Section 10 Innate Immunity Introduction of innate immunity

Section 10 Innate Immunity

Introduction of innate immunity • Innate immunity is the first line of defense against infections. • Innate immunity exist before encountering with microbes and are rapidly activated by microbes before the development of adaptive immune responses. • Innate immunity is present in all multicellular organisms, including plants and insects.

Characteristics: • • • Set up at birth Non–specific and early Heredity Racial or species difference No immune memory

Characteristics of Innate and Adaptive Immunity Innate Immunity Adaptive Immunity Antigen independent Antigen dependent No time lag A lag period No antigen specific No Immunologic memory Antigen specific Development of memory

Components of Innate and Adaptive Immunity Innate Immunity Adaptive Immunity physical barriers skin, gut Villi, lung cilia, etc none soluble factors many protein and non-protein secretions cells phagocytes, NK cell, B 1, γδT, APC Immunoglobulins (antibody) T , B lymphocytes APC

Contents Ø PartⅠ Components of innate immune system Ø PartⅡ Cells participating in innate immunity Ø PartⅢ Recognition features of the innate immune system

PartⅠ Components of innate immune system Ø Ⅰ. Barriers Ø Ⅱ. Humoral factors Ø Ⅲ. Cells

PartⅠ Components of innate immune system Ⅰ. Barriers: • Mechanical defense: skin & mucous membrane • Anatomic barrier: blood – brain barrier blood – placenta barrier blood – thymus barrier • Biotic barrier: normal flora • Chemical defense (lysozyme, acid)

PartⅠ Components of innate immune system Ⅱ. Humoral factors: Complement Cytokine---macrophage, neutrophil, NK cell Lysozyme Ⅲ. Cells: Mononuclear phagocyte, NK cell, Neutrophils, Dendritic cells，Eosinophil, Basophil, Mast cell， γδT cell, B 1 cell, Microfold cell

ICC

PartⅡ Cells participating in innate immunity Ø Natural killer cells (NK) Ø Mononulear phagocytes Ø Neutrophils Ø Dendritic cells Ø Other cells participating in innate immunity

PartⅡ Cells participating in innate immunity Ⅰ. Natural killer(NK)cells 1. Source: Bone marrow, exist mainly in peripheral blood(5 -7%) and spleen.

2. Characteristics of NK cells Ø Also called large granular lymphocytes (LGL) Ø Kill various infected and malignant cells spontaneously, without stimulation of antigen and MHC restriction Ø Identified by the presence of CD 56, CD 16 (Fc RⅢ) Ø Activated by IL-12 and produce IFN -γ

3. Recognition mechanism of NK cells • FcγRⅢ: recognize antibody covered cell ------ADCC • Killer activating receptor and killer inhibitory receptor

ADCC

Receptors associated with killer activation and killer inhibition on NK cells • NK receptors bind with class Ⅰ MHC molecules • NK receptors bind with non class Ⅰ MHC molecules

(1) NK Receptors bind with class Ⅰ molecules: -KIR(killer immunoglobin-like receptors): • Number of immunoglobin-like domain: KIR 2 D/KIR 3 D • Cytoplastic region: longer---KIR 2 DL/KIR 3 DL(ITIM), inhibitory receptor shorter---KIR 2 DS/KIR 3 DS, non-covalent combination with DAP-12(ITAM), activating receptor -KLR(killer lectin-like receptor): • Heterodimer of CD 94 & NKG 2 (C type lectin) CD 94: short cytoplastic region, no signal transmission NKG 2 A: ITIM in cytoplastic region ----CD 94/NKG 2 A, inhibitory receptor NKG 2 C: no signal transmission, bind with DAP-12(ITAM) ----CD 94/NKG 2 C, activating receptor ITIM：immunoreceptor tyrosine-based Inhibitory motif ITAM：immunoreceptor tyrosine-based activation motif

(2) NK receptors bind with non class Ⅰ MHC molecules --NKG 2 D: Express mainly on the surface of NK and γδT No signal transmission Non-covalent binding with DAP-10(ITAM) MHC class Ⅰ chain-related molecules A/B(MIC A/B) --Natural cytotoxic receptor(NCR): NKp 46, NKp 30, NKp 44 Ig. SF Express on the surface of NK cells Bind with other molecules(ITAM) Kill target cells when KIR/KLR lose their function

Receptors associated with killer activation and killer inhibition on NK cells Killer activatory receptor Killer inhibitory receptor Function KIR: KIR 2 DS, KIR 3 DS KIR 2 DL, KIR 3 DL Bind class I HLA KLR: CD 94/NKG 2 C CD 94/NKG 2 A molecules NKG 2 D NKp 46 NKp 30 NKp 44 NCR Bind non-class I HLA molecules

Figure 3 -23 These are important molecules for presentation of peptides to CD 8 T cells These are important NK inhibitory ligands（ CD 94/NKG 2 A/B/C）

Ø Normal condition(Class Ⅰ HLA molecules are expressed normally): Effect of Inhibitory recepter > Activatory recepter-----Killing effect of NK cell is inhibited Ø Abnormal condition(Class Ⅰ HLA molecules are expressed abnormally) : NK cells lose ability of distinguishing self from nonself------NK cells kill target cells（ NKG 2 D and NCR)

NK cells is tolerant to self-antigen: u. Only virus infected cells and tumor cells could be killed by NK cells, not the normal tissue cells. u. Virus infected cells or tumor cells MHC-I inhibitory signal Killed by NK cells。

4. Effector of NK cells • Secretion of cytokines, e. g. IFN-γ, to a activates macrophages • Cytotoxicity: -ADCC-mediated by FcγRⅢ(CD 16) -Granules like CTLs: Perforin: creates pores in target cell membranes Granzymes : enzymes which enter through perforin pores and induce apoptosis of target cells. -Fas. L/Fas pathway -TNF-α/TNFR-Ⅰ pathway

