Lecture 1. Innate Immunity-phagocytes/NK cells Lecture 2. Introduction to acquired immunity-T/B cells

Lecture objectives What are the components of the innate immune system? Phagocytes and phagocytosis Toll-like receptors (TLRs) NK cells and their receptors How is the innate immunity different from adaptive immunity? Hematopoiesis (sites and cytokines) Structure of lymphoid tissues

Lecture 1. Innate Immunity-phagocytes/NK cells

Autoimmunity or Allergy= 0 The goal of a balanced immune system [Pathogens]= 0 [Tumor cells]= 0 Autoimmunity or Allergy= 0

Pathogens: the primary targets of the immune system Parasites Bacteria Viruses Fungi

The territory to defend by the immune system and physical barriers Figure 1-4

Figure 8-6 part 2 of 2 Physical, chemical and microbiological barriers of our body

CORE 1-a. Antimicrobial factors on skin and mucous membranes and in the blood and tissues Mechanical antimicrobial factors Mechanical barrier of skin Mucous epithelial barrier Ciliated epithelium Normal microflora Mucous secretions

(2) Chemical antimicrobial factors CORE (2) Chemical antimicrobial factors Lysozyme Muramidase Spermine Peroxides Acids Complement Cytokines Antimicrobial peptides (defensins) IgA (adaptive immunity)

Figure 8-5 Immune system is activated at the moment when pathogens enter the body Neut Mac DC Phagocytes: Macrophages: tissue resident Neutrophils: recruited from blood Dendritic cells: tissue resident; migrate to lymph nodes

Components of pathogens activate immune and non-immune cells Immune cells that are activated: Receptors: Components of Pathogens: Peptides Proteins Glycoproteins/Proteoglycans Carbohydrates Glycolipids Phospholipids Peptidoglycans Nucleic acid Flagella ab-T cells T cell receptors B cells B cell receptors T cell receptors NKT cells gd-T cells Phagocyte receptors Tissue cells Macrophages Toll-like receptors Neutrophils Dendritic cells

6. Cells involved with the immune response, CORE 6. Cells involved with the immune response, a. Cells (description, function, important mediators they release, half-lives, relative concentrations in blood) (1) Non-antigen specific: neutrophils, basophils, eosinophil, mast cell, macrophage, dendritic cell, natural killer cells (NK), large granular lymphocyte morphology (2) Antigen-specific: T lymphocytes (TC, Th1, Th2), B lymphocytes (3) Antigen presenting cells (function, location, and important cell surface markers): dendritic cells, macrophages (Kupffer, intraglomerular, alveolar, serosal, brain [microglia], spleen sinus, lymph node sinus; central role of macrophages in immunity and inflammation (cytokines secreted, vasoactive molecules, tissue damage and healing), B-cells

Innate (immediate and non-specific) and adaptive (late but antigen-specific) immune responses Figure 1-7

Cells of Innate Immunity Neutrophils Macrophages NK cells Mast cells Eosinophils Basophils Other non-blood origin tissue cells (epithelial/fibroblast cells etc) Dendritic cells induce adaptive immunity Phagocytic cells

1-b. Phagocytic cells and the process of phagocytosis CORE 1-b. Phagocytic cells and the process of phagocytosis (1) Polymorphonuclear leukocytes, monocytes and macrophages (blood and tissue types; role of macrophage as antigen presenting cell and mediator of inflammation) (2) Phagocyte cell surface receptors and markers: complement, Fc, Class II, Toll-like receptors (3) Receptor-mediated chemotaxis (chemotactic agents: C5a, LTB4, chemokines [IL-8, MIP, MCP])

Phagocytic cells (continued) CORE Phagocytic cells (continued) (4) Adherence to endothelium (margination and emigration: ICAMs and selectins on endothelium, integrins and selectins on phagocytes) (5) Particle attachment, phagocytosis, formation of phagolysosomes and role of degranulation in tissue damage (6) Metabolic burst and mechanisms of bacterial killing and digestion (a) Oxygen-dependent antibacterial factors: Superoxide generated by NADPH oxidase; hydrogen peroxide generated by superoxide dismutase; hypochlorite and hypoiodite generated by myeloperoxidase (b) Oxygen-independent antimicrobial proteins: acid hydrolases, muramidase, lysozyme, lactoferrin, defensins.

