Complement J Ochotn Complement humoral component of nonspecific

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: C 1 -C 9 (C 3 is the central component) § other complement components: factor B, factor D, factor P § regulatory proteins: C 1 - inhibitor, factor I, factor H, C 4 bp, DAF, MCP, CR 1, factor S (vitronectin), CD 59 (protektin), anaphylatoxin inactivator

Pathways of complement activation • Classical pathway • Alternative pathway • Lectin pathway Riedem ann N. C.

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 MCP DAF Protectin

Complement regulation § C 1 inhibitor (C 1 -INH) – inhibits C 1; if missing→ HAE § factor I with cofactors: MCP (membrane cofactor protein), CR 1, factor H – C 3 b, C 4 b cleavage § DAF (decay-accelerating protein)-degradation of C 3 and C 5 convertase

Complement regulation § factor S (vitronectin) – inhibits complex C 5 b. C 6 § CD 59 (protectin) - prevents the polymerization of C 9 § anaphylatoxin inactivator (CPN)- inactivates anafylatoxins (C 3 a, C 4 a, C 5 a)

Complement receptors § Bind fragments of complement components § CR 1 - on various cells - promotes C 3 b, C 4 b decay - stimulate phagocytosis - erythrocyte transport of immunecomplexes § CR 2 - on B lymphocytes and FDC - activation of B cells

Complement receptors § CR 3, CR 4 - on phagocytes - participation in opsonization, adhesion Anaphylatoxin receptors § C 3 a. R, C 5 a. R – receptors for anaphylatoxins - mast cell activation

Biological significance § Opsonization (C 3 b, C 4 b) § Chemotaxis (C 3 a, C 5 a) § Osmotic lysis (MAC C 5 b-C 9) § Anaphylatoxins (C 3 a, C 4 a, C 5 a)

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 C 4. . . , participate in parasitosis and allergy § Connective tissue mast cells – in the connective tissue, producing tryptase, chymase, prostaglandin. D 2. . . , 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 Ig. E receptors (Fc RI) § anafylatoxins (C 3 a, C 4 a, C 5 a) § TLR

Mast cell activation by cross-linking of Ig. E Fc receptors § Binding of Ig. E to highaffinnity Fc receptor for Ig. E (Fc RI) § Binding of multivalent antigen (multicellular parasite) to Ig. E § 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 C 4, prostaglandin D 2) § 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 C 4, prostaglandin D 2) § 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 C 3 a, C 5 a, 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

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 k. Da (optimal size of the antigen molecules is about 40 k. Da)

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 k. Da § 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 MHCgp. II, 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 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 Th 2 and suppression of Th 1 -response § production of immunosuppressive cytokines (TGFβ) § Fas. L 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? v=vb. WYz 9 XDt. Lw • Complement – alternative pathway https: //www. youtube. com/watch? v=qga 3 Wn 76 d 9 w • Mast cells https: //www. youtube. com/watch? v=Mo. M 5 JY_Ee. Ro • Acute inflammation https: //www. youtube. com/watch? v=su. CKm 97 yvyk