2941 Complement System
-
Upload
roja-lakshmi -
Category
Documents
-
view
232 -
download
1
Transcript of 2941 Complement System
-
8/3/2019 2941 Complement System
1/38
COMPLEMENT SYSTEMCOMPLEMENT SYSTEM
A.EVANGELINE CHRISTINAA.EVANGELINE CHRISTINA
11STST M.Sc Applied Microbiology,M.Sc Applied Microbiology,
The Presidency College.The Presidency College.
-
8/3/2019 2941 Complement System
2/38
DEFINITIONDEFINITION
It refers to a system of factors which occurIt refers to a system of factors which occur
in normal serum and are activatedin normal serum and are activated
characteristically by ANTIGENcharacteristically by ANTIGEN--ANTIBODYANTIBODYinteraction and subsequently mediate ainteraction and subsequently mediate a
number of biologically significantnumber of biologically significant
consequences.consequences.
-
8/3/2019 2941 Complement System
3/38
HistoryHistory
By the end of the 19By the end of the 19thth century,it was noted thatcentury,it was noted thatbactericidal, bacteriostatic and hemolytic action ofbactericidal, bacteriostatic and hemolytic action ofthe appropriate antibodies required thethe appropriate antibodies required the
participation of a heat labile component present inparticipation of a heat labile component present inthe normal serum of humans and animals.the normal serum of humans and animals.
Buchner 1Buchner 1stst observed the bactericidal effect ofobserved the bactericidal effect ofserum was destroyed by heating at 55 C for 1 hr.serum was destroyed by heating at 55 C for 1 hr.
Pfieffer observed that cholera vibrios were lysedPfieffer observed that cholera vibrios were lysedwhen injected intraperitonially into specificallywhen injected intraperitonially into specificallyimmunised guniea pigs(bacteriolysisimmunised guniea pigs(bacteriolysis--PfieffersPfieffersphenomenon).phenomenon).
-
8/3/2019 2941 Complement System
4/38
Bordet established that immunologicalBordet established that immunologicalbacteriolysis and hemolysis required 2 factorsbacteriolysis and hemolysis required 2 factors1.a heat stable antibody and1.a heat stable antibody and
2. a heat labile factor called Alexine.2. a heat labile factor called Alexine.
The name Alexine was now replaced asThe name Alexine was now replaced asCOMPLEMENT by Ehrlich as it complementedCOMPLEMENT by Ehrlich as it complementedthe action of the antibody.the action of the antibody.
Bordet and Gengou described the ComplementBordet and Gengou described the Complementfixation test, the serological test to detectfixation test, the serological test to detectcomplement.complement.
-
8/3/2019 2941 Complement System
5/38
The other immunological test to detectThe other immunological test to detect
complement is Immuno adherence test.complement is Immuno adherence test.
The system belongs to the group of BiologicalThe system belongs to the group of Biological
Effector Mechanism called as Triggered enzymeEffector Mechanism called as Triggered enzyme
cascade which also includes Coagulation,cascade which also includes Coagulation,
Fibrinolytic and Kinin system. They areFibrinolytic and Kinin system. They are
advantageous.advantageous. Ex;Each enzyme in the cascade is able to activateEx;Each enzyme in the cascade is able to activate
many molecules of the succeeding componentmany molecules of the succeeding component
providing for amplification of the response at eachproviding for amplification of the response at each
step.step.
-
8/3/2019 2941 Complement System
6/38
Every step has its own control mechanismsEvery step has its own control mechanisms
so that the cascade can be regulated withso that the cascade can be regulated with
precision.precision.
-
8/3/2019 2941 Complement System
7/38
PROPERTIESPROPERTIES
Present in the sera of all mammals and also in thatPresent in the sera of all mammals and also in thatof most lower animals including birds,amphibiansof most lower animals including birds,amphibiansand fishes.and fishes.
It is a nonIt is a non--specific serological reagent in thatspecific serological reagent in thatcomplement from 1 species can react withcomplement from 1 species can react withantibody from other species though, the efficiencyantibody from other species though, the efficiencyof the reaction is influenced by the taxonomicof the reaction is influenced by the taxonomic
distance between the species.distance between the species. Complement constitutes about 5% of normalComplement constitutes about 5% of normal
serum proteins and is not increased as a result ofserum proteins and is not increased as a result ofimmunisation.immunisation.
-
8/3/2019 2941 Complement System
8/38
Though some of its components are heat stable,Though some of its components are heat stable,
complement as a whole is heat labile.complement as a whole is heat labile.
