APOPTOSIS OF MONONUCLEAR CELL INFILTRATES IN CARDIAC ALLOGRAFT BIOPSYSPECIMENS QUESTIONS STUDIES OF BIOPSY-CULTURED CELLS

During acute rejection, CD4 aad CD8 T cells infiltrate the myocardium and cause myocyte death and dropout. CD4 and CD8 cells use a number of cytotoxic mechanisms, including fas-fas ligand interactions, which le ad to apoptotic death. Since fas is expressed on myocytes, we investig ated endomyocardial biopsy specimens from cardiac transplant patients to determine whether apoptosis is one of the mechanisms of cell death in acute rejection. Serial sections of individual endomyocardial biops y specimens from patients histologically diagnosed as having grade 3A rejection (n=22 biopsy specimens), biopsy specimens showing a typical ''Quilty effect'' (n=10), and specimens with concurrent grade 3A rejec tion and the Quilty effect (n=6) were evaluated using the C-terminal d eoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TU NEL) technique for frequency of apoptosis in myocytes and mononuclear cell infiltrates, None of the examined sections showed detectable evid ence of apoptotic myocytes, even within regions clearly showing myocyt e damage, Of interest was our consistent finding that 85-98% of mononu clear cell infiltrates within biopsy specimens scored as having grade 3A rejection had undergone apoptosis. In marked contrast, 9 of the 10 specimens with Quilty lesions showed <5% apoptotic mononuclear cells i n the endomyocardial infiltrates. Of further interest was our finding of 85-98% apoptotic mononuclear cell infiltrates within Quilty lesions associated with biopsy specimens scored as having grade 3A rejection. The frequency of apoptotic cells determined by the TUNEL technique wa s confirmed by histological examination of the morphology of the cells and with a technique that involves detection of c-jun. These results prompt a note of caution in the interpretation of data on the phenotyp e, cytokine profile, V beta T cell receptor repertoire, and donor spec ificity of mononuclear cells cultured and propagated from such cardiac biopsy specimens. The possible reasons for apoptosis of graft-infiltr ating mononuclear cells are discussed.