complement system occur in animal serum for immune response to defense inflammation , incompatible blood transfusion, autoimmune disease.

1. Dhruvi Patel
Msc MLT

2. Definition
 Complement means system of factors occurs in normal
serum and activated by antigen – antibody interaction.
 Also present in mammals and other animals , including
birds, amphibians and fish.
 Location of binding site is Fc portion
 Complex of nine different fraction C1 to C9

3. Introduction
 1890 , Jules Bordet and Paul Ehrlich
 Heat-labile , Heat- stable
 Major effector of humoral branch of immune
system

4. Function of Complement System
 Opsonisation
 Chemo toxic
 Cell lysis
 Immune clearance
 Activation of inflammatory response

6. Pathways
 Three Major Pathways:
 Classical Pathways
 Lactin Pathways
 Alternative Pathways

7. Classical Pathway
 Activation step
 Binding of C1 to Antigen – Antibody Complex
 C1 binds with two molecules of IgG or one molecules
of IgM.
 Presence of calcium
 Once activated C1 is eventually cleaved in C4 and C2
 C4b and C2a come together to form the C4b2a which is
the C3 convertase

8. Classical Pathway
 Amplification
 C3 convertase activates C3 to C3a and C3b.
 Its bind with basophils receptors and triggers them to
release vasoactive compounds.
 C3a is called anaphylatoxin
 C3b serves as opsonisation
 C3b comes together in the form of C4b2a3b which is
C5 convertase

9. Classical Pathway
 Attack
 C5 convertase cleaved in C5a and C5b
 C5a is anaphylatoxin
 C5b continues with the cascade and C6 and C7 join
together
 C567 is a heat stable complex
 C8 and C9 enters
 Cell lysis

10. Alternative Pathway
 C4b2a known as alternative pathways
 C3b bound with factor B it is a serum protein
 Also known as C3 proactivator
 Complex further cleaved by factor D
 Also called C3 proactivator convertase
 Ba and Bb
 Ba released into medium
 C3bBb complex is a C3 convertase

11. Lectin pathway
 Lectin are protein that recognize and bind the specific
Carbohydrate target.
 The lectin pathway like the alternative pathway does
not depend on antibody for its activation
 The lectin pathway is activated by the binding of
mannose – binding lectin (MBL) to mannose residues
on the surface of microorganism including certain
salmonella, listeria, and Neisseria strains.

12. Lectin Pathway
 The function in complement pathway is similar to that
of C1q.
 After MBL binds to the surface of a cell or pathogen ,
MBL- associated serine proteases, MASP-1 and MASP-
2, binds and form C1 like complex.
 The active complex formed by this association causes
cleavage and activation of C4 and C2.
 The MASP-1 and -2 proteins have structural similarity
to c1r and c1s and mimic their activities.

13. Lectin Pathway
 this means of activating the C2-C4 components to
form a C5 convertase without need for specific
antibody binding represents an important defence
mechanism.

14. Pathways

15. Role of complement system
 The complement system plays a critical role in
inflammation and defence against some bacterial
infection .
 Complement may also be activated during reactions
against incompatible blood transfusion, and during
the damaging immune responses that accompany
autoimmune disease
 Deficiencies of individuals complement components
or inhibitors can lead to variety of disease.