Effects of Prebiotics on the Immune Response to Vaccination in the Elderly^*

Background:

Prebiotics stimulate the growth of bifidogenic bacteria in the gut. The aim of this work was to assess the effects of a prebiotic mixture on the immune response in healthy elderly people.

Methods:

Healthy free-living elderly people (age, ≥70 years), receiving a nutritional supplement that provided 1.6 MJ, 15 g of protein, and 50% of vitamin daily reference values per day, were randomly assigned to receive a prebiotic mixture (6 g/d of a 70% raftilose and 30% raftiline mixture) or placebo (6 g of maltodextrin powder) for 28 weeks. At week 2 of the study, all subjects were vaccinated with influenza and pneumococcal vaccines. At weeks 0, 2, and 8 of the study, serum total proteins, albumin, immunoglobulins, saliva secretory immunoglobulin A (IgA), and serum titers of influenza A and B and pneumococcal antibodies were measured. At week 8, cultured peripheral monocyte cell secretion of interleukin-4, interferon-γ, and lymphocyte proliferation, stimulated with phytohemagglutinin and influenza antigen, were measured.

Results:

Sixty-six subjects were considered eligible for the study, and 43 (20 receiving prebiotics and 23 receiving placebo) were considered for final analyses on a per protocol basis. No changes in serum proteins, albumin, immunoglobulins, and secretory IgA were observed. Antibodies against influenza B and pneumococcus increased significantly from weeks 0 to 8, with no significant differences between groups. Antibodies against influenza A did not increase. No effects of prebiotics on interleukin-4 and interferon-γ secretion by cultured monocytes were observed.

Conclusions:

No immunological effects of prebiotics were observed in this study. (Journal of Parenteral and Enteral Nutrition26: 372–376, 2002) A prebiotic is defined as a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth or activity of one or a limited number of bacteria in the colon.1 Chicory fructans (inulin and its enzymatic hydrolysate oligofructose) are thought to be the prototype prebiotics, because they resist digestion in the upper gastrointestinal tract and are fermented by bacteria, normally colonizing the large bowel. This fermentation leads to a selective growth of the bifidobacteria population.2 The beneficial effects of prebiotics are numerous. In experimental animals, prebiotics inhibited the formation of preneoplastic lesions in the colon, induced by azoxymethane.3 In the same model, prebiotics have shown suppressive effects of the synthesis of hepatic triglycerides and VLDL, leading to marked reductions in the serum levels of these lipids. However, this lipid lowering effect has not clearly been demonstrated in healthy or diabetic humans.4,5 Nondigestible oligosaccharides are known to increase calcium bioavailability and to prevent the loss of bone mass in gastrectomized rats.6

Prebiotics could have an immunostimulatory effect. Although there is no experimental data to support this effect in humans, probiotic organisms, whose growth is promoted by prebiotics, interact with the immune system at many levels, including cytokine production, mononuclear cell proliferation, macrophage phagocytosis and killing function, and immunity toward bacterial and protozoan pathogens.7 Clinical studies have consistently shown an enhancing of natural killer cell activity by lactobacilli.8,9 In mice, fructooligosaccharides protect against infections caused by the intraperitoneal injection of listeria and salmonella.10 In humans, the bifidogenic effect of prebiotics has been demonstrated in healthy volunteers.11 A preliminary report of a randomized trial in Indonesia showed that prebiotics improved the immunoglobulin G (IgG) response to measles vaccination in 8-month-old breast-fed children (Firmasyah F, Hasche F, 2002, unpublished observations).