Question

Learning Outcomes 1. Describe the nature and characteristics of antigens and how they stimulate the immune system. Understand the role of the Major Histocompatibilty Complex (MHC) in antigen processing. Differentiate autoantigens from alloantigens. 2. 3.

Answer 1

1, Nature and charecteristics of Antigen:
Antigen is an organism,molecules or substance..It has immune response and fight with antibodies..it can able to induce adaptive immunity called immunogens. It is an antigens they have the ability to stimulate an immune response..Foreign agents can act as an antigen,it may be a chemical substance like protein,biological substance like bacteria and its products.fungi, virus etc..Infectious agent macro-molecules can be recognized by immune system..Polysaccharides are in second protein in immunogens, lipids and nuclic acid is a infectious agent it can attached with proteins or polysaccharides..Biological products like milk,snake venom, are good source of antigen..gram- negative bacteria,cytoplasmic protein,exotoxins,endotoxins have antigenic property can have immune response against them..sometimes self-protein foreign substance against to control the Auto-immunity..There are some factors the power of antigen has that is molecular size, structural stability, degradability,chemical composition,foreignness ,conformation and accessibility,Antigen processing,hetrogenecity..
2, The Major Histocompatibility complex(MHC) molecules bind peptide fragments from pathogens and distributing that on cell surface as a T-cells..The consequences to the pathogens virus- infected cells are killed ,macro pages activated to kill bacteria intracellular vesicles B cells activated to produce antibodies that neutralize extracellular pathogens..
There are two seperate properties of the MHC make pathogens difficult to promote immune response..that is polygenic, it has class I and II MHC genes so each person has different range of MHC molecules of peptide-binding specificities..second one is polymorphic ..These has multiple variants of each gene with in the peoples..The MHC genes are mostly polymorphic genes..MHC class I and II glycoproteins that prevent peptides to the T-cells receptors..The polymorphism is important antigen recognition by T-cells..
T-cells recognize the action as a peptide by allelic variant of an MHC molecules, it restrict some peptide to MHC molecules..this T-cells behaviour called MHC restriction..MHC alleles differ from each person to person by multiple aminocaids substitutions ..the range of peptide bound,conformation of the bound peptide and direct interaction of MHC molecules with T cells receptor affected by MHC polymorphism..High polymorphic nature in critical role polymorphism immune response genetic mechanism can be seen in MHC alleles..Pressure of maintain MHC molecules in the population comes from infectious agents..
3, Autoantigens:
Any Antigens that stimulates autoantibodies in the organism that produced it..
Alloantigens :
Antigens present in some people but not all individuals and having capable of inducing the production of alloantibody by individuals..