ObjectiveTo determine the extent of the potentially protective heat shock protein 70 response in peripheral blood lymphocytes of patients with severe sepsis after ex vivo lipopolysaccharide stimulation.DesignEntry study of consecutive patients with severe sepsis, those who were critically ill or nonseptic after major surgery, and healthy blood donors.SettingSurgical intensive care unit in a university hospital.PatientsTen patients with diagnoses of severe sepsis; ten critically ill, nonseptic patients after major surgery; and ten healthy blood donors.InterventionsNone.Measurements and Main ResultsWe investigated the ex vivo endotoxin-inducible expression of heat shock protein 70 in peripheral blood lymphocytes of patients with severe sepsis by means of flow cytometry. Only negligible amounts of inducible intracellular heat shock protein 70 accumulation (<4.2% of lymphocytes) could be detected in peripheral blood lymphocytes without lipopolysaccharide stimulation. The proportion of cells accumulating heat shock protein 70 after treatment with lipopolysaccharide was distinctly lower in patients with severe sepsis (p < .05) than in critically ill, nonseptic patients after major surgery and healthy blood donors (38.3 +/- 3.3%, 82.2 +/- 4.5%, and 70.9 +/- 3.9%, respectively; mean +/- SEM; n = 10). Patients with clinical signs of recovery from severe sepsis showed an increase in heat shock protein 70 expression.ConclusionsInducibility of ex vivo heat shock protein 70 was impaired in peripheral blood lymphocytes of patients with severe sepsis. The impaired expression of the potentially protective heat shock protein 70 may contribute in vivo to immune dysfunction, because intact functioning of T and B lymphocyte responses is of central importance in resisting infection in severe sepsis. Monitoring of inducible heat shock protein 70 in peripheral blood lymphocytes may contribute to the evaluation of the immune consequences of severe sepsis. (Crit Care Med 1999; 27:1080-1084)