Experimental and clinical significance of endotoxin-dependent HLA-DR expression on monocytes

Abstract

For much of the last decade, an increasing number of surgeons have been interested in objective assessment of cellular contributors to host defense function. In order to study many of these processes, it is apparently desirable that the cells be isolated to the extent feasible for the purpose of analyzing a more or less pure population of cellular elements. The purpose of this paper is to describe the physiologic activation of mononuclear cells that occurs as a result of the isolation process. Therefore, it follows logically that such cells are therein intrinsically less responsive to further physiologic manipulation in vitro. Analyses of such data without an awareness of this intrinsic aberration will undoubtedly lead to misinterpretation of the capacity of such cells for further modulation by immunostimulants or by the intrinsic processes related to injury, anesthesia, and operation. Furthermore, it may indicate that certain agents, e.g., cytokines, are unable to stimulate cellular function when, in fact, the defense function of the cell has been initially stimulated by the isolation procedure. Fractionation of human peripheral blood over Hypaque-Ficoll and subsequent purification of monocytes by adherence to plastic lead to an increase in the relative density of HLA-DR on monocytes. This increase occurred when carried out in endotoxin lipopolysaccharide (LPS)-contaminated or LPS-depleted reagents. LPS, added experimentally to whole blood, enhanced HLA-DR expression on monocytes without further manipulation. Monocyte HLA-DR expression measured in whole blood was reduced in patients with major sepsis ( n = 19) compared to normal subjects ( n = 10). After LPS incubation, monocyte HLA-DR expression was enhanced significantly in septic patients who survived ( n = 10) compared to patients who died of sepsis ( n = 9). We suggest again that inappropriate stimulation of HLA-DR on isolated monocytes may result from LPS contamination of reagents as well as from factors intrinsic to isolation procedures. Furthermore, these data suggest the monocyte HLA-DR expression is a useful marker of infection. In the presence of sepsis, the inability to increase monocyte HLA-DR expression in vitro with LPS stimulation appears to be a predictor of mortality.