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Difficulty: MediumImmunologic and Inflammatory Processes

A 45-year-old man is evaluated in the hospital due to a new-onset diffuse rash and severe diarrhea. He underwent an allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia four weeks ago. His current medications include tacrolimus, acyclovir, and fluconazole. His temperature is 38.2°C (100.8°F), blood pressure is 110/70 mm Hg, and pulse is 98/min. Physical examination reveals a generalized maculopapular rash that prominently involves the palms and soles. His abdomen is mildly tender to palpation, and he reports having 6 to 8 large-volume watery stools daily over the past three days. Laboratory studies show markedly elevated alkaline phosphatase and total bilirubin levels. Which of the following best describes the primary immunopathologic mechanism responsible for this patient's current clinical presentation?

  1. Activation of donor-derived immunocompetent T lymphocytes against recipient cellular antigensAnswer
  2. B
    Activation of recipient-derived cytotoxic T lymphocytes against the newly engrafted donor cells
  3. C
    Widespread deposition of circulating immune complexes in the microvasculature with complement activation
  4. D
    Binding of preformed recipient immunoglobulin G antibodies to donor vascular endothelial antigens
  5. E
    Massive release of preformed inflammatory mediators from mucosal and cutaneous mast cells

Answer

Activation of donor-derived immunocompetent T lymphocytes against recipient cellular antigens
The clinical presentation of a maculopapular rash prominently involving the palms and soles, copious secretory diarrhea, and hepatobiliary dysfunction (evidenced by elevated alkaline phosphatase and total bilirubin) roughly four weeks after an allogeneic hematopoietic stem cell transplantation (HSCT) is the classic triad of acute graft-versus-host disease (GVHD). The fundamental mechanism underlying acute GVHD is an immunologic attack by donor-derived immunocompetent T cells (primarily CD8+ cytotoxic T cells) contained within the transplanted graft. These donor T cells recognize the recipient's human leukocyte antigens (HLAs) and minor histocompatibility antigens as foreign. This recognition triggers profound donor T-cell activation, proliferation, and subsequent targeted cell-mediated destruction of recipient epithelial cells, preferentially affecting the skin, gastrointestinal tract, and liver.

Step-by-Step Solution

1
Analyze the clinical presentation and patient history.
The patient developed a maculopapular rash (involving palms/soles), secretory diarrhea, and hepatobiliary dysfunction (elevated alkaline phosphatase and bilirubin) 4 weeks after an allogeneic stem cell transplant.
Identifying this classic clinical triad in the context of recent hematopoietic stem cell transplantation is essential to diagnose acute graft-versus-host disease (GVHD).
2
Determine the pathophysiologic mechanism of the diagnosed condition.
Acute GVHD is caused by immunocompetent donor T cells recognizing the recipient's human leukocyte antigens (HLAs) as foreign and initiating a cell-mediated immune attack.
The question specifically asks for the mechanism causing the symptoms, requiring a distinction between donor-versus-recipient and recipient-versus-donor responses.

Key Concept

Pathogenesis of acute graft-versus-host disease (GVHD)
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Topics

Immunologic and Inflammatory Processes

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