Complement J. Ochotná

Complement humoral component of nonspecific immunity helps remove microorganisms and own altered cells (apoptotic cells) complement proteins are synthesized in the liver, less by tissue macrophages and fibroblasts

Complement system of about 30 serum and membrane proteins complement components are present in serum in inactive form complement activation has cascade character

Complement the main complement components: C1-C9 (C3 is the central component) other complement components: factor B, factor D, factor P regulatory proteins: C1 - inhibitor, factor I, factor H, C4bp, DAF, MCP, CR1, factor S (vitronectin), CD59 (protektin), anaphylatoxin inactivator

Pathways of complement activation Riedemann N.C. Classical pathway Alternative pathway Lectin pathway

Classical and alternative pathway

Complement activation and efector functions

Complement regulation and protection of own cells Activation of complement cascade is controlled by the plasma and membrane inhibitors. Anaphylatoxin inactivator DAF Protectin MCP

Complement regulation C1 inhibitor (C1-INH) – inhibits C1; if missing→ HAE factor I with cofactors: MCP (membrane cofactor protein), CR1, factor H – C3b, C4b cleavage DAF (decay-accelerating protein)-degradation of C3 and C5 convertase

Complement regulation factor S (vitronectin) – inhibits complex C5bC6 CD 59 (protectin) - prevents the polymerization of C9 anaphylatoxin inactivator (CPN)- inactivates anafylatoxins (C3a, C4a, C5a)

Complement receptors Bind fragments of complement components CR1 - on various cells - promotes C3b, C4b decay - stimulate phagocytosis - erythrocyte transport of immunecomplexes CR2 - on B lymphocytes and FDC - activation of B cells

Anaphylatoxin receptors Complement receptors CR3, CR4 - on phagocytes - participation in opsonization, adhesion Anaphylatoxin receptors C3aR, C5aR – receptors for anaphylatoxins - mast cell activation

Biological significance Opsonization (C3b, C4b) Chemotaxis (C3a, C5a) Osmotic lysis (MAC C5b-C9) Anaphylatoxins (C3a, C4a, C5a)

Basophils and mast cells and their importance in immune responses

Mast cells Mucosal mast cells - in the mucous membranes of respiratory and gastrointestinal tract, produce histamine, serotonin, heparin, tryptase, leukotriene C4 ..., participate in parasitosis and allergy Connective tissue mast cells – in the connective tissue, producing tryptase, chymase, prostaglandinD2 ..., are multiplicated in fibrosis, in parasitosis and allergy are not participating

Mast cell functions Defense against parasitic infections In pathological circumstances, responsible for the early type of hypersensitivity (immunopathological reaction type I) Apply during inflammation, in angiogenesis, in tissue remodeling

Mast cell activation Mast cells can be stimulated to degranulate by: cross-linking of IgE receptors (FcRI) anafylatoxins (C3a, C4a, C5a) TLR

Mast cell activation by cross-linking of IgE Fc receptors Binding of IgE to highaffinnity Fc receptor for IgE (FcRI) Binding of multivalent antigen (multicellular parasite) to IgE Aggregation of several molecules of FcRI

Mast cell activation Mast cell degranulate (cytoplasmic granules mergers with the surface membrane and release their contents) Activation of arachidonic acid metabolism (leukotriene C4, prostaglandin D2) Start of production of cytokines (TNF, TGF, IL-4, 5,6 ...)

Secretory products of mast cells Cytoplasmatic granules: hydrolytic enzymes, histamine, heparin, chondroitin sulphate, serotonin Histamine - vasodilation, ↑ vascular permeability (erythema, edema, itching), bronchoconstriction, ↑ intestinal peristalsis, ↑mucus secretion in the respiratory tract and GIT (helps eliminate the parasite) Arachidonic acid metabolites (leukotriene C4, prostaglandin D2) Cytokines (TNF, TGF , IL-4, 5,6 ...)

Basophils Differentiate from myeloid precursor Receptor equipment, content of granules, the mechanisms of stimulation and functions are very similar to mast cells Play a role in parasitic infections and allergies Basophil activation markers: CD 63, (CD 203)

Immune mechanisms of inflammation (Local and systemic reactions)

Inflammation Is a protective physiological response leading to protection against infection in damaged sites, localization of damage, elimination of necrotic cells and tissue repair.

Local body's response to inflammation Classical signs - pain (dolor), fever (calor), redness (rubor), swelling (tumor)

Inflammation The first signals for the development of inflammatory response come from mast cells, phagocytes, and the substances released from damaged cells and components of extracellular matrix. With longer duration of local inflammation are activated an antigen-specific mechanisms (T and B lymphocytes).

