Passage
Viruses are known as obligate intracellular parasites because they cannot reproduce independently (outside of a host cell). Viral genomes (RNA or DNA) are enclosed by a protein shell known as the capsid. Some viruses, known as enveloped viruses, have an additional phospholipid bilayer that fully envelops the capsid. Viruses that lack this outermost phospholipid covering are labeled non-enveloped. The entry of either enveloped or nonenveloped viruses into a host cell enables the production of viral proteins and the subsequent assembly of viral progeny.Immune cells (B and T cells) protect host organisms against viral infections by recognizing viral particles (antigens) as foreign. In response to the recognition of foreign particles, antigen-presenting cells display cleaved antigens (also known as antigen fragments) on their surface, which enable the activation of other immune cells that stimulate an immune response, including the production of neutralizing antibodies.An example of an infectious disease is viral hepatitis (inflammation of the liver), which can be caused by any one of five distinct hepatitis viruses (A-E) that infect hepatocytes (liver cells). HAV, HCV, and HEV contain positive-sense, single-stranded RNA (+ssRNA) as genetic material. In contrast, HBV has a partially double-stranded circular DNA genome. HDV is unique because it has a negative-sense, single-stranded RNA (−ssRNA) genome.Researchers hypothesized that synthetic antibodies could be used to treat viral hepatitis in patients with compromised immune systems. Fluorescent antibodies, designed to bind the capsid proteins of the five hepatitis viruses, were added to separate wells containing each type of virus. The fluorescence assay that was performed detected only bound antibodies in media with HAV or HEV.
Adapted from Shin EC, Sung PS, Park SH. Immune responses and immunopathology in acute and chronic viral hepatitis. Nat Rev Immunol. 2016;16(8):509-23.
-An individual with hepatitis is suspected to have been exposed to either a bacterial strain of Bartonella henselae (0.5 µm) or HCV (0.055 µm). Healthy hepatocytes and hepatocytes infected with serum from the affected patient were grown on chamber slides separated by double membranes, as shown below. A cellular morphology similar to infected hepatocytes was observed in both chambers 2 and 3 after a 6 hour incubation time. Using a light microscope, can investigators observe the agent that caused the patient's hepatitis in chamber 3?

Question

Passage
Viruses are known as obligate intracellular parasites because they cannot reproduce independently (outside of a host cell).  Viral genomes (RNA or DNA) are enclosed by a protein shell known as the capsid.  Some viruses, known as enveloped viruses, have an additional phospholipid bilayer that fully envelops the capsid.  Viruses that lack this outermost phospholipid covering are labeled non-enveloped.  The entry of either enveloped or nonenveloped viruses into a host cell enables the production of viral proteins and the subsequent assembly of viral progeny.Immune cells (B and T cells) protect host organisms against viral infections by recognizing viral particles (antigens) as foreign.  In response to the recognition of foreign particles, antigen-presenting cells display cleaved antigens (also known as antigen fragments) on their surface, which enable the activation of other immune cells that stimulate an immune response, including the production of neutralizing antibodies.An example of an infectious disease is viral hepatitis (inflammation of the liver), which can be caused by any one of five distinct hepatitis viruses (A-E) that infect hepatocytes (liver cells).  HAV, HCV, and HEV contain positive-sense, single-stranded RNA (+ssRNA) as genetic material.  In contrast, HBV has a partially double-stranded circular DNA genome.  HDV is unique because it has a negative-sense, single-stranded RNA (−ssRNA) genome.Researchers hypothesized that synthetic antibodies could be used to treat viral hepatitis in patients with compromised immune systems.  Fluorescent antibodies, designed to bind the capsid proteins of the five hepatitis viruses, were added to separate wells containing each type of virus.  The fluorescence assay that was performed detected only bound antibodies in media with HAV or HEV.
Adapted from Shin EC, Sung PS, Park SH. Immune responses and immunopathology in acute and chronic viral hepatitis. Nat Rev Immunol. 2016;16(8):509-23.
-An individual with hepatitis is suspected to have been exposed to either a bacterial strain of Bartonella henselae (0.5 µm) or HCV (0.055 µm).  Healthy hepatocytes and hepatocytes infected with serum from the affected patient were grown on chamber slides separated by double membranes, as shown below.  A cellular morphology similar to infected hepatocytes was observed in both chambers 2 and 3 after a 6 hour incubation time.  Using a light microscope, can investigators observe the agent that caused the patient's hepatitis in chamber 3?

Quizplus · Accepted Answer

11ecba2d_0fe3_45d7_a3bf_372b8e9574a7_MD0008_00 The double-membrane system illustrated in the question was used to separate B. henselae and HCV on the basis of size. In comparison to eukaryotic cells (10-100 µm in diameter), B. henselae cells and viruses are much smaller. The average prokaryotic cell is 0.5-2 µm in diameter, and most viruses range between 0.02-0.3 µm in diameter. Therefore, both B. henselae and HCV can pass through the first membrane from chamber 1 into chamber 2 and infect healthy hepatocytes. In contrast, movement into chamber 3 is restricted to HCV because the 0.2-µm pores are too small for B. henselae (0.5 µm) to pass through. Because hepatocytes in both chambers 2 and 3 were infected, it can be concluded that HCV played a role in the infection and not B. henselae (Choices B and D). The question suggests the use of light microscopy in chamber 3 to observe the presence of the causative agent. A light microscope has a resolution of 200 nm (0.2 µm); consequently, investigators can use it only to observe cells larger than 0.2 µm. For viruses such as HCV, which are 100 times smaller than bacteria and 1,000 times smaller than eukaryotic cells, visual observations require greater resolution. As a result of the 0.2-µm pore size leading to chamber 3 and the low resolution of the instrument, investigators will be unable to observe the causative agent of the hepatitis visually using a light microscope. (Choice A) Although HCV is small enough to infect both chambers, investigators would be unable to observe the causative agent by analyzing chamber 3 with a light microscope due to its restrictive resolution. Educational objective: Prokaryotic cells such as bacteria are approximately 10 times smaller than eukaryotic cells. Viruses are about 100 times smaller than bacteria and 1,000 times smaller than eukaryotic cells. Unlike bacteria, viruses cannot be observed with a light microscope because viral particles are smaller than the microscope's maximum resolution.