Nature and significance of epicardial lymphoid infiltrates in cardiac allografts.

BACKGROUND: Myocardial lymphocytic infiltration after transplantation is usually a manifestation of acute cellular rejection. However, purely endocardial infiltrates are generally not regarded as rejection (so-called "Quilty lesions"). The nature of epicardial lymphoid infiltration in cardiac allografts and its significance when observed in endomyocardial biopsies or autopsies are uncertain.
METHODS: Twenty-seven cases of transplant-associated epicardial lymphoid infiltration were identified; 16 cases were identified from 1602 consecutive transplant biopsy specimens from 125 patients, and 11 from 14 autopsies, ranging from 1 to 35 months (mean 7.8 months) after transplantation.
RESULTS: The infiltrates were composed of aggregates of lymphocytes and histiocytes distributed throughout the epicardium. Plasma cells were found in 52% of cases, with occasional eosinophils and rare neutrophils. Most were vascular, and four autopsy cases had follicle formation. Twenty-four cases (93%) showed a mixed population of cells in a random distribution consisting of T cells in association with fewer B cells and histiocytes. Fifteen cases (nine autopsies, six biopsies) had acute rejection, and nine autopsies had chronic vascular rejection. Fourteen of twenty-four cases (58%) showed concurrent Quilty lesion (nine autopsies, five biopsies), and the remainder showed at least one Quilty lesion in an earlier biopsy.
CONCLUSION: Epicardial lymphoid infiltrates occur with significant frequency after heart transplantation and can be associated with, and mimic, acute cellular rejection. However, they exhibit morphologic and immunophenotypic features which are distinguishable from rejection-associated infiltrates.