ComplementComplement

J. Ochotná

ComplementComplement

system of about 30 serum and membrane proteins system of about 30 serum and membrane proteins (humoral component of nonspecific immunity) (humoral component of nonspecific immunity)

complement components in serum are present in complement components in serum are present in inactive forminactive form

complement activation has cascade charactercomplement activation has cascade character

complement proteins are synthesized in the liver, less complement proteins are synthesized in the liver, less by tissue macrophages and fibroblastsby tissue macrophages and fibroblasts

the main complement componentsthe main complement components: C1-C9 (C3 is the : C1-C9 (C3 is the central component)central component)

other complement componentsother complement components: factor B, factor D, : factor B, factor D, factor Pfactor P

regulatory proteinsregulatory proteins: C1 - inhibitor, factor I, factor H, : C1 - inhibitor, factor I, factor H, C4bp, DAF, MCP, CR1, factor S (vitronectin), CD59 C4bp, DAF, MCP, CR1, factor S (vitronectin), CD59 (protektin), inactivator of anafylatoxin(protektin), inactivator of anafylatoxin

Functions of complementFunctions of complement

OpsonizationOpsonization (C3b, C4b) (C3b, C4b)

ChemotaxisChemotaxis (C3a, C5a) (C3a, C5a)

Osmotic lysisOsmotic lysis (MAC C5b-C9) (MAC C5b-C9)

AnafylatoxinsAnafylatoxins (C3a, C4a, C5a) (C3a, C4a, C5a)

Complement activationComplement activation

Alternative pathwayAlternative pathway

Classical pathwayClassical pathway

Lektin pathwayLektin pathway

Riedemann N.C.

Alternative pathwayAlternative pathway C3C3 component of complement rarely spontaneously breaks component of complement rarely spontaneously breaks

into C3b and C3ainto C3b and C3a

C3b can covalently bind on the surface of a particle (own C3b can covalently bind on the surface of a particle (own cell, microorganism) or reacts with water and inactivate cell, microorganism) or reacts with water and inactivate

to bound C3b joins a factor B, which is cleaved by factor D to bound C3b joins a factor B, which is cleaved by factor D to Ba and Bb, resulting complex C3bBb is stabilized by to Ba and Bb, resulting complex C3bBb is stabilized by factor P and functions as an factor P and functions as an alternative C3 convertasealternative C3 convertase

C3 convertase cleaves C3 to C3a (chemotactic for C3 convertase cleaves C3 to C3a (chemotactic for phagocytes) and C3b, which binds to the surface phagocytes) and C3b, which binds to the surface of the particles (opsonization), or gives rise to of the particles (opsonization), or gives rise to other C3 convertasesother C3 convertases

from some C3 convertases form C3bBbC3b that from some C3 convertases form C3bBbC3b that act as an act as an alternative C5 convertasealternative C5 convertase, which cleaves , which cleaves C5 to C5a (chemotaxis) and C5b (starts terminal C5 to C5a (chemotaxis) and C5b (starts terminal lytic phase)lytic phase)

Alternative pathwayAlternative pathway

Classical pathwayClassical pathway can be initiated by antibodies IgG ( not by IgG4) can be initiated by antibodies IgG ( not by IgG4)

and IgM or by pentraxins (CRP, SAP - acute and IgM or by pentraxins (CRP, SAP - acute phase proteins)phase proteins)

after binding of antibodies to the bacteria after binding of antibodies to the bacteria surface, change its conformation and than can surface, change its conformation and than can bind C1 proteinbind C1 protein

C1 than change its conformation and get C1 than change its conformation and get proteolytic activity, than cleaves C4 and C2proteolytic activity, than cleaves C4 and C2proteinsproteins

fragments C4b and C2a bind to the surface of fragments C4b and C2a bind to the surface of microorganism and create the microorganism and create the classic C3 classic C3 convertaseconvertase (C4bC2a), which cleaves C3 to C3a (C4bC2a), which cleaves C3 to C3a and C3band C3b

then creates a then creates a classic C5 convertaseclassic C5 convertase (C4bC2aC3b) that cleaves C5 to C5a and C5b(C4bC2aC3b) that cleaves C5 to C5a and C5b

Zde dřívější nomenklatura – záměna 2a za 2b

Lectin pathwayLectin pathway

is initiated by serum mannose binding lectin (MBL)is initiated by serum mannose binding lectin (MBL)

MBL binds to carbohydrate structures on the MBL binds to carbohydrate structures on the surface of some microbes, after the binding starts surface of some microbes, after the binding starts cleave C4 and C2cleave C4 and C2

this way is similar to the classical pathwaythis way is similar to the classical pathway

Terminal (lytic) phase Terminal (lytic) phase of the complement cascadeof the complement cascade

C5bC5b fragments creates a complex with C6, C7 fragments creates a complex with C6, C7 and C8, the complex dive into the lipid and C8, the complex dive into the lipid membrane of the cell and attached to it into a membrane of the cell and attached to it into a circle 13-18 molecules of C9 (circle 13-18 molecules of C9 (MACMAC – membrane – membrane attack complex), thus create in the membrane attack complex), thus create in the membrane pores and cell can lysis pores and cell can lysis (G-bacteria, protozoans, some viruses). (G-bacteria, protozoans, some viruses).

