Comparison of in vivo lymphocyte proliferation between allogeneic and xenogeneic heart transplantation in mice

There are controversial in vitro data comparing the strength of the cellular immune response between allogeneic and xenogeneic stimulator/responder combinations. The present study therefore compares in vivo lymphocyte proliferation using heart transplantation (HTx) models in mice. Heterotopic HTx into BALB/c mice was performed using donor organs from mice (BALB/c and C57BL/6) or Lewis rats. Intraperitoneally given bromodeoxyuridine (BrdU) was incorporated into the DNA and was subsequently analyzed by flow cytometry. On postoperative days 3 and 5, proliferation of splenocytes, CD4 + T‐lymphocytes, and CD19 + B‐lymphocytes was significantly higher after xenogeneic than after allogeneic and isogeneic HTx. No significant difference was observed when proliferation of CD8 + lymphocytes was determined. The increased in vivo proliferation after xenotransplantation may reflect an earlier and probably stronger cellular immune response compared to allogeneic transplantation. The higher CD4 + lymphocyte proliferation underscores the importance of this cell population in xenograft rejection. © 2003 Wiley‐Liss, Inc. MICROSURGERY 23:498–502 2003