A Diketopiperazine Fragment of Human Serum Albumin Modulates T-Lymphocyte Cytokine Production Through Rap1

BACKGROUND: Aspartyl-alanyl- diketopiperazine (DA-DKP) is generated by cleavage and cyclization from the N-terminus of human albumin during the preparation of commercial serum albumin product. Antigen-stimulated human T lymphocytes produce significantly lower quantities of interferon-gamma and tumor necrosis factor-alpha after stimulation in vitro in the presence of DA-DKP. METHODS: T lymphocytes activated in the presence of DA-DKP were analyzed by pull-down western blot assay for the activation of the guanosine triphosphatase Rap1 and by quantitative immunoassay for the phosphorylated transcription factors ATF-2 (activating transcription factor-2) and c-jun, which regulate the production of interferon-gamma and tumor necrosis factor-alpha. RESULTS: Exposure of human T lymphocytes to DA-DKP resulted in increased levels of active Rap1 and decreased activation factors relevant to the T-cell receptor signal transduction pathway and subsequently, decreased phosphorylated ATF-2 and c-jun expression. CONCLUSION: The cyclized N- terminal fragment of human serum albumin, DA-DKP, can modulate the inflammatory immune response through a molecular pathway implicated in T- lymphocyte anergy.