Most microorganisms are resistant to this lytic Most microorganisms are resistant to this lytic effect of complement (protection by cell wall).effect of complement (protection by cell wall).

Regulation of complement and Regulation of complement and protection of own cellsprotection of own cells

Activation of complement cascade is controlled Activation of complement cascade is controlled by the plasma and membrane inhibitors.by the plasma and membrane inhibitors.

C1 inhibitorC1 inhibitor ( (C1-INH – inhibits C1, C1-INH – inhibits C1, when the when the deficit → HAE )deficit → HAE )

DAFDAF (decay-accelerating protein)-degradation of (decay-accelerating protein)-degradation of C3 and C5 convertaseC3 and C5 convertase

factor I, MCPfactor I, MCP (membrane cofactor protein), (membrane cofactor protein), CR1, factor HCR1, factor H – C3b cleavage – C3b cleavage

factor Sfactor S (vitronectin) – inhibits complex C5bC6 (vitronectin) – inhibits complex C5bC6

CD 59CD 59 (protectin) - prevents the polymerization (protectin) - prevents the polymerization of C9 of C9

inactivator of anafylatoxinsinactivator of anafylatoxins - inactivates - inactivates anafylatoxins (C3a, C4a, C5a)anafylatoxins (C3a, C4a, C5a)

Complement receptorsComplement receptors Bind fragments of complement componentsBind fragments of complement components

CR1CR1 - on various cells - on various cells - removing of immunecomplexes - removing of immunecomplexes

CR2CR2 - on B lymphocytes and FDC - on B lymphocytes and FDC - activation of B cells - activation of B cells

CR3, CR4CR3, CR4 - on phagocytes - on phagocytes - participation in opsonization, adhesion - participation in opsonization, adhesion

4 basic complement functions4 basic complement functions

OpsonizationOpsonization (C3b, C4b) (C3b, C4b)

ChemotaxisChemotaxis (C3a, C5a) (C3a, C5a)

Osmotic lysisOsmotic lysis (MAC C5b-C9) (MAC C5b-C9)

AnafylatoxinsAnafylatoxins (C3a, C4a, C5a) (C3a, C4a, C5a)

AntigensAntigens

Antigen (immunogen)Antigen (immunogen) substance that the immune system recognizes and substance that the immune system recognizes and

responds to itresponds to it

usually proteins or polysaccharides (lipids and nucleic usually proteins or polysaccharides (lipids and nucleic acids only in the combination with proteins or acids only in the combination with proteins or polysaccharides)polysaccharides)

molecules <5 kDa can´t trigger an immune response, molecules <5 kDa can´t trigger an immune response, the optimal size of the antigen molecules to initiate the optimal size of the antigen molecules to initiate immune response is about 40 kDaimmune response is about 40 kDa

HaptenHapten

small molecules, that are able to induce specific small molecules, that are able to induce specific immune response only immune response only after the establishment after the establishment to the macromolecular carrierto the macromolecular carrier

separate haptens are not immunogenicseparate haptens are not immunogenic

typically drugs (eg penicillin antibiotics, typically drugs (eg penicillin antibiotics, hydralazin)hydralazin)

EpitopeEpitope

= a part of the antigen which is recognized = a part of the antigen which is recognized by immune system (lymphocytes- BCR, by immune system (lymphocytes- BCR, TCR, Ig)TCR, Ig)

cross-reactive antigens - shares one or cross-reactive antigens - shares one or more identical or similar epitopesmore identical or similar epitopes

Interaction antigen – antibodyInteraction antigen – antibody

Binding site of antibody (Binding site of antibody (paratopparatop) ) form non-covalent complexes with form non-covalent complexes with the corresponding part on antigen the corresponding part on antigen molecule (molecule (epitopeepitope))

participation: the hydrogen bonds, participation: the hydrogen bonds, electrostatic and hydrophobic electrostatic and hydrophobic interactions, van der Waals forcesinteractions, van der Waals forces

antigen-antibody complex is reversibleantigen-antibody complex is reversible

AntigenAntigen

endogenous antigensendogenous antigens - autoantigens (self Ag) - autoantigens (self Ag)

exogenous antigensexogenous antigens - foreign substances from - foreign substances from the environmentthe environment

allergen is exoantigen that in the susceptible allergen is exoantigen that in the susceptible individualsindividuals can cause pathological (allergic) can cause pathological (allergic) immune responseimmune response

