Spleen dendritic cells of recipients of allogeneic but not syngeneic heart grafts internalize donor DNA fragments.

Microchimerism after allogeneic organ transplantation has been widely documented using DNA identification techniques. However, the question as to whether the detected donor DNA is present in the surviving donor cells, recipient macrophages phagocytizing rejected donor cells or recipient dendritic cells internalizing donor apoptotic bodies or cell fragments has not been answered. We provide evidence that allogeneic organ transplantation is followed not only by cellular microchimerism caused by release of graft passenger cells but also dissemination of donor DNA from the rejecting graft cells and its internalization in recipient dendritic cells (DC). Identification of allogeneic donor DNA was based on detection of the male Sry-PCR product in extracts of DNA from recipient tissues, dendritic cells and their nuclei. Most interestingly, donor DNA could be detected at high concentration in all recipient tissues at the time of rejection. Search for specific localization of allogeneic donor Sry fragments in recipient cells revealed its presence preferrentially in the DC. No donor Sry fragments were detected in recipient DC after syngeneic transplantation. Detection of allogeneic but not syngeneic donor Sry in DC nuclei further strengthens our concept that DC specifically incorporate allogeneic donor DNA fragments. The mechanism of this process requires further studies.