T lymphocytes and the cellular responseAQA A-Level Biology: Subtopic test

1. 1
   A researcher infected mice with a virus and later examined their immune cells. Macrophages that had engulfed viral particles were found to have fragments of viral protein on their surface. Only a small proportion of the helper T cells in each mouse became active and divided.

   (a)

   What name is given to a cell, such as the macrophage in this investigation, that displays fragments of a pathogen's antigens on its surface?

   [1 mark]

   • AA plasma cell
   • BAn antigen-presenting cell
   • CA cytotoxic T cell
   • DA memory cell

   (b)

   Which of the following best explains why only a small proportion of helper T cells became active?

   [1 mark]

   • AOnly helper T cells with receptors complementary to the presented viral antigen bind to it and are activated
   • BHelper T cells can only be activated if they are outside the thymus
   • CMost helper T cells were destroyed by lysozymes in the macrophage
   • DHelper T cells only respond to antibodies on the macrophage surface

   (c)

   Explain why only certain helper T cells are activated in response to the viral antigen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Mice were genetically engineered so that they could not produce helper T cells (TH cells). They were infected with a virus, alongside normal mice. Compared with the normal mice, the engineered mice produced few cytotoxic T cells and few antibodies, and the concentration of virus in their tissues stayed high.

   (a)

   Which statement best explains why the engineered mice produced few cytotoxic T cells?

   [1 mark]

   • AThere were no macrophages to engulf the virus
   • BCytotoxic T cells are produced only from B cells, which the mice lacked
   • CThere were no helper T cells to release the cytokines that stimulate cytotoxic T cells to divide
   • DAntibodies destroyed the cytotoxic T cells

   (b)

   Which process would still have occurred in the engineered mice?

   [1 mark]

   • AStimulation of B cells by cytokines from helper T cells
   • BDivision of cytotoxic T cells in response to cytokines
   • CIncreased phagocytic activity stimulated by helper T cell cytokines
   • DPhagocytosis of viral particles by macrophages

   (c)

   Explain why the concentration of virus stayed high in the engineered mice.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A virus infects liver cells. A scientist mixed cytotoxic T cells from an infected mouse with two cultures: liver cells infected with the virus, and uninfected liver cells. Only the infected liver cells were killed.

   (a)

   Explain why the cytotoxic T cells killed only the infected liver cells.

   [3 marks]

   (b)

   Antibodies are present in the blood plasma of an infected mouse. Explain why they cannot remove virus from inside infected liver cells and why the cellular response is needed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A person's lung epithelial cells are infected with a respiratory virus. In the lung tissue, a macrophage engulfs and digests some of the virus particles. Over the next few days the person's cellular immune response develops, and the virus is eventually cleared.

   (a)

   Explain how the engulfing of virus particles by the macrophage leads to the activation of helper T cells.

   [6 marks]

   (b)

   Evaluate the role of helper T cells in clearing the virus from the person's body.

   [6 marks]

   Total for question 4: 12 marks

End of questions