Date Published: December 6, 2011
Publisher: BioMed Central
Author(s): Cin L Thang, Bushansingh Baurhoo, Joyce I Boye, Benjamin K Simpson, Xin Zhao.
Cow’s milk allergy (CMA) is one of the most prevalent human food-borne allergies, particularly in infants and young children from developed countries. Our study aims to evaluate the effects of Lactobacillus rhamnosus GG (LGG) administration on CMA development using whole cow’s milk proteins (CMP) sensitized Balb/C mice by two different sensitization methods.
LGG supplemented mice were either sensitized orally with CMP and cholera toxin B-subunit (CTB) as adjuvant, or intraperitoneally (IP) with CMP but without the adjuvant. Mice were then orally challenged with CMP and allergic responses were accessed by monitoring hypersensitivity scores, measuring the levels of CMP-specific immunoglobulins (IgG1, IgG2a and IgG) and total IgE from sera, and cytokines (IL-4 and IFN-γ) from spleen lysates.
Sensitization to CMP was successful only in IP sensitized mice, but not in orally sensitized mice with CMP and CTB. Interestingly, LGG supplementation appeared to have reduced cow’s milk allergy (CMA) in the IP group of mice, as indicated by lowered allergic responses.
Adjuvant-free IP sensitization with CMP was successful in inducing CMA in the Balb/C mice model. LGG supplementation favourably modulated immune reactions by shifting Th2-dominated trends toward Th1-dominated responses in CMP sensitized mice. Our results also suggest that oral sensitization by the co-administration of CMP and CTB, as adjuvant, might not be appropriate to induce CMA in mice.
Cow’s milk allergy (CMA), an immunologically mediated reaction to cow’s milk proteins , is one of the most prevalent human food-borne allergies, particularly in infants and young children. In North America, incidence of CMA is estimated at 2.5% in children and about 1% in adults with a 75% outgrowing rate at 16 years of age . Milk protein comprises a mixture of multiple proteins, including whey (such as β-lactoglobulin, α-lactalbumin and bovine serum albumin) and casein (such as α-S1-, α-S2-, β-, κ-, and γ-caseins) proteins. Hypersensitivity reactions may occur upon exposure to a single or multiple milk protein(s). Numerous attempts have been made to reduce or eliminate the allergenicity of milk proteins. Of these attempts, most have focussed on two approaches: to alter the structure and property of milk proteins through thermal treatments, biochemical processes (enzymatic digestion), irradiation  and high pressure treatments , and to modulate immune responses through sensitization and tolerance induction by means of controlled exposure to a specific allergen which is commonly referred to as specific immunotherapy . Nevertheless, total avoidance of cow’s milk or its associated products still remains as the best remedy for CMA. Hypersensitivity to orally ingested food usually occurs upon failure to induce oral tolerance. Research with germ-free mice has indicated that the interaction between allergens and host’s gut microbiota plays a crucial role in oral tolerance development  and in reducing secretions of allergen-specific antibodies . The gut microbiota is also reported to favour anti-allergenic reactions by mediating T-helper-1 (Th1) type of immunity  or inducing IL-10 and transforming growth factor-β (TGF-β) that suppresses T-helper-2 (Th2) type of immunity . Recently, delayed microbial exposure and/or reduced diversity of the gut microbiota among children have been associated with higher allergy incidences . This concept was first reported by Strachan  and later widely known as the ‘hygiene hypothesis’. Interestingly, whereas the gut microbiota of allergic infants contained higher levels of Clostridia, intestinal Lactobacilli and Bifidobacteria were more predominant among healthy infants [12,13]. Such findings have triggered considerable scientific interests in probiotics, particularly Lactobacilli and Bifidobacteria, for prevention or treatment of allergies among infants. The allergy reducing effects of probiotics against food allergens such as egg ovalbumin [14,15] and whey proteins  have been demonstrated in mouse allergy models. But, to the best of our knowledge, probiotic effects of Lactobacillus rhamnosus GG (LGG) to reduce or control allergy to whole cow’s milk protein (CMP) have not yet been reported in a mouse allergy model. We used the Balb/C mice model based on its similarity with the human immune system, particularly the Th1 and Th2 responses .
CMA is a global health concern that occurs more frequently among children than adults. In infants, high CMA incidence occurs upon first exposure to CMP, for example through infant formulas, while the immune system is still immature. On the other hand, the intestinal immune-modulating effects of probiotics  have been shown to reduce the risks of developing allergic diseases in both mice [14,15,24] and humans [27,28]. The present study evaluated whether oral LGG administration could help reduce or control CMA in Balb/C mice that were sensitized with CMP either via the oral (gavage) or systemic (IP) route. Moreover, to better simulate CMA in infants, we specifically used 3 week-old newly weaned Balb/C mice as an animal model and whole CMP as allergen rather than purified single CMPs.
To our knowledge, we are the first to investigate the effects of LGG supplementation on CMA in mice that were sensitized with the whole CMP. We believe that the adjuvant-free systemic sensitization model may be particularly useful in the testing of food products with low allergenicity. LGG administration seems to favour suppression of Th2 responses such as reduced hypersensitivity scores and lowered serum CMP-specific IgG1 while promoting Th1 responses by causing elevated IFN-γ and CMP-specific IgG2a levels. Although further experimental and clinical studies are required to elucidate the mechanism involved and complete beneficial effects of LGG, the current study suggests LGG as a potential preventive tool in the fight against CMA.
The authors declare that they have no competing interests.
CLT, JIB, and XZ designed the research; CLT conducted the research and analyzed the data; BB performed PCR and statistical analysis; CLT and XZ wrote the paper; JIB, BKS and XZ helped to edit the manuscript and CLT and XZ had primary responsibility for final content. All authors read and approved the final manuscript.