Macrophages engulf bacteria and produce inflammatory cytokines Figure 1-14

Figure 1-5 Complement-mediated phagocytosis

Host receptors that sense the molecules of pathogens

Figure 8-13 TLRs on the cell surface recognize microbial products They act as the receptors to sense the presence of pathogens. Figure 8-13

Activation of TLRs induces immune cell activation and production of inflammatory cytokines Figure 8-14

Figure 8-12 part 1 of 2 Recognize microbial products Bind pathogens Surface receptors of macrophages Figure 8-12 part 1 of 2 Recognize microbial products Bind pathogens

Figure 8-12 part 2 of 2

Figure 8-20 Neutrophil receptors that are important for phagocytosis Presence of neutrophils in tissue sites (not blood) is a sign of acute inflammation

Figure 8-21 What is happening in phagolysosomes?

Figure 1-13 Neutrophils: disposable phagocytes to clear pathogens Formation of Pus

Leukocyte recruitment to sites of infection: rolling on selectins Figure 8-19 part 1 of 2 Important for infiltration of tissues during inflammation

Leukocyte recruitment to sites of infection: a multi-step navigation Figure 8-19 part 2 of 2 1. Selectins 2. Chemokines 3. Integrins

Figure 8-5 Neut Mac DC Phagocytes: Macrophages: tissue resident Neutrophils: recruited from blood Dendritic cells: initially tissue resident but migrate to lymph nodes upon infection

CORE 9-f. NK cells Distribution: 10-15% of circulating lymphocytes; lack typical T cell markers (i.e. TCR, CD3, CD4, CD8, etc.). Markers: CD16 (IgG Fc receptor),CD28, CD56 (CD16 & 56 used to identify NK cells) Cytokines secreted: IFNg, IL-1, GM-CSF, TNFa ; secretion induced by IL-12 Cytotoxic mechanisms: Attack cells with reduced MHC class I expression. Release perforin. CD-28/B7-1 co-stimulating signal important This is important mainly for T cell activation but also can be important for NK cells Can also kill by antibody-dependent cell mediated cytotoxicity (ADCC)

Innate Adaptive/acquired NK cell recruitment NK. IFN-a chemokines Virus NK. IFN-a chemokines epithelial cells and DCs Neutr. recruitment Neutr. Effector T cells (CD4/CD8) Antibodies Macrophage activation DC activation DCs Lymph nodes Activate T cells and B cells Adaptive/acquired

Roles of aIFNs Figure 8-26

Figure 8-28 Kinetics of immune responses after viral infection IFNa/b, TNF-a, and IL-12 activate NK cells Figure 8-28

NK cell receptors allow killing of infected but not healthy cells Figure 8-32

NK cells can attack tumor cells lacking MHC I expression

Figure 8-29 NK receptors for MHC class I, MICA, MICB, and antibody (IgG). CD16=FcgRIII

Antibody-dependent cell-mediated cytotoxicity (ADCC) Through a activating receptor CD16/Fc-gamma-RIII. This is a collaboration of innate (NK cells) and adaptive immunity (antibody).

IgG Fc Receptors: serve as receptors for antibody IgGs FcgRI (CD64): Macrophages, Monocytes FcgRII (CD32): B cells, Macrophages, Neutrophils, Monocytes. FcgRIII (CD16): NK Cells, Macrophages, Neutrophils Most CD4 or CD8 T cells do not express Fc receptors. FceRI on Mast cells: IgE binds this and activates mast cells

Functions of Fc receptors: Effector Mechanisms (Fc g-RIII on NK cells) Mediator release (e.g. Fc e-RI on Mast cells) Enhancement of antigen presentation B cell negative feedback Complement Activation (we will revisit these later)

