Question of the Day (13-Apr-17)
Answer the question based on the passage given below.
In the hierarchy of transplant surgery, replacing a bronchus (the passage from the main windpipe, the trachea, into a lung) does not sound difficult compared with, say, plumbing in a new heart. In fact it had never been attempted and transplant surgeons have left well-enough alone. The reason was not that the surgery itself would be hard, but that the tissue in question, which is the first line of defence against the bacteria and viruses that come with every lungful of air, has a remarkably active immune response. So active, indeed, that if you transferred part of an airway from one person to another, the resulting immunological conflict would probably kill the recipient.
Which of the following (assumptions) has led the transplant surgeons to leave the bronchus well-enough alone?