It is denatured spontaneously slowly at RT andIt is denatured spontaneously slowly at RT and
being destroyed in 30 mins at serum thus deprivedbeing destroyed in 30 mins at serum thus deprived
of its complement activity is said to be inactivated.of its complement activity is said to be inactivated.
It ordinarily does not bind to free antigen orIt ordinarily does not bind to free antigen or
antibody but only to antibody which has combinedantibody but only to antibody which has combinedwith its antigen.with its antigen.
Though some of its components are heat stable,Though some of its components are heat stable,
complement as a whole is heat labile.complement as a whole is heat labile.
It is denatured spontaneously slowly at RT andIt is denatured spontaneously slowly at RT and
being destroyed in 30 mins at serum thus deprivedbeing destroyed in 30 mins at serum thus deprived
of its complement activity is said to be inactivated.of its complement activity is said to be inactivated.
It ordinarily does not bind to free antigen orIt ordinarily does not bind to free antigen or
antibody but only to antibody which has combinedantibody but only to antibody which has combinedwith its antigen.with its antigen.
-
8/3/2019 2941 Complement System
9/38
Fixation of the complement to the AgFixation of the complement to the Ag--AbAb
complex leads to the activation of classicalcomplex leads to the activation of classical
C pathway.C pathway. All classes of Ig do not fix C. Only IgM 3,1All classes of Ig do not fix C. Only IgM 3,1
and 2 fix C but not IgG4, IgD, IgA or IgE.and 2 fix C but not IgG4, IgD, IgA or IgE.
It binds at the Fc portion of the Ig molecule.It binds at the Fc portion of the Ig molecule. Fixation of C is not influenced by the natureFixation of C is not influenced by the nature
of Ag, but only by the class of the Ig.of Ag, but only by the class of the Ig.
-
8/3/2019 2941 Complement System
10/38
COMPONENTSCOMPONENTS
20 Chemically and Immunologically distinct serum20 Chemically and Immunologically distinct serumproteins comprising the complement components,proteins comprising the complement components,the Properdin system and the control proteins.the Properdin system and the control proteins.
It is a complex of 9 different fractions C1 to C9.It is a complex of 9 different fractions C1 to C9. C1 present in the serum as a calcium ionC1 present in the serum as a calcium ion
dependent complex, which on chelation withdependent complex, which on chelation withEDTA yields 3 protein subunits called as C1q, r s.EDTA yields 3 protein subunits called as C1q, r s.
So C is made up of 11 proteins totally.So C is made up of 11 proteins totally.
C fractions are named C1 to C9 in the sequenceC fractions are named C1 to C9 in the sequenceof the cascading reaction except that C4 comesof the cascading reaction except that C4 comesafter C1 and before C2.after C1 and before C2.
-
8/3/2019 2941 Complement System
11/38
Erythrocyte Antibody complex called as EA, theErythrocyte Antibody complex called as EA, theproduct is called as EAC, followed by theproduct is called as EAC, followed by thecomponents that have reacted ex. EAC14235 orcomponents that have reacted ex. EAC14235 or
EAC1EAC1--5.5. When C component acquires enzymatic or otherWhen C component acquires enzymatic or other
biological activity, it is indicated by a bar over thebiological activity, it is indicated by a bar over thecomponent number. ex: enzymatically activatedcomponent number. ex: enzymatically activated
C1 is shown as C1.C1 is shown as C1. When it is inactivated, it is indicated by a prefix iWhen it is inactivated, it is indicated by a prefix i
iC3b.iC3b.
Fragments cleaved indicated in small lettersFragments cleaved indicated in small letters
smaller fragment a, and a larger fragment b.smaller fragment a, and a larger fragment b.
-
8/3/2019 2941 Complement System
12/38
C ACTIVATIONC ACTIVATION
Activation of the C system initiated either byActivation of the C system initiated either by
AgAg--Ab complexes or by a variety of nonAb complexes or by a variety of non--
immunologic molecules.immunologic molecules.
