| Summary: | The complex and multifactorial pathogenesis of ischemia-reperfusion injury (IRI) has
made IRI one of the major challenges faced by organ transplantation. Recently, many attempts
have been made to establish a relationship between IRI and organ rejection. IRI is now believed
to increase the chance of organ rejection via the release of inflammatory mediators such as
platelet-activating factor (PAF) which leads to activation of inflammatory cells, causing tissue
damage and increased immunogenecity of the graft. To our knowledge, all studies have focused
on the effect of IRI on the transplanted donor organ. However, whether IRI can induce an
immune response in the host has not been investigated. The objective of this thesis was to
investigate whether ischemia-reperfusion injury, independent of tissue incompatibility, could
induce MHC H-up-regulation in host peripheral T lymphocytes in a swine model of single-lung
transplantation and whether PAF played a role in the mechanism of MHC II up-regulation due to
IRI.
Single lung transplantation was performed on three groups of domestic swine. Group
A/E (n=7) and group B (n=6) had ex vivo preservation times of 4 hr and 15 hr respectively at
4°C hypothermia. To eliminate the allogenecity effect, group C (n=6) underwent 2 hours of
warm ischemia via dissection and isolation of the left lung with ligation of its bronchial artery and
cross-clamping of the left pulmonary artery, vein, and bronchus without explantation. PAFantagonist,
TCV-309, in combination with prostaglandin Et (PGEj) was administered before and
during surgery in group E. The sham-operated group (group D, n=6) was used as the control
group. Blood samples were collected at pre, one, two, three day post-reperfusion for two-color
flow cytometry analysis using swine anti-CD3 and anti-MHC II-DR-β antibodies. Blood
samples were also collected for semi-quantitative and competitive reverse transcription
polymerase chain reaction (RT-PCR) analysis at pre, two hr, one, two, and three day postreperfusion.
Tissue culture experiments were performed using purified resting/proliferating T lymphocytes and T lymphocytes in the presence of accessory cells [peripheral blood lymphocytes
(PBL)] treated with PAF only and PAF + TCV-309. The cells were incubated for 4 days at
37°C. Samples were removed every day, and the level of MHC II intensity in T lymphocytes
was measured.
The results indicated that the level of MHC II-DR-β intensity on host's peripheral T
lymphocytes increased significantly (p<0.05) on day 2 post-reperfusion for group A, B, and C.
Comparison between groups suggested that the level of MHC II intensity increased as the ex
vivo preservation time was extended from 4 hr to 15 hr. The intensity of MHC II on peripheral
T cells in group C appeared to be higher than that in group A and B. Results from group D
indicated that administration of TCV-309 + PGEj inhibited the up-regulation of MHC II. RTPCR
analysis indicated that the steady state level of MHC II mRNA in T cells significantly
increased by 2 hr post-reperfusion (p<0.01) for group B and C. The results of tissue culture
experiments indicated that PAF at 10⁻¹ M caused a small but significant increase (p<0.05) in
MHC II surface expression in T cells only in the presence of accessory cells by day 2 posttreatment.
The results of this study indicated that IRI by itself, independent of tissue incompatibility,
induced an immune response in the host manifested by MHC II up-regulation in host peripheral T
cells. The result also suggested that MHC II up-regulation increased further as the ex vivo
preservation time increased. Furthermore, PAF appeared to play a role in the mechanism of MHC
II up-regulation in T cells. However, this effect appeared to be an indirect one via intervention of
accessory cells. TCV-309 in combination with PGE₁ appeared to have preventive effects against
IRI-induced immune response and a potential for clinical application. === Medicine, Faculty of === Pathology and Laboratory Medicine, Department of === Graduate
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