Antigenic Variation
Antigenic variation refers to the ability of pathogens, such as viruses and bacteria, to alter their surface antigens in order to evade the host's immune response. This process allows the pathogen to avoid recognition by the immune system, leading to recurrent infections and making it challenging to develop effective vaccines or treatments.
3 Key excerpts on "Antigenic Variation"
eBook - ePubThe Arboviruses:
Epidemiology and Ecology
- Thomas P. Monath(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...Enhancement mediated by reorganization of proteins following antibody binding might explain some of the conflicting observations on immune enhancement of flaviviruses. Regardless of mechanism, it appears that immune enhancement is epitope dependent. Virus strains possessing these epitopes would have a distinct selective advantage over similar strains mutant in the “enhancement epitopes”. Under such circumstances, enrichment of variant virus subpopulations possessing enhancement epitopes could readily occur, and a new antigenically distinct virus population would result. E. Summary of Immune Mechanisms in Antigenic Variability of Arboviruses A number of immune mechanisms by which subpopulations of mutant viruses could be amplified have been discussed. The importance of these mechanisms in nature is currently unknown. The effects that antigenic diversity has on the phenotypic markers of adsorption, replication, pathogenesis, and virulence are also unknown. It will be important to determine whether those antigenic variants produced in the laboratory resemble naturally occurring viruses. It is obvious that rampant Antigenic Variation does not occur. In fact, many of the arbovirus populations are extremely stable (e.g., EEE virus). This antigenic stability probably results from the exquisite checks and balances between immune response and the structural constraints on the association of virus with its cellular receptors in vertebrate and invertebrate hosts. With such potent control mechanisms in place, it is probably not unusual that significant virus Antigenic Variation occurs only infrequently. V. Epidemiologic Significance One can only speculate concerning the epidemiologic implications of arbovirus evolution. Dramatic changes in the epidemiology of certain arboviruses may or may not be attributable to evolutionary events. There are examples of disease outbreaks or altered arbovirus epidemiology in which virus variation could have played an important role...
eBook - ePub- Barry R. Bloom, Barry R. Bloom, Paul-Henri Lambert, Barry R. Bloom, Barry R. Bloom, Paul-Henri Lambert(Authors)
- 2002(Publication Date)
- Academic Press(Publisher)
...Innumerable specificities of antibodies are usually induced by virus infection, but only neutralizing antibodies are protective [ 3, 19 ]; other antibodies, particularly those against internal viral antigens, are virtually irrelevant for protection. Those infections that tend to persist, including many viruses [ 15, 40, 61 ] such as HBV, HCV, and HIV, facultative intracellular bacteria such as mycobacteria [ 8, 9, 33, 37 ], and other intracellular parasites, are usually controlled initially by T cells. II. THE ROLES OF EARLY EVENTS AND PARASITE VARIABILITY IN HOST–PARASITE RELATIONSHIPS Most cytopathic agents leave little leeway between death and survival. In contrast, a wide range of relationships is possible between low or noncytopathic infections and the host. Many parameters, such as interferon production and susceptibility of the infection to interferons, influence this equilibrium. In addition, mutation rates of the pathogens play a major role. Variability of antigens permits infectious agents to escape T cells or neutralizing antibodies, in the individual as well as at the population level. The variability of the parasite genome plays a major role in these selections. Selection of mutations is driven by epidemiological forces, either in the whole population, such as antigenic drift and shift in acute influenza viruses, or within an individual host for persistent viruses, such as HBV and possibly HIV or LCMV in mice. Therefore, RNA viruses that have an error-prone genome are particularly variable and can escape host immune responses efficiently...
eBook - ePubBacterial Pathogenesis
A Molecular Approach
- Brenda A. Wilson, Malcolm Winkler, Brian T. Ho(Authors)
- 2019(Publication Date)
- ASM Press(Publisher)
...The phage-host arms race: shaping the evolution of microbes. BioEssays 33 : 43–51. [PubMed] [CrossRef] Touchon M, Moura de Sousa JA, Rocha EP. 2017. Embracing the enemy: the diversification of microbial gene repertoires by phage-mediated horizontal gene transfer. Curr Opin Microbiol 38 : 66–73. [PubMed] [CrossRef] Wilson BA, Salyers AA. 2003. Is the evolution of bacterial pathogens an out-of-body experience? Trends Microbiol 11 : 347–350. [PubMed] [CrossRef] Questions 1. Should microbiologists be alarmed about the unknown risks posed by bacteria gaining potential virulence traits from external environmental sources? 2. Is acquisition of a PAI sufficient to transform an organism into a pathogen? 3. What is the advantage of incorporating virulence genes into the chromosome over retaining them on plasmids? 4. You have identified an operon on a new strain of E. coli that encodes for three genes involved in capsule biosynthesis as well as a regulatory gene. After careful analysis of the operon and its flanking DNA sequences, you suspect that the operon is located on a pathogenicity island that is a lysogenic prophage. What possible evidence might have led you to propose this? 5. Neisseria species are known to undergo both phase and Antigenic Variation. Define phase versus Antigenic Variation and describe how each might occur. What advantage do they provide for a pathogen? 6. What role have bacteriophages played in pathogen evolution? 7. Some researchers have tried to identify the pathogenicity islands in Salmonella by comparing the E. coli K12 genome with that of S. typhimurium. What are the advantages and disadvantages of this approach? 8. Which types of variation in surface antigens would still be seen in a strain of N. gonorrhoeae that was deficient in the ability to carry out homologous recombination? 9. Bacterial cells have the ability to change the set of genes that they express in response to changes in the environment...
