The complement The complement systemsystem

Evy Sulistyoningrum

Outlines Components of complement

systemComplement system activationEffector mechanism of

complement systemRegulation of complement

system activityComplement abnormality-related

disease

Introduction Introduction Jules Bordet

◦Heat labile protein → inactive at 56°C for 30 min◦Augments opsonization and bacterial

killing by antibody→ complement

Definition:A group of protein which possess enzymatic property, they interact with one to another attending specific and non-specific immune reponse.

Complement proteinComplement proteinProduced by:

◦ Hepatocytes◦ Monocyte/Macrophage◦ Fibroblasts◦ Endothelial◦ Reproductive◦ Adipocytes◦ Astrocytes

Stored in inactive form (proenzyme)2 form:

◦ Soluble: C1q, C1r, C1s, C2-C9, Factor B, D, H◦ Membrane bound: CR1, C3aR, DAF, MCP

Components of complement Components of complement systemsystemIntrinsic components: main component in

complement cascadeEx: C1-C9, MBL, MASP, Factor B, Factor D

Regulatory proteinsEx: C1 inhibitor, C4-binding protein, Factor H, DAF (Decay-accelerating factor), MCP (Membrane cofactor protein), etc

Complements receptorsEx: CR1, CR2, C3aR, etc

How the complements How the complements work?work?Enzymatic cascadeActivation:

◦Classical pathway◦Lectin pathway◦Alternative pathway

Effector phase:◦Recruitment of inflammatory and

immunocompetent cells◦Opsonization◦Pathogen killing

How the complements How the complements work?work?

Complement activationComplement activationClassical pathways: antigen-

antibody complexMBL pathway: interaction of

microbial carbohydrates with mannose binding lectin (MBL) in the plasma and tissue fluids.

Alternative pathway: spontaneously cleavage C3 → C3b binding to microbial surfaces and to antibody molecules

Complement activationComplement activation

CCLLAASSSSIICCAALL

PPAATTHHWWAAYY

Trigerring substance: Ag-Ab complexComponents: C1 (C1q, C1r, C1s), C2-C9

Classical pathway: Classical pathway: processprocess

◦Recognition step Binding of C1q to Ag-Ab complexes Autocatalysis of C1r → altered C1r cleaves

C1s→ active C1s capable of cleaving both C4 and C2 (C4-C2 convertase)

◦Activation step Activated C1s cleaves C4  into C4a and

C4b C4b bind to C2 Activated C1s cleaves C2  into C2a and

C2b forming C4b2a complex (C3 convertase)

Classical pathway: Classical pathway: activationactivation

Classical pathway: Classical pathway: activationactivation

Classical pathway: Classical pathway: activationactivation

Classical pathway: Classical pathway: activationactivation

MMBBLL

PPAATTHHWWAAYY

Triggering substance : interaction of microbial carbohydrates with mannose binding lectin (MBL) in the plasma and tissue fluids

Components: MBL, MASP1, MASP2, C2-C9

Process:◦ Recognition step

Mannan-binding lectin (MBL) binds mannose of bacteria and interacts with serine protease resulting in MBL-associated serine protease (MASP)

MASP2 is analogous to C1r and C1s and leads to cleaving of C4 and C2.

◦ Activation step ≈ Classical pathway

AAL L TTEERRNNAATTIIVVEE

PPAATTHHWWAAYY

Trigerring substance: LPS, endotoxin, etcComponents: C3,C5~C9, factor B, factor D,

factor P

Cont’d…Cont’d…Process:

◦ Spontaneous activation of C3 C3 is hydrolyzed producing C3(H2O) C3b bind to factor B Factor B is cleaved by Factor D to

produce C3bBb complex (C3 convertase)

◦ Stabilization of C3 convertase C3b or C3bBb need a suitable stabilizing

membrane or molecule (C3 activator) Bacteria or their products (LPS, etc),

factor P (properdin)

