Effector mechanisms of immunity Jan eromski 20132014 Nobel

Effector mechanisms of immunity Jan Żeromski 2013/2014

Nobel 2011 in physiology and medicine – devoted to key findings in immunology prof. Bruce Beutler (USA) prof. Jules A. Hoffmann (France) They determined conditions of activation of nonspecific (innate) immunity and detected close links between the induction of infection and the reactivity of Toll-like receptors at molecular level prof. Ralph Steinmann (USA) Detected dendritic cells and determined their function as antigen presenting cells (APC).

POINTS TO BE DISCUSSED • Cytokines, their receptors and effector function • Macrophages • Granulocyte effector functions • Cytotoxic T cell function • Natural killer cells and natural killer T cells • Effector action of antibodies • Antibody dependent cell mediated cytotoxicity (ADCC) • Complement functions

GENERAL PROPERTIES OF CYTOKINES (CT) • Production induced by: a) microbial products in innate immunity, b) foreign antigens in acquired immunity, c) own metabolites • Short secretion – transient and unstable activation of transcription • Lack of stability of m. RNA • Pleiotropic action on various cells, organs and systems

FEATURES OF ACTIVATED MACROPHAGES • Increased expression of MHC molecules • Increased expression of costimulators (B 7 -1 and B 7 -2, CD 40) • Secretion of cytokines (TNF, IL-12, IL-18, IFNγ, PDGF) • Secretion of chemokines • Expression of enzymes catalysing the production of microbicidal substances in phagolysosomes (ROI, nitric oxide, proteolytic enzymes)

POTENTIAL MECHANISMS OF CYTOTOXICITY OF MYELOID CELLS • Cationic proteins (defensins): small peptides, comprise up to 50% of the granule proteins. Form ion-permeable channels in lipid bilayers of bacteria • Lysozyme, C 3 a • BPI (bactericidal/permeability increasing factor)

POTENTIAL MECHANISMS OF CYTOTOXICITY OF MYELOID CELLS-2 • Hydrolases • Reactive oxygen intermediates (ROIs) • NO and reactive nitrogen intermediates (RNI) • Tumor necrosis factor-alpha (TNF-alpha)

NET-osis – novel mechanism of killing bacteria by neutrophils • Neutrophils form network-like structures, consisting of nucleic acids, histones and enzymes, These nets have the ability of immobilizing and killing pathogens • Neutrophils released from the net undergo apoptosis • Net may be formed only by fully mature and intact cells

MAIN CYTOTOXIC AGENTS OF LYMPHOCYTES • Perforin, granzymes (fragmentins) (induction of apoptosis) • Lysosomal enzymes (proteolysis, induction of apoptosis) • Granulolysin (lipid binding protein, membrane damage) • Fas - Fas. L (induction of apoptosis)

MAIN CYTOTOXIC AGENTS OF LYMPHOCYTES - 2 • TNF (tumor necrosis factor) • LT-alpha (lymphotoxin alpha) • TRAIL (TNF-related apoptosis inducing ligand) • Leukoregulin (sensitizer for cytotoxic action) • ATP, ROI, RNI (increased membrane permeability)

CYTOTOXIC FACTORS OF LYMPHOCYTE GRANULES • Granzymes (fragmentins) – serine proteases. Penetrate cell through perforin channels. Induce apoptosis. Hydrolize extracellular matrix components • Granulolysin – belongs to saponins, lipid binding proteins. Destroys cell and mitochondrial membranes.

