Irradiation of a unit of Red Blood Cells is done to prevent the replication of donor?

Irradiation of a unit of Red Blood Cells is primarily performed to prevent the replication of donor lymphocytes. When blood products are transfused, they can introduce immune cells from the donor into the recipient's body. In particular, donor lymphocytes can potentially recognize the recipient's tissues as foreign and mount an immune response, leading to a serious condition known as transfusion-associated graft-versus-host disease (TA-GvHD). This is especially a risk in immunocompromised patients, who are less capable of mounting an effective response against these foreign cells.

Irradiation works by targeting the DNA of these lymphocytes. The process effectively eliminates their ability to proliferate, thereby reducing the risk of TA-GvHD. This method does not adversely affect the red blood cells themselves, which is why the primary focus remains on the lymphocytes present in the blood bag.

In the context of the other options, granulocytes, red cells, and platelets do not present the same risk in terms of transfusion-associated graft-versus-host disease, since it is the lymphocytes that are responsible for this immune reaction. Thus, irradiation is specifically indicated to target and inactivate lymphocytes to keep recipients safe during transfusion.