Antibacterial functions of macrophages in experimental protein-calorie malnutrition. I. Description of the model, morphologic observations, and macrophage surface IgG receptors

Protein-calorie malnutrition impairs host defense against Candida albicans

Protein-calorie malnutrition (PCM) impairs immune responsiveness predisposing to Candida albicans sepsis, but mechanisms are unclear. This study examined the effect of PCM on enteric-derived C. albicans intestinal translocation and the ability of in vivo interferon-gamma (IFN-gamma) to upregulate macrophage (MO) candidacidal mechanisms in PCM mice. Control (24% casein) and low protein (2.5%) diets were given for 4 weeks. Mice (n = 160) were fed C. albicans in their drinking water for 3 days and C. albicans translocation (mean colony-forming units (CFU)/g tissue +/- SEM) to the GI tract, liver, spleen, and kidney was assessed at 1 and 5 days following endotoxin challenge of 1, 5, and 10 mg/kg body wt. In a separate study (n = 100 mice), IFN-gamma (1000-10,000 U/day ip) vs saline was given for 3 days prior to harvesting peritoneal macrophages for assay of superoxide anion (O2-), percentage macrophage phagocytosis of C. albicans, and percentage killing of C. albicans. On Day 1, fungal translocation to the intestinal wall and systemic organs in the PCM group was significantly higher. On Day 5, mean CFU were significantly higher in the PCM group, indicating impaired organ clearance. Mean O2-, phagocytosis, and killing were significantly impaired in the PCM group (P less than 0.05), but IFN-gamma improved all functions. PCM significantly depressed host responses to C. albicans. IFN-gamma treatment enhanced candidacidal mechanisms, suggesting a therapeutic role in the malnourished host predisposed to C. albicans sepsis.

Reduced natural killer cell activity and IL-2 production in malnourished cancer patients

Natural killer (NK) cell activity was measured in the peripheral blood mononuclear cells (PBMC) from malnourished (MN) and well-nourished (WN) cancer patients and in healthy controls. A marked depression of NK activity was observed in MN cancer patients with moderate protein-calorie malnutrition (PCM), but not in WN cancer patients nor in the healthy controls. The depression of NK activity did not correlate with the localisation of the tumour, patient's age or body weight reduction. The defective NK activity of PBMC from MN cancer patients was restored to normal by rIL-2, but not by alfa-rIFN. Parenteral nutrition of MN patients with the proper amount of proteins and calories quickly corrected the depressed NK activity, indicating a central role of malnutrition in the genesis of their immune disfunction. PBMC from MN cancer patients produced lower amounts of IL-2, as compared with healthy controls, when stimulated in vitro; the most frequently affected were the responses to recall antigens such as influenza virus vaccine (FLU), while those to allogeneic PBMC (ALLO) and phytohaemagglutinin (PHA) were less affected. However, for each patient the ability to produce IL-2 in vitro did not correlate with NK activity, thus showing how the impairment of NK activity is not subsequent to a decreased production of endogenous IL-2. In summary, it can be concluded that malnutrition, rather than malignancy, plays a major role in the immune dysfunction of cancer patients.

Low protein diets improve survival from peritonitis in guinea pigs

Enteral diets with different protein content were tested to determine their effect on outcome in a model of protracted bacterial peritonitis. Hartley guinea pigs were provided with gastrostomies, and 1 week later, osmotic pumps were implanted into the peritoneal cavity to allow for continuous release of live bacteria over the course of 1 week. Three days after pump implantation, the animals began receiving isocaloric enteral diets that contained 5%, 10%, 15%, or 20% of total calories as protein. After 2 weeks of observation, the survivors were killed. All animals lost weight during the 2-weeks period, but there was no difference in weight lost. Nitrogen balance correlated with dietary protein. The mortality rate was significantly higher in the groups that received 15% and 20% of total calories compared with the group that received 5% (p less than 0.05). Although dietary protein in the 5% group was insufficient for meeting the nutritional needs of the animal, survival was best in this group. Possible explanations are that protein restriction in this model may either augment host defence or impair bacterial virulence.

Effect of protein malnutrition on salmonellosis and fever

Protein-malnourished rats had greater numbers of bacteria in their livers and spleens compared with numbers in control rats following a sublethal intraperitoneal dose of Salmonella typhimurium. However, the febrile responses of both groups of rats to infection were similar. The ability to mount a normal febrile response does not necessarily reflect the ability of the host to contain an infection.

Current concepts in immune derangement due to undernutrition

Protein-calorie malnutrition (PCM) adversely affects more or less all immune competent cells. Nonspecific immunity is impaired, particularly adherence and chemotaxis of phagocytes, although the responsiveness of circulating cells may not be the same as that of noncirculating cells. PCM results in numerical and functional impairment in lymphocytes. PCM markedly affects IgG class antibodies which have the highest affinity when directed against T-dependent antigens. These impairments are interrelated, since cooperation between T-helper cell and B-cells is depressed, and the antigen presentation to T-helper cells by macrophages is deficient.

Alterations of pulmonary defense mechanisms by protein depletion diet

Pulmonary defense mechanisms were quantitated in mice that were fed a protein-free diet (PFD) for periods of 2 and 3 weeks. Despite the severe weight loss and emaciation induced by the diet, the bactericidal mechanisms in their lungs were preserved against aerogenic challenges with staphylococcus aureus, Proteus mirabilis, and Listeria monocytogenes. Phagocytic assays of alveolar macrophages that were retrieved by pulmonary lavage from PFD-fed animals showed a decrease in Fc receptor-mediated binding activity but no alteration in the ingestion of sensitized erythrocytes. In contrast, the PFD induced defects in both the attachment phase and the engulfment phase of the phagocytic process when the challenge organism was Candida krusei. The PFD suppressed the pulmonary inflammatory response after mice were infected with influenza virus strain PR8; such mice also failed to eliminate infectious virus from their lungs. Virus infection in control mice suppressed pulmonary antibacterial defenses against challenges with S. aureus and P. mirabilis, and defect that was ameliorated in the lungs of PFD-fed mice with viral pneumonia. The data demonstrated that pulmonary defense mechanisms were modulated by a PFD but that the observed effect was dependent on the agent used to test host defenses.

Host defense mechanisms in protein energy malnutrition

This review has focused on effects of protein energy malnutrition on immune responses in the human host. These studies document major impairment of the T-cell and complement systems in severe PEM, and less profound, but probably significant, effects upon B-cells and immunoglobulins, particularly SIgA. While mild-moderate malnutrition also alters the T-cell system and may predispose to infection, there is less evidence to suggest that complement is similarly affected. Indeed, some data suggest that the host with mild to moderate malnutrition is still able to respond to stress with an acute phase serum protein response and to boost serum levels of complement and complement activity. This may be a functionally significant distinction, serving to separate the more from the less severely ill. Because many other factors alter immune responses, including vitamins, calories, and trace metals, and few clinical studies have examined these parameters, it is uncertain how much of the problem in malnutrition is due to protein, to energy intake, to iron, to other micronutrients and trace minerals, to vitamin E or to other vitamins alone or in combination with deficiencies in protein and energy. Other chapters in this volume attempt to sort out these questions in animal studies, but the relevance of these data for the human situation will remain uncertain until the investigations are carried out in humans as well.