Immune System Needs Food To Function Well
Researchers studying deer mice have discovered evidence to support what mothers everywhere have long suspected: the immune system needs food to function properly. In a new study Lynn Martin and coauthors find that reduced food intake leads to a decline in immune function in their subjects. The findings could have profound implications for human health.
Immune System Overview
Why immune activity is variable in many wild animals is a question that has long puzzled researchers. “Animals live different lifestyles, so they may use different types of defenses against infection depending on the situation. Perhaps this is why immune defenses vary seasonally in most species; some may be too expensive to use all the time,” Martin said, referring to previous work on Peromyscus and other small mammals and birds.
While it is known that the immune system expends energy when it gears up to fight a virus or an infection–a fever, for example–the researchers found that restricting their subjects’ diet by 30% significantly decreased the amount of available B cells, which produce antibodies and maintain immune memory. Without these cells, the immune system must relearn how to fight a threat if it reappears.
Research on the relationship between food and the immune system could have profound implications for humans. Martin and fellow researchers cite previous studies that have found that infections are “more frequent and tend to be chronic in malnourished children.” Vaccines, in order to work effectively, must provoke B cells to produce sufficient antibodies for immune memory.
Previous studies have found that vaccines such as those for measles have a significantly lower rate of efficacy among the malnourished. “A 30% restriction in food intake doesn’t affect body mass and only minimally reduces activity in deer mice, but it eliminates the long-term immune protection provided by antibodies. One wonders whether similar moderate food restriction has comparable immune effects in humans,” Martin asked. Although other variables may be at work, the authors propose that for both wild animals and humans, food availability impinges on immunity and future research should determine what specific components of a diet (calories, protein, micronutrients) are responsible.
Physiological and Biochemical Zoology. Volume 81, Issue 3, Page 366–372, May 2008
Food Restriction Compromises Immune Memory in Deer Mice (Peromyscus maniculatus) by Reducing Spleen‐Derived Antibody‐Producing B Cell Numbers
Lynn B. Martin II, Kristen J. Navara, Michael T. Bailey, Chelsea R. Hutch, Nicole D. Powell, John F. Sheridan, and Randy J. Nelson
Immune activity is variable in many wild animals, despite presumed strong selection against immune incompetence. Much variation may be due to changes in prevalence and abundance of pathogens (and/or their vectors) in time and space, but the costs of immune defenses themselves may also be important. Induction of immune activity often increases energy and protein expenditure, sometimes to the point of compromising fitness. Whether immune defenses are expensive to maintain once they are generated, however, is less well appreciated. If so, organisms would face persistent challenges of allocating resources between immunity and other expensive physiological processes, which would mandate trade-offs. Mild food restriction (70% ad lib. diet) reduces secondary antibody responses in deer mice (Peromyscus maniculatus), functionally representing a cost of immune memory. In this study, we asked whether compromised immune memory was mediated by a decrease in size of the B cell population responsible for producing antibodies (i.e., spleen-derived B lymphocytes producing immunoglobulin G [IgG]). Two weeks of food restriction reduced total splenocytes, total splenic B lymphocytes (B220+ cells), and splenic B lymphocytes producing IgG (B220+/IgG+ cells) but did not affect body mass or two circulating antibody subclasses (IgG1 and IgG2a) in deer mice. These results further indicate that maintenance of immune memory is expensive and may be subject to trade-offs with other physiological processes.