Antigen featuresAntigen features

immunogenicityimmunogenicity

proteins> carbohydrates> macromolecule proteins> carbohydrates> macromolecule complexes (glycoproteins, nucleoproteins, and complexes (glycoproteins, nucleoproteins, and glycolipids)> lipidsglycolipids)> lipids

specificityspecificity

Factors affecting the immunogenicityFactors affecting the immunogenicity

Physical:Physical:solubility - insoluble more immunogenicsolubility - insoluble more immunogenicmolecular weight - ideal 5-40 kDamolecular weight - ideal 5-40 kDa

Chemical:Chemical:structure - the number of determinantsstructure - the number of determinantsdegradability - "ease" of uncovering the determinants in degradability - "ease" of uncovering the determinants in antigen presenting cells (APC cell)antigen presenting cells (APC cell)

Biological:Biological:biological heterogeneitybiological heterogeneitygenetic and physiological disposition of the body genetic and physiological disposition of the body

Degree of foreignnessDegree of foreignness

AutogeneicAutogeneic - antigens of the same individual - antigens of the same individual

SyngeneicSyngeneic - antigens of genetically identical - antigens of genetically identical individuals (eg twins)individuals (eg twins)

AllogeneicAllogeneic (alloantigens) - antigens genetically (alloantigens) - antigens genetically different individuals of the same speciesdifferent individuals of the same species

XenogeneicXenogeneic (heterologous) - antigens derived (heterologous) - antigens derived from individuals of different species from individuals of different species (eg monkey (eg monkey kidney transplant man) kidney transplant man)

Types of antigens according to Types of antigens according to antigen presentationantigen presentation

thymus dependent antigensthymus dependent antigens

thymus independent antigensthymus independent antigens

Thymus dependent antigensThymus dependent antigens

more frequently, mostly protein Agmore frequently, mostly protein Ag

for specific humoral immune response to antigen for specific humoral immune response to antigen is necessary to cooperate with Tis necessary to cooperate with THH lymphocytes lymphocytes

(or response isn´t enough effective)(or response isn´t enough effective)

assistance implemented in the form of cytokines assistance implemented in the form of cytokines produced by Tproduced by THH lymphocytes lymphocytes

Thymus independent antigensThymus independent antigens

in a small number of antigens can be induced in a small number of antigens can be induced antibodies production directly without the antibodies production directly without the participation of T lymphocytesparticipation of T lymphocytes

mainly bacterial polysaccharides, mainly bacterial polysaccharides, lipopolysaccharides and polymer forms of lipopolysaccharides and polymer forms of proteins (e.g. Haemophilus, Str.pneumoniae)proteins (e.g. Haemophilus, Str.pneumoniae)

SuperantigensSuperantigens

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

stimulate polyclonaly and massively stimulate polyclonaly and massively

massive activation of T lymphocytes can cause shockmassive activation of T lymphocytes can cause shock

e.g. bacterial toxins (Staph.aureus, Str.pyogenes, e.g. bacterial toxins (Staph.aureus, Str.pyogenes, Pseud.aeruginosa) Pseud.aeruginosa)

Differcence between antigen and superantigen bindingDiffercence between antigen and superantigen binding

Sequestered Sequestered antigensantigens

autoantigens that are normally hidden to autoantigens that are normally hidden to immune system and therefore unknow (e.g. immune system and therefore unknow (e.g. brain, the lens of the eye , testes)brain, the lens of the eye , testes)

if they are "uncovered" by demage, exposed to if they are "uncovered" by demage, exposed to the immune system, are recognized as foreign the immune system, are recognized as foreign (one of the theories of autoimmune processes)(one of the theories of autoimmune processes)

Immunologically privileged sitesImmunologically privileged sites brain, eye, gonadsbrain, eye, gonads

are protected from potentially damaging are protected from potentially damaging inflammatory immune responsesinflammatory immune responses

this tissues are far less rejected in allogeneic this tissues are far less rejected in allogeneic transplant (cornea)transplant (cornea)

this privileged position is not absolute this privileged position is not absolute

Immunologically privileged sitesImmunologically privileged sites

Mechanisms of protection from the immune Mechanisms of protection from the immune system:system: isolation from the immune system (blood-brain barrier)isolation from the immune system (blood-brain barrier) preferences of Th2 and suppression of Th1-responsepreferences of Th2 and suppression of Th1-response active protection against effector T-lymphocytesactive protection against effector T-lymphocytes production of immunosuppressive cytokines (TGFβ)production of immunosuppressive cytokines (TGFβ) FasL expressionFasL expression iincreased expression of membrane complement ncreased expression of membrane complement

inhibitinhibitors ors

Thank you for your attentionThank you for your attention