STPM Biology - Chapter 12: Immunity Q5

There are two kidney transplant patients, one was given a kidney from their identical twin (both genetically identical) and the other from their fraternal twin (not genetically identical).  How would the immune system for each patient respond to a new kidney being introduced into their body?  Explain your answer.

Answer

The immune response for each transplant patient would be different, with the identical twin’s immune system treating the introduced kidney as if it was tissue from their own body; therefore, there would be no immune response.  The fraternal twin’s immune system would treat the introduced kidney as foreign tissue and mount an immune response; the transplant patient would require special medication to prevent tissue rejection.   The reason for the difference occurs with the cell surface markers that the immune system recognizes, which are the same in the identical twins, but different on the cell surfaces of fraternal twins.