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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. Its normal serum concentration ranges from 9.5 to 12.5 mg/ml. About 40-50% of IgG circulates in the blood, while the remaining portion is found in tissues. With a molecular weight of around 150,000 Daltons, IgG is primarily present as a monomer in human serum. There are four major subclasses of IgG: IgG1 (60-70%), IgG2 (15-20%), IgG3 (5-10%), and IgG4 (1-7%). These subclasses differ in their ability to activate the classical complement pathway, contributing to varied immune responses.
IgG is mainly produced by plasma cells located in the spleen and lymph nodes. It is unique among immunoglobulins because 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 their levels reach adult concentrations by the age of 2 to 3 years. 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 environmental and physiological conditions.
Most antibodies generated in response to bacterial, viral, or toxic antigens are of the IgG class. Additionally, many autoantibodies, such as the LE factor in systemic lupus erythematosus and anti-thyroglobulin antibodies, are also IgG. As the primary antibody involved in immune defense, IgG plays a critical role in protecting the body against infections and maintaining long-term immunity.
Immunoglobulins are a group of globulins with distinct chemical structures and immune functions, found in body fluids and on the surface of lymphocytes. They serve as the structural basis for antibodies and are classified into five main types: IgG, IgM, IgA, IgD, and IgE. Each type has unique characteristics, including molecular size, charge, amino acid composition, and carbohydrate content, which contribute to their diverse biological functions.
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)—held together by disulfide bonds. This symmetrical arrangement forms a monomeric structure. The heavy chains determine the class of the immunoglobulin, and they are categorized into five types: γ, μ, α, δ, and ε. Light chains are further divided into κ and λ types, each with distinct antigenic properties.
The variable region (V region) at the N-terminus of both heavy and light chains is responsible for antigen recognition, while the constant region (C region) at the C-terminus determines the functional properties of the antibody, such as complement activation and Fc receptor binding. Enzymatic digestion of Ig molecules by papain produces two Fab fragments and one Fc fragment, while pepsin cleavage results in an F(ab')â‚‚ fragment and a pFc' fragment.
Immunoglobulins exhibit different levels of specificity, including homologous, heterotypic, and unique (Id) specificities. Homologous specificity refers to common antigenic markers shared by all members of a particular immunoglobulin class. Heterotypic specificity involves differences in antigenic determinants among members of the same class. Unique specificity arises from the individual variability of each Ig molecule, allowing for a vast repertoire of antigen-binding sites.
Biologically, IgG plays a dual role: it binds to antigens and stimulates the production of more antibodies. It contributes to immune defense by neutralizing pathogens, activating complement, enhancing phagocytosis, and participating in allergic reactions. Additionally, IgG can pass through the placenta, offering passive immunity to newborns. However, when IgG binds to self-antigens, it can contribute to autoimmune diseases like hemolytic anemia, thrombocytopenia, and rheumatoid arthritis.
Each immunoglobulin class has distinct features. For example, IgM is the largest and is the first antibody produced during infection, making it useful for early diagnosis. IgA is predominantly found in secretions, where it provides mucosal immunity. IgD's function is less understood but may involve B-cell activation. IgE is associated with allergic responses and binds to mast cells, triggering the release of histamine and other mediators.
Antibody diversity arises from multiple mechanisms, including somatic mutation, V(D)J recombination, junctional diversity, and gene insertion. These processes allow the immune system to generate millions of distinct antibodies capable of recognizing a wide range of antigens. When B cells are activated by antigens, they differentiate into plasma cells that secrete Ig molecules with unique antigen-binding sites, enabling effective immune responses against ever-changing threats.
In clinical settings, immunoglobulin preparations are used to treat various conditions, including infections, tumors, and immunodeficiency disorders. Techniques such as ELISA, Western blot, immunohistochemistry, and radioimmunoassay are commonly employed to detect and quantify immunoglobulins. Reagents like SOD kits, IgG and IgM kits, and products from companies like GIBCO and AMRESCO-Shanghai Xinfan are widely used in research and diagnostics.