Immunoglobulin A (IgA) is an antibody that plays a crucial role in the immune function of mucous membranes, providing protection against toxins and pathogenic microorganisms, and inhibiting inflammatory effects of other immunoglobulins. It also plays an important role in protecting against upper respiratory tract infections (URTI). There is growing evidence to support an immunomodulatory effect of probiotics, specifically through the modulation of IgA levels, although such effects are strain specific (Ashraf & Shah 2014).
Studies conducted with L. casei Shirota in healthy adults (Harbige et al. 2016, O’Connell et al. 2010) and elite athletes (Gleeson et al. 2011) have shown that consumption of this probiotic can help to maintain salivary IgA levels, which in the athletes’ study was associated with a reduced incidence of URTI.
Study: Upper Respiratory Tract Infections
Effect on incidence of common colds and salivary IgA in athletes - Gleeson et al. (2011) Int J Sport Nutr Exerc Metab 21:55-64.
Methods: This double-blind, placebo-controlled study conducted in the UK aimed to investigate the effects of the probiotic L. casei Shirota on the incidence of upper respiratory-tract infections (URTI) and immune markers, in 84 male and female athletes engaged in endurance-based physical activity. Subjects were randomised to consume either a fermented milk drink containing L. casei Shirota (6.5 × 109 live cells of LcS) (n=42) or placebo (n=42) daily for 16 weeks. Fifty-eight subjects completed the study (probiotic n=32, placebo n=26).
Results: The proportion of subjects who experienced 1 or more weeks with URTI symptoms was 27% lower in the probiotic group compared to placebo (0.66 vs 0.90 respectively, P=0.021) and the mean number of URTI episodes was also significantly lower in the probiotic group compared to the placebo (1.2 vs 2.1 respectively, P<0.01)
The main finding from the immune analysis was that saliva IgA concentrations were significantly higher in the probiotic group than the placebo group at both week 8 (P=0.03) and 16 (P=0.01).
Thus, daily consumption of L. casei Shirota appeared to reduce the frequency of URTI in this group of athletes, which is likely to be attributable to the maintenance of saliva IgA levels which would otherwise have decreased during a winter period of intense sports traini