The document is an assignment on the complement system, a crucial component of the immune system composed of over 30 proteins that help protect the body against infections by marking pathogens, attracting immune cells, and removing cell debris. It discusses the regulation, activation pathways (classical, alternative, and lectin), and biological functions of the complement system, including its role in inflammation regulation and immune response. Dysregulation of the complement system can lead to various diseases, emphasizing its importance in maintaining immune homeostasis.

1. VIVEKANANDHA
Submitted to
Ms.S.Anandhi
Assistant Professor
PG & Research Department of Biotechnology
Vivekanandha Arts and Science College For Women
Sankari
Submitted by
SRINITHI.V
II – B.Sc Biotechnology
Vivekanandha Arts and Science College For Women
Veerachipalayam, Sankari
Assignment on “ COMPLEMENT SYSTEM ”
IMMUNE SYSTEM AND IMMUNOTECHNOLOGY
ARTS & SCIENCE COLLEGE FOR WOMEN
[An ISO 9001:2015 Certified Institution]
(Affiliated to Periyar University, Salem
Recognised Under Section 2(f) &12(B) of the UGC Act, 1956)
Veerachipalayam, Sankari West (Post) – 637 303, Sankari Tk, Salem Dt., Tamil Nadu
PG & RESEARCH DEPARTMENT OF BIOTECHNOLOGY

2. COMPLEMENT SYSTEM

3. SYNOPSIS
Introduction
Regulation
Activation
Classical pathway
Alternative pathway
Lectin pathway
Biological function

4. INTRODUCTION OF COMPLEMENT SYSTEM
The complement system is a group of proteins in the immune system that work together to help
protect the body against infections and diseases. It is a complex system that plays a crucial role in:
1. Marking pathogens for destruction:
Complement proteins identify and label foreign substances, making it easier for
immune cells to recognize and attack them.
2. Attracting immune cells:
Complement proteins attract immune cells, such as neutrophils and
macrophages, to the site of infection.
3. Creating holes in membranes:
Certain complement proteins can create holes in the membranes of foreign
cells, leading to their destruction.
4. Removing dead cells and debris:
Complement proteins help remove dead cells and debris from the body.The
complement system consists of over 30 proteins that work together in a cascade-like sequence.

5. REGULATION OF COMPLEMENT SYSTEM
The complement system is tightly regulated to prevent excessive activation, which can lead to tissue
damage and disease. Regulation occurs at multiple levels:
1. Protein inhibitors:
- C1 inhibitor (C1-INH): regulates classical pathway
- Factor H: regulates alternative pathway
- Factor I: regulates C3b and C4b
- Decay-accelerating factor (DAF): regulates C3 convertase
2. Cell surface receptors:
- Complement receptor 1 (CR1): regulates C3 convertase
- CD55 (decay-accelerating factor): regulates C3 convertase
- CD59 (protectin): prevents membrane attack complex formation
3. Soluble regulators:
- C4-binding protein (C4BP): regulates classical pathway

6. 4. Cellular regulation:
- Phagocytic cells (e.g., neutrophils, macrophages): remove complement-
coated pathogens
- Immune cells (e.g., T cells, B cells): modulate complement activation
5. Genetic regulation:
- Genetic variants: affect complement protein levels and function
- Epigenetic modifications: influence complement gene expression
Dysregulation of the complement system can lead to:
1. Autoimmune diseases (e.g., lupus, rheumatoid arthritis)
2. Inflammatory disorders (e.g., asthma, allergic reactions)
3. Infectious diseases (e.g., meningitis, sepsis)
4. Cancer (e.g., complement-mediated tumor growth)

7. ACTIVATION OF COMPLEMENT SYSTEM
The complement system consists of over 30 proteins that work together in a
cascade-like sequence. There are three main pathways:
1. Classical pathway:
Activated by antibodies binding to pathogens.
2. Lectin pathway:
Activated by lectins (proteins that recognize carbohydrates)
binding to pathogens.
3. Alternative pathway:
Activated by the presence of foreign substances or pathogens.

8. CLASSICAL PATHWAY OF COMPLEMENT SYSTEM
The Classical Pathway of the Complement System is a crucial part of the immune system,
providing a defense against infections.
Activation:
Antigen-Antibody Complex Formation: Antibodies (IgG or IgM) bind to pathogens or foreign
substances, forming antigen-antibody complexes.
Classical Pathway Activation:
1. C1q Binding:
C1q, a protein complex, binds to the antigen-antibody complex.
2. C1r and C1s Activation:
C1q activates C1r and C1s, two serine proteases.
3. C4 and C2 Activation:
C1s cleaves C4 and C2, forming C4b and C2a.
4. C3 Convertase Formation:
C4b and C2a combine to form C3 convertase (C4b2a).

