MICR 2537 Test 2 Notes - Antigens: Molecules that bind to...

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Antigens: Molecules that bind to antibodies Antigenicity: Ability to react to antibody Immunogens: Molecules that induce an immune response (humoral response, and cell mediated response). Immunogenicity: Ability to induce immune response. In most cases, antigens are immunogens are used interchangeably. Exceptions - Haptens Haptens: molecules are not immunogenic consist only of a determinant group and are too small by themselves to elicit an immune response. not immunogenic by itself but can react with specific antibody. Usually small molecules but some high-moleculer weight nucleic acids are haptons as well many drugs, eg, Penicllins, are haptons . Catechol in the plant oil that causes poision oak and poision ivy is a hapten . Haptons not immunogenic b/c cannot activate helper T cells. The failure of haptens to activate is due to their inability to bind to MHC proteins; they cannot bind because they are not polypeptides and only polypeptides can be presented by MHC proteins. Haptons are univalent and cannot activate B cells by themselves. Haptons cannot stimulate a primary or secondary response by themselves, they can do so when covalently bound to a carrier Protein (figure). H ow haptens interact? Haptens (such as drugs penicillin and poison oak oil) bind to our normal proteins, to which we are tolerant. The hapten- protein combination now becomes immunogenic, and recognized as foreign. Most haptens are univalent, type 1 hypersensitivity reactions such as anaphylaxis require cross linking of adjacent IgEs to trigger the release of the mediators. By itself, a univalent hapten cannot cross-link, but when many hapten molecules are bound to the carrier protein, they are arranged in such a way that cross-linking can occur. Requirements for Immunogenicity: Foreignness : Molecules recognized as “self” are not immunogenic. Molecular Size : The most potent immunogens are proteins with high molecular weight (above 100,000, Proteins and polysaccharides are the most first and second potent immunogen respectively). Chemical Structural Complexity A certain amount of complexity is required. Amino acids homopolymers are weaker immunogen than heteropolymers containing two or three different amines Antigenic Deteminant ( Epitopes) Epitopes are small chemical group of the antigen molecule that can elicit and react with antibody. An antigen can have one or more determinants. Most antigens have many epitopes and are multivalent. The overall three-dimensional structure is the main criterion of antigenic specificity. The immune system recognizes epitopes. Dosage, Route, and Timing of Antigen/ Immunogen Administration: These factors also can affect immunogenicity.
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Genetic The genetic constitution of the host determine whether a molecule is immunogenic. Adjuvant
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MICR 2537 Test 2 Notes - Antigens: Molecules that bind to...

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