Genetic susceptibility to food allergy is linked to differential TH2-TH1 responses in C3H/HeJ and BALB/c mice (1)
There is great similarity between human and murine immune systems in most of the important mechanisms, such as TH1 and TH2 responses, involved in allergic responses. In mice an allergic phenotype can be created under controlled environmental conditions and within defined genetic backgrounds, and because there is a large variety of homozygous inbred strains, cross-breeding allows segregation analyses of polygenic traits.
Several strains of mice, including BALB/c, AKR/J, CBA/J, and C3H/HeJ were tested.Unlike C3H/HeJ mice, the cow’s milk allergy (CMA) models were unable to be induced in BALB/c or AKR/J mice and induced only a minimal reaction in CBA/J mice after the same cow’s milk (CM) sensitization-challenge regimen used for C3H/HeJ mice.
Three-week-old female C3H/HeJ and BALB/c mice were intragastrically sensitized with homogenized CM (equivalent to 1 mg/g body weight CM proteins)-CT adjuvant (0.3 μg/g body weight), and boosted weekly for 5 weeks. Six weeks after the initial sensitization, all mice were challenged intragastrically with homogenized CM equivalent to 33 mg per mouse of CM proteins.
5-week-old C3H/HeJ and BALB/c mice were sensitized intragastrically with 10 mg of equivalent peanut protein with CT (20 μg per mouse) in 0.5 mL of PBS-containing 1.5% NaHCO3 and boosted 5 times with the sensitization dose at weekly intervals and an additional 2 boostings at 2-week intervals with 50 mg of equivalent protein-CT. Mice were challenged intragastrically with 50 mg of equivalent peanut protein at week 14 after the initial sensitization. Mice were fasted for 2 hours before each oral sensitization, boosting and challenge.
CM-specific IgE levels were markedly increased in C3H/HeJ mice at the time of challenge at week 6. CM-specific IgE levels in BALB/c mice, however, were only slightly greater than those of naive mice. Plasma histamine levels were increased in sensitized C3H/HeJ mice, but not in BALB/c mice. Anaphylactic reactions were observed in 87% of C3H/HeJ mice.
Peanut-specific IgE levels were markedly increased at week 6 after peanut sensitization-boosting in C3H/HeJ mice. IgE levels were also increased at week 6 in BALB/c mice and further increased after this more rigorous sensitization-boosting protocol, but they were significantly lower than in C3H/HeJ mice at each time point. Histamine levels were markedly increased after the peanut challenge of peanut-sensitized C3H/HeJ mice. 100% of C3H/HeJ mice had anaphylactic symptoms after intragastric peanut challenge. Despite significant levels of peanut-specific IgE at the time of challenge at week 14, plasma histamine levels in BALB/c mice remained at baseline levels, and no symptoms were observed in BALB/c mice.
IL-4 levels were significantly increased in CM-sensitized C3H/HeJ splenocyte culture supernatants but only negligibly increased in supernatants of splenocyte cultures from BALB/c mice. IFN-γ levels were negligible or low in C3H/HeJ splenocyte cultures but markedly increased in BALB/c cultures in both allergen challenges. Splenocytes from CM- and peanut-sensitized C3H/HeJ mice released significantly more IL-10 than splenocytes from BALB/c mice.
T-cell clones generated from infants with CMA produced high levels of IL-4, IL-5, and IL-13 and low levels of IFN-γ, whereas infants without CMA produced high levels of IFN-γ and low levels of IL-4, IL-5, and IL-13. IL-10 is associated with induction of TH2-mediated food allergy rather than suppression of food allergy, perhaps by means of its known suppression of IFN-γ production. TLR4 is unlikely to play a significant role in susceptibility or tolerance to CMA or PNA in C3H/HeJ and BALB/c mice. Thus other mechanisms, such as differing properties of intestinal antigen-presenting cells in the processing food allergens, might determine predisposition to TH2 responses and food allergy of C3H/HeJ mice.