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, > or = 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‐gamma, 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‐gamma secretion by cultured monocytes were observed. CONCLUSIONS: No immunological effects of prebiotics were observed in this study.