The costimulatory pathways play a key role in T cell activation during allograft rejection (AR). Inhibition of the T cell costimulatory molecule CD154 (CD40 ligand) has been effective in producing long-term allograft survival in rodents and non-human primates. The role of the CD40-CD154 pathway in human orthotopic liver transplantation (OLT) has not been examined.
Aim: To describe the patterns of CD154, CD69 and CD152 (CTLA4) expression in OLT recipients and to determine their temporal relationship to AR.
Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from 15 OLT allograft recipients just prior to and for seven consecutive days postoperatively. Gene and protein expression of CD154, CD69 and CD154 were examined by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry (FC), respectively.
Results: FC failed to demonstrate an up-regulation of CD154 and CD152 protein expression during the first postoperative week. Intracellular FC did not increase the sensitivity. There was an increased level of CD3+ CD8+ T cells expressing CD69 at the time of rejection compared to that on day 0. RT-PCR demonstrated a sporadic expression of CD154 and CD69 mRNA, with no correlation to episodes of acute cellular rejection. In vitro stimulation of PBMCs revealed an impaired up-regulation of CD154 in patients receiving conventional immunosuppression compared to healthy controls. The assays were validated using positive and negative controls, including a family with X-linked hyper-IgM syndrome.
Conclusion: We found no evidence of spontaneous CD154 gene or protein expression in PBMCs associated with acute rejection episodes following OLT. Immunosuppression resulted in impaired responses to ex vivo stimulation. Lymphocyte costimulatory pathways play a critical role in mediating acute allograft rejection. However, we found no evidence of spontaneous CD154 gene or protein expression in PBMCs associated with acute rejection episodes following OLT. Furthermore, stimulation in vitro resulted in less up-regulation of CD154 than for healthy controls.