelial venules (vessels)” or HEVs.

• Lymphocytes move from circulation into the lymph node via the post-capillary venules called high endothelial venules (HEV) • HEVs display certain adhesion molecules and chemokines on their surfaces Chemokine: small cytokines whose main function is as chemoattractants

A naïve T cells extravasates through HEVs using a process termed ‘diapedesis’ Adhesion receptors and chemokines mediate this process

The lymph node is designed to bring T and B cells into contact with APCs

• Naïve T and B cells enter the node through HEV • Dendritic cells – T cell zone – Resident cells capture antigen entering through the afferent lymphatic vessels – Dendritic cells in the periphery migrate into the lymph node • Follicular dendritic cells – B cell areas – Capture antigen for B cell recognition

• B cells are in follicles • Proliferating B cells are concentrated in the germinal center • T cells in the paracortical area

IV_10_5_Germinal_Centers Janeway’s Immunobiology

Figure 2 -12: Morphology of a lymph node. A, Schematic diagram of a lymph node illustrating the T cell–rich and B cell–rich zones and the routes of entry of lymphocytes and antigen (shown captured by a dendritic cell). B, Light micrograph of a lymph node illustrating the T cell and B cell zones.

• Naïve T and B cells enter through an artery, and are drawn to different areas of the node by chemokines • Dendritic cells enter through afferent lymphatic vessels, and migrate to the T cell-rich area

III_7_2_Lymph_Node_Dev Janeway’s Immunobiology

Peripheral Lymph Node Structure

IV_10_1_The_Immune_Response-H 264 Janeway’s Immunobiology

Secondary lymphoid organs Spleen (1) Ø acts as a filter of antigen from the blood Ø white pulp is structurally similar to peripheral LNs Ø compartments optimize antigen/lymphocyte interactions

Blood borne antigens are picked up by antigen presenting cells (eg, macrophages, dendritic cells) in the spleen

Spleen structure The spleen functions as a ‘filter’ for the blood – removes pathogens, collects antigens for presentation, and collects/disposes of old RBCs. The bulk of the spleen is the red pulp – the site of RBC disposal. Lymphoid cells are organized in the white pulp.

The spleen is the major site of immune responses to blood-borne antigens • White pulp • Lymphocyte-rich region • Periarteriolar lymphoid sheaths around central arteries: T cell zone • B cell zone • Marginal zone B cell • Red pulp • Erythrocytes, macrophages, dendritic cells, lymphocytes, plasma cells

Spleen structure • Antigens enter the spleen via arterioles (instead of lymphatics) • Sinuses pass through the white pulp where the lymphocytes reside. • Antigens are trapped in the marginal zone by resident APCs. • Lymphocytes and antigen meet in the periarteriolar lymphoid sheath (PALS).

T cells in the spleen

B cells in the spleen

Spleen structure The PALS is primarily composed of T cells The B cells are located in the germinal center and B cell corona The marginal zone contains macrophages and MZ B cells

Antigen enters mucosal lymphoid tissues through specialized cells • Antigen is delivered to mucosal lymphoid tissues through M cells • M cells deliver viruses and bacteria to dendritic cells • B cell follicles of gut lymphoid tissue are active with germinal centers

Mucosa-associated lymphoid tissue (MALT) MALT are specialized areas of tissue beneath mucosal surfaces that are designed to collect antigen and stimulate localized adaptive immune responses to protect the mucosal surfaces. The architecture is different from LNs, but employs the same basic process – trap antigen and present it to lymphocytes in organized follicles.

Gut-associated lymphoid tissue (GALT) A subdivision of MALT – most important tissues are the Peyer’s patches. These are large, highly organized areas of lymphoid tissue found along the small intestine. Antigen is collected from the GI epithelial surface by specialized M cells.

Cutaneous immune system • Langerhans cells in the epidermis; immature dendritic cells, capture antigens • Intraepithelial T cells, gd T cells • Dermal dendritic cells • T cells

Thymus • The site of T cell maturation • Thymocyte: lymphocytes in the thymus at various stages of maturation • Immature T cell lineage cells enter the cortex through the blood vessels • As thymocytes mature, they migrate toward the medulla and exit the thymus and enter the blood • Cortex • Medulla • Hassall’s corpuscle

