The RNA Content of Alveolar Macrophages in Canine Lung Allografts

To evaluate the utility of RNA synthesis by alveolar macrophages (AM) in lung allografts as a marker of acute rejection, we performed canine left lung allotransplantation and measured the AM RNA content during immunosuppressive therapy with azathioprine (AZ), cyclosporine A (CsA), or CsA combined with AZ and prednisolone (Pr). We determined the RNA content by determining the RNA index (RI) (peak channel number of AM/peak RNA channel number of peripheral blood lymphocytes) by flow cytometry. The dogs were classified into one of five treatment groups: Group 1 ( n = 18), control (no surgery) dogs; Group 2 ( n = 11), allotransplanted dogs without pre- or postoperative immunosuppressive therapy; Group 3 ( n = 14), received AZ at dose of 5 mg/kg/day orally; Group 4 ( n = 17), received CsA at dose of 20 mg/kg/day orally; Group 5 ( n = 15), CsA combined with AZ (5 mg/kg/day) and Pr (0.5 mg/kg/day). The RI of normal lungs was 2.14 ± 0.20 (mean ± SD) ( n = 18). The RI of rejected lungs was significantly higher than the RI of normal lungs in Group 2 (2.51 ± 0.21, n = 8, P < 0.05) or Group 3 (2.76 ± 0.36, n = 7, P < 0.05), but did not differ significantly from that in Group 4 (2.19 ± 0.20, n = 7) or Group 5 (2.05 ± 0.45, n = 8). The RI of rejected lungs was higher than the RI of nonrejected lungs in Group 2 (vs 2.18 ± 0.12, n = 3, P < 0.05) or in Group 3 (vs 2.18 ± 0.22, n = 7, P < 0.01). There was no significant difference in RI between normal lungs and nonrejected lungs in any group. We demonstrated that RNA synthesis by AM in the canine allograft lung reflected acute rejection and that the increase in RNA synthesis seen during rejection was inhibited by CsA, and probably Pr. Therefore, the AM RI may be not useful clinically in monitoring the rejection of canine lung allografts during treatment with CsA.