Malnutrition-induced macrophage apoptosis

Background, Human and murine studies suggest protein-calorie malnutrition ( PCM) results in significant host immunosuppression resulting in increased m orbidity and mortality. Apoptosis has been implicated as an important media tor in the immunosuppression observed in several disease states. This study was designed to characterize macrophage apoptosis in a murine model of PCM and investigate components that regulate the apoptotic process, such as pr otein kinase C (PKC) and Bcl-2 activity. Methods. Swiss-Webster mice (n = 50) were randomly assigned to receive eith er a control (24% protein) or a PCM dirt (0% protein) for 7 days. Peritonea l macrophages were harvested and detection of apoptosis was performed by te rminal deoxy-transferase-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) and propidium iodide DNA staining under baseline and pro- apoptotic conditions. Pro-apoptotic conditions included cells treated with tumor necrosis factor-alpha (TNF-alpha) (10 ng/mL), interferon-gamma (IFN-g amma) (50 mu /mL) and a combination of both agents. In addition, levels of PKC activity and expression of Bcl-2 and p53 protein were measured. Results. Peritoneal macrophages from PCM mice had a significantly greater a mount of apoptosis at baseline and under stimulated conditions compared wit h controls. Levels of PCM apoptosis were elevated at baseline by TUNEL stai ning compared with macrophages from the control group (16.5% +/- 1.4%, vers us 4.5% +/- 1.1%, P <.01). In addition, peritoneal macrophages from the mal nourished animals were significantly more susceptible to the apoptotic effe ct of TNF-<alpha> and the effects of IFN-gamma (27.3% +/- 2.1% and 31% +/- 1.4%) compared with control mice (5.5% +/- 0.7% and 7.2% +/- 0.5%, P <.01), respectively. Again, an increase in the baseline apoptosis rate tons demon strated In peritoneal macrophages from PCM mice compared with control fed m ice (13.2% +/- 4.4% versus 4.3% +/- 3.1%, P <.01) as measured by propidium iodine staining. The combination of agents, TNF alpha and INF-gamma, result ed in an additive apoptotic effect in the malnourished host compared with t he control animals (43.4% +/- 4.7% versus 10.5% +/- 2.2%, P <.01), respecti vely. Furthermore, there runs a significant decrease in the mean total PKC activity in the malnourished macrophages compared with results in controls (110,000 +/- 8000 versus 60,000 +/- 4000 cpm, p <.01). Similar changes were also observed in PKC cytosolic and membrane activity between both groups. In addition, Bcl-2 protein expression was significantly decreased in PCM an imals compared with control animals. Conclusions. Thus, peritoneal macrophages from PCM mice exhibit significant ly greater levels of apoptosis at baseline and when stimulated with pro-apo ptotic agents compared with controls. The propensity of macrophages from PC M mice to undergo apoptosis may be attributable in part to decreased PKC ac tivity and Bcl-2 protein expression. These findings may help to explain the associated immune dysfunction observed in malnutrition.