Prebiotics and human immune function

Abstract

Prebiotics are defined as “non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth, and/or activity, of one or a limited number of beneficial bacteria in the colon and thus improve host health”. Prebiotics include the 1^2-1 fructans, molecules which contain fructosyl-fructose linkages. A review of studies conducted in laboratory animals and in humans indicated that 82-1 fructans may modulate some aspects of immune function, improve the host's ability to respond to
certain intestinal infections, and to modify some inflammatory outcomes. Studies looking at these same outcomes in humans supplemented with probiotics were also reviewed, and overall, the picture that emerges from these studies is mixed and there appear to be large species and strain differences in effects seen. This thesis describes a study that investigated the effect of Orafti* Synergy 1 on the functioning of the immune system in healthy human middle-aged adults, an age group that is underrepresented in the literature. A pilot study was conducted initially in order to develop a vaccination protocol, as response to vaccination has been identified as the
most meaningful measure of the immune response. This protocol was then used in an intervention study to investigate the effect of 82-1 fructans on human immune responses. Healthy adults aged 45 - 65 years (n = 22 in test group, n = 21 in placebo group) were supplemented with Orafti' Synergyl (8 g/d for eight weeks) or maltodextrin, and vaccinated with the 2008/2009 seasonal influenza vaccination after four weeks. Fasting blood samples were taken at baseline (week zero) and weeks four, six and eight for analysis of various systemic immune parameters; anti-vaccine antibodies (the primary outcome), total antibody concentrations, immune cell phenotypes, neutrophil and monocyte phagocytosis and oxidative burst, ex vivo lymphocyte responsiveness (activation, proliferation and cytokine production) to the
mitogen concanavalin A (ConA) and the vaccine. Faecal bifidobacteria were measured at weeks zero and four. Supplementation with Orafti* Synergyl (8 g/d) for four weeks had a bifidogengic effect. However, no effect of the supplement was seen on immune function measured in the absence of vaccination. Furthermore, few differences were seen between groups in most immune outcomes measured post-vaccination. However, two important and novel observations were made. First, the prebiotic supplement enhanced the antibody response to the HAH3_UR strain of the vaccine (p = 0.0019), and enhanced the IgCl-specific antibody response to the vaccine (p = 0.0019). Therefore, it can be concluded that Orafti* Synergyl is able to alter some aspects of immune function in healthy middle-aged adults.

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