Computed Tomography for Rejection Monitoring in a Murine Orthotopic Lung Transplantation Model

Objectives: Orthotopic lung transplantation (OLTx) in mice is a challenging, extremely useful experimental model. Obliterative bronchiolitis (OB) models in mice are intensely sought after. Non-invasive lung rejection monitoring methods are needed in the model.

Methods: Left OLTx in mice was performed from B10 donors into B6 recipients (minor histocompatibility mismatch), and from B6 into B6 as negative controls (n = 6). Following transplantation, 3 different doses of immune suppression with cyclosporine at 5 mg/kg (n = 3), 15 mg/kg (n = 10) and 25 mg/kg (n = 4) daily in the 1^st week were applied. Positive controls (n = 3) did not receive it. Three days after transplantation, CTs were performed to rule out technical failures/atelectasis. Eight weeks after transplantation, a second CT was performed and the Hounsfield units, indicating tissue densities from −1000 HU (air) to 0 HU (water) were recorded. The mice were sacrificed and histologic rejection grading was performed.

Results: According to the 3-day CT, mice with atelectasis and/or diaphragmatic paralysis were excluded. In the remaining animals, all mice of the negative control group did not show acute rejection (A0), small airway inflammation (B0) or chronic rejection (C0, n = 5). Positive controls revealed moderate acute rejection (A3, 100%), low- to high-grade small airway inflammation (B1R or B2R, respectively), and C0 (n = 2). In transplants with 5mg/kg cyclosporine, A3 with B2R and C0 was seen (n = 2). In the 15mg/kg group (n = 7), A3 in 4 mice (57%) and mild acute rejection (A2) in 3 were seen with corresponding B1R. In this group, 4 mice also had OB (C1, 57%). Mice in the 25 mg/kg group (n = 3) showed A3 in 1 (33%) and A2 in 2, B1R and C0.

On examination of the 8 week CT scans, those with A0 had −387 ± 78 HU in the left lung. Those with A2 or A3 were −194 ± 167 and 187 ± 64 HU, respectively. On grouping in animals without (A0) or with acute rejection (A2+3), significant differences of the HU were detected: −387 ± 78 versus −189 ± 108 HU, p < 0.001. Upon separation into two groups according to the B classification, there were also significant differences: B0 and B1R+2R; −376 ± 75 versus −180 ± 103 HU, p < 0.001. The C0 lungs had −284 ± 112 HU. All lungs with C1 had atelectasis with −83 ± 54 HU (C0 vs. C1, p < 0.002).

Conclusion: OB can be modeled in a murine minor histocompatibility mismatch OLTx model with subtherapeutic cyclosporine administration. CT scans are a valid tool for sequential rejection monitoring in this model.

No conflict of interest has been declared by the author(s).