Antigen-Antibody Interaction | Antibody | Humoral Immunity Immunology

It is not easy to understand concepts related to the immune system. sqadia.com has made it simple for you in this immunology video!

The antigen-antibody interaction is a chemical reaction between an antigen and an antibody.

Antibodies are secreted by the B-cells, which react with antigens to form the antigen-antibody complex or the immune complex.

This video on the antigen-antibody interaction will take you through what is an antigen, what is an antibody, and how the antigen-antibody reactions occur.

▬ 📌 Antigen ▬▬▬▬▬▬▬▬▬▬
An antigen, by definition, stimulates the production of antibodies, which in turn combine with the antigen.

The three broad ways to define antigen include

👉 Exogenous antigen
The antigen which is foreign to the host immune system is known as an exogenous antigen.

👉 Endogenous antigen
The antigen produced by, intracellular bacteria and viruses replicating inside a host cell is an endogenous antigen.

👉 Autoantigens
Autoantigen is the antigen produced by the host itself.

👉 Epitope
An epitope is the region of the antigen where an antibody binds. Thus, it plays a very important role in the antigen-antibody interaction. It is also known as antigen determinant. Epitopes are further classified as conformational and linear epitopes.

👉 Types - Partial and Complete Antigen
The partial antigen also known as Hapten, cannot initiate the production of antibodies and can only elicit an immune response with the help of a carrier protein.

Complete antigen however can stimulate the B-cells to secrete antibodies and elicit an immune response without the help of carrier protein.

▬ 📌 Antigen Presentation and Processing ▬▬▬▬▬▬▬▬▬▬
The major histocompatibility complex presents the two types of antigens, exogenous and endogenous antigens.

The MHC class 1 expresses the endogenous antigen while the MHC class 2 expresses the exogenous antigen.

▬ 📌 Antibody ▬▬▬▬▬▬▬▬▬▬
An antibody is also known as an immunoglobulin. It is the soldier of the immune system that recognizes and binds the antigen to fight off foreign invaders or pathogens. They are made up of different peptide chains.
🔹The simplest antibody molecule has a Y shape and consists of four polypeptide chains:
🔹Two Light chains or L chains, and two Heavy chains or H chains. The heavy chain contributes to Fc and Fab regions while the light chain contributes only to the Fab region.
🔹The Fab or variable regions of both the light and heavy chain are responsible for antigen-binding
🔹Fab and Fc region of the heavy chain is responsible for various biological functions such as complement activation and binding to cell surface receptors.

You can learn about the structure of the antibody and its different types in detail by watching the full video.

▬ 📌 Antigen-Antibody Interaction ▬▬▬▬▬▬▬▬▬▬
Antigen-Antibody Interaction or the antigen-antibody reaction is the reaction by which an antibody binds with an antigen to form immune complexes. The circulating antibodies bind to specific antigens with high affinity to form an antigen-antibody complex.

🔵 The antigen-antibody interactions can be classified into primary and secondary interactions.

🔵 Primary antigen-antibody interaction takes place due to the presence of non-covalent forces between the epitope of an antigen and the paratope of an antibody.

🔵 The weak and noncovalent interactions such as
🔸Van Der Waals Forces
🔸Hydrogen Bonds
🔸Electrostatic Interactions
🔸Hydrophobic Interactions

As these are weak forces of attraction, antigens and antibodies must come close to binding.

The two properties of an antibody that is affinity and avidity also play a major role in the antigen-antibody interaction.

👉 Affinity
The strength with which one antigen binding site binds to the epitope.

👉 Avidity
The total strength with which an antibody binds to epitopes, or the strength of all interactions combined.

Secondary antigen-antibody interaction involves the stimulation of complementary systems after the formation of immune complexes.

Following the classical pathway of the complimentary activation, the first complement protein which is the C1 protein is made up of three distinct subunits, C1q, C1r, and C1s. C1q binds to the Fc portion of the complexed antibody. Forming the immune complex that stimulates the other complement proteins, starting the cascade of events.

Do remember that it was just a glimpse of the content of this video. For detailed, knowledge you need to watch the video.

▬ 🎬 5500+ sqadia.com Medical Videos ▬▬▬▬▬▬▬▬▬▬
👩🏻‍⚕️ Accessible Medical Student Education 24/7/365
💡 Simplifying Medical Learning
💪 Study Hard, Dream Big, Achieve More