Imaging mouse lung allograft rejection with (1)H MRI

Abstract

Purpose: To demonstrate that longitudinal, noninvasive monitoring via MRI can characterize acute cellular rejection in mouse orthotopic lung allografts.

Methods: Nineteen Balb/c donor to C57BL/6 recipient orthotopic left lung transplants were performed, further divided into control-Ig versus anti-CD4/anti-CD8 treated groups. A two-dimensional multislice gradient-echo pulse sequence synchronized with ventilation was used on a small-animal MR scanner to acquire proton images of lung at postoperative days 3, 7, and 14, just before sacrifice. Lung volume and parenchymal signal were measured, and lung compliance was calculated as volume change per pressure difference between high and low pressures.

Results: Normalized parenchymal signal in the control-Ig allograft increased over time, with statistical significance between day 14 and day 3 posttransplantation (0.046→0.789; P < 0.05), despite large intermouse variations; this was consistent with histopathologic evidence of rejection. Compliance of the control-Ig allograft decreased significantly over time (0.013→0.003; P < 0.05), but remained constant in mice treated with anti-CD4/anti-CD8 antibodies.

Conclusion: Lung allograft rejection in individual mice can be monitored by lung parenchymal signal changes and by lung compliance through MRI. Longitudinal imaging can help us better understand the time course of individual lung allograft rejection and response to treatment.

Keywords: MRI; acute cellular rejection; compliance; lung transplant.

Fig. 1. Experimental plan

Fig. 2. Schematic of ventilation and MRI acquisition

Fig. 3

(a) Representative axial ¹H MR images (TE = 0.954 ms, flip angle = 20°) of a control-Ig treated mouse at POD 3, POD 7 and POD 14 (in-slice allograft [left lung] lung signal: 0.043, 0.077 and 0.701 respectively; allograft compliance: 0.010, 0.005 and 0.001 in cc/cm H₂O respectively), and one corresponding histological slice (H & E, 200×) of the allograft at POD 14. (b) Corresponding ¹H MR images and histological slice (H & E, 200×) of an anti-CD4/anti-CD8 treated mouse (allograft signal: 0.045, 0.049 and 0.042 respectively; allograft compliance: 0.015, 0.017 and 0.016 in cc/cm H₂O respectively). Rejection is visually apparent in the control-Ig treated allograft at POD 14, though signal increases slightly at POD 7.

Fig. 3

(a) Representative axial ¹H MR images (TE = 0.954 ms, flip angle = 20°) of a control-Ig treated mouse at POD 3, POD 7 and POD 14 (in-slice allograft [left lung] lung signal: 0.043, 0.077 and 0.701 respectively; allograft compliance: 0.010, 0.005 and 0.001 in cc/cm H₂O respectively), and one corresponding histological slice (H & E, 200×) of the allograft at POD 14. (b) Corresponding ¹H MR images and histological slice (H & E, 200×) of an anti-CD4/anti-CD8 treated mouse (allograft signal: 0.045, 0.049 and 0.042 respectively; allograft compliance: 0.015, 0.017 and 0.016 in cc/cm H₂O respectively). Rejection is visually apparent in the control-Ig treated allograft at POD 14, though signal increases slightly at POD 7.

Fig. 4

Mean parenchymal signal (mean ± SD) of control-Ig treated and anti-CD4/anti-CD8 treated mice as percent of mean soft-tissue signal at POD 3, POD 7 and POD 14. We note that the anti-CD4/anti-CD8 treated allograft signal increases at POD 7 & POD 14, which we believe results from edema and/or atelectasis in the transplanted lung in mouse 217 at POD 7 and mouse 278 at POD 14. ^aP = 0.04 compared to POD 3, allograft, control-Ig. ^bP = 0.04 compared to POD 14, allograft, control-Ig.

Fig. 5

Compliance (mean ± SD) of control-Ig treated and anti-CD4/anti-CD8 treated mice at 3 timepoints. ^aP < 0.05 compared to POD 3, allograft, control-Ig. ^bP = 0.04 compared to POD 3, native lung, anti-CD4/anti-CD8. ^cP < 0.05 compared to allograft, anti-CD4/anti-CD8, at POD 7 and POD 14 respectively.

Fig. 6

An array of histological slides from 2 anti-CD4/anti-CD8 treated and 1 control-Ig treated mice demonstrating (a) some residual edema and cellular consolidation, (c) resolution of POD 7 edema, (e) near-complete consolidation & rejection, and (b, d, f) corresponding control, native lungs (H & E, 100×).

Fig. 7

Negative correlation between the volume percentage of high-intensity signal in the allografts and allograft compliance.