The role of L-alanyl-L-glutamine in the immune response in vitro

INTRODUCTION: The amino acid glutamine plays an important role in the immune system by providing energy and precursors for biosynthetic processes. For lack of stability it could not so far be generally supplied in total parenteral nutrition. The development of dipeptides consisting of glutamine and a second amino acid offers a solution to this problem. METHODS: In vitro effects of the dipeptide L-alanyl-L-glutamine on different cells of the immune system are assessed and compared to those of glutamine on its own. RESULTS: T-lymphocyte proliferation stimulated with mitogens and alloantigens increased significantly and dose-dependently after addition of L-alanyl-L-glutamine or glutamine. Maximal effects were observed with a concentration of 2 mmol/l of either substance. The stimulatory effects were partly attributed to enhanced cytokine production following glutamine or L-alanyl-L-glutamine treatment. In contrast, the activity of natural killer and cytotoxic T-cells was not influenced by neither amino acid at concentrations of 0.2 and 2 mmol/l, and suppressed at 20 mmol/l. In all experiments, early addition of the amino acids to the cultures proved crucial. CONCLUSION: In this series of in vitro experiments the dipeptide L-alanyl-L-glutamine exerted almost identical immunostimulatory activities to glutamine alone. Its provision in parenteral nutrition appears commendable.