WBR0340

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Immunology
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::To study the cellular responses to Influenza virus infection, a student exposes 2 groups of mice to the virus, one group with completely ablated bone marrows, and another control group with intact bone marrows. The student notices that in the control group, levels of an intracellular protein (Protein A) in muscle cells rises in parallel with the intracellular activity of 2′–5′ oligoadenylate synthetase and serum levels of IFN-α/β. This reaction is absent in the group with ablated bone marrows, whereas Influenza viral load is much more elevated than the control group. What is the most likely function of protein A?]]
Answer A	AnswerA::Phospholipase
Answer A Explanation	AnswerAExp::Interferons do not induce an antiviral response by activating phospholipases.
Answer B	AnswerB::Endonuclease
Answer B Explanation	AnswerBExp::Interferons do not induce an antiviral response by activating endonucleases.
Answer C	AnswerC::Protease
Answer C Explanation	AnswerCExp::Interferons do not induce an antiviral response by activating proteases.
Answer D	AnswerD::Deoxyribonuclease
Answer D Explanation	AnswerDExp::Interferons do not induce an antiviral response by activating deoxyribonuclease.
Answer E	AnswerE::Ribonuclease
Answer E Explanation	AnswerEExp::Interferons activate a ribonuclease (RNase L) that creates an antiviral state in neighboring cells by destroying viral RNA.
Right Answer	RightAnswer::E
Explanation	[[Explanation::Interferons represent a diverse family of proteins involved in cell growth, antiviral defense, and immune activation. Interferons are of 2 major types. Type I interferons are the product of a direct response to viral infection consisting of IFN-α produced mainly by the immune system, and IFN-β produced by most cell types. Type II interferons represent the IFN-γ product that is usually produced after the recognition of infected cells by T-lymphocytes. IFNs induce an antiviral state within target cells by activating RNAse L a ribonuclease that breaks down viral RNA and inhibits viral replication. RNAse L is activated by 2′–5′ oligoadenylate synthetases, a group of enzymes induced by interferon binding to its receptor. Educational objective: Interferons create an antiviral state within the target cells by activating RNAse L a ribonuclease that breaks down viral RNA. Reference: Goodbourn S, Didcock L, Randall RE. Interferons: cell signalling, immune modulation, antiviral response and virus countermeasures. J Gen Virol. 2000;81(Pt 10):2341-64. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Interferon, WBRKeyword::Ribonuclease, WBRKeyword::RNAse L
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::