Maturation of T cells in the thymus

Table 10 -1. Importance of Antimicrobial Defenses for Infectious Agents NK cells CD 4 Th 1, DTH CD 8 CTL Antibody ++++ +++* ++++ + ++ Fungi +++ ++ + ++++ ++ (Ig. E)† Extracellular Intracellular - Complement Interferon-α/β Neutrophils Macrophages Bacteria Viruses - *By activation of macrophages. †Immunoglobulin E and mast cells are especially important for worm infections. CTL, cytotoxic T lymphocytes; DTH, delayed type hypersensitivity; NK, natural killer; Th 1, T helper Parasites ++ +

1 -1 Cells of the Immune System: Differentiation in the Bone Marrow 1. Which of the following cells belong to the myeloid lineage? a) macrophages b) neutrophils c) mast cells d) NK cells 2. Which of the following statements are true? a) Hematopoietins do not stimulate the production of myeloidlineage cells. b) Growth factors required for the production of different types of hematopoietic cells are produced both consititutively by some tissue cells and inducibly by tissue cells and immune cells in response to infection. c) Interleukins are cytokines that signal between immune cells and can also serve as growth factors for specific cell types.

1 -2 Cells of the Immune System: Functional Characteristics Work through the following questions, checking all the correct answers. For each question there may be more than one correct answer. 1. Which of the following are phagocytic cells? a) eosinophils b) macrophages c) dendritic cells d) basophils 2. Which of the following statements are true? a) Plasma cells are naïve lymphocytes that circulate through blood and lymph before they have encountered antigen. b) Neutrophils, basophils, mast cells and eosinophils all store inflammatory mediators in cytoplasmic granules. c) The two major classes of effector T lymphocytes are T helper cells and cytotoxic T cells. d) T helper cells activate B cells and macrophages.

1 -3 Macrophage and Dendritic Cell Subsets 1. Which of the following are specialized properties of macrophages? a) Ingestion and destruction of microorganisms b) Tissue maintenance and repair c) Migration to lymphoid tissues in the presence of infection d) Activation of naïve T cells 2. Which of the following statements are true? a) Dendritic cells can differentiate from either lymphoid or myeloid precursors. b) Dendritic cells have a sentinel role as immature dendritic cells in lymphoid as well as peripheral tissues. c) Dendritic cells include specialized cells known as Kupffer cells. d) Dendritic cells are especially abundant at epithelial surfaces.

1 -5 Major Histocompatibility Molecules and the Detection of Infection a) MHC molecules are highly variable because they must recognize the variable receptors of T lymphocytes. b) MHC molecules are highly variable because they must bind antigenic fragments of diverse and variable pathogens. c) MHC class I molecules are specialized to bind antigen fragments generated in the cytoplasmic compartment of cells. d) MHC class I molecules are particularly important for presenting antigenic fragments of viruses. e) MHC class I molecules are recognized by T lymphocytes bearing CD 4 coreceptor molecules.

1 -6 The Lymphoid System and Lymphocyte Circulation 1. Peyer's patches are: a) the lymphoid areas of the spleen. b) regions of highly organized lymphoid tissue in the small intestine. c) the T cell areas of the lymph nodes. 2. Which of the following statements are true? a) The primary lymphoid tissues are the bone marrow and thymus. b) Naïve lymphocytes enter lymph nodes from the lymphatic vessels. c) Germinal centers are the regions in secondary lymphoid tissue where T lymphocytes are activated by dendritic cells. d) In the spleen, the lymphoid tissues ensheath arterioles.

1 -7 Architecture of Secondary Lymphoid Tissues 1. Which of the following are routes of entry for antigen into secondary lymphoid tissues? a) Afferent lymphatic vessels. b) The marginal sinus of the spleen. c) High endothelial venules (HEV). d) M cells in mucosal epithelia. 2. Which of the following statements are true? a) The marginal zone of the spleen contains B cells specialized to respond rapidly to blood-borne bacteria. b) Follicular dendritic cells are dendritic cells that activate T cells that migrate into B cell follicles. c) Germinal centers are present throughout the lymphoid tissues of the small intestine. d) Intact microorganisms can enter gut-associated lymphoid tissues through M cells.