AAL L TTEERRNNAATTIIVVEE

PPAATTHHWWAAYY

Alternative pathway: Alternative pathway: activationactivation

Alternative pathway: Alternative pathway: activationactivation

Cont’d…Cont’d…

Cont’d…Cont’d…

Cont’d…Cont’d…

Cont’d…Cont’d…

Cont’d…Cont’d…

Cont’d…Cont’d…

Complement activationComplement activation

Late events on complement Late events on complement cascadecascadeForming C5 convertase:Forming C5 convertase:

C3 convertase cleaves C3 into C3a and C3bClassical& MBL pathwaysC3b binds to the C4b2a complex →

C4b2a3b complex (C5 convertase)

Alternative pathways C3b binds to C3bBb complex → C3b2Bb

complex (C5 convertase)C5 convertase will cleave C5 into C5a and C5b

Forming C5 convertaseForming C5 convertaseC4b2a

Cont’d…Cont’d…Lytic terminal sequence: MAC

C5 convertase cleaves C5 into C5a and C5bC5b binds the membrane and C6 and C7→

C5b67 complex which attaches quickly to the cell membrane.

C8 binds to this complex form C5b678 and inserts to the plasma membrane

C9 binds to C5b678 molecules and polymerizeC5b6789 complex = MAC (Membrane

attack complex) → formation of a hole in the membrane → cell lysis

Lytic terminal sequence: Lytic terminal sequence: MACMAC

Membrane attack complexMembrane attack complex

Complement-Mediated Lysis of E. coliAlive Killed

Complement’s movie movie

Complement components on Complement components on late eventslate events

Effector activity of Effector activity of complementscomplements

Cell lysis◦ MAC mediates lysis of target cell

Opsonization◦ C3b and C5a attach to CR on phagocytic cells and

promote phagocytosisMediating inflammation response

◦ Anaphylatoxins (C4a, C3a,C5a) : basophil/mast cell degranulation → dilatation of blood vessels, contraction of smooth muscles

◦ Chemotactic factors : attract neutrophils and phagocytes

◦ Induce cytokine release, adhesion molecule and acute phase protein expression

◦

OOPPSSOONNIIZ Z AATT IIOONN

Small complement fragments (C3a, C4a and C5a) induce local inflammatory response

IINNFFLLAAMMM M AATTOORRYY

EEFFFFEECCTT

Complement ReceptorsComplement Receptors

Figure 2-19Figure 2-19

Self regulation◦Spontaneous decay of complement

components C3b, C4b, C5b; C3 convertase, C5 convertase

◦Limited half-life for the convertases

Effect of regulative factors

COMPLEMENT COMPLEMENT REGULATIONREGULATION

Effect of regulative Effect of regulative factorsfactors

Effect of regulative Effect of regulative factorsfactors

Effect of regulative Effect of regulative factorsfactors

Effect of regulative Effect of regulative factorsfactors

Complement deficienciesComplement deficienciesActivation components

◦Classical pathway : C2 & C4 deficiencies : defects in clearing

immune complex, ex: SLE C3 deficiencies: frequent pyogenic

bacterial◦Alternative pathway

Properdin & factor D : increase susceptibility to pyogenic bacterial

◦MBL Some immunodeficiency patients

Terminal complement componentsC5, C6, C7, C8, C9: recurrent bacterial

infections (N. Meningitidis, N. Gonorrhoea)Regulatory Components

◦ C1-Inhibitor deficiency: Hereditary Angioneurotic Edema

◦ DAF, CD59: Paroxysmal Nocturnal Haemoglobinuria

Receptors◦ CR1: SLE◦ CR3, CR4: Leucocyte adhesion deficiency

recurrent threatening bacterial infection

Complement deficienciesComplement deficiencies

Hereditary Angioneurotic Hereditary Angioneurotic EdemaEdema

Terima kasih………..Terima kasih………..

Referensi Referensi Murphy K, Travers P, Walport M,

Janeway’s Immunobiology, 7th edAbbas AK dan Lichtman AH, Basic

ImmnunologyRoitt, IM., Delves, PJ, Roitt’s

Essential ImmunologyBurmester, Colour Atlas of

Immunology