Comment on: Dietary yeast reduce inflammation in central nerve system via microflora.

Abstract

We recently read with great interest the article on the possible immunomodulatory effects of dietary yeast, specifically Candida kefir, on the central nervous system, notably the experimental autoimmune encephalomyelitis (EAE) mouse model by Takata et al.1 The role of yeast in inflammatory and autoimmune phenomena is nowadays controversial.2 The experiment from Takata et al. raises an important observation that not all yeast lead to the same effect on immunity. For instance, a significant reduction of proinflammatory cytokines such as IL‐17 and IFN‐γ was observed only in mice exposed to Candida kefir. Moreover, changes in microflora were different according to the microorganism used to feed EAE prone mice, with Saccharomyces cerevisiae being unable to reduce the ratio of Bacteroides or to ameliorate toluene‐2,4‐di‐isocyanate‐induced autoimmune dermatitis in mice. On the other hand, commensal microbiota which is not classically considered pathogenic can prompt and flare autoimmunity when fine regulation of immune tolerance does not work properly.2 This was indeed suggested for S. cerevisiae. Anti‐S. cerevisiae autoantibodies (ASCA) are associated with Crohn's disease and can be found even before clinical onset in ~30% of patients.3 Moreover, these antibodies can be found in several other autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and antiphospholipid syndrome (APS), more frequently than in control subjects. Saccharomyces cerevisiae has immune‐modulating properties since cross‐reactive epitopes on β 2‐glycoprotein‐I and S. cerevisiae have been detected in ASCA‐positive APS patients.4 Several other overlaps in molecular sequence between yeast phosphopeptidomannan and conserved protein domains of specific autoantigens in humans have been analyzed and identified through the National Center for Biotechnology Information (NCBI) database.2 Saccharomyces cerevisiae proteins has been used as an adjuvant in vaccines such as hepatitis B vaccination and studies from our group led to the suspicion of an association with postvaccination autoimmune phenomena such as those described in the autoimmune/inflammatory syndrome induced by adjuvants (ASIA).5 Thus, the interesting experiment by Takata et al. may have revealed the importance of different dietary yeast in contribution to inflammation and autoimmunity. From one side, it is possible that some types (such as Saccharomyces boulardii) can be used as probiotics acting in a microbiome competition model leading to amelioration of autoimmune conditions.1 Nonetheless, it is fundamental to address the exact role of those types which, on the contrary, may even worsen an autoimmune/inflammatory condition.