Following infections with many viruses, host cells often down-regulate MHC class
ID: 259203 • Letter: F
Question
Following infections with many viruses, host cells often down-regulate MHC class I expression. This immune evasion mechanism allows the virus to hide from CD8 T lymphocytes that normally detect virus-infected cells by using their T cell antigen receptor to recognize viral peptides bound to MHC class I proteins on the surface of the infected cell. To counteract this immune evasion strategy, NK cells have [complete the sentence and assess the resulting statements (37-41) as either factually correct (true) or incorrect (false)]: 37. activating receptors that recognize viral capsid proteins. 38. activating receptors that recognize MHC class I proteins. 39. inhibitory receptors that recognize viral capsid proteins. 40. inhibitory receptors that recognize MHC class I proteins. 41. a special mechanism to augment the secretion of antiviral peptides.
Explanation / Answer
Ans. For this case,
37). True. NK cells will express activating receptors that recognize viral capsid particles.
38). False. NK cells will recognize and kill infected cells having no MHC class I molecules or low level of class I MHC.
39). False. NK cells do not inhibitory receptors for viral capsid proteins.
40). False. In this case, if NK cells show inhibitory receptors that recognize MHC class I proteins, function of NK cells will inhibit.
41). True.For infected cells, NK cells will show a special mechanism to augment the secretion of antiviral peptides, such as degranulation to release granzyme and perforin.