Every person contains endogenous retroviruses that are permanently integrated into the human genome.

Although autoimmune diseases exhibit diversity in the affected tissues and severity of symptoms, a breach of T cell tolerance appears to be an important driver of autoimmunity in general. (a) How could a breach of T cell tolerance occur? (b) Describe the evidence that suggests a key role for T cells in mediating autoimmune disease. Your answer should include one or two specific pieces of evidence and an explanation for why the evidence points to the involvement of T cells.

The human immune system defends against a wide variety of pathogens. Unicellular pathogens can be classified as intracellular or extracellular, and the immune system must target these two types of pathogens differently. (a) Contrast intracellular and extracellular infections and the pathogens that cause them. Describe key differences. (b) Contrast the innate immune system response to intracellular and extracellular infections and the pathogens that cause them. Describe key differences.

Which of the following events would cause urticaria?

 Which of the following events occurs in a person infected with HIV?

Why is a randomly-placed, small rectangular plot used for the sampling?

Which of the following statements regarding immunological memory is true?

Which of the following best explains why most vaccinations require at least two doses to be effective?

Memory T cells survive in the body even in the absence of antigen.

Match the stage with the correct description of task.