Why do some white blood cells sometimes cause tissue rejection?

Some white blood cells, particularly T cells, can cause tissue rejection because they recognize transplanted tissue or organs as foreign. This occurs when the donor's human leukocyte antigens (HLAs) differ from those of the recipient, triggering an immune response. The white blood cells attack the foreign tissue to eliminate what they perceive as a threat, leading to rejection. This is a crucial aspect of the immune system but poses a significant challenge in transplantation medicine.