Understanding IgG: Function and Malfunction

By SWA

Introduction to IgG

Immunoglobulin G (IgG) is a type of antibody, serving as a critical component of the immune system. Antibodies are proteins produced to identify and neutralize foreign objects like bacteria and viruses. IgG is the most abundant antibody in the human body and plays a vital role in immune defense.

Functions of IgG

Neutralization: IgG antibodies can neutralize pathogens by binding to them and preventing them from infecting cells. This function is particularly crucial for combating viruses and toxins.

Opsonization: IgG enhances the phagocytosis of pathogens by marking them for destruction. Phagocytes, such as macrophages and neutrophils, have receptors that bind to the Fc region of IgG, leading to the engulfment and destruction of the pathogen.

Complement Activation: IgG can activate the complement system, a series of proteins that assist in destroying pathogens. This system can lead to the formation of a membrane attack complex that lyses bacterial cells.

Antibody-Dependent Cellular Cytotoxicity (ADCC): IgG can mediate ADCC, a process where immune cells, such as natural killer (NK) cells, recognize and kill infected or cancerous cells that are coated with IgG antibodies.

Immune Memory: IgG is involved in the immune system’s memory. Upon re-exposure to a pathogen, IgG antibodies are rapidly produced to provide a quicker and more effective immune response.

Possible Malfunctions of IgG

Autoimmune Diseases: Sometimes, IgG antibodies can mistakenly target the body’s own tissues, leading to autoimmune diseases. Examples include rheumatoid arthritis, where IgG targets joint tissues, and systemic lupus erythematosus (SLE), where IgG targets various body tissues.

Allergies: In some cases, IgG can contribute to allergic reactions. Although IgE is the primary antibody involved in allergies, IgG can also play a role, particularly in conditions like hypersensitivity pneumonitis.

Immunodeficiency: Immunodeficiency disorders can result from insufficient production or malfunctioning IgG antibodies, making individuals more susceptible to infections. Common variable immunodeficiency (CVID) is an example where there is a significant reduction in IgG levels.

Chronic Infections: Persistent infections can occur when the IgG response is inadequate or malfunctioning. This can be due to genetic factors or acquired conditions that affect IgG production or function.

Hypergammaglobulinemia: Excessive production of IgG can lead to conditions like hypergammaglobulinemia, which can be associated with chronic infections, liver disease, or certain cancers like multiple myeloma.

Prof. Akiko Iwasaki's Research on Long COVID and Autoantibodies

Paper: A causal link between autoantibodies and neurological symptoms in long COVID
https://www.medrxiv.org/content/10.1101/2024.06.18.24309100v1

In this recent study, Prof. Akiko Iwasaki and her team explored the link between autoantibodies and neurological symptoms in long COVID. Their research, published on medRxiv, highlights a significant connection between autoantibodies and various long COVID pathogenesis mechanisms, including persistent SARS-CoV-2 virus, dysbiosis, herpesvirus reactivation, and autoimmunity.

The study focused on the role of autoantibodies, particularly IgG, and its pathological impact. The researchers found positive staining in the human pons, mouse sciatic nerve, meninges, and cerebellum with IgG isolated from patients with long COVID, but not in controls. Notably, IgG reactivity to mouse meninges was enriched in patients reporting headache and dizziness. One example of a staining pattern showed that a patient's IgG stained the pericytes and surrounding tissues within mouse meninges.

Conclusion

IgG plays a crucial role in the immune system’s ability to fight off infections and provide long-term immunity. However, malfunctions in IgG production or function can lead to various diseases and conditions, ranging from autoimmune diseases and allergies to immunodeficiency and chronic infections. Prof. Iwasaki's research underscores the importance of understanding IgG's role and its potential malfunctions in long COVID to develop better diagnostic and therapeutic strategies. Understanding the balance and regulation of IgG is essential for maintaining health and developing treatments for related disorders.

Note: By reading my blog, you acknowledge that I do not provide medical diagnoses or treatments. The information provided is meant to answer frequently asked questions and is gathered from reputable scientific papers.  

 

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