Dual Effect of Amino Acid Compositions on Antibacterial Activity of Human Neutrophilic Granulocytes

It is known that amino acid compositions for parenteral nutrition exhibit an immunomodulatory effect on T and B lymphocytes and phagocytes. The aim of the study was to evaluate the effect of amino acid compositions on the antibacterial functions of human peripheral blood neutrophilic granulocytes (neutrophils) under various experimental conditions. Materials and methods. Neutrophils were preincubated with amino acid compositions Amin or Vamin 14, then phorbol-myristate-acetate (PMA) was added and the respiratory burst of neutrophils was evaluated by flow cytometry. In another model, neutrophils were incubated with bacteria (S. aureus) at a ratio of 1 : 10 or 10 : 1, washed, incubated with amino acid compositions, washed again, lysed, and inoculated on meat-peptone agar to account for the colonies formed by surviving bacteria. Results. Amin and Vamin 14 had a weak immunostimulating effect on the respiratory burst of neutrophils activated by PMA. The addition of amino acid compositions to neutrophils, which phagocytized bacteria at a neutrophil to bacteria ratio of 1 : 10, led to an increase in the number of colonies formed by the surviving bacteria. With a neutrophil/bacteria ratio of 10 : 1, the studied amino acid compositions enhanced the bactericidal activity of neutrophils, causing a decrease in the number of surviving bacteria forming colonies. Direct addition of amino acid compositions enhanced colony formation by bacteria. Conclusions. The amino acid compositions Amin and Vamin 14 enhance the growth of bacteria, including those phagocytized by neutrophils at a cell to bacteria ratio of 1 : 10 but stimulate the bactericidal activity of neutrophils that phagocytized S. aureus at a cell to bacteria ratio of 10 : 1 as well as in the respiratory burst induction test in neutrophils activated by PMA.