RESUMO
BACKGROUND: Previous investigations have shown that the plasma levels of the cardiac hormone brain natriuretic peptide (BNP) increase during acute cardiac allograft rejection as diagnosed by endomyocardial biopsy. Successful immunosuppressant treatment decreased plasma BNP levels, suggesting a role for BNP in transplantation immunity. We tested a possible immunomodulatory effect of the natriuretic peptides (NPs) BNP, atrial natriuretic factor (ANF), and C-type NP (CNP) using the unidirectional mixed lymphocyte reaction (MLR). METHODS: Lymphocytes were isolated from the lymph nodes of Brown Norway (BN) and Lewis (L) rats. BN lymphocytes were gamma-irradiated to inhibit DNA synthesis. Lymphocytes at 2.5 x 10(6) cell/ml were mixed (at an L:BN ratio of 4:1) and incubated. On Days 2 and 3, ANF (10(-6) to 10(-11) mol/liter), BNP (10(-5) to 10(-11) mol/liter), or CNP (10(-6) to 10(-12) mol/liter) were added. Cell proliferation was measured on Day 4. RESULTS: Reverse transcript-polymerase chain reaction (RT-PCR) analysis of BN and L lymphocytes detected NP receptor (NPR) mRNA amplicons of the expected size. MLR induced an increase in relative receptor abundance as follows: NPRA > NPRB > NPRC. ANF and BNP significantly inhibited up to approximately 50% lymphocyte proliferation in a dose-dependent manner in the range of 10(-11) to 10(-6) mol/liter, whereas CNP significantly decreased lymphocyte proliferation only modestly (approximately 20%) at 10(-8) mol/liter and at 10(-6) mol/liter. CONCLUSIONS: Both ANF and BNP have immunomodulatory functions, although the response to cardiac rejection observed clinically involves increases in plasma levels of BNP only. This is likely related to BNP gene promoter sequences previously reported to be responsive to specific cytokines and related substances. The modulation of the MLR by NP suggests a possible clinical use of these peptides in transplantation immunity.