Action of Antibodies: Neutralization, Opsonization, Complement Activation and ADCC (FL-Immuno/37)

Summary

This video explains how antibodies protect the body from pathogens. Once B cells recognize antigens, they produce antibodies that neutralize infections by blocking pathogen entry into host cells. The video covers four key mechanisms: neutralization, where antibodies block pathogens; opsonization, which enhances phagocytosis; complement activation, leading to pathogen destruction; and antibody-dependent cell-mediated cytotoxicity (ADCC), where antibodies help cytotoxic cells eliminate infected or large pathogens. These strategies collectively play a vital role in immune defense, preventing infections caused by viruses, toxins, and parasites.

Takeaways

• 😀 Antibodies are produced by plasma cells after B cells recognize specific antigens, and they play a crucial role in immune defense.
• 😀 When antibodies bind to their specific antigens, they prevent pathogens from entering host cells, which is known as neutralization.
• 😀 Neutralization helps block the infectivity of viruses, bacterial toxins, and even venomous substances like snake venom.
• 😀 Opsonization is the process where antibodies coat pathogens, marking them for easier recognition and elimination by phagocytes.
• 😀 Phagocytic cells recognize antibody-coated pathogens through specific receptors, facilitating their destruction.
• 😀 Complement activation is triggered when antibodies bind to pathogens, leading to their destruction through various mechanisms, such as inflammation and lysis.
• 😀 The complement system consists of about 20 proteins in the blood that assist in pathogen destruction once activated by antibody binding.
• 😀 Antibody-dependent cell-mediated cytotoxicity (ADCC) involves immune cells like natural killer (NK) cells and eosinophils, which destroy infected cells marked by antibodies.
• 😀 ADCC is especially useful against intracellular infections (like viruses) and large pathogens (like parasitic worms) that cannot be eliminated by phagocytosis.
• 😀 The FC region of antibodies is recognized by immune cells, facilitating the release of cytotoxic chemicals to kill target cells.
• 😀 All these antibody mechanisms—neutralization, opsonization, complement activation, and ADCC—work together to protect the body from various pathogens.

Q & A

What happens when B cells recognize antigens?

When B cells recognize antigens, they differentiate into plasma cells, which then produce and secrete antibodies specific to the antigen.

How do antibodies provide protection against pathogens?

Antibodies provide protection through two main strategies: neutralization, where they block pathogens from entering host cells, and by recruiting effector cells and molecules to kill the pathogen through processes like opsonization, complement activation, and antibody-dependent cell-mediated cytotoxicity.

What is the structure of an antibody?

An antibody is a Y-shaped molecule with two antigen-binding sites. The stalk of the Y is known as the FC region, which interacts with immune cells.

What is the function of neutralization in immunity?

Neutralization occurs when antibodies bind to microbes or microbial toxins, blocking their ability to enter host cells and neutralizing their infectivity. This process prevents the pathogen from initiating an infection.

How does neutralization help protect the body?

Neutralization helps protect the body by preventing pathogens such as viruses, bacterial toxins, and poisons (like insect or snake venom) from infecting host cells. Neutralized pathogens are eventually eliminated by phagocytosis.

What is opsonization and how does it aid in pathogen elimination?

Opsonization is the process where antibodies coat the surface of a pathogen, enhancing its recognition by phagocytic cells. This makes it easier for the phagocytes to identify and eliminate the pathogen.

How does the complement system contribute to pathogen destruction?

The complement system is activated when antibodies bind to pathogens. This initiates the classical pathway, leading to pathogen destruction through mechanisms like membrane attack complex formation, opsonization, and inflammation.

What is antibody-dependent cell-mediated cytotoxicity (ADCC)?

ADCC is a process where antibodies coat infected or abnormal cells (like virus-infected cells or parasitic worms). The FC region of these antibodies is recognized by cytotoxic leukocytes, which then release chemicals to kill the target cell.

What types of cells are involved in ADCC?

Cytotoxic leukocytes, such as natural killer cells and eosinophils, are involved in ADCC. These cells have specific FC receptors that bind to the antibodies on the target cells, leading to the release of cytotoxic chemicals.

Why is ADCC important for immunity against large pathogens?

ADCC is crucial for eliminating large pathogens, such as parasitic worms, that cannot be phagocytized. It also plays a role in targeting infected cells where phagocytosis is not possible.