DEFINITION AND PROPERTIES OF ANTIGEN IMMUNOLOGICAL DEFINITION Any chemical structure Soluble or corpuscle Simple or complex Originated from the body or comes from outside Genetically self or non-self Natural or artificial

DEFINITIONS ANTIGEN (Ag) - any substance, which is recognized by the mature immune system of a given organism ANTIGENICITY– capability of an antigen to bind specifically with certain product of the adaptive immunity: TCR or BCR/antibody, immunogenicity - capability of an antigen to induce an (adaptive) immune response, tolerogenicity - capability to induce immunological tolerance, specific immune non-responsiveness

FACTORS INFLUENCING IMMUNOGENICITY I. Foreignness Size Genetics Species Individual Age Dose Route subcutaneous > intravenous > oral / intranasal Not true for live vaccines (i.e. oral polio vaccine) Foreignness: evolutionary the farther the species are from each other the more their antigens induce immune response in another Size: i.e. haptenes (too small to induce immune response without carriers) Genetics: differences of the immune response between species from the same family/order and between individuals of the same species Age: the old mainly rely on the immunological memory, they can hardly get over a new kind of infection. Moreover there are differences in the immune response generated by EBV and mumps viruses in childhood and adulthood

FACTORS INFLUENCING IMMUNOGENICITY II. Adjuvant (vaccination) substances that enhance an immune response to an antigen (aluminum salts, LPS, Freund’s adjuvant, TLR ligands) complex effects depot effect – slower biodegradation, prolonged antigen intake by antigen presenting cells activation of innate immunity Physical status corpuscle (cell, colloid) or soluble denatured or native Degradability antigen presentation by APC

ANTIGENIC DETERMINANT (=EPITOPE) part of the antigen which is recognized by a defined immunoglobulin (BCR / antibody) or by T cell receptor

Ig (antibody) BCR (mIg)

TYPES (STRUCTURE) OF ANTIGEN DETERMINANTS linear determinant conformational determinant (TCR, BCR, Ig) (BCR, Ig) conformational determinant Ab2 Ab1 surface/accessible determinants cleveage denaturation hidden/revealed determinant new/neoantigen determinant conformational/linear determinant

B cell epitope T cell epitope recognized by B cells proteins polysaccharides lipids DNA steroids etc. (many artificial molecules) cell or matrix associated or soluble recognized by T cells proteins mainly (8-23 amino acids) requires processing by APC Some T cells are able to recognise glycolipids bound to non-conventional MHC molecules (e.g. CD1) too

ANTIGEN RECOGNITION ≠ CELL ACTIVATION

ANTIGEN RECOGNITION BY NAIVE T CELLS REQUIRES PRESENTATION VIA MHC MOLECULES Recognition/ No activation The mature naive cytotoxic T cells (Tc) activate by recognizing antigens bound to MHC I molecules on the surface of antigen presenting cells (APCs) with the help of costimulatory molecules and then they are able to recognize these antigenes bound to MHC I molecules on the surface of host cells (HC) too. CD4 is the co-receptor of helper T cells (Th) and CD8 is the co-receptor of the cytotoxic T cells (Tc). Recognition/ Activation

SUPERANTIGENS Fever Microbial proteins that bind to and activate all the T cells that express a particular set or family of TCR molecules resulting in a polyclonal activation. Interaction is not via the peptide binding cleft of MHC molecule. The superantigens can aspecifically bind to the TCR and MHC molecules thereby stabilizing their connection, resulting in the activation of the T-cell subpopulation Hypotension Rash Desquamation

monoclonal/oligoclonal SUPERANTIGENS Microbial proteins that bind to and activate all the T cells in an individual that express a particular set or family of TCR molecules conventional antigen superantigen polyclonal T cell response 1:4 - 1:10 monoclonal/oligoclonal T cell response 1:104 - 1:105 activated T cells 107 – 108 / 1011 1010 / 1011