CORE Lymphoid tissues (LT): the tissues that mainly contain lymphocytes and serve as sites of lymphocyte activation & functional differentiation c. Primary (central) and secondary (peripheral) lymphoid tissues (functions and histologic organization as it pertains to immune function) (1) Primary: bone marrow and fetal liver (B cells); thymus (T cells) (2) Secondary: spleen, lymph nodes, mucosa-associated lymphoid tissue (MALT) Examples of MALT: Tonsils, adenoids; Bronchial Gastrointestinal (appendix and Peyer’s patches (M cells)) Genitourinary tract lymphoid tissues

Figure 1-15 The lymphatic system Peripheral lymph nodes Mesenteric lymph nodes

d. Lymphocyte (lymph) traffic: CORE d. Lymphocyte (lymph) traffic: High endothelial venules, efferent lymphatic vessels, thoracic duct, blood lymphocyte pool, and afferent lymphatic vessels

Lymphocytes traffic to and from a lymph node Thoracic duct Blood Efferent lymphatic vessel Most lymphocytes LN Artery HEV Afferent lymphatic vessel Some cells Tissue sites (e.g. skin) Antigens/DCs pathogens

T and B cells (which become memory cells) recirculate, but (disposable) myeloid cells don’t Examples: CD3+ T cells: Thymus Blood  LN (Ag)   Blood  inflamed tissues CD19+ B cells: BM Blood LN (Ag)   Blood  plasma cell sites (BM, spleen, mucosal tissues) or circulation Neutrophils: BMBlood  Sites of infection  Death Macrophages: BM (monocytes)Blood  Sites of infection (macrophages)  Granuloma or death

2o LT collects antigens, dendritic cells and lymphocytes for adaptive immune responses. Figure 1-17 CD3+ naïve T cells become functional cells (memory /effector cells; Th1/Th2 cells) in cortex (In cortex) CD19+ naïve B cells undergo differentiation to Ab-producing plasma cells in GCs.

Figure 1-19 Immune responses Hematopoiesis & Filtering blood

Structure of spleen Lymphocytes are collected here Lymphocytes go through central arterioles to enter the spleen. Spleen filters blood to collect antigens and remove old red cells. Red cells are filtered here

Peyer’s patches Figure 1-20

2. Introduction to acquired immunity CORE 2. Introduction to acquired immunity a . Specificity and heterogeneity: Reaction to extracellular versus intracellular pathogens. Antigen (pathogen) A versus antigen B. c. Immunological memory d. Discrimination between self and non-self antigens e. Active (e.g. immunization) and passive (e.g. transfusion of anti-venom) immunity f. Natural (infection) versus artificial immunization (vaccination)

Multi-step trans-endothelial cell migration Floating Selectin-mediated rolling on endothelial cells Chemokine receptor activation Integrin-mediated firm adhesion Extravasation Chemokine gradient Chemotaxis Center of inflammation

Figure 1-18 Dendritic cell migration to lymph nodes

Different pathogens, different immune response Figure 8-4

Typical time course of adaptive immune responses Primary response Slow (2 weeks) Outcome: Weak Secondary Fast (several days) Outcome: More vigorous e.g. Hepatitis A Hepatitis A and Hepatitis B

Figure 1-21 Antigen receptors of B cells and T cells B cell Receptor Effector molecule T cell Receptor

Figure 1-22 Antigen Specificity Antibodies neutralize pathogens in an antigen-specific manner Antigen Specificity

Figure 1-24 Antibodies (B cells) bind whole proteins while TCRs (T cells) bind small peptides presented by dendritic cells

Peptides are presented to TCR by MHC class I or II molecules on APC (antigen presenting cells: B cells, dendritic cells and macrophages) Figure 1-25 CD4+ T cells CD8+ T cells Activate Activate

Figure 1-26 Activation of CD8+ T cells by antigen peptides CD4 T cells = helper T cells: control B cells and macrophages T cells CD8 T cells = cytotoxic cells: kill virus-infected cells

Selection and expansion of antigen specific T and B cells Marrow or thymus Lymph nodes Lymph nodes & Sites of infection Immunological memory