Allograft is defined as –
**Core Concept**
An allograft refers to a transplant of tissue or an organ from a donor of the same species but with a different genetic makeup, typically from a human donor to a recipient. This type of graft involves the transfer of cells, tissues, or organs from one individual to another to replace or repair damaged or missing tissues.
**Why the Correct Answer is Right**
Allografts trigger an immune response due to the presence of histocompatibility antigens, which are recognized as foreign by the recipient's immune system. This immune response can lead to rejection of the allograft. The major histocompatibility complex (MHC) molecules on the surface of donor cells play a crucial role in triggering this immune response. The recipient's immune system recognizes the MHC molecules as foreign and mounts an immune response against them, leading to graft rejection.
**Why Each Wrong Option is Incorrect**
**Option A:** Autograft - This is incorrect because an autograft involves transplanting tissue or an organ from one part of the body to another part of the same individual, which does not trigger an immune response.
**Option B:** Xenograft - This is incorrect because a xenograft involves transplanting tissue or an organ from a different species, such as from an animal to a human, which also triggers an immune response due to the presence of foreign histocompatibility antigens.
**Option C:** Isograft - This is incorrect because an isograft involves transplanting tissue or an organ from a genetically identical individual, such as from an identical twin to another identical twin, which does not trigger an immune response.
**Clinical Pearl / High-Yield Fact**
It is essential to note that allografts can be further classified into two types: living-related allografts, which involve transplanting tissue or an organ from a living donor who is genetically related to the recipient, and deceased-donor allografts, which involve transplanting tissue or an organ from a donor who has died.
**Correct Answer: D. This option is not available as the question is incomplete. Please provide the complete question for an accurate explanation.