Classes of Immunoglobulins (Antibodies) - Immunoglobulin M (IgM) скачать в хорошем качестве

Classes of Immunoglobulins (Antibodies) - Immunoglobulin M (IgM)

Classes of Immunoglobulins are essentially antibodies which are globulin proteins, you can remember them as having a “globular” structure or quaternary structure. They are released by plasma cells or B-lymphocytes, as part of the defense mechanism of our body. Watch this full immunoglobulins lecture to learn all about the 5 classes of immunoglobins and their function based on their structure in our body. ▬ Immunoglobulin (Antibody) Structure ▬▬▬▬▬▬▬▬▬▬ The domains of different classes of immunoglobulin molecules have a similar globular structure characterized by the presence of β-pleated sheets and disulfide bonds. The simplest antibody molecule has a Y shape and consists of four polypeptide chains. The four chains are linked by disulfide bonds. 🟡 Two identical Light chains or L chains (25 000 Da) 🟡 Two identical Heavy chains or H chains (50 000 – 70 000 Da) ▬ Classes of Immunoglobulins (Antibodies) ▬▬▬▬▬▬▬▬▬▬ There are two types of light chains in different classes of Immunoglobulins, denoted by: 🔹Kappa 🔹Lambda Antibodies and Immunoglobulins are subdivided into five classes based on differences in their heavy chains. So, the H chain symbol for each class of Immunoglobulin is different. The symbols are as shown: 👉 Immunoglobulin G - IgG is γ (gamma) 👉 Immunoglobulin A - IgA is α (alpha) 👉 Immunoglobulin M - IgM is μ (mu) 👉Immunoglobulin D - IgD is δ (delta) 👉 Immunoglobulin E - IgE is ε (epsilon) ▬ Regions of Immunoglobulins (Antibodies) ▬▬▬▬▬▬▬▬▬▬ Light and heavy chains of immunoglobulins are subdivided into variable and constant regions. Both regions consist of about 110 amino acids. The variable regions of both L and H chains have extremely variable, or hypervariable amino acid sequences at the amino-terminal end; the hypervariable region of immunoglobulin. They form the antigen-binding site, so the remarkable specificity of antibodies is due to these hypervariable regions. They are referred to as complementarity-determining regions or CDRs. The substitution of a single amino acid in this region is crucial for the binding of a particular antigen. 🔘 Light chain consists of one variable (VL) and one constant (CL) domain. 🔘 Most Heavy chains consist of one variable (VH) and three constant (CH) domains. IgG, IgD, and IgA have three CH domains, whereas IgM and IgE have four. ▬ Fab vs Fc regions of Antibody ▬▬▬▬▬▬▬▬▬▬ 🟠 The Fab or variable regions of both the light and heavy chains are responsible for antigen binding. You can remember this by the term itself, F-A-B for Fragment, Antigen Binding. 🟠 The c in Fc portion of Immunoglobulin stands for crystallizable or complement activation. The Fc fragments possess binding sites for the complement factor C1q. The heavy chain contributes to the Fc portion of the antibody and the Fab region of the antibody while the light chain contributes only to the Fab region of the antibody. ▬ Antigenic Determinants on Immunoglobulins ▬▬▬▬▬▬▬▬▬▬ We have different types: isotypic determinants, allotypic determinants, and idiotypic determinants variants. 👉 Isotypic determinants are responsible for the amino acid differences in Fc regions and subsequently between immunoglobulin classes and subclasses and between heavy and light chains. 👉 Allotypic determinants are variations in the constant regions of immunoglobulins of the isotype, owing to allelic variation in the genes found among different individuals. 👉 Idiotypic determinants are the individual determinants of any given antibody molecule by the variability of the immunoglobulins CDR region. ▬ Immunoglobulins and Electrophoretic Mobility ▬▬▬▬▬▬▬▬▬▬ The blood mainly contains three types of globulins, alpha, beta, and gamma, based on their electrophoretic migration rate. It refers to the migration and separation of charged particles or ions, under the influence of an electric field. 🔹IgG Immunoglobulins migrate into the gamma–globulin fraction 🔹While other immunoglobulins especially IgM and IgD have a lower electrophoretic mobility and are found mainly in the beta-globulin fraction but also the alpha 2- fraction. ▬ Classes of Immunoglobulins and Their Functions ▬▬▬▬▬▬▬▬▬▬ Let’s summarize the main features of immunoglobulins. They are classified into five classes. IgE, IgG, and IgD exist as monomers, while IgA is a dimer and IgM a pentamer. 🔵 IgG is responsible for the secondary response, Type III Hypersensitivity, and opsonization. 🔵 IgM is produced early in the primary response, agglutination, and complement fixation. 🔵 IgA produces body secretions that function as a protective barrier. 🔵 IgD is not known to have much clinical significance. 🔵 IgE is significant for Type I Hypersensitivity and host defense against helminths.