Inflammation

Inflammation – local reaction vasodilation, ↑ vascular permeability (histamine, serotonin, bradykinin, complement components C3a, C5a, leukotrienes , prostaglandins, …) → rednes, swelling ↑expression of adhesion molecules on endothelia (TNFa, IL-1) → leukocyte adhesion to the endothelium influence of local nerve endings via prostaglandins → pain Increased local temperature (IL-1, IL-6, TNF, prostaglandins)

Inflammation - systemic reaction Leukocytosis Fever (TNF, IL-1, IL-6, IFN ) ↑ tissue metabolism ↑ mobility of leukocytes ↑ formation of IFN, cytokines, Ig ↑ expression of Hsp Acute phase proteins (IL-6, TNFa, IL-1) CRP, SAP - opsonization and complement activation

Inflammation - systemic reaction Septic shock - the massive penetration of microorganisms into the bloodstream (TNF) Anaphylactic shock - basophil and mast cells activation with allergen (histamine)

Tissue repair elimination of damaged cells with phagocytes activation of fibroplastic mechanisms activation of angiogenesis regeneration and tissue remodeling TGF b

Antigens

Antigen (immunogen) substance which provokes specific immune response usually proteins or polysaccharides (lipids and nucleic acids only in the combination with proteins or polysaccharides) molecules > 5 kDa (optimal size of the antigen molecules is about 40 kDa)

Hapten small molecules, that are able to induce specific immune response only after the attachment to the macromolecular carrier separate haptens are not immunogenic typically drugs (eg penicillin antibiotics, hydralazin)

Epitope (antigenic determinant) part of the antigen which is recognized by immune system (lymphocytes- BCR, TCR, Ig) cross-reactive antigens - share one or more identical or similar epitopes

Interaction antigen – antibody Binding site of antibody (paratop) form non-covalent complexes with the corresponding part on antigen molecule (epitope) participation: the hydrogen bonds, electrostatic and hydrophobic interactions, van der Waals forces antigen-antibody complex is reversible

Antigen endogenous antigens - autoantigens (self Ag) exogenous antigens - foreign substances from the environment allergen is exoantigen that in the susceptible individuals can cause pathological (allergic) immune response

Properties of antigen immunogenicity proteins> carbohydrates> macromolecule complexes (glycoproteins, nucleoproteins, and glycolipids)> lipids specificity

Factors affecting immunogenicity Physical: solubility - insoluble Ag more immunogenic molecular weight - ideal 5-40 kDa Chemical: structure - the number of determinants degradability - "ease" of uncovering the determinants in antigen presenting cells (APC cell)

Properties of antigen Biological: biological heterogeneity genetic and physiological disposition of the body

Degree of foreignness Autogeneic - antigens of the same individual Syngeneic - antigens of genetically identical individuals (eg twins) Allogeneic (alloantigens) - antigens genetically different individuals of the same species Xenogeneic (heterologous) - antigens derived from individuals of different species (eg monkey kidney transplant man)

Types of antigens according to antigen presentation T- dependent antigens T- independent antigens

Thymus dependent antigens more frequently, mostly protein Ag for specific humoral immune response to antigen is necessary assistance of TH lymphocytes (or response isn´t enough effective) assistance implemented in the form of cytokines produced by TH lymphocytes

T- independent antigens can stimulate B cells directly mainly bacterial polysaccharides, lipopolysaccharides and polymer forms of proteins (e.g. Haemophilus, Str.pneumoniae)

T-independent pathway

Superantigens stimulate T cells polyclonaly and massively (massive cytokine release) massive activation of T cells can cause shock e.g. bacterial toxins (Staph.aureus, Str.pyogenes, Pseud.aeruginosa)

Superantigens Proteins (microbial products) which have 2 binding sites, one interacts with the epitope presented on all MHCgpII, second interacts with other structures presented in many different TCR molecules (connection of T lymphocyte with APC)

Differcence between antigen and superantigen binding

Sequestered antigens autoantigens, that are normally hidden to immune system and therefore unknow (e.g. brain, the lens of the eye , testes) if they are "uncovered" by demage, exposed to the immune system, are recognized as foreign (one of the theories of autoimmune processes)

Immunologically privileged sites brain, eye, gonads are protected from potentially damaging inflammatory immune responses this tissues are far less rejected in allogeneic transplant (cornea) this privileged position is not absolute

Immunologically privileged sites Mechanisms of protection from the immune system: isolation from the immune system (blood-brain barrier) preferences of Th2 and suppression of Th1-response production of immunosuppressive cytokines (TGFβ) FasL expression -active protection against effector T-lymphocytes increased expression of membrane complement inhibitors

Thank you for your attention

Complement – clasical pathway https://www. youtube. com/watch Complement – alternative pathway https://www.youtube.com/watch?v=qga3Wn76d9w Mast cells https://www.youtube.com/watch?v=MoM5JY_EeRo Acute inflammation https://www.youtube.com/watch?v=suCKm97yvyk