Effect of Bovine or Human Milk on the Establishment ofBifidobacterium bifidumand Some Other Bacteria from the Human Neonatal Microflora in Gnotobiotic Mice

Intestinal barrier function and cow's milk sensitization in guinea pigs fed milk or fermented milk

BACKGROUND

The respective effect of milk and fermented milks on intestinal barrier capacity and on sensitization to beta-lactoglobulin was studied using a guinea pig model of cow's milk allergy.

METHODS

Guinea pigs were fed a control diet or the same diet supplemented with milk, fermented milk (Streptococcus thermophilus and Bifidobacterium breve), or dehydrated fermented milk. Intestinal barrier capacity to macromolecules was assessed in an Ussing chamber, and sensitization to cow's milk proteins was measured by systemic anti-beta-lactoglobulin immunoglobulin G1 titers and by intestinal anaphylaxis, the latter assessed by the beta-lactoglobulin-induced increase in short-circuit current of jejunal fragments (deltaIsc(beta-LG)).

RESULTS

The electrical resistance of jejunum was similar in the four groups (approximately 80 omega/cm2) suggesting the same paracellular permeability. The transport of 14C-beta-lactoglobulin from mucosa to serosa was significantly decreased in the animals fed dehydrated fermented milk (403+/-131 ng / hr x cm2) compared with that in control animals or animals fed milk (767+/-250 ng / hr x cm2 and 749+/-475 ng / hr x cm2, respectively; p < 0.05). Milk fermentation did not modify native beta-lactoglobulin concentration but anti-beta-lactoglobulin immunoglobulin G1 titers were higher in fermented milk and dehydrated fermented milk (log10 titer = 2.86 and 2.79, respectively) than in guinea pigs fed milk (log10 titer = 2.5; p < 0.007). However, beta-lactoglobulin-induced intestinal anaphylaxis remained the same in the three groups (deltaIsc(beta-LG), 9.6+/-4.1 microA/cm2, 8.5+/-4.3 microA/cm2, and 8.5+/-3.4 microA/cm2 in milk-fed, fermented milk-fed, and dehydrated fermented milk-fed guinea pigs, respectively).

CONCLUSIONS

The intestinal barrier capacity to milk proteins seems to be reinforced by dehydrated fermented milk, but milk and fermented milks are equally efficient in inducing cow's milk allergy in guinea pigs.

Gut flora allows recovery of oral tolerance to ovalbumin in mice after transient breakdown mediated by cholera toxin or Escherichia coli heat-labile enterotoxin

Oral tolerance, the antigen-specific immunologic unresponsiveness after antigen (Ag) feeding, is of physiologic importance in preventing antibody (Ab) responses to dietary proteins. This is important in the young, especially at weaning when numerous dietary Ag are encountered for the first time. Two related enterotoxins responsible for much diarrhea in the infant, cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT), have been shown to abrogate oral tolerance to an unrelated Ag fed simultaneously. The main objective of this study was to determine whether the gut flora can play a role in the CT- or LT-mediated abrogation of oral tolerance to the dietary protein ovalbumin (OVA), on a short-term and long-term basis. Conventional and germ-free mice were fed once or twice with toxin plus OVA. After two intraperitoneal immunizations with OVA, anti-OVA IgG and IgE Ab levels were measured. Because IgG and IgE Ab responses were detected, both CT and LT abrogated oral tolerance to OVA in conventional and germ-free mice. As time progressed (observations over 3 mo), whereas the specific IgG Ab response in the germ-free mice remained similar to that of the bicarbonate-fed controls, a hyporesponsive state was observed in conventional mice. The results showed that, although the gut flora did not prevent the CT- and LT-mediated abrogation of oral tolerance, it did shorten the effect and allow oral tolerance to be recovered.