In vivo studies demonstrating that only specific dietary-fibers contribute to immunity are still inconclusive, as measuring immune effects in healthy humans remains difficult. We applied a relatively inefficacious vaccination-challenge to study chain length-dependent effects of inulin-type fructan (ITF) dietary fibers on human immunity.Methods and results
ITFs with two different ‘degree of polymerization-’ (DP)-profiles were tested in vitro for effects on PBMC-cytokines and TLR2 activation. In a double-blind placebo-controlled trial, 40 healthy volunteers (18–29 years) were divided into three groups and supplemented from day 1 to day 14 with DP10–60 ITF, DP2–25 ITF (both n = 13), or fructose placebo (n = 14), 8 g/day. On day 7, all volunteers were vaccinated against hepatitis B. Anti-HbsAg-titer development and lymphocyte subsets were studied. In vitro, DP10–60 ITFs stimulated a Th1-like cytokine profile and stimulated TLR2 more strongly than DP2–25 ITFs. In vivo, DP10–60 increased anti-HBsAg titers, Th1-cells, and transitional B-cells. Both ITFs increased CD45ROhi CTLs at day 35, and CD161+ cytokine producing NK-cells at day 21 and 35.Conclusion
Support of immunity is determined by the chain length of ITFs. Only long-chain ITFs support immunity against pathogenic hepB-epitopes introduced by vaccination. Our findings demonstrate that specific dietary fibers need to be selected for immunity support.