Examples of antigenic variation in the following topics:
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- This is referred to as antigenic variation.
- The constant change of these antigens is why vaccines have not been created.
- Another common strategy that is used is to mask antigens with host molecules in order to evade detection by the immune system.
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- Phase and Antigenic Variation in Bacteria. pA is the promoter for FimA, pB is the promoter for FimB and pE is the promoter for FimE.
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- If one of these new forms of an antigen is sufficiently different from the old antigen, it will no longer bind to the receptors and viruses with these new antigens can evade immunity to the original strain of the virus.
- Two processes drive the antigens to change: antigenic drift and antigenic shift (antigenic drift being the more common).
- Antigenic drift is a mechanism for variation by viruses that involves the accumulation of mutations within the antibody-binding sites so that the resulting viruses cannot be inhibited as well by antibodies against previous strains, making it easier for them to spread throughout a partially immune population.
- Antigenic drift occurs in both influenza A and influenza B viruses.
- Alternatively, the change can occur by antigenic shift .
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- Precipitation reactions are based on the interaction of antibodies and antigens.
- These reactions depend on the formation of lattices (cross-links) when antigen and antibody exist in optimal proportions.
- Precipitation reactions differ from agglutination reactions in the size and solubility of the antigen and sensitivity.
- Antigens are soluble molecules and larger in size in precipitation reactions.
- Precipitation methods include double immunodiffusion (qualitative gel technique that determines the relationship between antigen and antibody), radial immunodiffusion (semi-quantitation of proteins by gel diffusion using antibody incorporated in agar), and electroimmunodiffusion (variation of the double immunodiffusion method reaction that uses an electric current to enhance the mobility of the reactants toward each other).
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- Enzyme-linked immunosorbent assay (ELISA) is a method of quantifying an antigen immobilized on a solid surface.
- The amount of antibody that binds the antigen is proportional to the amount of antigen present, which is determined by spectrophotometrically measuring the conversion of a clear substance to a colored product by the coupled enzyme.
- Several variations of ELISA, seen in , exist but the most commonly used method is the sandwich ELISA.
- The antigen serves as bridge, so the more antigen in the test solution, the more enzyme-linked antibody will bind .
- The concentration of antigens can be inferred from absorbance readings of standard solutions.
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- The misconception that an individual's immune system is totally incapable of recognizing self antigens is not new.
- Second, autoimmunity may have a role in allowing a rapid immune response in the early stages of an infection when the availability of foreign antigens limits the response (i.e., when there are few pathogens present).
- Immunoglobulins and T-cell receptors are involved in the recognition of antigens and they are inherently variable and susceptible to recombination.
- These variations enable the immune system to respond to a very wide variety of invaders, but may also give rise to lymphocytes capable of self-reactivity.
- HLA-DR is a MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31.
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- The misconception that an individual's immune system is totally incapable of recognizing self antigens is not new.
- Now, it is accepted that autoimmune responses are an integral part of vertebrate immune systems (sometimes termed 'natural autoimmunity'), normally prevented from causing disease by the phenomenon of immunological tolerance to self-antigens.
- Immunoglobulins and the T-cell receptors are involved in the recognition of antigens and they are inherently variable and susceptible to recombination.
- These variations enable the immune system to respond to a very wide variety of invaders, but may also give rise to lymphocytes capable of self-reactivity.
- HLA-DR is a MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31.
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- Diversity of antigen presentation, mediated by MHC classes I and II, is attained in multiple ways:
- Human MHC class I and II are also called human leukocyte antigen (HLA).
- The variations in the MHC molecules (responsible for the polymorphism) are the result of the inheritance of different MHC molecules, and they are not induced by recombination, as it is the case for the antigen receptors.
- The human leukocyte antigen (HLA) system is the name of the major histocompatibility complex (MHC) in humans.
- This group of genes resides on chromosome 6, encodes cell-surface antigen-presenting proteins and has many other functions.
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- They have antigen receptors that are structurally related to antibodies.
- These structures help recognize antigens only in the form of peptides displayed on the surface of antigen-presenting cells.
- These include naive T cells that recognize antigens and are activated in peripheral lymphoid organs.
- Memory T cells are an expanded population of T cells specific for antigens that can respond rapidly to subsequent encounter with that antigen and differentiate into effector cell to eliminate the antigen.
- T cells promote the killing of cells that have ingested microorganisms and present foreign antigens on their surface.
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- Agglutination is the visible expression of the aggregation of antigens and antibodies.
- Agglutination reactions apply to particulate test antigens that have been conjugated to a carrier.
- The endpoint of the test is the observation of clumps resulting from that antigen-antibody complex formation.
- Direct bacterial agglutination uses whole pathogens as a source of antigen.
- The binding of antibodies to surface antigens on the bacteria results in visible clumps.