Complement system

1. Complement system • main humoral mechanism of nonspecific immunity • - > 40 glykoproteins • - blood • - on the surface of immune cells • Complement componentsinter-react be precise and regulated manner to eliminate microbs, foreign cells or material. • Charles Bordet 1896 - fresh serum of immunized animals agglutinate in vitro and lyse bacteria used for immunization • - serum heated to 60oC agglutinate bacteria, but do not lyse • - system responsible for lysis was named alexin

2. Complement components Classical pathaway C1q, C1r, C1s, C2, C3, C4 Alternative pathway C3, faktor B, D, I, H, P Lactin pathway C3, MBP, MASP Regulatory functions C1-inhibitor, C4-binding factor, I factor, H factor, S- protein, properdin, inactivator of anaphylaxis, DAF, MCP, MIRL Receptors of C CR1- binds C3b, CR3 – binds iC3b, ... MAC C5, C6, C7, C8, C9 Abnormálne proteíny C3 – nefritický faktor

3. Biosynthesis of Complement 1. Hepatocytes 2. Mononuclear phagocytes– inflammatory site 3. Epithelial cells

4. Genetics of Complemet System • Isolated genes • - C3 - chromosome 19 • - I factor - chromosome 4 • - C1-INH - chromosome 11 • Genes in clusters • chromosome 6 - C2, C4, B factor • chromosome 1 - C4 bp, H factor, CR1, CR2, DAF, MCP

5. Activation of Immune System • Complemets of componentsare innactive in serum • 3 pathways of activation • Classical pathway • Alternative pathway • Lectin pathway Cascade system of activation – active component serve as enzyme and activate (split) following component

6. Activation of Complement Classical pathway • Activation signals: • Immune complexes • complex Ag + Ab (IgM, IgG3, IgG1) • CRP – C-reactive protein • During inflammation rise its • concentration 100 times. • CRP binds polysaccharides of bacteria, • fungi, parasites and viruses. • Its binding to Ag is non specific 3. Aggregated IgG 4. Polycationic and polyanionic compounds 5. RNA, DNA 6. LPS G- bacteria 7. Some viral proteins

7. Activation of Complement Classical pathway C1 – macromolecular complex - 3 subunitsC1q, C1r, C1s Recognition function - C1q Effector functions - tetramolecular complex (C1r, C1s)2 C1q - 3 types of chains (A, B,C) - triplet of chains A+B+C form subunit with binding site for - CH2 domain IgG - CH4 domain IgM Activation signal = binding of C1q to immunocomplex (IgM,IgG + Ag)

8. Activation of Complement Classical pathway Binding of C1q to immune complex  auto-catalytic splitting of proenzyme C1r for active enzyme C1r  conversion of C1s for active serine protease C1s  splitting of C2 na C2a a C2b and C4 na C4a a C4b C4b2a = C3 convertase – split C3 for C3a a C3b  C4b2a3b = C5 convertase – split C5 C5a a C5b

9. Activation of Complement Alternative pathway Activation signals : 1. Aggregated IgG4, IgA1, IgA2, IgE 2. Polysaccharides 3. LPS of bacteria (low content of sialic acid) 4. Various components of viruses, fungi, protozoa, cancer cells Spontaneous conversion of C3 for C3b. C3b rapidly inactivated(H factor)binding to sialc (typical for cells MAO) Cells with low content of sialic acid (MIO) cause low affinity of H factor to C3b. C3b persist and binds B factor – further activation of C3 alternative pathway of activation

10. Activation of Complement Lectin pathway Resemble of classical pathway – 2 differences A) C1q is supplied by MBP (mannose binding protein) – strucrurally close to C1q B) MASP (MBP asssociated serine protease) – strucrurally close to C1r a C1s After binding of MBP to mannose or N-acetylglukoseamin – activation of MASP – splitting C4 a C2

11. Activation of Complement MAC

12. Biological funcions • Lysis • Opsonization – C3b, C3bi • Chemotaxis – C5a • Inflammation - anaphylatoxins: C3a, C4a, C5a • Modulation of immune complexes • Immunoregulation

13. Deficiences C3 – inherited >> susceptibility to bacterial infections C2 -immune complex diseases - autoimmune disseases Systemic lupus erythematosus (SLE) C1INH - hereditary angioneuroticoedem (HANE).