Pulmonary Pathology Society

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April, 2025
Case of the Month

Clinical History:

A 62-year-old male patient underwent bilateral lung transplantation for connective tissue disease-associated interstitial lung disease (CTD-ILD). He had a significant 10-year history of gastroesophageal reflux disease (GERD) complicated by a Grade 4 hiatus hernia. Pre-transplant immunologic evaluations, including single-antigen bead (SAB) testing for HLA class I and II antibodies, virtual crossmatch, and flow cytometry-based lymphocyte crossmatch, were all negative. Three weeks post-transplant, he successfully underwent a planned laparoscopic fundoplication without complications.

However, six weeks after transplantation, the patient presented with new-onset fatigue and a mild increase in his oxygen requirements. High-resolution computed tomography (HRCT) of the chest demonstrated bilateral ground-glass opacities (GGOs), raising concerns for potential infection, acute rejection, or early antibody-mediated rejection (AMR). Diagnostic bronchoscopy with bronchoalveolar lavage (BAL) microbiologic analysis returned negative for bacterial, mycobacterial, fungal, and viral pathogens. Repeat SAB testing, however, revealed the emergence of high mean fluorescence intensity (MFI) donor-specific antibodies (DSAs) against HLA Class II antigens: DQA1*06:01 (MFI 13,600; cutoff 1,000) and DQA1*03:01 (MFI 9,560; cutoff 1,000).

Given persistent allograft dysfunction, fluoroscopy-guided transbronchial lung biopsy (TBLB) was performed from the anterior segment of the right lower lobe. Histologically, the biopsy consisted of six fragments of well-expanded, alveolated lung parenchyma along with bronchial walls and blood vessels (Fig 2). Examination revealed interstitial edema (Fig 3) with moderate inflammatory infiltrate composed predominantly of lymphomononuclear cells, macrophages, and scattered neutrophils (Fig 4). Capillary inflammation (capillaritis) was prominent, characterized by back-to-back neutrophils and focal nuclear fragmentation (Fig 5, 6). Additionally, focal intra-alveolar fibrin deposits and Type II pneumocyte hyperplasia were noted (Fig 7). Large airways (Fig 8) and blood vessels (Fig 9) were unremarkable, without perivascular inflammation characteristic of acute cellular rejection (ACR) (Fig 10). No evidence of lymphocytic bronchiolitis, aspirated material, granuloma formation, viral cytopathic changes, or malignancy was observed. Special stains for mycobacterial (AFB) and fungal organisms (GMS) were negative. Immunohistochemistry (IHC) for cytomegalovirus (CMV) was negative, whereas C4d staining demonstrated focal circumferential endothelial positivity in less than 50% of capillaries (Fig 11).

Based on the clinical presentation, positive DSAs, characteristic histologic findings, and focal C4d endothelial positivity, the patient was diagnosed with definite antibody-mediated rejection (AMR) according to the International Society for Heart and Lung Transplantation (ISHLT) criteria. He subsequently received treatment with plasmapheresis, intravenous immunoglobulin (IVIG), and bortezomib.

Q1. The following are the histological features which can suggest AMR except:

Acute lung injury
Capillaritis
Hyaline membranes
None of the above

Q2. The Triple test for the diagnosis of Definite AMR includes:

Allograft dysfunction
Circulating donor-specific antibodies
Pathologic findings
All the above

Q3. C4d staining is considered positive when it stains

Elastic tissue of vessels
Septal capillaries
Serum protein
Airway basement membrane

Answers to Quiz

Q1. D
Q2. D
Q3. B

Diagnosis

Definite AMR according to the International Society for Heart and Lung Transplantation (ISHLT) criteria, based on the presence of allograft dysfunction, positive DSAs, characteristic histologic findings, and C4d positivity.

Discussion

Rejection in lung allografts is broadly categorized into acute cellular rejection (ACR), antibody-mediated rejection (AMR), and chronic lung allograft rejection. Acute cellular rejection is diagnosed histologically by identifying perivascular and interstitial T-cell–rich mononuclear infiltrates. In contrast, AMR arises due to interactions between preexisting or de novo donor-specific antibodies (DSAs) and donor antigens, predominantly human leukocyte antigen (HLA) class I or II antigens expressed on endothelial cells of capillaries within the donor organ. This antibody–antigen interaction can lead to graft injury either through activation of the complement cascade or by recruitment of leukocytes, such as natural killer cells, resulting in graft damage.

Unlike other organ systems such as the heart and kidney, well-established criteria for diagnosing pulmonary AMR remain lacking. In 2013, the International Society for Heart and Lung Transplantation (ISHLT) published a summary statement outlining consensus pathologic features of AMR in lung allografts. Morphologic patterns commonly observed in patients with graft dysfunction and de novo DSAs include neutrophilic capillaritis, neutrophilic margination, high-grade ACR (>A3), high-grade lymphocytic bronchiolitis (B2R), arteritis, acute lung injury with or without diffuse alveolar damage (DAD), and obliterative bronchiolitis. Acute lung injury encompasses a range of histologic changes from paucicellular interstitial edema and pneumocyte hypertrophy with intra-alveolar fibrin deposition to severe cases characterized by diffuse alveolar damage with hyaline membrane formation. However, these morphologic findings are nonspecific and must be interpreted alongside clinical and serologic findings (DSA positivity).

The role of C4d immunohistochemical staining in lung transplant biopsies remains controversial. Some institutions report a correlation between C4d immunoreactivity and histopathologic injury patterns, whereas others argue that C4d staining is unreliable as a definitive marker for AMR due to insufficient sensitivity and specificity. The ISHLT consensus suggests only diffuse (>50%) capillary C4d staining should be considered significantly positive.

Currently, pulmonary AMR is the subject of active multidisciplinary research. All histopathologic features linked to AMR, including C4d deposition, remain nonspecific, yet histologic evaluation can serve effectively as an initial screening tool to identify potential AMR cases. Ultimately, the "triple test," integrating clinical manifestations, serologic evidence of DSAs, and supportive pathologic findings, offers the most reliable approach for diagnosing pulmonary AMR.

Take home message for trainees:

Accurate diagnosis of pulmonary AMR requires integration of clinical symptoms, serologic DSA testing, and histologic findings. Be aware of nonspecific morphologic features, and interpret biopsy results within the broader clinical and immunologic context. Understanding the limitations and appropriate use of C4d staining can also guide accurate diagnosis and management of AMR in lung transplant patients

References

1. Berry G, Burke M, Andersen C et al. Pathology of pulmonary antibody-mediated rejection: 2012 update from the Pathology Council of the ISHLT. J Heart Lung Transplant. 2013;32:14-21.

2. Wallace WD, Li N, Andersen CB et al. Banff study of pathologic changes in lung allograft biopsy specimens with donor-specific antibodies. J Heart Lung Transplant. 2016;35:40-48.

Contributors