Major histocompatibility complex class I and class II expression by myocytes in cardiac biopsies posttransplantation.

: A total of 85 cardiac biopsies from patients 23-265 days posttransplant were studied for the correlation of the rejection grade score with the level of major histocompatibility complex (MHC) class I and class II expression on cardiac myocytes and endothelial cells, the quantitative level of leukocytic infiltrate, and the immunophenotype of the leukocytes. Results indicate a lack of absolute correlation between rejection grade scores and levels of MHC antigen expression. Further, a lack of absolute correlation was also seen with quantitation of leukocytic infiltrates and relative levels of MHC antigen expression. Of great interest was our preliminary finding that as early as 4 weeks prior to a rejection episode scored by routine histological criteria as grade 4, cardiac biopsy from the patient demonstrated high levels of MHC class I and class II expression. Similar increases of MHC antigen expression prior to an increase in histological rejection score grades were also noted in serial biopsies of 2 other patients. These data suggest that it may be quite useful to examine levels of MHC antigens on cardiac biopsies posttransplantation as an additional parameter for monitoring of cardiac rejection episodes.