Background: Despite improvements in supportive care and pharmacologic therapies, sepsis and related disorders such as systemic inflammatory response syndrome (SIRS) continue to be a leading cause of death in the intensive care unit. We hypothesized that immune dysfunction in this setting may in part be mediated at the level of early signal transduction in monocytes and neutrophils as manifested by changes in intracellular free Ca2+.
Methods: Monocytes and neutrophils were isolated from patients in the intensive care unit who met the criteria for SIRS and from normal volunteers. Cells were loaded with the Ca(2+)-sensitive fluorescent dye Indo-1 and stimulated with the chemotactic peptide f-Met-Leu-Phe (fMLP). Changes in intracellular calcium ion concentration were measured by flow cytometry.
Results: Patient monocytes exhibited a decreased Ca2+ flux (43% +/- 3.1%) as compared with normal monocytes (63% +/- 2.5%) (p < 0.05). Patient neutrophils also exhibited a decreased Ca2+ flux in response to fMLP of 58% +/- 3.7% versus 69.3% +/- 3.1% for normal neutrophils (p < 0.05). Incubation of patient cells in normal plasma reversed this dysfunction and showed an improved Ca2+ flux to 60% +/- 2.7% for monocytes and 71% +/- 3.7% for neutrophils (p < 0.05). Conversely, calcium flux was decreased in both normal monocytes (42.3% +/- 3.1%) and normal neutrophils (55.4% +/- 3.8%) after incubation in SIRS patient plasma (p < 0.05). Incubation of normal monocytes and neutrophils in interleukin-1, interleukin-2, interleukin-6, tumor necrosis factor, or lipopolysaccharide did not show a statistically significant alteration in calcium flux in response to fMLP.
Conclusions: Patients with SIRS exhibit alterations in early signal transduction after stimulation with fMLP in monocytes and neutrophils. This effect appears to be mediated by a soluble factor because the defect in SIRS patient cells can be reversed by incubation in normal plasma and normal cells appear to acquire this defect after incubation in patient plasma. Further studies are underway to identify the factor or factors responsible for this functional defect.