WBR0346

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A researcher is studying the variability of viral envelopes and their function in viral pathogenesis. In one of his experiments, he attempts to identify viruses by the properties of their envelopes. He mixes lysates of cells infected with 5 different viral species with sheep red blood cells and obtains the grid shown below. Which of the following viruses is most likely to represent cell 4? ]]
Answer A	AnswerA::Measles virus
Answer A Explanation	AnswerAExp::The measles virus envelope contains hemagglutinin and would cause RBCs to agglutinate.
Answer B	AnswerB::Mumps virus
Answer B Explanation	AnswerBExp::The mumps virus envelope contains hemagglutinin and would cause RBCs to agglutinate.
Answer C	AnswerC::Influenza virus
Answer C Explanation	AnswerCExp::The influenza virus envelope contains hemagglutinin and would cause RBCs to agglutinate.
Answer D	AnswerD::Parainfluenza virus
Answer D Explanation	AnswerDExp::The parainfluenza virus envelope contains hemagglutinin and would cause RBCs to agglutinate.
Answer E	AnswerE::Herpes virus
Answer E Explanation	AnswerEExp::The herpes virus envelope lacks hemagglutinin, thus shows a lack of sheep RBC agglutination.
Right Answer	RightAnswer::E
Explanation	[[Explanation::Hemagglutinin is a glycoprotein found on the surface of many viruses including measles, mumps, influenza, and parainfluenza. It allows the virus to bind to the tissue and determines its tropism. When examined in vitro, it has the ability to agglutinate red blood cells thus the name. Not all hemagglutinins are the same. Each has a different binding target and function, they only share their ability to agglutinate red blood cells. The most studied hemagglutinin type is the inflenza virus hemagglutinin that binds to sialic acid and determines the viral strain (subtypes are named H1 through H18). Educational Objective: Hemagglutinin, a type of glycoprotein found on the surface of many viruses including measles, mumps, influenza, and parainfluenza, has the ability to agglutinate RBCs. References: Skehel JJ, Wiley DC. Receptor binding and membrane fusion in virus entry: the influenza hemagglutinin. Annu Rev Biochem. 2000;69:531-69.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Hemagglutinin, WBRKeyword::Measles, WBRKeyword::Mumps, WBRKeyword::Influenza, WBRKeyword::Parainfluenza, WBRKeyword::Agglutination
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