Immunology - Antibodies (Function)

Summary

This video explains the five main immunoglobulin (Ig) isotopes: IgG, IgM, IgD, IgE, and IgA. It delves into the properties and functions of each, emphasizing IgG's crucial role in immunity, including opsonization, agglutination, and toxin neutralization, as well as its ability to cross the placenta. IgM is the first antibody produced during infection, IgD serves as a marker for B-cell maturity, IgE is linked to allergic reactions, and IgA is vital in mucosal immunity. The video offers an insightful look into how these antibodies protect the body from pathogens, toxins, and infections.

Takeaways

• 😀 IgG is the most abundant immunoglobulin in the blood and lymph, making up 15% of total serum proteins.
• 😀 IgG is the only antibody that can cross the placenta, transferring immunity from mother to baby.
• 😀 IgG has many subclasses (IgG1, IgG2, IgG3, IgG4), each with distinct functions in immune responses.
• 😀 IgG performs opsonization by coating pathogens, making them easier for phagocytes like macrophages to engulf and destroy.
• 😀 IgG also performs agglutination, binding bacteria together, allowing for easier detection and destruction.
• 😀 IgG neutralizes toxins and viruses, preventing their harmful effects on the body.
• 😀 IgG activates the classical pathway of complement, stimulating an immune response.
• 😀 IgM is the first antibody to be produced after exposure to an infectious agent, and it forms a pentameric structure.
• 😀 IgM is effective in activating complement and agglutination but has poor toxin and viral neutralization abilities.
• 😀 IgE is involved in allergic reactions, binding to mast cells and basophils to release histamine and promote inflammation.
• 😀 IgA is important in the mucosal immune system, protecting against infections in the respiratory tract, gut, and genital areas.

Q & A

What are the five immunoglobulin isotopes mentioned in the transcript?

The five immunoglobulin isotopes are IgM, IgD, IgG, IgE, and IgA. These are classified based on the constant region of the antibody.

Why is IgG the primary focus in the video?

IgG is the primary focus because it is the most abundant immunoglobulin in the blood, lymph, cerebrospinal fluid, and peritoneal fluid, making up about 15% of total serum proteins.

How does IgG contribute to immunity?

IgG contributes to immunity by performing functions such as opsonization (coating pathogens for easier destruction), agglutination (clumping pathogens together for easier identification), and neutralizing toxins and viruses.

What is opsonization and how does it work?

Opsonization is the process where IgG antibodies bind to pathogens, marking them for easy identification and destruction by phagocytes, such as macrophages.

What are the subclasses of IgG, and what do they indicate?

IgG has four subclasses: IgG1, IgG2, IgG3, and IgG4. Deficiencies in these subclasses can indicate specific conditions, such as an IgG4 deficiency being linked to allergies.

Can IgG cross the placenta? If so, why is this important?

Yes, IgG can cross the placenta, which allows the transfer of immunity from the mother to the fetus. This helps protect the baby from infections during early life.

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

ADCC is a process where IgG binds to abnormal cells, such as tumor cells, and allows natural killer cells to recognize and destroy these cells by releasing cytotoxic toxins.

How does IgM differ from IgG in terms of structure and function?

IgM is a pentameric antibody, meaning it forms a five-unit structure, whereas IgG is a monomer. IgM is the first antibody produced after exposure to an infectious agent but has a shorter half-life and does not cross the placenta.

What is the role of IgD in the immune system?

IgD is a membrane-bound immunoglobulin that is expressed on the surface of B cells. It serves as a marker for B cell maturity and is co-expressed with IgM on immature B cells.

What is the primary function of IgE in the body?

IgE plays a key role in allergic reactions and hypersensitivity by binding to mast cells and basophils, which release histamine upon encountering an antigen, leading to inflammation.

What is the role of IgA in mucosal immunity?

IgA is the dominant immunoglobulin in mucosal systems, such as the respiratory and gastrointestinal tracts. It defends against infections in these areas by agglutinating pathogens and preventing their entry.