1039 The purpose of the present study was to investigate the relation between intragraft gene expression of immunologic markers and occurrence of acute cardiac allograft rejection. A series of 46 samples of endomyocardial biopsies (EMB) obtained from 10 adult cardiac transplant recipients within the first six months posttransplantation was evaluated for the presence of mRNA for CD3, CD40L, IFN-γ, IL-8, granzyme B and FasL, using the RT-PCR method. Twenty-two biopsies with at least grade 1B, according to the ISHLT criteria, were considered with rejection. EMB with grade 3B and/or those that were followed by anti-rejection treatment were considered as severe rejections (n=9). Zero grade EMB that were preceded or followed within 15 days by a EMB with rejection were considered as borderline biopsies (n=10); otherwise, the 0 grade biopsies were considered without rejection (n=14). CD3 gene transcripts were found in all EMB, indicating the presence of T cells, regardless of rejection. CD40L mRNA was present in 77% of the biopsies with and in 36% of the biopsies without rejection; IFN-γ mRNA, in 82 and 21%; IL-8 mRNA, in 73 and 14%; granzyme B mRNA, in 77 and 29%; FasL mRNA, in 86 and 43% of the biopsies with and without rejection, respectively, being all the differences statistically significant. The detection of CD40L mRNA (100% vs. 62%, p<0.05) and the simultaneous detection of CD40L and IFN-γ mRNA (100% vs. 46%, p<0.02) were more frequent in biopsies with severe rejection than in biopsies with non-severe rejection. The detection of IFN-γ and IL-8 mRNA was higher in grade 0 biopsies collected less than 15 days before rejection than in biopsies considered as without rejection, suggesting the predictive value of these markers for the occurrence of rejection. In conclusion, our results clearly indicate that intragraft mRNA detection of cell surface (CD40L), messenger (IFN-γ, IL-8), and effector molecules (granzyme B, FasL) of the immune system represents a valuable tool, in addition to histology, in the monitoring of cardiac allograft rejection.