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The water-accessible surface area of an IgG antibody. Immunoglobulin G (IgG) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. [1] IgG molecules are created and released by plasma B cells. Each IgG antibody has two paratopes.
The IgG responses to bacterial capsular polysaccharide antigens are mediated primarily via IgG2 subclass, and deficiencies in this subclass result in susceptibility to certain bacterial species. [8] IgG2 represents the major antibody subclass reacting to glycan antigens but IgG1 and IgG3 subclasses have also been observed in such responses ...
It is possible to have either a global IgG deficiency, or a deficiency of one or more specific subclasses of IgG. [1] [2] The main clinically relevant form of IgG deficiency is IgG 2. IgG 3 deficiency is not usually encountered without other concomitant immunoglobulin deficiencies, and IgG 4 deficiency is very common but usually asymptomatic. [3]
IgG4-related disease (IgG4-RD), formerly known as IgG4-related systemic disease, is a chronic inflammatory condition characterized by tissue infiltration with lymphocytes and IgG4-secreting plasma cells, various degrees of fibrosis (scarring) and a usually prompt response to oral steroids.
In IgG, IgA and IgD antibody isotypes, the Fc region is composed of two identical protein fragments, derived from the second and third constant domains of the antibody's two heavy chains; IgM and IgE Fc regions contain three heavy chain constant domains (C H domains 2–4) in each polypeptide chain.
The main ligand is Protein G (prepared from Group C or G Streptococcus or by recombinant technology), which has high affinity for all four IgG subclasses. Another ReACT ligand is Protein A (from Group A Staphylococcus), which binds to IgG 1, 2, and 4. A study published in 2002 showed a loss of sensitivity for detecting significant antibodies.
Once set, light chain class remains fixed for the life of the B lymphocyte. In a healthy individual, the total kappa-to-lambda ratio is roughly 2:1 in serum (measuring intact whole antibodies) or 1:1.5 if measuring free light chains, with a highly divergent ratio indicative of neoplasm. The free light chain ratio ranges from 0.26 to 1.65. [1]
The basic tests performed when an immunodeficiency is suspected should include a full blood count (including accurate lymphocyte and granulocyte counts) and immunoglobulin levels (the three most important types of antibodies: IgG, IgA and IgM). [6] [5] Other tests are performed depending on the suspected disorder: [5] [6]