Background: After transplantation, passenger leukocytes move to lymphoid organs of the recipient. These cells appear to initiate allograft rejection, but they also might be involved in tolerance induction.
Materials and methods: Orthotopic left lung transplantation was performed in the Dark Agouti to Lewis rat strain combination with no immunosuppression. Recipient spleens were removed at intervals of 24 h until day 6 after transplantation. For comparison, spleens from renal allograft recipients were analysed. Donor-derived major histocompatibility complex (MHC) class II antigens were detected by monoclonal antibody OX76. In double-staining experiments with antibodies specific for leukocyte subpopulations, their localisation and identity was analysed.
Results: OX76-positive leukocytes were already detected in recipient spleens on day 1 post-transplantation. They increased in number until day 3 and decreased in number thereafter. Most of them were localised in splenic follicles and expressed the B cell variant of CD45R and IgG. Cell surface antigens typical for other leukocyte subpopulations were not detected. In the spleens of renal allograft recipients, only few donor-derived cells were seen.
Conclusion: After lung transplantation, numerous MHC class II-positive B cells migrate to the splenic follicles of the recipient. These cells might, in part, be responsible for immunologic differences observed between renal and pulmonary allografts.