Hyperacute rejection occurs within:-
**Core Concept**
Hyperacute rejection is a rapid and severe form of transplant rejection that occurs within minutes to hours after transplantation. It is primarily caused by pre-existing antibodies in the recipient's blood that target the graft, leading to activation of the complement system and subsequent tissue damage. This reaction is often seen in kidney transplants, particularly when the recipient has pre-formed antibodies against the donor's blood group antigens.
**Why the Correct Answer is Right**
Hyperacute rejection occurs due to the presence of pre-formed antibodies in the recipient's blood that bind to the donor's graft. This binding activates the complement system, leading to the formation of the membrane attack complex (MAC) and subsequent cell lysis. The activation of the complement system is mediated by the classical pathway, which is initiated by the binding of antibodies to the graft's antigens. The rapid onset of hyperacute rejection is due to the pre-existing antibodies in the recipient's blood, which are able to immediately bind to the graft's antigens and initiate the rejection process.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as hyperacute rejection occurs within minutes to hours after transplantation, not days to weeks.
**Option B:** This option is incorrect as hyperacute rejection is not typically associated with the cellular immune response, but rather with the humoral immune response and pre-existing antibodies.
**Option C:** This option is incorrect as hyperacute rejection is a specific type of rejection that occurs within minutes to hours after transplantation, and is not a general term for all types of rejection.
**Clinical Pearl / High-Yield Fact**
It is essential to perform careful cross-matching between the donor's blood and the recipient's blood before transplantation to minimize the risk of hyperacute rejection. This involves testing for the presence of pre-formed antibodies in the recipient's blood that may target the donor's blood group antigens.
**Correct Answer: A, within minutes to hours after transplantation.**