Au

Abbreviation: AU, arbitrary units

Figure 3 Adjuvant effect of the fecal microbiota of breast-fed babies on the intestinal anti-rotavirus antibody response measured in gnotobiotic mice. Source: From Ref. 72.

(Gram-negative bacteria), two other groups of gnotobiotic mice were created. Results presented in Table 2 obviously show the adjuvant capacity of the strain of Bifidobacterium bifidum on the intestinal sIgA anti-rotavirus response while, in contrast, E. coli exerted a suppressive effect, as compared with GF mouse response. These results show how the presence of Bifidobacterium bifidum in the fecal microbiota of babies modulates the suppressive effect exerted by the presence of E. coli. Given the importance of rotavirus infections as a cause of infantile diarrhea worldwide, the presence of Bifidobacterium in the intestinal microbiota of babies is of great interest to stimulate this protective Ab sIgA response. These results can be compared to those found previously, which showed that a strain of Lactobacillus rhamnosus GG, used as a probiotic, and given to babies suffering from rotavirus diarrhea, shortened the diarrhea duration, and stimulated the specific IgA anti-rotavirus response (73,74). Other studies have shown an enhancement of serum or intestinal Ab response to orally administered Ags by Gram-positive bacteria (75), especially lactic acid producing bacteria used as probiotics (76).

These results also showed that GF mice are able to mount a sIgA anti-rotavirus response while its IIS is poorly developed suggesting a lack of correlation between the non-specific IgA response induced after bacterial colonization and the specific anti-rotavirus Ab response. The latter findings confirm previous results from Cebra and coworkers (77). Such data have also been described in humans where one-week-old babies are capable of developing protective immunity following oral vaccination with poliovirus or hepatitis B virus while the complete development of natural sIgA is only achieved several months later (78). Consequently, the ability to give a highly specific sIgA anti-rotavirus Ab response could be correlated with the modulatory effect of intestinal bacteria rather than with the development of IIS. Mechanistic studies are required to clarify the molecular basis upon which some digestive bacteria modulate the sIgA Ab response to enteric pathogens.

The adjuvant effect of Bifidobacterium sp. may be strain-dependent. In a recent study we have shown that four different species of Bifidobacterium isolated from the fecal

Table 2 The Gut Colonization of Different Bacterial Strains Modulates the Intestinal Anti-rotavirus IgA Antibody Response Measured in Gnotobiotic Mice

Anti-rotavirus sIgA antibody Intestinal microflora of gnotobiotic mice level (AU/g of feces)

Bifidobacterium bifidum (from baby) 31 + 7a[

Bifidobacterium DN 173 010 (a commercial strain) 21 + 3a[

Germ-free (control) 11+2

Bifidobacterium infantisCB. pseudocatenulatumC 4+1aY

B. angulatumCB. sp (from human adult)

E. coli (from infants) or Bacteroides vulgatus (from 4+ 1aY human adult)

a Significant difference with germ-free mice (p<0.01). Abbreviation: AU, arbitrary units. Source: From Refs. 72, 79.

microbiota of an adult human lacked the adjuvant ability to stimulate the sIgA anti-rotavirus response in gnotobiotic mice but, on the contrary, exerted a suppressive effect as do E. coli (Table 2) (79). Thus, the modulating effect of Bifidobacterium is strain-dependent, as it has also been described for different Lactobacillus strains used as probiotics in other mice studies (80). Taken together, these data suggest that it is important to define the modulatory effect of the strains of bifidobacteria either normally colonizing the digestive tract of babies after birth or given as probiotics, to modulate in a good protective way a specific intestinal immune response.

In conclusion, and on the basis of the experimental and clinical data, we may consider that the presence of certain bacterial strains in the infantile intestinal microbiota, namely some strains of Bifidobacterium, or some transiting strains of probiotics, enable activation of the mechanisms that result in optimization of the anti-rotavirus protective IgA Ab response. Elucidation of the immunomodulatory mechanisms must now be pursued.

Pregnancy And Childbirth

Pregnancy And Childbirth

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