Introduction to Immunoglobulin and Its Functions


Immunoglobulin abbreviated as Ig is the antibody (-ies) produced by the plasma cells upon identification of antigens and pathogens, used by our immune system. They are Y-shaped and large in structure. It consists of four polypeptide chains connected via disulfide bonds: two identical heavy chains and two identical light chains. Heavy chains are of five types: α, δ, ε, γ, and µ, while light chains are of two types: λ (lambda) and κ (kappa). Igs are of approx. 150 kD weight and are known as heavy globular plasma proteins. Antibodies are glycoproteins and belong to immunoglobulin superfamily, as they have glycans (sugar chains) added to conserved residues of amino acids. The structure of an Ig is composed of two regions: a variable (V) region and a constant (C) region. These antibodies are specific to every foreign substance.

Igs are of five different classes/isotypes and of two different types. Igs are of five different classes: IgA (alpha heavy chains), IgE (epsilon heavy chains), IgD (delta heavy chains), IgG (gamma heavy chains), and IgM (mu heavy chains). Different Ig classes and their features are summarized in Table 1. All of these Igs are found in mammals, except two: IgY (birds and reptiles) and IgW (sharks and skates).

Table 1. Immunoglobulin Classes and Features

S. No.Ig classTypesAntibody complexesMolecular mass (kD)Heavy chainLight chainFunctionReference range
1.IgA2 (IgA1 and IgA2)Dimer160ακ and λBody surfaces protection60—400 mg/dL
2.IgD1Monomer180δκ and λAct as antigen receptor on B-cells0—14 mg/dL
3.IgE1Monomer190εκ and λReleases histamine3–423 IU/mL
4.IgG4 (IgG1, IgG2, IgG3, and IgG4)Monomer140–170γκ and λResponsible for humoral immunity700—1500 mg/dL
5.IgM1Pentamer970µκ and λServes as first line of defense60—300 mg/dL

Ig test is important because Igs play important functions in our body like precipitation, opsonization, neutralization, mucosa protection, complement activation, cellular toxicity antibody dependent, and agglutination. Antibody or Ig is produced when a specific antigen is encountered by it. The antibody binds to it and kills it. Next time when the antigen is encountered, the immune system has the response in the memory and thus produces more antibodies quickly. This way a specific Ig in the blood can be detected and used to rule out any infection(s), illness, and to evaluate the autoimmune disease condition by a simple blood test. For this test, log on to and order. A missed call on 0124-222-3197 can also be given and you can take benefit of the free doctor consultation facility. Another benefit with NextDoorLab is free home sample collection. But when to choose this test? Are there any symptoms for an elevated or decreased Ig level in the blood? The symptoms related to changes in Ig levels are allergies, recurrent infections of respiratory tract or gestational tract, chronic inflammation, and/or chronic diarrhea.

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