You are studying transplant rejection in a wild and genetically diverse population of mice. You have captured some of the mice for laboratory studies. You have four mice from a family. Mouse 1, mouse 2, and mouse 3 are littermates, thus they all share the same mother and father. Mouse 4 is the father of the other three mice. You transplant a small patch of skin from mouse 2 (the donor) onto mouse 1 (the recipient). There is a delayed inflammatory response and two weeks later the skin is necrotic due to transplant rejection. You decide to attempt another transplant. Which follow-up transplant is LEAST likely to be rejected?

a. skin from mouse 1
b. skin from mouse 2
c. skin from mouse 3
d. skin from mouse 4-incorrect

According to this question, a mice skin transplant is being conducted. Four mice labelled Mouse 1, Mouse 2, Mouse 3 and Mouse 4 are used for this experiment. A small patch of skin from mouse 2 (the donor) was transplanted onto mouse 1 (the recipient), however, it was eventually rejected by the recipient (mouse 1).

This transplant rejection is due to the fact that the recipient's immune system identifies the tansplanted skin as foreign, hence, begins to attack it, leading to the skin's necrosis or death. Based on this, the same transplant rejection will occur if skin patches from mouse 3 and 4 are used.

However, the immune system of mouse 1, which is the recipient, will identify skin patches from MOUSE 2 as less foreign than any other skin from other mice. This is because skin from that mouse has been used before, hence, the recipient's immune recognizes it when a follow-up transplant is conducted. This makes a follow-up transplant from MOUSE 2 be the least likely to be rejected.