Complement J. Ochotná. Complement humoral component of nonspecific immunity helps remove microorganisms and own altered cells (apoptotic cells)

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

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

Complement

Biological significance

Opsonization (C3b, C4b)

Chemotaxis (C3a, C5a)

Osmotic lysis (MAC C5b-C9)

Anaphylatoxins (C3a, C4a, C5a)

Riedemann N.C.

Pathways of complement activation

• Classical pathway

• Alternative pathway

• Lectin pathway

Classical and alternative pathway

Alternative complement pathway

C3 component of complement rarely spontaneously

breaks into C3b and C3a

C3b can covalently bind on the surface of a particle (own

cell, microorganism) or reacts with water, thereby

inactivates

to bound C3b joins a factor B, which is cleaved by

factor D to Ba and Bb, resulting complex C3bBb is

stabilized by factor P (properdin) and functions as

an alternative C3 convertase

Alternative complement pathway

C3 convertase cleaves C3 to C3a (chemotaxis)

and C3b, which binds to the surface of the

particles (opsonization), or gives rise to other C3

convertases

Alternative complement pathway

some C3 convertases form C3bBbC3b that act as

an alternative C5 convertase, which cleaves

C5 to C5a (chemotaxis) and C5b (starts terminal

lytic phase)

Alternative complement pathway

Alternative complement pathway

C5b starts terminal lytic phase

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

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

proteins)

after binding of antibodies to the bacteria

surface, Ab changes its conformation and than

can bind C1 protein

C1 changes its conformation and acquires

proteolytic activity, than cleaves C4 and C2

proteins

Classical complement pathway

fragments C4b and C2a bind to the surface of

microorganism and create the classic C3

convertase (C4bC2a), which cleaves C3 to C3a

and C3b

Classical complement pathway

Description of C3

convertase has

been modified to

C4bC2a

then creates a classic C5 convertase

(C4bC2aC3b) that cleaves C5 to C5a and C5b

Classical complement pathway

Lectin complement pathway

is initiated by serum mannose binding lectin (MBL)

MBL binds to mannose residues on the surface of

some microbes, after this binding starts cleave C4

and C2

this way is similar to the classical pathway

Lectin complement pathway

Terminal (lytic) phase of the complement cascade C5b fragments creates a complex with C6, C7 and C8,

the complex dive into the lipid membrane of the cell and

attache into a circle 13-18 molecules of C9 => MAC

(membrane attack complex), forms a transmembrane

channel, which causes osmotic lysis of the target cell

(G-bacteria, protozoans, some viruses).

Most microorganisms are resistant to this lytic effect of

complement (protection by cell wall).

Terminal phase of the complement cascade

Complement activation and efector functions

Complement regulation and protection of own cells

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

MCP DAF Protectin

Anaphylatoxin inactivator

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

factor S (vitronectin) – inhibits complex C5bC6

CD 59 (protectin) - prevents the polymerization of C9

anaphylatoxin inactivator (CPN)- inactivates

anafylatoxins (C3a, C4a, C5a)

Complement regulation

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

CR3, CR4 - on phagocytes

- participation in opsonization,

adhesion

C3aR, C5aR – receptors for anaphylatoxins

- mast cell activation

Complement receptors

4 basic complement functions

Opsonization (C3b, C4b)

Chemotaxis (C3a, C5a)

Osmotic lysis (MAC C5b-C9)

Anafylatoxins (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 (FcRI)

anafylatoxins (C3a, C4a, C5a)

TLR

Mast cell activation by cross-linking of IgE Fc receptors

Binding of IgE to highaffinnity Fc

receptor for IgE (FcRI)

Binding of multivalent antigen

(multicellular parasite) to IgE

Aggregation of several

molecules of FcRI

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

(TNF, 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, TNF, 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

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 - shares 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)

Biological:

biological heterogeneity

genetic and physiological disposition of the body

Properties of antigen

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)

• 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)

Superantigens

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 attentionThank you for your attention

• Komplement – klasická cestahttps://www.youtube.com/watch?v=vbWYz9XDtLw

• Komplement – klasická a alternativní cestahttps://www.youtube.com/watch?v=aNh5A0gtuLE

• Komplement – alternativní cestahttps://www.youtube.com/watch?v=qga3Wn76d9w

• Akutní záněthttps://www.youtube.com/watch?v=suCKm97yvyk