Hypertonic saline increases γδT cell-mediated killing of activated neutrophils

Objective: Hypertonic saline fluids used to resuscitate trauma patients can prevent neutrophil-mediated lung tissue damage, making them attractive alternatives to conventional resuscitation fluids. We have previously shown that gamma delta T cells, a small T lymphocyte subset, reduce acute inflammatory lung damage by eliminating activated neutrophils that express heat shock protein 72 on the cell surface. Here, we studied whether these protective effects of hypertonic saline are related to improved gamma delta T cell-mediated neutrophil killing. Design: Laboratory investigation. Setting: University research laboratory. Subjects: Human peripheral blood from healthy subjects-isolated gamma delta T lymphocytes and neutrophils. Interventions: Isolated blood cells were treated with different concentrations of hypertonic saline and endotoxin of Escherichia coli 0111:B4 (lipopolysaccharide). In some experiments, gamma delta T cells were activated by CD3 cross-linking or by phorbol-myristate acetate and ionomycin, or by phytohemagglutinin. Measurements and Main Results: Clinically relevant concentrations of hypertonic saline (20 mM) significantly augmented CD69 expression of gamma delta T cells that were stimulated with 100 ng/mL lipopolysaccharide. Additionally, lipopolysaccharide induced a three- to five-fold increase in tumor necrosis factor-alpha and interleukin-10 expression by gamma delta T cells. This response was completely abrogated by hypertonic saline. These data indicate that hypertonic saline can modulate gamma delta T cell functions. Stimulation of neutrophils with 1-1,000 ng/mL lipopolysaccharide caused a greater than 3-fold increase in heat shock protein-72 expression on the cell surface, which was significantly augmented by hypertonic saline. In cocultures of gamma delta T cells with autologous neutrophils, 15.6 +/- 3.4% of all neutrophils were killed within 120 min. In the presence of lipopolysaccharide (1 mu g/mL), this percentage increased to 23.7 +/- 2.1%, and it was further increased to 31.8 +/- 3.1% when 20 mM hypertonic saline was added with lipopolysaccharide. Conclusions: Our findings suggest that hypertonic saline enhances the elimination of inflammatory neutrophils by gamma delta T cells by augmenting heat shock protein-72 expression on the cell surface of neutrophils. Hypertonic saline resuscitation may therefore protect host tissues by enhancing neutrophil clearance from the lungs. (Crit Care Med 2008; 36:3220-3225)