## **Core Concept**
Acute graft-versus-host disease (GVHD) is a major complication following allogeneic hematopoietic stem cell transplantation. It occurs when the immune cells from the donor (the graft) recognize the recipient's body (the host) as foreign and mount an immune response against it. This condition commonly affects several organs.

## **Why the Correct Answer is Right**
The organs commonly involved in acute GVHD include the **skin**, **liver**, and **gastrointestinal tract**. These organs are targeted because the donor T cells recognize the host's cells as foreign and initiate an immune response against them. The skin is often the first organ to be affected, presenting with rash or erythema. The liver is involved, leading to elevated liver enzymes and bilirubin. The gastrointestinal tract involvement can range from mild diarrhea to severe abdominal pain and bloody diarrhea.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The skin is a common site for acute GVHD manifestations, making it an incorrect choice as an exception.
- **Option B:** The liver is frequently involved, with symptoms such as jaundice and abnormal liver function tests, so it's not the correct answer.
- **Option C:** The gastrointestinal tract is another commonly affected organ, presenting with nausea, vomiting, diarrhea, and abdominal pain, which rules it out as the exception.
- **Option D:** The **lungs** are not typically considered a primary site for acute GVHD. While pulmonary complications can occur post-transplant, they are more commonly associated with other conditions such as idiopathic pneumonia syndrome, bronchiolitis obliterans syndrome, or infections.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the **skin, liver, and gastrointestinal tract** are the classic organs involved in acute GVHD. Clinicians often assess these systems closely in patients post-transplant. The lungs, while critical for consideration in post-transplant patients, are not primarily involved in acute GVHD but can be affected by other transplant-related complications.

## **Correct Answer:** D. lungs