The Effect of Protein-Energy Malnutrition on Immune Competence

摘要

The most common relationship between protein-energy malnutrition and infection is the synergism expressed in the concept of the malnutrition-infection cycle. Recently, this important concept has been developed further by an analysis showing that primary protein-energy malnutrition increases the risk of childhood mortality from infection in a potent multiplicative manner and with no threshold effect (1). The results pertaining to wasting disease were particularly clear cut, and the impact of all degrees of wasting was revealed to be greater than previously realized. A qualitatively similar impact of the stunting form of protein-energy malnutrition was also apparent (1). Immunodepression is accepted as a determining factor in the infection-related morbidity and mortality of childhood protein-energy malnutrition. In an extension of this concept, immune competence may be a critical but under-recognized factor in the management of malnutrition, at least where primary malnutrition in childhood is concerned (2). Nutritional deficits typically depress diverse immunologic barriers simultaneously. This is fundamental to the impact of protein-energy malnutrition on a multitiered and tightly integrated physiologic system such as the immune system. Data on stunting malnutrition and immune defenses are scant but suggestive (3), whereas information relating wasting malnutrition to immunocompetence is abundant, although skewed toward grade 3 disease. Therefore, in this chapter the term protein-energy malnutrition, when used without qualification, refers to the acute forms of malnutrition. The focus here is on the impact of protein-energy malnutrition on the physiologically labile immune system of the prepubescent individual. For this purpose, it is assumed that extrapolation from the study of adults requires caution, particularly where an immunologic impact of protein-energy malnutrition is unapparent in the adult. Recent progress of a descriptive nature includes aspects of both innate and adaptive defenses. It is important that our catalogue of descriptive information should continue to grow, but the goal is mechanistic knowledge that will permit rational, targeted interventions and dietary recommendations. Published reports on experimental animals are an invaluable source of insight for this purpose, and an objective here is to show the need to improve the relevance of animal systems to childhood protein-energy malnutrition in its various forms. Finally, the thesis is advanced that the physiologic (including immunologic) response to deficiency of dietary protein and energy is governed by endocrine-mediated metabolic priorities rather than by nonselective distribution of amino acids and energy simply in proportion to level of intake.