ANTIGENS AND MAJOR HISTOCOMPATIBILITY COMPLEX

• Immunogens are macromolecules capable of triggering an adaptive immune response by inducing formation of antibodies or sensitized T cells in an immunocompetent host.
• Antigens are Substances that react with an antibody or sensitized T cells but may not be able to evoke an immune response in the first place
• The larger the immunogen the more potent the response and the more likely it is to be detected by the antibody.
• Immunogens must be at least 10000 Dalton and those with more than 100000 Dalton are more potent.
• Weak immunogens are more than 1000 daltons but less than 6000 daltons.
• Foreignness is the degree to which antigenic determinants are recognized as nonself.
• The more foreign the immuniogen the more potent it is, more likely to be recognized by the immune system
• Autoantigens are antigens that belongs to the host. Autoantigens elicits no immune response.
• Alloantigens are antigens from other members of host species. Same species different individual.
• Heteroantigens or xenoantigens are antigens from other species.
• Heterophile Antigens are antigens that exist in unrelated plants or animals but are identical or closely related in structure.
• Proteins and polysaccharides are the most effective immunogens. But between the two, proteins are more immunogenic.
• Polymers such as nylon and teflon are non immunogenic.
• Haptens are incomplete immunogens but when attached to larger molecules they can elicit an immune response.
• Pure nucleic acids and lipids are non immunogenic on their own but are haptens.
• T-cells need MHC molecules in order to recognise foreign antigens.
• CD4 is the co receptor for Helper T-cells
• CD8+ is the receptor for Cytotoxic T-cells
• Epitopes are the site of attachment to where antibodies bind and this can help determine the antigen present.
• Sequential/linear epitopes are for antibodies that has a single chain Or linear chain.
• Conformational epitope is folding of one or multiple chains bringing certain amino acids from different segments of a linear sequence in close proximity.
• B cells can react to both linear and conformational epitopes
• T-cells can only react to peptides presented by Antigen-presenting Cells. Specifically to conformational epitope.
• Linear epitope is the only epitope to produce an IgM due to B-cell.
• Adjuvants are substance administered with an immunogen that increases the immune response in order to provide immunity to the host
• Adjuvants protects immunogen from degradation allowing a longer response. This helps in redusing necessity to booster immunizations. But Adjuvants must cause minimal toxicity.
• Monoclonal Activators are subtansces that stimulate cells to generate a population of 1 clone. One population of cell to responds.
• Oligoclonal activators are substances taht stimulate a subset of cells that has a common feature in the antigen receptor to generate a population of few different clones.
• Super antigens is a form of oligoclonal activator
• Most antigens are monoclonal activators
• Polyclonal Activators are substances that binds to molecules present to all T cells and/or B cells; whole cell population becomes activated and generates many clones
• Artificial Reagents from plant like mytogens are examples of polyclonal activators
• Major Histocompatibility Comples is the genetic capability of an individual to mount an immune response is linked to a group of molecules
• Major Histocompatibility Complex (MHC) are originally referred to as human leukocyte antigen (HLA)
• MHC is found on all of the nucleated cells in the body and plays an important role in humoral and cell mediated immunity.
• MHC genes are found on the short arm of chromosome 6
• MHC genes is the most polymorphic system in humans.
• Polymorphism allows for an immune response to diverse immunogens.
• Class 1 Gene is found in three different loci (A, B, C); only one gene is coding for each molecules
• Class 2 Gene is located located in the D region with different loci (DR, DQ, DP); 1 gene for Alpha chain; 1 or more gene for beta chain.