Recently, Rizzardini et al. (B. J. Nutr. 2011) showed that in a vaccination model in healthy subjects supplementation with either Bifidobacterium BB-12 or Lactobacillus casei 431 resulted in significantly greater mean fold increases in total and vaccine-specific antibody titers.

However, the question remains whether the observed and statistically significant differences will also be perceived as physiologically relevant by EFSA in the context of a health claim evaluation.

The biomarker that was chosen as the read-out of immune modulation by the probiotic strains was ’substantial increase in vaccine-specific antibody titer’, defined as a ≥2-fold increase above baseline. Will EFSA consider this a physiologically meaningful increase?

Indeed, the immune system possesses a great degree of redundancy such that an excess functional capacity of some component may compensate for a reduced functional capacity of another component. This ‘robustness of homeostasis’ clearly hampers the identification of relevant biomarkers of immune function.

Needless to say that claiming a significant effect of a food, food ingredient or potentially beneficial live microorganism on immune function turns out to be a perilous enterprise. Let alone, to claim a physiologically relevant effect!

To illustrate the redundancy of the immune system, Rizzardini et al. refer to Gleeson et al. (Clin. Exp. Immunol. 1996), who showed that elite athletes with antibody levels in the 10th percentile relative to clinical norms were still able to mount clinically appropriate antibody responses to a pneumococcal vaccine!