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Shanghai Xinfan Bio: Pig Immunoglobulin G (IgG) Instructions
Immunoglobulin G (IgG) is the most abundant class of immunoglobulins in human serum, making up approximately 75% of the total immunoglobulin content. The normal serum concentration of IgG ranges from 9.5 to 12.5 mg/ml. About 40–50% of IgG circulates in the blood, while the remaining portion is distributed in tissues. With a molecular weight of around 150,000 Daltons, IgG primarily exists as a monomer in human serum. It consists of four subclasses—IgG1 (60–70%), IgG2 (15–20%), IgG3 (5–10%), and IgG4 (1–7%)—each with distinct abilities to activate the classical complement pathway.
IgG is mainly produced by plasma cells located in the spleen and lymph nodes. One of its unique properties is that it can cross the placenta, providing passive immunity to newborns during the first few weeks of life. Infants begin synthesizing IgG at around three months of age and reach adult levels by 2 to 3 years old. However, IgG levels tend to decline gradually after the age of 40. The concentration of IgG varies significantly between individuals and can fluctuate depending on various physiological conditions.
Most antibodies generated against bacteria, viruses, and toxins are IgG, as well as many autoantibodies such as the LE factor in systemic lupus erythematosus and anti-thyroglobulin antibodies. As the primary antibody involved in immune defense, IgG plays a critical role in neutralizing pathogens and enhancing phagocytosis.
Immunoglobulins are a group of globulins with specific chemical structures and immune functions, found in body fluids and on the surface of lymphocytes. They are classified into five major types: IgG, IgM, IgA, IgD, and IgE. Each type has distinct structural features and biological functions. For example, IgM is the largest immunoglobulin and is typically the first antibody produced during an immune response, while IgA is predominant in mucosal secretions, offering protection at epithelial surfaces.
The basic structure of an Ig molecule consists of four polypeptide chains: two identical heavy chains (H chains) and two identical light chains (L chains), linked by disulfide bonds. This forms a symmetrical structure known as a monomer. The variable region (V region) at the N-terminus is responsible for antigen recognition, while the constant region (C region) determines the effector functions of the antibody. Proteolytic enzymes like papain and pepsin can cleave Ig molecules into functional fragments, such as Fab and Fc regions.
Each immunoglobulin class has unique characteristics. For instance, IgG is the main component of the humoral immune response, capable of crossing the placenta and providing long-term immunity. IgM, on the other hand, is the first antibody produced during an infection and is crucial for early immune defense. IgA is essential for protecting mucosal surfaces, while IgD remains poorly understood, and IgE is primarily involved in allergic responses and parasitic infections.
Antibody diversity arises from multiple genetic mechanisms, including V(D)J recombination, somatic hypermutation, and junctional diversity. These processes allow the immune system to generate millions of distinct antibodies, each capable of recognizing specific antigens. This diversity ensures that the immune system can respond effectively to a vast array of pathogens and foreign substances.
In clinical settings, immunoglobulin preparations are used to treat immunodeficiency disorders, prevent infections, and manage certain autoimmune conditions. Understanding the structure, function, and diversity of immunoglobulins is fundamental to advancing research in immunology and improving therapeutic strategies.