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Capillary thrombosis
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Germinal centers
Interstitial fibrosis
Lymphocytic infiltrates
Parenchymal atrophy
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This patient who presents with signs of heart failure (dyspnea, orthopnea, and peripheral edema) 3 weeks after a cardiac transplant most likely has acute rejection. On pathology, acute rejection is seen as lymphocytic infiltrates. Acute rejection reactions occur weeks to months after transplantation. This type of reaction can occur through 2 major mechanisms, but both require the activation of the adaptive immune system. Cellular rejection is a type IV hypersensitivity reaction where recipient CD8+ T-cells react to donor antigens that are presented on antigen-presenting cells. These cytotoxic T-cells then infiltrate the tissue and cause lysis of donor tissues. Humoral rejection instead involves the activation of B-cells and the formation of anti-graft antibodies. No matter the cause, acute rejection can be seen on pathology as graft vessel vasculitis with lymphocytic infiltrates. In heart transplant patients, acute transplant presents with decreased cardiac output and signs of heart failure. These will manifest as dyspnea, orthopnea, and peripheral edema. Treatment involves steroids, anti-thymocyte globulin, and the murine monoclonal antibody OKT3 which inhibits CD3 function. Frank et al. studied the role of donor factors in acute rejection reactions of cardiac transplantations. They found that donor-specific antibodies are an important factor in understanding the severity of acute rejection responses. Incorrect Answers: Answer 1: Capillary thrombosis would be seen in patients with a hyper-acute rejection reaction. This presents minutes to hours after transplantation and is caused by pre-existing recipient antibodies that prevent revascularization of the transplanted organ. Answer 2: Germinal centers would be seen in patients with graft versus host disease. This presents with maculopapular rash, jaundice, diarrhea, and hepatosplenomegaly, and is caused by donor immune cells reacting to host antigens. Answers 3 & 5: Interstitial fibrosis and parenchymal atrophy would be seen in patients with chronic transplant rejection. This presents months to years after transplant and is caused by T-cell mediated destruction of parenchymal cells in the transplanted organ. Bullet Summary: Acute rejection occurs weeks to months after a transplant and is seen on histology as lymphocytic infiltrates.
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