-
8/3/2019 2941 Complement System
13/38
Sequential activation of C componentsSequential activation of C components
occur through 3 pathways namely:occur through 3 pathways namely:
-
8/3/2019 2941 Complement System
14/38
1.1. The Classical pathwayThe Classical pathway
2.2. The Alternative pathwayThe Alternative pathway
3.3. The Lectin pathwayThe Lectin pathway
-
8/3/2019 2941 Complement System
15/38
The classical pathwayThe classical pathway
It is named so because it was the 1It is named so because it was the 1stst to beto be
identifiedidentified
EA+C1 EAC1+C4 EAC14b+C2
C3+EAC14b2aEAC14b2a3bEAC14b2a3b5
b67
EAC14b2a3b5b6789 CYTOLYSIS
C1q,r,s
Ca+
C4a
Mg+ C2b
C3aC5,6,7
C8,9
c5aMAC
-
8/3/2019 2941 Complement System
16/38
Classical pathway consists of the followingClassical pathway consists of the following
steps;steps;
-
8/3/2019 2941 Complement System
17/38
Binding of C1 to AgBinding of C1 to Ag--Ab complex. The recognitionAb complex. The recognitionunit of C1 is C1q, which reacts with Fc piece ofunit of C1 is C1q, which reacts with Fc piece ofthe bound IgM or IgG. C1q binding in thethe bound IgM or IgG. C1q binding in the
presence of calcium ions leads to sequentialpresence of calcium ions leads to sequentialactivation of C1r, s.activation of C1r, s.
Activated C1s is an esterase. 1 molecule ofActivated C1s is an esterase. 1 molecule ofwhich can cleave several molecules of C4.C4 iswhich can cleave several molecules of C4.C4 is
split into C4a, which is an anaphylatoxin, andsplit into C4a, which is an anaphylatoxin, andC4b, which binds to cell membranes along withC4b, which binds to cell membranes along withC1.C1.
-
8/3/2019 2941 Complement System
18/38
C14b in the presence of Mg+ ions cleaves C2C14b in the presence of Mg+ ions cleaves C2into C2a, which remains bound to C4b and C2binto C2a, which remains bound to C4b and C2bis released. C4b2a has enzymatic activity and isis released. C4b2a has enzymatic activity and is
referred to as the CLASSICAL PATHWAY C3referred to as the CLASSICAL PATHWAY C3CONVERTASE.CONVERTASE.
C3 convertase splits C3 into 2 fragments: C3aC3 convertase splits C3 into 2 fragments: C3aan anaphylatoxin and C3b which remains cellan anaphylatoxin and C3b which remains cell
bound along with C4b2a and forms a tribound along with C4b2a and forms a tri--molecular complex C4b2a3b which hasmolecular complex C4b2a3b which hasenzymatic activity and is called C5enzymatic activity and is called C5CONVERTASE.CONVERTASE.
-
8/3/2019 2941 Complement System
19/38
THE MEMBRANE ATTACK phase of
complement activity begins at this stage
with C5 convertase cleaving C5 into C5a,an anaphylatoxin and C5b which
continues the cascade.
C6 and C7 then join to form C567 which
prepares the cell for lysis by C8 and C9
which join the reaction subsequently.
-
8/3/2019 2941 Complement System
20/38
Most of C567 escape and serve to amplify theMost of C567 escape and serve to amplify thereaction by adsorbing onto unsensitisedreaction by adsorbing onto unsensitisedbystander cells and rendering them susceptible tobystander cells and rendering them susceptible to
lysis by C8 and C9.lysis by C8 and C9. The unbound C567 has chemotactic activity.The unbound C567 has chemotactic activity.
The mechanism of complement mediatedThe mechanism of complement mediatedcytolysis is the production of HOLES on the cellcytolysis is the production of HOLES on the cell
membrane which disrupts the OSMOTICmembrane which disrupts the OSMOTICINTEGRITY of the membrane, leading to theINTEGRITY of the membrane, leading to therelease of the cell contents.release of the cell contents.
-
8/3/2019 2941 Complement System
21/38
The Alternative C PathwayThe Alternative C Pathway
It is a central process which involves theIt is a central process which involves the
activation of C3.activation of C3.
In the Classical Pathway, activation of C3 isIn the Classical Pathway, activation of C3 isachieved by C42.achieved by C42.
Activation of C3 without prior participation ofActivation of C3 without prior participation of
C142 is known as THE ALTERNATIVEC142 is known as THE ALTERNATIVEPATHWAY.PATHWAY.
-
8/3/2019 2941 Complement System
22/38
Example of the alternative pathway was theExample of the alternative pathway was thedemonstration by Pillemer of thedemonstration by Pillemer of thePROPERDIN SYSTEM as a group of serumPROPERDIN SYSTEM as a group of serum
proteins contributing to antiproteins contributing to anti--microbialmicrobialdefense without requiring specific antibody.defense without requiring specific antibody.
