Nutrition and Immunity - Complex Interactions

There are few, perhaps no, diseases in which the pathogenesis does not in any way involve the immune system. The involvement may be primary as in hypersensitivities, secondary as in infectious diseases, or in more obscure and surprising ways such as in the effect of obesity on immunity. Immune function ranges from simple, innate, barrier defenses, through to complex, highly adaptive, antigen-specific multi-cellular responses.

From basic to complex, the immune system is, like any other body system, dependant on the appropriate supply of nutrients and sensitive to nutritional deficiencies and imbalances. But unlike other body systems, the rapid changes in nutrient requirements associated with cellular replication, cellular synthesis, and highly energetic activities makes the immune system very responsive to both long term and short term nutrition. Given the vital role that the immune system has both for the benefit, and in certain diseases the detriment of the animal, it is important to understand how nutrition affects immunity in health and disease. This chapter aims to explore some of the most important aspects of how nutrition affects immunity in cats.

Nicholas J. CAVE
BVSc, MVSc, MACVSc, Dipl. ACVN

Nick Cave graduated from Massey University (New Zealand) in 1990 and worked in private practice for 7 years before completing a residency in internal medicine and Masters in Veterinary Science at Massey University. He then completed a residency in clinical nutrition and studied for a PhD in nutrition and immunology at the University of California, Davis, and became a diplomate of the American College of Veterinary Nutrition in 2004. He is now senior lecturer in small animal medicine and nutrition at Massey University.

1. Nutrition and Immunity – Complex Interactions

As indicated in Figure 1 and Figure 2, nutrition directly affects the immune response.

This can be in three general ways:
1. enhancement or exaggeration of the response
2. suppression or limitation of the response
3. changing the nature of the response

Whether a change is good or bad depends upon the specific disease state, and the individual patient. Attenuation of an immune response may be beneficial in hypersensitivity diseases (e.g., atopic dermatitis) or in overwhelming systemic immune activation (i.e., systemic inflammatory response syndrome or SIRS). Likewise, enhancement of an immune response may be desirable for prevention or elimination of infection, or immunity to tumor development.

Figure 1. Nutrition and immunity.

Figure 2. Nutrition pathogen and immunity.

In contrast, modulation of immunity can be detrimental or even fatal to the host. Immunosuppression in the face of infection can lead to prolonged morbidity or even overwhelming sepsis. Enhancement of immunity may lead to increased self-damage in states already characterized by excessive or poorly regulated immune activation (e.g., SIRS, hypersensitivity diseases). Clearly then, one diet cannot fit the needs of all.

To understand how nutrition can affect immunity, once must first understand the nature of immunity.