Cells and Tissues of the Immune System Question 1 • The cells labeled 1, 2, and 3 shown in the figure are: A) 1, plasma cell; 2, monocyte; 3, resting lymphocyte B) 1, monocyte; 2, plasma cell; 3, resting lymphocyte C) 1, plasma cell; 2, resting lymphocyte; 3, monocyte D) 1, resting lymphocyte; 2, monocyte; 3, plasma cell E) 1, resting lymphocyte; 2, plasma cell; 3, monocyte

Resting lymphocytes can be found in blood and tissues and may be naïve or memory cells. They are 8 to 10 μm in diameter and have a large nucleus with dense nuclear chromatin and little visible cytoplasm. Plasma cells, which are differentiated antibody-secreting B lymphocytes, are found in tissues. They are larger than resting lymphocytes and have eccentric nuclei with heterogeneous chromatin staining and abundant cytoplasm with a distinct perinuclear halo. The plasma cell has an eccentric, largely heterochromatic nucleus with central nucleolus and heterochromatin clumped in a "clockface" or "wagon wheel" arrangement around the inner face of the nuclear membrane. There is extensive r. ER. Golgi complexes are typically visible. Fawcett DW, The Cell: An Atlas of Fine Structure, WB Saunders, Philadelphia, 1966, p. 153. Monocytes are the circulating precursors of tissue macrophages. They are 10 to 15 μm in diameter and have a typically beanshaped (kidney-shaped) nucleus and abundant cytoplasm.

Question 2. A 52 -year-old man who receives radiation therapy and cytotoxic drugs for treatment of cancer sustains significant damage to his bone marrow. Which of the following changes will most likely occurs? A) Decreased production of B lymphocytes but not T lymphocytes B) Decreased production of T lymphocyte but not B lymphocytes C) Decreased production of neutrophils and monocytes but not B or T lymphocytes D) Decreased production of B lymphocytes and T lymphocytes E) Normal production of all blood cells due to compensatory extramedullary hematopoiesis. Decreased production of histiocytes (macrophages) but not other cell type.

Question 4. Tissue macrophages are derived from which type of circulating blood cell? A) Polymorphonuclear leukocyte B) Small lymphocyte C) Monocyte D) Basophil E) Lymphoblast

Question 5. A 5 -year old boy with recurrent infections is discovered to have a genetic defect that impairs B cell maturation. Which of the following abnormalities is most likely to be found in this patient? A) Small thymus B) Absence of follicles in lymph nodes and spleen C) Enlarged tonsils D) Diminished parafollicular zones in lymph nodes E) Hypocellular bone marrow

1. Which of the following cells serve as antigenpresenting cells that travel from the site of an infection to the lymph system to activate cells in the adaptive immune system? Dendritic cells Macrophages B-cells Mast cells

1. 2 The role of Toll-like receptors is . to: * Im mun olog y Rev iew I: Cell s of the Im mun e Syst em Which of the following is a phagocytic cell of the innate immune system that circulates through the bloodstream until "summoned"? * a. Helper T-cell a. Present a gathered antigen to Tcells b. Recognize molecular patterns characteristic of common pathogens c. Provide a binding site for antibody and cognate antigen d. None of the above Post test Inst ruct ions : To rece ive cred it for your parti cipa tion in this acti vity, plea se com plet e the follo win g step s: 1. Pa rtici pate in the onli ne acti vity. b. Macrophage 2. Co mpl ete the Postt est, sele ctin g the most appr opri ate resp onse to eac h ques tion. 3. Co mpl ete the Eval uati on (Ple ase be sure to indi cate how long it took to com plet e this acti vity. The amo unt of tim e you atte st to on this eval uati on will be refl ecte d on you r cert ifica te. ) c. Neutrophil d. Mast cell 3. Which of the following cells serve as antigen-presenting cells that travel from the site of an infection to the lymph system to activate cells in the adaptive immune system? * 4. Pri nt out your certi ficat e. * All Que stion s Are Req uire d a. Dendritic cells 1. Which of the following is a phagocytic cell of the innate immune system that circulates through the bloodstream until "summoned"? * a. Helper T-cell b. Macrophage c. Neutrophil d. Mast cell b. Macrophages c. B-cells d. Mast cells

Question 1 (10 points). DRAW AND DESCRIBE the basic structure of a lymph node. Use the following terms: afferent efferent cortex medulla germinal center HEV Where are B cells located in your lymph node? Where are T cells located in your lymph node? How would the antigen get there? How would the T cells get there?

Question 2 (3 points). 1 2 3 4 5 6 7 8 These are different cell types from blood (1 -7) or tissue (8). What are their name and their lineage (lymphoid, myeloid or erythroid)? Question 3 (2 points). Some tissues contain specialized resident macrophages and dendritic cells. What are their names ?

Question 4 (2 points) Fill out the table using the following key words: class I, class II, extracellular, intracellular, cytotoxic, helper CD 4 T cells MHC restriction Recognized antigen Function CD 8 T cells Class II Class I extracellular intracellular helper cytotoxic Question 5 (3 points) Explain “inflammation”, using the following key words: rubor (redness), color (heat), tumor (swelling) and dolor (pain)