Activator ZYMOSAN, a polysaccharide fromActivator ZYMOSAN, a polysaccharide from
yeast cell wall. Other activators includeyeast cell wall. Other activators includeBactericidal endotoxin, IgA, IgD, cobraBactericidal endotoxin, IgA, IgD, cobravenom etc.venom etc.
-
8/3/2019 2941 Complement System
23/38
C3b activator complex is inactivated by 2C3b activator complex is inactivated by 2
protein factors H and I.protein factors H and I.
Bound C3b protected from such inactivationBound C3b protected from such inactivationinteracts with a magnesium dependentinteracts with a magnesium dependent
serum protein factor called Factor B which isserum protein factor called Factor B which is
called C3 Procalled C3 Pro--activator.activator.
-
8/3/2019 2941 Complement System
24/38
C3b+B C3bB+ Factor D (C3 proactivator
convertase)
P+C3bBb
Ba
Alternate
pathway C3convertase
stablize
Further steps in classical
pathway follows
-
8/3/2019 2941 Complement System
25/38
The Lectin PathwayThe Lectin Pathway
Lectins are proteins that recognize and bindLectins are proteins that recognize and bind
to specific carbohydrate targets (mannose).to specific carbohydrate targets (mannose).
Like Alternative pathway it does not dependLike Alternative pathway it does not dependon antibody for its activation, however theon antibody for its activation, however the
mechanism is more like that of classicalmechanism is more like that of classical
pathway, because after initiation it proceedspathway, because after initiation it proceeds
through the action of C4 and C2, to producethrough the action of C4 and C2, to produce
a C5 CONVRETASE.a C5 CONVRETASE.
-
8/3/2019 2941 Complement System
26/38
The Lectin pathway is activated by theThe Lectin pathway is activated by thebinding of mannose binding lectin (MBL) tobinding of mannose binding lectin (MBL) tomannose residues on glycomannose residues on glyco--proteins orproteins or
carbohydrates on the surface of microcarbohydrates on the surface of microorganisms.organisms.
MBL is an ACUTE PHASE PROTEINMBL is an ACUTE PHASE PROTEIN
produced in inflammatory response.produced in inflammatory response. Its function is similar to that of C1q which itIts function is similar to that of C1q which it
resembles in structure.resembles in structure.
-
8/3/2019 2941 Complement System
27/38
After MBL binds to the surface of a cell or aAfter MBL binds to the surface of a cell or a
pathogen, MBL assosiated serine proteases,pathogen, MBL assosiated serine proteases,
MASPMASP--1 and MASP1 and MASP--2, bind to MBL.2, bind to MBL.
The active complex formed by this associationThe active complex formed by this association
causes cleavage and activation of C4 and C2.causes cleavage and activation of C4 and C2.
The MASPThe MASP--1 and MASP1 and MASP--2 proteins have structural2 proteins have structural
similarity to C1r and C1s and mimic their activities.similarity to C1r and C1s and mimic their activities.
-
8/3/2019 2941 Complement System
28/38
This means of activating the C2This means of activating the C2--C4C4
components to form a C3 convertasecomponents to form a C3 convertase
without need for specific Ab bindingwithout need for specific Ab bindingrepresents an important innate defenserepresents an important innate defense
mechanism comparable to the alternativemechanism comparable to the alternative
pathway, but utilizing the elements of thepathway, but utilizing the elements of the
classical pathway except for the C1classical pathway except for the C1proteins.proteins.
-
8/3/2019 2941 Complement System
29/38
MBL binds
foreign surfaceMASP-1 AND 2 bind
MBL, generateactivated C1like
complex
Bind to activatedC1 & the cascade
continues
-
8/3/2019 2941 Complement System
30/38
REGULATIONREGULATION
Uncontrolled C activity can cause not onlyUncontrolled C activity can cause not only
exhaustion of the complement system butexhaustion of the complement system but
also serious damage to tissues.also serious damage to tissues. Several inbuilt control mechanisms regulateSeveral inbuilt control mechanisms regulate
the complement cascade at different steps.the complement cascade at different steps.
