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Question | Answer |
Immunoglobulin Structure and Functions | Immunoglobulins, synthesized by B cells, are antigen-binding glycoproteins (antibodies) that function in the recognition of and defense against antigens |
Chain Structure of Immunoglobulins | Each monomeric antibody molecule comprises two identical heavy (H) chains and two identical light (L) chains (k or lambda) Antigenic specificity is determined by the amino acid sequence of the variable domains near the amino-terminal end of each chain. Light chains contain one variable domain and one constant domain. Sequence differences in the constant-region domain define two types of light chains, k and lambda. Heavy chains contain one variable domain (VH) and three or four constant domains (CH1, CH2 etc) Sequence differences in the constant region domains define five major types of heavy chains u, y, alpa, epsiv, |
Adjuvant | Substance that enhances immune response to an antigen when administered with it; used to improve response to vaccines. |
Affinity | Binding strength of a single variable region of an antibody for corresponding epitope on the larger antigen structure. |
Antigen | Substance that binds to antibodies and T cell receptors. Although most antigens are also immunogens, some small molecules are antigenic but not immunogenic. |
Avidity | Combined binding strength of the multiple interactions between a multivalent antibody molecule and all the corresponding epitopes on an antigen. |
Epitope (antigenic determinant) | Region on an antigen molecule to which a single antibody molecule or T cell receptor binds. An antigen usually have multiple epitopes and thus can react with antibodies of different specificities. |
Fab fragment | Portion of antibody molecule, produced by papain digestion, that contains a single antigen-binding site. All antibodies have two or more Fab regions and thus are bivalent or multivalent. |
Fc fragment | Portion of antibody molecule, produced by papain digestion, that fixes complement and binds to Fc receptors, varies among immunoglobulin isotypes |
Hinge region | Flexible portion of antibody heavy chains located between the Fab and Fc region and containing intrachain disulfide bonds; present in IgG, IgA and IgD |
Immunogen | Substance capable of eliciting a specific immune response |
Monoclonal antibody | Homogenous antibody that recognizes only one epitope; produced by a single clone of plasma cells |
Polyclonal antibody | Mixture of antibodies that recognize different epitopes on an antigen; produced by different clones of plasma cells in response to an antigen containing different epitopes. Natural antiserum to a microbial antigen is polyclonal. |
Thymus-dependent antigen | Antigens that require helper T cells to induce antibody production (humoral response), most protein antigens |
Thymus independent antigens | Antigens possessing many repetitive structures (eg flagellin, polysaccharide, and LPS) that can induce antibody production (humoral response) without helper T cells |
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