Immunoglobulin and its Isotypes: an overview
Susmita Majumder1, Santanu Nath2
- Division of Physiology & Climatology, ICAR-IVRI Bareilly (U.P.)
- Division of Livestock Products Technology, ICAR-IVRI Bareilly (U.P.)
Introduction
Glycoprotein molecules known as antibodies, or immunoglobulins, are created by plasma cells (white blood cells). They play a crucial role in the immune response by selectively identifying and attaching to specific antigens, such as viruses or bacteria, and assisting in their eradication. The immune system’s antibody reaction is extremely intricate and focused. The distribution, target specificity, biological characteristics, and structure of the various immunoglobulin isotypes vary. As a result, understanding the immunoglobulin isotype can be helpful in understanding complex humoral immune response.
Immunoglobulins are categorized into two main forms
- The synthesis of surface-bound B-cell receptors and released antibodies by B cells is controlled by alternative splicing.
- soluble antibodies
- membrane-bound antibodies (contains a hydrophobic transmembrane region)
Membrane-bound Immunoglobulin
The B-cell antigen receptor complex is made up of two auxiliary peptides and membrane-bound immunoglobulin. IgM and IgD are the initial antigen receptors that are produced by B cells. The B cell is preparing to generate an antibody, and the receptor is a model for that antibody. Only antigens can be bound by the B cell receptor (BCR). The ability of the cell to transduce the signal and react to the presence of antigens on the cell surface is provided by the heterodimer of Ig alpha and Ig beta. The B cell grows and multiplies as a result of the signal produced, and the plasma cell produces antibodies as a result.
Isotypes:
Isotypes are used to categorize the numerous antibodies that plasma cells make, and they differ in function and antigen responses mostly due to structural heterogeneity. Placental mammals can be divided into five main isotypes: IgG, IgM, IgA, IgD, and E.
Different amino acid sequences in the constant region (Fc) of the antibody heavy chains are used to classify different antibody isotypes. The amino acid heavy chain sequences of the immunoglobulins IgG and IgA are further divided into subclasses (for example, Human IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2) based on further slight variations.
When evaluating primary immuno-deficiencies or immune responses, it is important to identify each subclass, particularly if the total IgG or IgA concentration is not changed or elevated.
Immunoglobulins can be further sub-classified by identifying the type of light chain based on variations in the amino acid sequence in the constant region of the light chain (kappa light chain or lambda light chain). One constant domain and one variable domain follow one another in a light chain. Each species has a different ratio of these two light chains, but they are always both kappa or lambda and never just one of either.
Isotype Class Switching
One of the main roles of B cells in adaptive immunity is to address invading bodies and their harmful byproducts by a humoral response through the release of particular antibodies. A “class switch” in some of these cells can result in the expression of a different antibody isotype. For instance, the antibody isotype may change from IgM to any other class of antibodies (e.g. IgG1, IgG4, IgE). The heavy chain’s constant area is modified during this switch, but the heavy chain’s variable region is left unchanged.
The effector capabilities of each class of antibody are altered by this flip, but the antibody’s specificity for its antigen is unaffected. The type of cytokine present has a significant impact on the antibody class switch. It is recognized that different cytokines, including IL-4, IL-5, IFN-gamma, and TGF-beta, are accountable for class switching. The cell will eventually lose the ability to switch to a class that has already been produced.
Importance of Isotype:
Quantifying specific antibody levels aids in interpreting the immunological response following immunization or vaccination because immune responses might vary depending on the antigen given to the immune system.
A common diagnostic tool for identifying immunoglobulin-deficiency disorders, such as autoimmune diseases and gastro-intestinal conditions, which are characterized by specific isotype deficiencies or variable concentrations of one or more isotypes, is the assessment of human monoclonal antibody levels. The absence of one isotype class or subclass to a complete lack of immunoglobulin classes are examples of disease states.
The capacity of the various isotypes to bind to particular resins also varies. Knowing the isotype is crucial for determining the best purification methods to use to obtain the desired antibody with the highest yield and purity.
Conclusion:
These immunoglobulins are essential for maintaining the body’s immune system. The immune system of the body weakens and disease risk increases if immunoglobulin in the body is not functioning properly. The immune system needs to be maintained in any situation.
