How antibodies work in the Immune system?

 How antibodies work in the Immune system?

Introduction

The system that protects the body from pathogen invaders is the immune system, which works with the help of different types of cells like B-lymphocytes, T-lymphocytes, Plasma cells, Macrophages, Neutrophils, etc.

The type of immune system that involves the antibodies formation and their action is the Humoral Immune system, that's the specific immunity.

Humoral Immune System

The humoral immune system involves the B-lymphocytes cells. When the infection invades the body and comes in contact with the specific B-cells, then the differentiation process occurs and leads to the formation of Antibodies.

How are Anti-bodies Formed?

When the B-cells come in contact with the specific antigens, they start proliferation and differentiation. The first cell that is formed is the lymphoblast, then few cells still undergo further differentiation and lead to the formation of Plasmablast.

These plasmablasts are the precursors of the plasma cells. The plasmablast starts proliferation at the speed of 500 cells in 4 days. Now the formed cells are Plasma cells that produce gamma-globulins at a speed of 2000 molecules per second.

How do Antibodies Work?

There are two mechanisms that are involved in the action of antibodies, which are given below:

• Direct action of Antibodies on invading cells
• By the activation of the complement system

Direct action of Antibodies

In this mechanism, the antibody directly attacks the invaders, and inactivate them in the following ways:

1. Agglutination:  In this process, the large particles and antigens binds with each other and start clumping.
2. Precipitation:  In this process, the soluble antigen and antibody complex is formed, which is of large size and insoluble, forms precipitate.
3. Neutralization:  In this process, the antibody molecule covers the toxic sites of antigens so that it can not affect the individual.
4. Lysis: The antibodies destroy or damage the membranes of antigens, which leads to the lysis of that antigen then.

Complement System

The complement system is a collective term that describes the 20 complement proteins. The 9 complement proteins from C1-C9, B, and D proteins, total of 11 proteins are the principal actors of this system. This system is activated by different pathways.

Types of Activation Pathways

There are three types of Activation pathways, that are given below:

• Classical Pathway
• Alternate Pathway
• Lectin Pathway 

Classical Pathway

When the complement system is activated by C1 protein, that pathway is called the Classical Pathway. In this pathway, the first antibody comes and binds with the invader, then C1 protein attaches to the site of the Antibody. After C1, then one by one other protein comes and binds in this series C1, C4, C2, C3, C5, C6, C7, C8, and C9. 

Like the C4, C3, and C5 bind, the enzymes act on them and cleave all the three into C3a and C3b, C4a, and C4b, C5a, and C5b. The Proteins (C3a, C4a, C5a) are released, but others remain in their positions. In the end, the protein complex formed is C5b6789 called as Membrane Attack Complex (MAC).

Alternate Pathway

In this pathway, the antigens present in the membrane of invaders are the site where the complement protein attaches. This pathway directly starts from the Complement protein C3 that attaches with the antigen, then the process is the same as of the classical pathway.

Lectin Pathway

This pathway is initiated by the binding of Mannose-binding lectin that binds with the antigen present at the infection. Then followed by C4, C2, and so on till the C9. Here the Mannose-binding lectin binds with the antigen instead of C1, that's why called Lectin Pathway.

Effects of Complement System

Among the most important effects of the complement system, some are given below:

1.  Phagocytosis/Opsonization: The complement protein C3b leads to the binding of macrophage or neutrophil that phagocytes the infection then.
2. Lysis: The last product that is obtained is the MAC that is C5b6789, which binds with the membrane of that infection, and leads to the lysis of that particle.
3. Agglutination: Products of the complement system lead to the changes in the surfaces infections, then they adhere with each other and lead to agglutination.
4. Chemotaxis: The released factor C5a causes the chemotaxis of neutrophils and macrophages towards the site of inflammation.
5. Neutralization: Complement proteins and enzymes attack the infection or virus and make it nonvirulent so that it can not lead to damage.
6. Activation of mast cells and basophils: Complement proteins C5a, C4a, and C3a activate the mast cells and basophils so that they release histamines, heparin, etc that help to immobilize or inactivate the antigen.

Conclusion

Normally, antibodies work by direct mechanism and mostly they fail through it, then the activation of complement system occurs. As the complement system is activated in the presence or absence of antibodies, that's why it occurs in both Immune systems that are innate and acquired Immune systems.