Which type of rejection occurs months to years after transplantation?

Chronic rejection is characterized by a gradual decline in the function of the transplanted organ and can occur months to years after transplantation. This type of rejection is primarily mediated by the immune system, specifically through the mechanisms of ongoing inflammation and fibrosis within the transplanted tissue. Unlike acute rejection, which typically happens shortly after the transplant (within days to weeks), chronic rejection is more insidious, often presenting itself as a slow deterioration of the organ's function over time.

During chronic rejection, the transplant continuously faces immunological attack, leading to changes that can be seen histologically, such as arteriosclerosis in kidney transplants or bronchiolitis obliterans in lung transplants. This type reflects the long-term effects of the immune response that can persist even when acute rejection episodes are managed or resolved.

Understanding the timeline and mechanism behind chronic rejection is crucial for post-transplant care and monitoring, making it easier to implement preventive strategies or interventions to improve transplant longevity.