Host-pathogen interactions: can micronutrients tip the balance?

Nutrients are essential to the human host and to its invading pathogens. The purpose of this International Nutrition Council symposium on Micronutrient Regulation of Host-Pathogen Interactions held at Experimental Biology 2006 was to examine new knowledge about the mechanisms by which certain limiting micronutrients can mediate the balance of power between the human host and its numerous potential pathogens. In this introductory article, we briefly review how competition for nutrients is critical to the survival of both host and pathogen and describe some of the evolved mechanisms by which each attempts to gain supremacy over the other. We provide examples of how the presence or absence of certain mechanisms for nutrient acquisition can govern the niche specificity of organisms. We then describe some of the extensive evidence suggesting that, of all the nutrients, iron plays an especially crucial role in host-pathogen interactions. To this end, we provide a reminder of early studies suggesting that universal iron administration under conditions of high pathogen exposure may lead to adverse consequences. Finally, we provide some cautionary tales in the form of intervention studies in which the administration of other micronutrients yielded unpredicted adverse effects. These lessons emphasize the need to step back from an unbalanced concentration of research funds on empirical trials (often built on an inadequate theoretical basis) and toward a greater concentration on integrated clinical research into nutrient effects on host defenses and pathogen virulence.