9. Amplification:
1. C3 Cleavage:
C3 convertase cleaves C3 into C3a and C3b.
2. C5 Convertase Formation:
C3b binds to C4b2a, forming C5 convertase (C4b2a3b).
3. C5 Cleavage:
C5 convertase cleaves C5 into C5a and C5b.
Membrane Attack Complex (MAC) Formation:
1. C5b-9 Assembly:
C5b binds to C6, C7, C8, and C9, forming the MAC.
2. Pathogen Lysis:
The MAC creates a pore in the pathogen's membrane, leading to its lysis and death.
The Classical Pathway is a critical component of the immune response, providing a powerful
mechanism for eliminating pathogens.

10. CLASSICAL PATHWAY
https://images.app.goo.gl/Td9rf1B9smU6bgBa7

11. ALTERNATIVE PATHWAY OF COMPLEMENT SYSTEM
The Alternative Pathway of the Complement System is a crucial defense mechanism against infections.
Activation:
1. Spontaneous Hydrolysis:
C3, a central complement protein, undergoes spontaneous hydrolysis, forming C3(H2O).
2. Factor B Binding:
Factor B binds to C3(H2O), forming a complex.
3. Factor D Activation:
Factor D, a serine protease, activates the C3(H2O)-Factor B complex.
Amplification Loop:
1. C3b Formation:
Activated Factor B cleaves C3, forming C3b.
2. C3b Deposition:
C3b deposits on nearby surfaces, including pathogens.
3. Factor B Binding:
Factor B binds to C3b, forming a new complex.
4. Continuous Activation:
The cycle repeats, amplifying the response.

12. Regulation:
1. Properdin Stabilization:
Properdin stabilizes the C3bBb complex, preventing its decay.
2. Factor H Regulation:
Factor H, a regulatory protein, competes with Factor B for C3b binding, preventing excessive
activation.
Terminal Pathway:
1. C5 Cleavage:
C3bBb complex cleaves C5, forming C5a and C5b.
2. MAC Formation:
C5b assembles with C6, C7, C8, and C9, forming the Membrane Attack Complex (MAC).
3. Pathogen Lysis:
The MAC creates a pore in the pathogen's membrane, leading to its lysis and death.
The Alternative Pathway provides a continuous, low-level activation against pathogens, and is
especially important for defending against Neisseria and other Gram-negative bacteria.

13. ALTERNATIVE PATHWAY
https://images.app.goo.gl/amWtXGgL8ni7Nbs47

14. LECTIN PATHWAY OF COMPLEMENT SYSTEM
The Lectin Pathway of the Complement System is a vital defense mechanism against infections.
Activation:
1. Lectin Binding:
Lectins (e.g., MBL, Ficolin) bind to carbohydrate patterns on pathogens.
2. MASP-1 and MASP-2 Activation:
Bound lectins activate MASP-1 and MASP-2, serine proteases.
3. C4 and C2 Activation:
MASP-2 cleaves C4 and C2, forming C4b and C2a.
C3 Convertase Formation:
1. C4b2a Complex:
C4b and C2a combine to form the C3 convertase (C4b2a).
2. C3 Cleavage:
C4b2a cleaves C3 into C3a and C3b.

15. Amplification Loop:
1. C3b Deposition:
C3b deposits on nearby surfaces, including pathogens.
2. C3bBb Complex:
C3b binds to Factor B, forming the C3bBb complex.
3. Continuous Activation:
The cycle repeats, amplifying the response.
Terminal Pathway:
1. C5 Cleavage:
C3bBb complex cleaves C5, forming C5a and C5b.
2. MAC Formation:
C5b assembles with C6, C7, C8, and C9, forming the Membrane Attack Complex (MAC).
3. Pathogen Lysis:
The MAC creates a pore in the pathogen's membrane, leading to its lysis and death.
The Lectin Pathway recognizes carbohydrate patterns on pathogens, providing a rapid response to infections.
It works in conjunction with the Classical and Alternative Pathways to defend against a wide range of
pathogens.

16. LECTIN PATHWAY
https://images.app.goo.gl/cvXKq6ai4NYEkT6L7

17. BIOLOGICAL FUNCTIONS
The Complement System has several crucial biological functions:
1. Pathogen Elimination: Helps remove pathogens, such as bacteria, viruses,
and fungi, from the body.
2. Inflammation Regulation: Regulates inflammation by attracting immune
cells to the site of infection.
3. Immune Complex Clearance: Removes immune complexes (antigen-
antibody complexes) from the circulation.
4. Cell Lysis: Lyzes (kills) cells that are infected or damaged.
5. Opsonization: Marks pathogens for destruction by coating them with
complement proteins.
6. Antibody-Dependent Complement-Mediated Cytotoxicity (ADCC):
Enhances antibody-mediated killing of target cells.

18. 7. Immune Response Regulation: Regulates the immune response by
modulating the activity of immune cells.
8. Tissue Repair: Contributes to tissue repair and regeneration.
9. Cancer Surveillance: Helps eliminate cancer cells.
10. Neuroprotection: Protects against neurodegenerative diseases.
The Complement System plays a vital role in protecting against infections
and maintaining immune homeostasis. Its dysregulation can lead to various
diseases, including autoimmune disorders, cancer, and neurological
conditions.

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20. THANK YOU!!