Early up-regulation of macrophages and myofibroblasts: a new marker for development of chronic renal allograft rejection.

Background: Increased numbers of macrophages and myofibroblasts are observed to occur in chronic renal allograft rejection (CR). The aim of this study was to examine the expression of cellular markers for the macrophage and myofibroblast in early renal transplant biopsy specimens and correlate these findings with allograft outcome.
Methods: The first postengraftment biopsy specimens from 53 patients who underwent renal transplantation between January 1993 and December 1995 were studied using immunohistochemistry with antibodies to alpha-smooth muscle actin, which identifies myofibroblasts and CD68, a marker for monocytes and macrophages. Patients were followed until December 1998 (mean follow-up 4.7+/-1.2 years).
Results: Nine patients had progressed to CR by the time of the study, whereas 44 patients continued to have stable renal function. A marked increase in both macrophages (P=0.02) and myofibroblasts (P=0.04) was noted in the first biopsy specimen obtained after engraftment in the patients who developed CR compared with those with stable allograft function. There was a positive correlation between alpha-smooth muscle actin and collagen expression (P=0.0001).
Conclusion: Significant increases in macrophages and myofibroblasts occur in the first renal biopsy specimen in those patients who later develop CR.