Regulation is by means of 2 mechanisms:Regulation is by means of 2 mechanisms:
-
8/3/2019 2941 Complement System
31/38
INHIBITORSINHIBITORS which halt the C activitywhich halt the C activity
INACTIVATORSINACTIVATORS which destroy C proteinswhich destroy C proteins
-
8/3/2019 2941 Complement System
32/38
InhibitorsInhibitors
Normal serum contains inhibitor of C1Normal serum contains inhibitor of C1esterase. This heat labile alphaesterase. This heat labile alphaneuraminoglycoprotein also inhibits manyneuraminoglycoprotein also inhibits many
other esterases found in blood such asother esterases found in blood such asPlasmin, Kininogen and the HagemanPlasmin, Kininogen and the Hagemanfactors.factors.
S protein in normal serum binds to C567S protein in normal serum binds to C567and modulates the cytolytic action of theand modulates the cytolytic action of themembrane attack complex.membrane attack complex.
-
8/3/2019 2941 Complement System
33/38
InactivatorsInactivators
A serum beta globulin called as factor I, providesA serum beta globulin called as factor I, provideshomeostatic control of C3 activation, particularlyhomeostatic control of C3 activation, particularlyby alternative pathway.by alternative pathway.
Factor H along with Factor I modulates C3Factor H along with Factor I modulates C3activation.activation.
Anaphylatoxin inactivator is an alpha globulin thatAnaphylatoxin inactivator is an alpha globulin thatenzymatically degrades C3a, C4a, and C5a whichenzymatically degrades C3a, C4a, and C5a whichare anaphylatoxins released during the Care anaphylatoxins released during the C
cascade.cascade. C4 binding protein controls the activity of cellC4 binding protein controls the activity of cell
bound C4b.bound C4b.
-
8/3/2019 2941 Complement System
34/38
Biological activityBiological activity
OPSONISATIONOPSONISATION Cells, AgCells, Ag--Ab complexesAb complexes
and other particles are phagocytosed muchand other particles are phagocytosed much
more efficiently in the presence of C3bmore efficiently in the presence of C3bbecause of the presence of C3b receptorsbecause of the presence of C3b receptors
on the surface of many phagocytes.on the surface of many phagocytes.
CHEMOTAXISCHEMOTAXIS C5a stimulates movementC5a stimulates movement
of neutrophils and monocytes towards sitesof neutrophils and monocytes towards sites
of Ag deposition.of Ag deposition.
-
8/3/2019 2941 Complement System
35/38
ANAPHYLATOXINSANAPHYLATOXINS C5a,C4a and C5aC5a,C4a and C5acan produce increased vascularcan produce increased vascularpermeability and smooth musclepermeability and smooth muscle
contraction. C3a and C5a also stimulatecontraction. C3a and C5a also stimulatemast cells to release Histamine.mast cells to release Histamine.
CYTOLYSISCYTOLYSIS Insertion of C56789 complexInsertion of C56789 complex
into the cell surface leads to killing or lysis ofinto the cell surface leads to killing or lysis ofmany types of cells, including Erythrocytes,many types of cells, including Erythrocytes,Bacteria and Tumor cells.Bacteria and Tumor cells.
-
8/3/2019 2941 Complement System
36/38
BIOSYNTHESIS OF CBIOSYNTHESIS OF C
Intestinal epitheliumIntestinal epithelium C1C1
MacrophagesMacrophages C2,C4C2,C4
SpleenSpleen C5,C8C5,C8LiverLiver C3,C6,C9C3,C6,C9
C4,C3,C5,C6C4,C3,C5,C6 some extent found in acutesome extent found in acute
phase of inflammationphase of inflammation
-
8/3/2019 2941 Complement System
37/38
DEFICIENCY OF C SYSTEMDEFICIENCY OF C SYSTEM
C1 inhibitor deficiencyC1 inhibitor deficiency heriditary angioneuroticheriditary angioneuroticedema (may be fatal)edema (may be fatal)
C2 deficiencyC2 deficiency serious pyogenic bacterial infectionserious pyogenic bacterial infection
Membrane attack complex deficiencyMembrane attack complex deficiency enhancesenhancessusceptibility to Neisserial infectionsusceptibility to Neisserial infection
Deficiency in components of the alternativeDeficiency in components of the alternativepathwaypathway ex: Properdin deficiency is associatedex: Properdin deficiency is associated
with greater susceptibility to Meningococcalwith greater susceptibility to Meningococcaldiseasedisease
C5 to C8C5 to C8 BacterimiaBacterimia
-
8/3/2019 2941 Complement System
38/38
Generalized deficiency of the complementGeneralized deficiency of the complement
components lead to the lack or impairmentcomponents lead to the lack or impairment
of nonof non--specific defense system of the body.specific defense system of the body.