SUPERANTIGENS Classification Sources Endogenous Exogenous   Exogenous 1.Mouse mammary tomor virus (MMTV) Epstein-Barr virus (EBV) Staphylococcal enterotoxins (SEs): A, B, C1 to C3, D, E, G to Q Staphylococcal toxic shock syndrome toxin-1 (TSST-1) Staphylococcal exfoliative toxins: exoliatin A, exfoliatin B Staphylococcal enterotoxin-like toxins formed due to recombination within enterotoxin gene cluster: U2, V Streptococcal pyrogenic exotoxins (SPEs): A1 to A4, C, G to M Streptococcal mitogenic exotoxins: SMEZ Streptococcal superantigen :SSA Yersinia pseudotuberculosis: Yersinia pseudotuberculosis-derived mitogen (YAM) Mycoplasma species: Mycoplasma arthritidis-derived mitogen (MAM) Cholera toxin:  subunit A of cholera toxin Prevotella intermedia* Mycobacterium tuberculosis* Viral superantigens:  (a) Mouse leukemia virus                                         (b) IDDMK1222- Ppol-ENV-U3                                         (c) HIV-Nef                                         (d) Rabies virus-nucleoside protein The superantigens can be broadly classified into following families: i. Endogenous superantigens: These superantigens are encoded by various viruses integrated into the genome. Examples are superantigens produced by mouse mammary tumor virus (MMTV) and Epstein-Barr virus (EBV) associated superantigen. ii. Exogenous superantigens: These include the exotoxins secreted by microorganisms. Examples are staphylococcal enterotoxins (A, B, C1 to C3, etc.), streptococcal pyrogenic exotoxins (A1 to A4, C, etc) and others (see Table 1) [7, 12-18]. iii. B-cell superantigens: Those superantigens which stimulate predominantly B cells. Examples include staphylococcal protein A and protein Fv.   .

T CELL-DEPENDENT B CELL ACTIVATION Polysacharides are not presented! cytokines CD4 TCR MHCII +peptide T cell 2 1 Polysacharides are not presented!

B CELL ACTIVATION WITHOUT THE HELP OF T CELLS T-INDEPENDENT ANTIGEN TI-1 T-INDEPENDENT ANTIGEN TI-2 B cell Simultaneous activation of BCR and other receptors on B cells (i.e. LPS binding protein /CD14) induces the B cells to proliferate and differentiate Strong crosslinking of BCR by repetitive polysaccharide or protein epitopes B CELL ACTIVATION (extra activation signal) (extensive receptor-aggregation)

B CELL ACTIVATION WITHOUT THE HELP OF T CELLS (A lot of small ones or a large with multiple epitopes. Usually the same kind, like polysaccharides.)

Microorganisms have several different cell surface epitopes

COMPLEX ANTIGENS CONSIST OF THE CARRIER AND MULTIPLE EPITOPES (=ANTIGEN DETERMINANTS) HAPTEN substance that is non-immunogenic but which can react with the products of a specific immune response. Haptens are small molecules which could never induce an immune response when administered by themselves but which can when coupled to a carrier molecule. Free haptens, however, can react with products of the immune response after such products have been elicited. Haptens have the property of antigenicity but not immunogenicity. Haptenic/antigen determinant (epitope) part of the antigen which are recognized by a defined immunoglobulin (B cell receptor or antibody) or by T cell receptor Carrier part of the antigen directly not involved in connection with the defined Ig/BCR or TCR These terms can only be used to describe the interaction of particular antigenic determinant and single immunoglobulin or T cell receptor

Antibody response generated against a hapten-carrier conjugate carrier + hapten antibodies Hapten-carrier conjugates have native antigenic determinants of the carrier as well as new determinants of the hapten. carrier specific hapten specific carrier + hapten specific

ACUTE INFLAMMATION AND ACUTE-PHASE RESPONSE

THE INFLAMMATORY RESPONSE Illustrated here are the events following an abrasion of the skin. Bacteria invade the underlying connective tissue and stimulate the innate immune response.

ACUTE INFLAMMATION Acute inflammation is a rapid response to an injurious agent that serves to deliver mediators of host defense — leukocytes and plasma proteins — to the site of injury. Vascular phase Vasoconstrictionvasodilation Increased permeability  edema, leakage of plasma proteins (acute phase proteins, antibodies) Cellular phase Migration of leukocites from the circulation to the site of inflammation Acute inflammation has three major components: alterations in vascular caliber that lead to an increase in blood flow structural changes in the microvasculature that permit plasma proteins and leukocytes to leave the circulation emigration of the leukocytes from the micro-circulation, their accumulation in the focus of injury, and their activation to eliminate the offending agent

