9.2.2 Protective Proteins of Complement System

The complement system consists of over fifty types of small proteins found in the blood, synthesized by the liver, and normally circulating in inactive state. They are activated on the entry of foreign particles. Once a complement protein is activated, it activates another protein, which further activates other proteins of the system and so on. The complement system is an important supporter of the immune system that enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells from the body, promotes inflammation, and attacks the pathogen's plasma membrane.

Definition

Complement System: The complement system consists of over fifty types of small proteins found in the blood, synthesized by the liver, and normally circulating in inactive state.

Main Idea

• The complement system consists of over fifty types of small proteins.
• They are found in the blood.
• They are synthesized by the liver.
• They normally circulate in inactive state.
• They are activated on the entry of foreign particles.
• Once a complement protein is activated, it activates another protein, which further activates other proteins of the system and so on.
• As a result:
• Phagocytes clear foreign and damaged material.
• Development of inflammation to attract additional phagocytes at the site of infection.
• This activates cell killing membrane attack complexes.
• The complement system is an important supporter of the immune system.
• It enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells.
• It promotes inflammation.
• It attacks the pathogen's plasma membrane.

Core Concept

• Complement system = over fifty types of small proteins
• **Source** = blood
• **Synthesis** = liver
• **State** = inactive
• Activation = on entry of foreign particles
• Cascade = one protein activates another
• Functions:
• Clear foreign and damaged material
• Develop inflammation
• Attract additional phagocytes
• Activate cell killing membrane attack complexes
• Membrane attack complex (MAC) = produces holes in bacterial cell walls
• Result = bacterial cell swells and bursts

Detailed Explanation

Protective Proteins of Complement System

• The complement system consists over fifty types of small proteins found in the blood, synthesized by the liver, and normally circulating in inactive state.
• They are activated on the entry of foreign particles.
• Once a complement protein is activated, it activates another protein, which further activates other proteins of the system and so on.
• As a result:
• Phagocytes clear foreign and damaged material.
• Development of inflammation to attract additional phagocytes at the site of infection.
• This activates cell killing membrane attack complexes.
• The complement system is an important supporter of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from the body, promotes inflammation, and attacks the pathogen's plasma membrane.

Membrane Attack Complex (MAC)

• An example of protective proteins of complement system is membrane attack complex (MAC) that produces holes in the bacterial cell walls and plasma membranes of pathogens.
• The holes allow fluids and salts to enter the bacterial cell, thus, bacterial cell swells and eventually burst.

Summary Table of Complement System

Summary of Membrane Attack Complex

Intermediate Level

Complement System

Membrane Attack Complex

Functions of Complement System

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Complement system consists of over fifty types of small proteins.
• 2. They are found in the blood.
• 3. They are synthesized by the liver.
• 4. They normally circulate in inactive state.
• 5. They are activated on entry of foreign particles.
• 6. Activation is a cascade.
• 7. One protein activates another.
• 8. Phagocytes clear foreign and damaged material.
• 9. Inflammation develops to attract additional phagocytes.
• 10. Membrane attack complexes are activated.
• 11. Membrane attack complex produces holes in bacterial cell walls.
• 12. Water and salts enter the bacterium.
• 13. Bacterium swells and bursts.
• 14. Complement system enhances the immune system.
• 15. It enhances the ability of antibodies and phagocytic cells.
• 16. It promotes inflammation.
• 17. It attacks the pathogen's plasma membrane.
• 18. It is an important supporter of the immune system.
• 19. It is part of the second line of defence.
• 20. It is nonspecific.

Remember

• - Complement system = over fifty types of small proteins
• - **Source** = blood
• - **Synthesis** = liver
• - **State** = inactive
• - Activation = on entry of foreign particles
• - Cascade = one protein activates another
• - Functions = clear foreign material; inflammation; attract phagocytes; activate MAC
• - Membrane attack complex = produces holes in bacterial cell walls

Common Mistakes

• 1. Forgetting the number of proteins — Over fifty types.
• 2. Mixing up the source — Blood.
• 3. Mixing up the synthesis site — Liver.
• 4. Forgetting the inactive state — Complement proteins circulate in inactive state.
• 5. Mixing up the activation trigger — Entry of foreign particles.
• 6. Forgetting the cascade — One protein activates another.
• 7. Mixing up the functions — Clear foreign material; inflammation; attract phagocytes; activate MAC.
• 8. Forgetting the role of MAC — Produces holes in bacterial cell walls.
• 9. Believing complement system is specific — It is nonspecific.
• 10. Mixing up the result — Bacterium swells and bursts.

Quick Revision

The complement system consists over fifty types of small proteins found in the blood, synthesized by the liver, and normally circulating in inactive state. They are activated on the entry of foreign particles. Once a complement protein is activated, it activates another protein, which further activates other proteins of the system and so on. As a result, phagocytes clear foreign and damaged material. Development of inflammation to attract additional phagocytes at the site of infection. This activates cell killing membrane attack complexes. The complement system is an important supporter of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from the body, promotes inflammation, and attacks the pathogen's plasma membrane. An example of protective proteins of complement system is membrane attack complex (MAC) that produces holes in the bacterial cell walls and plasma membranes of pathogens. The holes allow fluids and salts to enter the bacterial cell, thus, bacterial cell swells and eventually burst.

60-Second Revision

• Complement system = over fifty types of small proteins
• Source = blood
• Synthesis = liver
• State = inactive
• Activation = on entry of foreign particles
• Cascade = one protein activates another
• Functions = clear foreign material; inflammation; attract phagocytes; activate MAC
• Membrane attack complex = produces holes in bacterial cell walls
• Warning: Complement system is nonspecific; it is part of the second line of defence

NEXT TOPIC

• Chapter:
• 9. Immunity

• Topic:
• 9.2.3 INFLAMMATORY RESPONSE

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