1. Complement
J. Ochotná

2. Complement
system of about 30 serum and membrane proteins (humoral component of nonspecific immunity)
complement components in serum are present in inactive form
complement activation has cascade character

3. complement proteins are synthesized in the liver, less by tissue macrophages and fibroblasts
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), inactivator of anafylatoxin

4. Functions of complement
Opsonization (C3b, C4b)
Chemotaxis (C3a, C5a)
Osmotic lysis (MAC C5b-C9)
Anafylatoxins (C3a, C4a, C5a)

5. Complement activation
Alternative pathway
Classical pathway
Lektin pathway

6. Riedemann N.C.

7. Alternative 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 and inactivate
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 and functions as an alternative C3 convertase

8. C3 convertase cleaves C3 to C3a (chemotactic for phagocytes) and C3b, which binds to the surface of the particles (opsonization), or gives rise to other C3 convertases
from some C3 convertases form C3bBbC3b that act as an alternative C5 convertase, which cleaves C5 to C5a (chemotaxis) and C5b (starts terminal lytic phase)

9. Classical pathway
can be initiated by antibodies (IgG, not by IgG4; IgM) or so-called pentraxins (CRP, SAP - acute phase proteins)
after binding of antibodies to the bacteria surface, there is a change in its conformation and C1 protein can bind
C1 have to bind to the 2 molecules of antibodies, change their conformation and get proteolytic activity - will cleave proteins C4 and C2

15. fragments C4b and C2a bind to the surface of organism and create the classic C3 convertase (C4bC2a), which cleaves C3 to C3a and C3b
then creates a classic C5 convertase (C4bC2aC3b) that cleaves C5 to C5a and C5b

16. Zde dřívější nomenklatura – záměna 2a za 2b

19. Lectin pathway is initiated by serum mannose binding lectin (MBL)
MBL binds to carbohydrate structures on the surface of some microbes, after the binding starts cleave C4 and C2
this way is similar to the classical pathway

20. 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 attached to it into a circle molecules of C9 (MAC – membrane attack complex), thus create in the membrane pores and cell can lysis (G-bacteria, protozoans, some viruses).
Most microorganisms are resistant to this lytic effect of complement (protection by cell wall).

26. Regulation of complement and protection of own cells
Activation of complement cascade is controlled by the plasma and membrane inhibitors.
C1 inhibitor (C1-INH – inhibits C1, when the deficit → HAE )
DAF (decay-accelerating protein)-degradation of C3 and C5 convertase

27. factor I, MCP (membrane cofactor protein), CR1, factor H – C3b cleavage
CD 59 (protectin) - prevents the polymerization of C9
factor S (vitronectin) – inhibits complex C5bC6
inactivator of anafylatoxins - inactivates anafylatoxins (C3a, C4a, C5a)

28. Complement receptors Bind fragments of complement components
CR1 - on various cells removing of immunecomplexes
CR2 - on B lymphocytes and FDC activation of B cells
CR3, CR4 - on phagocytes participation in opsonization, adhesion

29. 4 basic complement functions
Opsonization (C3b, C4b)
Chemotaxis (C3a, C5a)
Osmotic lysis (MAC C5b-C9)
Anafylatoxins (C3a, C4a, C5a)

31. Antigens

32. Antigen (immunogen)
substance that the immune system recognizes and responds to it
usually proteins or polysaccharides (lipids and nucleic acids only in the combination with proteins or polysaccharides)
molecules <5 kDa can´t trigger an immune response, the optimal size of the antigen molecules to initiate immune response is about 40 kDa

33. Hapten
small molecules, that are able to induce specific immune response only after the establishment to the macromolecular carrier
separate haptens are not immunogenic
typically drugs (eg penicillin antibiotics, hydralazin)

34. Epitope
= a part of the antigen which is recognized by immune system (lymphocytes- BCR, TCR, Ig)
 linear epitope (AA sequence) - critical is amino acid composition
 conformational epitope - critical is tertiary structure
cross-reactive antigens - shares one or more identical or similar epitopes

35. 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

36. 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

37. Antigen features immunogenicity
proteins> carbohydrates> macromolecule complexes (glycoproteins, nucleoproteins, and glycolipids)> lipids
specificity

38. Factors affecting the immunogenicity
Physical: solubility - insoluble 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

39. 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)

40. Types of antigens according to antigen presentation
thymus dependent antigens
thymus independent antigens

41. Thymus dependent antigens
more frequently, mostly protein Ag
for specific humoral immune response to antigen is necessary to cooperate with TH lymphocytes (or response isn´t enough effective)
assistance implemented in the form of cytokines produced by TH lymphocytes

42. Thymus independent antigens
in a small number of antigens can be induced antibodies production directly without the participation of T lymphocytes
this are mainly a bacterial polysaccharides, lipopolysaccharides and polymer forms of proteins (e.g. Haemophilus, Str.pneumoniae)

43. Superantigens
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)
stimulate polyclonaly and massively
massive activation of T lymphocytes can cause shock
e.g. bacterial toxins (Staph.aureus, Str.pyogenes, Pseud.aeruginosa)

44. Differcence between antigen and superantigen binding

45. 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)

46. Immunologically privileged sites
Some tissues in allogeneic transplant are far less rejected (eg CNS, cornea, gonads)
Mechanisms of protection from the immune system:
isolation from the immune system (blood-brain barrier)
preferences Th2 and suppression of Th1-response active protection against effector T-lymphocytes
This privileged position is not absolute

47. Thank you for your attention