Current knowledge of antigen recognition and T-cell activation suggests that cell adhesion molecules play a role in allograft rejection. ICAM-1, which is involved in leukocyte migration and cytokine release, may influence this response. We therefore studied allografts from normal mice (+/+) and those genetically deficient in ICAM-1 (-/-) to compare the expression of tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin (IL)-1β, IL-2, IL-4, and IL-10; as well as the lymphocyte surface molecules CD4 and CD8; using reverse transcription polymerase chain reaction (RT-PCR). Methods: Heterotopic abdominal cardiac transplants (Tx) were performed between H-2 disparate mice, and allografts harvested at time of peak rejection and snap frozen. Non-Tx control (C) hearts were harvested in a similar fashion. Samples analyzed included the following:+/+ C (n=2), -/- C (n=3), -/- D from +/+ R (n=3), +/+ D from +/+ R (n=3), and+/+ D from -/- R (n=3). After RNA extraction, samples were analyzed for cytokine mRNA by oligo(dT) priming and RT, followed by PCR of cDNA using specific primer pairs. All samples were run simultaneously with β-actin primers to compare relative abundance of PCR products. Products were confirmed by sequencing, restriction digests, or Southern blot. Results: Myocardial samples from 4/5 C mice had baseline expression of TNF-α, however the other cytokines studied were not detected with the exception of expression of IFN-γ and IL-10 in one sample. In contrast, all cytokines studied were detected by RT-PCR in all allografts, regardless of whether D heart or R was deficient in ICAM-1. CD8, but not CD4 mRNA, was detected in all C samples; however both CD8 and CD4 mRNA was detected in rejecting allografts, again regardless of the presence or absence of ICAM-1.Conclusions: (1) Of the cytokines studied, only TNF-α was consistently detected in normal murine myocardium. (2) Deficiency of ICAM-1 in either D heart or R does not appear to alter the pattern of expression of these cytokines during allograft rejection. (3) CD4 and CD8 mRNA was detected in both normal and mutant allografts, suggesting that lack of ICAM-1 alone does not alter graft infiltration by these lymphocyte subsets.