Nutrition, immunity and infection: from basic knowledge of dietary manipulation of immune responses to practical application of ameliorating suffering and improving survival.

The causal relationship between the conjugal pair of famine and pestilence has been known for millennia. It is recognized that malnutrition and infection are the two major obstacles for health, development, and survival worldwide, and poverty and ignorance are the most significant contributing factors (1, 2). Epidemiological observations have confirmed that infection and malnutrition aggravate each other. However, nutrition does not influence all infections equally (3, 4). For some infections (e.g., pneumonia, bacterial and viral diarrhea, measles, tuberculosis), there is overwhelming evidence that the clinical course and final outcome are affected adversely by nutritional deficiency. For others (e.g., viral encephalitis, tetanus), the effect of nutritional status is minimal. For still others (e.g., influenza virus, human immunodeficiency virus), nutrition exerts amoderate influence. It is now established that nutritional deficiency is commonly associated with impaired immune responses, particularly cell-mediated immunity, phagocyte function, cytokine production, secretory antibody response, antibody affinity, and the complement system (1, 5, 6). In fact, malnutrition is the commonest cause of immunodeficiency worldwide. There was a three-pronged impetus for systematic studies of immune responses in undernourished individuals. First, there was a plethora of public health data indicating an interaction, usually synergistic but occasionally antagonistic, between malnutrition and infection (3). Second, new concepts and novel techniques in immunology emerged in the 1960s and 1970s. Third, dramatic human stories and demographic data stimulated individual scientists, as the following example shows (7).