T lymphocytes and the cellular responseAQA A-Level Biology: Mind map

Exam questions on T lymphocytes and the cellular response

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.
   Explain why only certain helper T cells are activated in response to the viral antigen.2 marks
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.
   Explain why the concentration of virus stayed high in the engineered mice.2 marks
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.
   Explain why the cytotoxic T cells killed only the infected liver cells.3 marks