Evidence for recipient derived fibroblast recruitment and activation during the development of chronic cardiac allograft rejection.

BACKGROUND: Allograft fibrosis is a prominent feature of chronic rejection. Although intragraft fibroblasts contribute to this process, their origin and exact role remain poorly understood.
METHODS: Using a rat model of chronic rejection, LEW to F344, cardiac fibroblasts were isolated at the point of rejection and examined in a collagen gel contraction assay to measure fibroblast activation. The allograft microenvironment was examined using immunohistochemistry for fibrogenic markers (transforming growth factor [TGF]-beta, platelet-derived growth factor [PDGF], tissue plasminogen activator [TPA], plasminogen activator inhibitor [PAI]-1, matrix metalloproteinase [MMP]-2, and tissue inhibitor of matrix metalloproteinase [TIMP]-2). The origin of intragraft fibroblasts was studied using female to male allografts followed by polymerase chain reaction [PCR] and in situ hybridization for the male sry gene.
RESULTS: The cardiac fibroblasts isolated from allografts with chronic rejection exhibited higher gel contractibility (50.9% +/- 6.1% and 68.2% +/- 3.8% at 4 and 24 hr) compared with naive cardiac fibroblasts (30.7% +/- 3.5% and 55.3% +/- 6.6% at 4 and 24 hr; P<0.05 and <0.05, respectively). Immunostaining for TGF-beta, PDGF, TPA, PAI-1, MMP-2 and TIMP-2 was observed in all allografts at the time of rejection. In situ hybridization demonstrated the presence of sry positive cells in female allografts rejected by male recipients. Sixty-five percent of fibroblast colonies (55 of 85) isolated from female heart allografts expressed the male sry gene.
CONCLUSION: Cardiac fibroblasts are activated and exist in a profibrogenic microenvironment in allografts undergoing chronic rejection. A substantial proportion of intragraft fibroblasts are recruited from allograft recipients in this experimental model of chronic cardiac allograft rejection.