We thank Hetzel et al. for their interest in our recent article (1) and are pleased to address the issues they have raised concerning our results.
We share the concern that analysis of diagnostic biopsy specimens introduces the possibility that excess transforming growth factor (TGF)-β1 expression might be due to rejection rather than medication. However, we would draw the attention of Hetzel et al. to our comments on this issue in both the abstract of our article and the final paragraph of the discussion. We have been able to include protocol biopsies in further experiments and now have data that clearly support our contention that higher levels of TGF-β1 are found in transplant biopsy specimens from patients receiving CsA than from those immunosuppressed with FK506.
In their letter, Hetzel et al. present data on the effect of CsA and FK506 on the level of circulating TGF-β1; these results are essentially similar to that presented more fully by Hughes et al. (2) in an earlier article. We would point out, however, that the observation in our correspondents’ letter that patients respond similarly to both CsA and FK506 therapy is flawed to some extent by failure to comment on the time before plasma sampling of conversion from CsA to FK506-based immunosuppression.
We are satisfied that measurement of TGF-β1 expression within biopsy tissues, rather than the systemic circulation, provides a simple and reproducible means for investigation of the role of this important growth factor within a transplanted organ.
M.A. S. Mohamed
1. Mohamed MAS, Robertson H, Booth TA, Balupuri S, Kirby JA, Talbot D. TGF-beta expression in renal transplant biopsies: a comparative study between cyclosporin-A and tacrolimus. Transplantation 2000; 69: 1002.
2. Hughes JR, Hughes VF, Trull AK, Metcalfe SM. Blood levels of TGFβ1 in liver transplant recipients receiving either tacrolimus or micro-emulsified cyclosporine. Transplantation 1999; 68: 583.