CTL EFFECTOR FUNCTIONS 1. Cytotoxicity – Granule exocytosis pathway (perforin, granzymes) – Fas /Fas. L pathway, TNF/TNF-R (? ) 2. Inflammation and immunity – – Cytokine and chemokine production (IFN- , TNF- , MIP 1 , RANTES) Macrophage activation Direct antiviral effects

CYTOTOXIC FACTORS OF LYMPHOCYTE GRANULES • Cytolytic granules are the product of Golgi apparatus • Perforin – glycoprotein (555 aminoacids), similar to C 6 -C 9 complement components, Ca ions dependent; its polymerization leads to formation of channels in cell membrane

CYTOTOXIC T LYMPHOCYTES (1): Provide partial protection from: • Most viruses • Some bacteria (e. g. Listeria monocytogenes, Mycobacterium tuberculosis) • Some protozoa (e. g. Trypanosoma cruzi, Toxoplasma gondi, Plasmodium falciparum • Tumors

CYTOTOXIC T LYMPHOCYTES (2): Contribute to or cause: 1. Hypersensitivity reactions such as tissue damage in several infectious diseases, 2. Some autoimmune diseases, 3. Organ transplant rejection, 4. Graft-vs-host disease.

FEATURES OF NK CELLS • Granular lymphocytes, express CD 16 and CD 56, but NOT CD 3 • Spontaneously cytotoxic to certain tumors and virally infected cells • Found in the blood, spleen, lung, liver, GI tract and uterine decidua • Activated by IL-2, IL-15 or IL-18

FEATURES OF NK CELLS -2 • Subsets express killer immunoglobulin-like receptors (KIR) for class I MHC antigens. Long ones possess ITIM (immunoreceptor tyrosine based inhibitory motif) domain (inhibitory), while short ones – have ITAM domain providing activatory (death) signal • Target cell lysis via perforin/granzymes pathways and receptor induced apoptosis

Mechanisms of NK cell cytotoxicity • Release of cytokines (IFN gamma, TNF and others) • Release of cytolytic granules for lysis of infected or transformed cells • Induction of target cell death through cell surface receptors

RECEPTORS AND LIGANDS OF NK CELLS Receptors • immunoglobulin-like receptors Ligands • Class I HLA-C alleles • C-type lectins - CD 94 NKG 2 A-F in man • HLA-E with HLA-A: C leader peptide • Natural cytototoxicity receptors • Influenza hemaglutinin, Ctype lectin

NKT (CD 3+, CD 56+) cells • Recognize antigens in the context of CD 1 d (one of five nonpolymorphic MHC class I glycoproteins (CD 1 a-e), • CD 1 d molecules present nonprotein and glycolipid antigens (components of mycobacterial walls) • NKT cells are few in the blood (0, 3%) but abundant in liver (4% of all lymphocytes) • They secrete IFN-γ, TNF, but may also IL-4, IL-10, IL-13 Cytotoxicity – CD 1 d restricted, either Fas mediated or perforin dependent

EFFECTOR FUNCTIONS OF ANTIBODIES • Neutralization of microbes (bacteria and viruses) • Inactivation of toxins • Opsonization of microbes with subsequent phagocytosis • Antibody dependent cellular cytotoxicity (ADCC) • Activation of classical pathway of complement (Ig. G, Ig. M) • Mast cell and basophil degranulation (Ig. E)

CLASS SWITCHING AND AFFINITY MATURATION ENHANCE THE PROTECTIVE FUNCTIONS OF ANTIBODIES • Heavy chain class switching –cf. From Ig. M to Ig. G or Ig. A – results in production of antibodies with distinct Fc regions, ready to perform various effector functions, • Affinity maturation – prolonged antigen stimulation leads the production of antibodies with higher and higher affinities for the antigen. This results in increased ability of antibodies to neutralize or eliminate microbes, • Avidity – the sum of affinity receptors

ANTIBODY DEPENDENT CELLMEDIATED CYTOTOXICITY (ADCC) • Is due to Fc receptor for Ig. G (CD 16) on effector cell • Fc receptor on effector cell binds Fc fragment of antibody bound to target cell, what enables direct contact between effector and its target • Cells possessing Fc receptor are called killer cells (Kcells). They include NK cells, T cells, monocytes, eosinophils, some other myeloid cells (polymorphs? )

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