CAUSES LEADING TO ACUTE INFLAMMATORY REACTIONS: Infections (pathogenic microbes and microbial toxins) Trauma (blunt and penetrating) Physical and chemical agents (thermal injury e.g. burns or frostbite; irradiation; some environmental chemicals) Foreign bodies (splinters, dirt, sutures) Immune reactions (hypersensitivity and autoimmune reactions) Except for Chuck Norris

The classic symptoms of inflammation: redness (rubor) - vasodilation, swelling (tumor) - edema, heat (calor) – increased perfusion, pain (dolor) – factors stimulating nociceptors, loss of function (functio laesa)

CHEMICAL MEDIATORS OF INFLAMMATION I. Vasodilation Prostaglandins (PG..), nitric oxide (NO) Increased vascular permeability vasoactive amines (histamine, serotonin), C3a and C5a, bradykinin, leukotrienes (LT..), PAF Chemotaxic leukocyte activation C3a, C5a, LTB4, chemokines

CHEMICAL MEDIATORS OF INFLAMMATION II. Fever IL-1, IL-6, TNF, prostaglandins Pain prostaglandins, bradykinin Tissue damage neutrophil and macrophage products lysosomal enzymes oxygen radicals nitric oxide (NO)

MIGRATION OF NEUTROPHILS FROM BLOOD TO INFLAMMED TISSUE

MIGRATION OF NEUTROPHILS

Neutrophil Transendothelial Migration (Diapedesis)

ENDOTHELIAL ADHESION MOLECULES DURING INFLAMMATION (A) The extent of leukocyte adhesion and expression of adhesion molecules on endothelial cells before and after inflammation. (B) Endothelial adhesion molecules and the moieties to which they bind on leukocytes. (C) The changes over time in expression of particular endothelial adhesion molecules following endothelial stimulation. CHO, Carbohydrate; HIMECs, human intestinal microvascular endothelial cells. Part C Haraldsen G. et al. (1996). Cytokine-regulated expression of E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) in human intestinal microvascular endothelial cells. With information from The Journal of Immunology 156, 2558–2565.

PUS Pus = transudate (liquor puris) + dead pathogens + dead neutrophils + dead tissue cells Pus is a whitish-yellow, yellow, or yellow-brown exudate produced by vertebrates during inflammatory pyogenic bacterial infections. Pus consists of a thin, protein-rich fluid, known as liquor puris, and dead cells.

CONSEQUENCES OF MACROPHAGE ACTIVATION SYNTHESIS OF CYTOKINES

ACUTE-PHASE REACTION proinflammatory cytokines hypothalamic control of body temperature increased ‚set-point’ value fever

Mannose binding lectin/protein ACUTE PHASE REACTION IL-6 Complement Liver C-reactive protein (CRP) Mannose binding lectin/protein MBL/MBP Fibrinogen Stimulation and synthesis of positive acute-phase reactants during inflammation. Inflammation caused by infection or tissue damage stimulates the circulating inflammation-associated cytokines, including interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF)-. These cytokines stimulate hepatocytes to increase the synthesis and release of positive acute-phase proteins, including CRP. IL-6 is the major cytokine stimulus for CRP production. Serum amyloid protein (SAP) UNDER THE INFLUENCE OF IL-6 THE LIVER PRODUCES A BUNCH OF ACUTE-PHASE PROTEINS

ACUTE-PHASE RESPONSE

RESOLUTION OF ACUTE INFLAMMATION

SEPTIC SHOCK Result: Triggering factors : systemic infection (bacteraemia) microbial cell wall products and/or toxins released from the pathogens Result: Systemic activation of neutrophils and macrophages  High level of cytokine (TNF-alpha) production: „cytokine storm” Excessive inflammatory response

SEPTIC SHOCK The key molecule of the process: TNF-alpha TNF-alpha and other inflammatory cytokines multiorgan failure (MOF) is caused by the systemic vasodilation and hypoperfusion in shock and by multiple tromboses in DIC DIC capillar permeability blood pressure high fever multiorgan failure disseminated intravascular coagulation Therapy: anti-TNF-alpha antibody

DIC Disseminated Intravascular Coagulation pathologic activation of thrombotic process distress of thrombotic process, bleeding other causes: snake bite, septic abortion, acute obstetric complications, malignant tumors, leukemias Proinflammatory cytokines (IL-1, TNFα) and LPS/endotoxin leads to the release of Tissue Factor (TF) from cells which triggers the coagulation cascade. The complement system also has an effect on blood clothing.

DIC: Disseminated Intravascular Coagulation