Target cell TNFR-I TNF- α Contact tightly NK cell ADCC

5. Functions of NK cells Ø Participate in anti-tumor and anti-virus immunity Ø Participate in immunological regulation

PartⅡ Cells participating in innate immunity Ⅱ. Mononuclear phagocytes

monocytes and macrophages

Phagocytes are the Most Important Cells George Bernard Shaw wrote: “There is at bottom only one genuine treatment for all diseases, …to stimulate the phagocytes. Drugs are a delusion. …(when) the phagocytes are stimulated; they devour the disease…”

Tissues Blood macrophage

Macrophages u Phagocytose & kill intracellularly u Characteristic nucleus and identified by CD 14 u Act as APC u Activated by cytokines u Kill malignant and altered self targets u Adherent of plastic and glass surfaces

Macrophages phagocytose and degrade foreign particles, bacteria and dead (and dying) host cells. Receptors on Macrophages: Fcγ receptors Complement receptors IFN-g receptor Chemokine receptors Mannose receptor Toll-like receptors(TLRs) Scavenger receptors(SRs) LPS receptor(CD 14)

1. Recognizing and excluding pathogens Recognizing Ingestion recognizing Digestion Exclusion exclusion digestion ingestion

(1) Recognition Mechanism Pattern recognition receptor(PRR): The receptor on macrophage which can recognize and bind specific molecular structure on some pathogens , injured or apoptotic cells.

The receptor associated with antigenrecognition of macrophage Ø Pattern recognition receptor (PRR) or non-opsonic receptor ------Mannose receptor(MR) Scavenger receptor(SR) Toll like receptor(TLR) Ø Opsonic receptor ------FcγR and C 3 b. R/C 4 b. R

Initiation of Phagocytosis Scavenger. R Ig. G Fc. R CR

Pathways of Intracellular Killing

(2) Ingesting and digesting the pathogen Ø Oxygen-dependent system: ---Reactive oxygen intermediates, ROIs : O 2 -, OH-, H 2 O 2, 1 O 2 ---Reactive nitrogen intermediates, RNIs: NO Ø Oxygen-independent system: ---Low p. H(3. 5 -4) , Lysozyme, Defensin

(3) Excluding the pathogen

2. Functions of macrophage ① Recognizing and excluding pathogens and died cells; Killing target cells(tumor cells and virus-infected cells) ② Participating in and stimulating inflammation ③ Participating in immunological regulation ④ Processing and presenting antigen, initiating adaptive immune response

PartⅡ Cells participating in innate immunity Ⅲ. Neutrophil

Neutrophils Ø Phagocytosis, intracellular killing, inflammation and tissue damage Ø Characteristic nucleus, cytoplasm Ø Granules and CD 66 membrane marker Ø FcγR and CR

PartⅡ Cells participating in innate immunity Ⅳ. Other cells • Dendritic cells • • • Mast cells and eosinophils Microfold cells NKT cells γδ T cells B 1 cells

PartⅢ Features of innate immune recognition • Molecular patterns(pathogen associated molecular pattern, PAMP): ds. RNA, Cp. G DNA, LPS. • Pattern recognition receptors（PRR） : the receptors that bind these conserved structures.

PAMP : 1. Structures that are characteristic of microbial pathogens and are not present on mammalian cells. 2. Microbial products that are often essential for survival of the microbes.

The receptors of the innate immune system( PRRs) are encoded in the germline. • Very conserved • Limited diversity PRRs including: Scavenger receptor, SR Mannose receptor，MR Toll-like receptor, TLR

Part Ⅳ Role of innate immunity 1. Defense against microbes • The early local reaction of innate immunity is the inflammatory response, in which leukocytes are recruited to the site of infection and activated to eradicate the infection. • Inflammation produces a variety of systemic changes in the host that enhance the ability of the innate immune system to eradicate infection and, in sever infections, can contribute to systemic tissue injury or death.

Progression of Immunity Figure 8. 5 At least three cell types reside within or beneath the epithelium and induce inflammation in response to trauma or microbial products: Macrophages, Mast Cells, and Langerhan’s cells (a skin dendritic cell)

2. Stimulating adaptive immune responses • Provides signals that function in concert with antigen to stimulate the proliferation and differentiation of antigen-specific T and B lymphocytes. • Works as effector cells or molecules

Important functions of innate immunity: • Innate immunity is the initial response to microbes • The effector mechanisms of innate immunity are often used to eliminate microbes even in adaptive immune responses • Innate immunity to microbes stimulates adaptive immune responses and can influence the nature of the adaptive responses to make them optimally effective against different types of microbes.

Components Principle Functions Barriers Physical barriers Prevent entry Chemical barriers Microbial killing Biotic barriers Competition of microbial Circulating and Tissue Effector Cells Neutrophils Early phagocytosis and killing of microbes Macrophages Efficient phagocytosis and killing of microbes: cytokines NK cells Lysis of infected cells, activation of macrophages Eosinophils Nasty toxic cells designed to kill helminths (worms) Mast Cells Release of inflammatory granules Circulating Proteins C Killing of microbes, opsonization of microbes, activation leukocytes Mannose-binding protein Opsonization of microbes and activation of C C-reactive protein Opsonization of microbes and activation of C Lysozyme Bacterial cell wall lysis Cytokines TNF, IL-1, 6, 18 Inflammation IFN a, b Resistence to viral infection IFN g Macrophage activation IL-12 IFNg production by NK cells IL-15 Proliferation of NK cells, memory T cells IL-10, TGF b Control of Inflammation