PHAGOCYTIC AND ALKALINE PHOSPHATASE ACTIVITY OF LEUKOCYTES IN KWASHIORKOR

The immune system in children with malnutrition--a systematic review

BACKGROUND

Malnourished children have increased risk of dying, with most deaths caused by infectious diseases. One mechanism behind this may be impaired immune function. However, this immune deficiency of malnutrition has not previously been systematically reviewed.

OBJECTIVES

To review the scientific literature about immune function in children with malnutrition.

METHODS

A systematic literature search was done in PubMed, and additional articles identified in reference lists and by correspondence with experts in the field. The inclusion criteria were studies investigating immune parameters in children aged 1-60 months, in relation to malnutrition, defined as wasting, underweight, stunting, or oedematous malnutrition.

RESULTS

The literature search yielded 3402 articles, of which 245 met the inclusion criteria. Most were published between 1970 and 1990, and only 33 after 2003. Malnutrition is associated with impaired gut-barrier function, reduced exocrine secretion of protective substances, and low levels of plasma complement. Lymphatic tissue, particularly the thymus, undergoes atrophy, and delayed-type hypersensitivity responses are reduced. Levels of antibodies produced after vaccination are reduced in severely malnourished children, but intact in moderate malnutrition. Cytokine patterns are skewed towards a Th2-response. Other immune parameters seem intact or elevated: leukocyte and lymphocyte counts are unaffected, and levels of immunoglobulins, particularly immunoglobulin A, are high. The acute phase response appears intact, and sometimes present in the absence of clinical infection. Limitations to the studies include their observational and often cross-sectional design and frequent confounding by infections in the children studied.

CONCLUSION

The immunological alterations associated with malnutrition in children may contribute to increased mortality. However, the underlying mechanisms are still inadequately understood, as well as why different types of malnutrition are associated with different immunological alterations. Better designed prospective studies are needed, based on current understanding of immunology and with state-of-the-art methods.

INCAP Studies of Hematologic and Gastrointestinal Function in Healthy Individuals and those with Protein–Energy Malnutrition and Infection

Anemia is highly prevalent, especially in poorly nourished populations living in unsanitary conditions. Studies of the Central American population showed that iron was the predominant deficient hematopoyetic micronutrient and that correction of nutrient deficiencies led to hematological normality as defined by WHO. The bioavailability of diverse iron compounds added to the mostly vegetable diets of such populations showed the superior absorption of chelated iron (NaFeEDTA) and its strong effectiveness in correcting iron deficiency when added to sugar. The consequences on development and mental behavioral functions as well as on work capacity of iron deficiency and anemia in infants, children and adults, and the positive effects of their correction was demonstrated. In protein-energy malnourished (PEM) children, the deficit in active tissue mass (basal oxygen consumption) and in total hemoglobin content were closely related. This relationship persisted as the rates of active tissue mass repletion was modified by levels of protein intake. This demonstrated the strong adaptive nature of hemoglobin content in response to oxygen needs in PEM and during recovery.

Gastrointestinal functions in PEM and in populations demonstrated the bacterial invasion of the upper GI tract and how this resulted in secondary bile acids that are toxic to the intestinal mucosal cells impairing their absorptive functions. Environmental hygiene in populations reversed gut bacterial migration and improved GI function.

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.

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.

The effects of malnutrition on secretory and cellular immune processes

About 15 million children under 5 years of age die each year due to suppressed immunity and the resulting increased infection. In severely malnourished children and animals some immune systems such as T-cell function, secretory IgA and complement are significantly suppressed. Other systems, such as the serum IgG or IgA, are normal or even elevated. Some of these changes are apparently caused by nutritional stress while others may be due to stimulation by increased incidence of infection and antigen load. On the other hand, marginal malnutrition stimulates increased phagocytosis and T-cell function with increased immunity to cancer but decreased resistance to certain microbial agents. The mechanisms of immune suppression by malnutrition, persistence of these effects after renutrition, and the effect of maternal malnutrition on newborn immunity are critically reviewed. Possible non-nutritional means of rapid immunological restoration of malnourished children are described.

Fasting (acute energy deprivation) in man: effect on polymorphonuclear granulocyte functions, plasma iron and serum transferrin

The effect of 10 days of total fasting (energy deprivation) on blood polymorphonuclear granulocyte functions, leukocyte numbers, iron and transferrin levels was evaluated in 14 healthy, normal-weight males. Granulocytes from 7 of the subjects were tested in vitro. A statistically significant depression was noted in their bactericidal capacity against Staph. aureus. The 14 subjects showed a marked decrease in the stainable activity of granulocyte alkaline phosphatase and decreases were noted in plasma iron and serum transferrin levels. The iron saturation of serum transferrin was unchanged. Thus, impairment of granulocyte bactericidal functions may occur secondarily to short-term total energy deprivation, in the absence of iron deficiency.