Prophylactic effects of oral administration of Lactobacillus casei on house dust mite-induced asthma in mice (1)
In the T-cells from patients with eosinophilic asthma, the adaptive T helper 2 (Th2) cells secrete interleukin (IL)-5, IL-4, IL-13, and IL-9. IL-5 promotes the survival and maturation of eosinophils. The chemokines of eosinophils promote the recruitment of eosinophils to the lung mucosa. These eosinophils secrete oxygen free radicals and toxic granules that lead to chronic airway inflammation. In the B-cells, IL-4 promotes the synthesis of immunoglobulin E (IgE), which binds to the IgE receptors located on the mast cells. The cross-linking of allergen and IgE promotes the secretion of biologically active mediators, such as histamine from the activated mast cells and promotes airway inflammation.
Probiotics (mainly Lactobacillus and Bifidobacterium) can colonize the intestine and stimulate host immunity and affect the gut microbiota composition. Probiotic stimulation has been shown to benefit intestinal diseases, such as inflammatory bowel disease, because probiotics could enhance the intestinal barrier, increase the host’s antioxidant status, modulate gut microbial composition, and enhance microbial metabolite levels (mainly short 61 chain fatty acids (SCFA))
In the HDM-induced asthma model, female Balb/c mice (5-6 weeks old) were exposed intranasally to purified 25 μg Dermatophagoides pteronyssinus extract dissolved in 10 μL sterile saline for 5 days/week from 0 to 5 consecutive weeks (model group); control groups received 10 μL sterile saline. Mice in each test group was administered 250 μL of L. casei strain, which were L. casei1 (M2-07-F01-L4-2-1), L. casei2 (M2-06-F01-L4-2-3), L. casei3 (CCFM1073), L. casei4 (RS8-5), or L. casei5 (FGDLZ41), every day, starting one week before the first sensitization and continuing over the whole process.
The levels of Th2 cytokines (IL-4, IL-5, IL-13, IL-9) and Th17 cytokine (IL-17A) were analyzed in the BALF. The mice in L.casei 2, L. casei 3, L. casei 4 and L. casei 5 groups significantly decreased the levels of IL-13 and IL-5. Mice in the L. casei5 group significantly decreased the levels of IL-4. L. casei1 and L. casei4 significantly decreased the levels of IL-9. L. casei3 significantly decreased the levels of both IL-4 and IL-9. All five L. casei strains significantly decreased the levels of IL-17A. The model group exhibited increased levels of Th2 and Th17 cytokines. L. casei1 and L. casei2 did not suppress the production of chemokines, which indicated that these L. casei strains inhibited eosinophilic and neutrophilic asthma through a mechanism that was not dependent on the suppression of chemokine production in mice.
L. casei strains differentially suppress asthma-related immunoglobulins (Igs) in the serum. The levels of total IgE and HDM-specific IgG1 in the L. casei-test groups were downregulated when compared with those in the model group. Supplementation with L. casei strains did not affect the levels of HDM specific IgG2a antibody levels. HDM-specific IgE was undetectable in any group. L. casei3 and L. casei5 significantly decreased the levels of both total IgE and HDM-specific IgG1. L. casei1 significantly decreased (p < 0.05) the levels of total IgE, while L. casei4 significantly decreased (p < 0.01) the levels of HDM-specific IgG1. L. casei2 did not affect the levels of these indicators. In addition, HDM-specific IgG1/HDM-specific IgG2a was often used to evaluate Th2/Th1 immune balance. This balance in L. casei1, L. casei3 and L. casei5 groups were partly restored when compared with those in the model group. These results indicate that the different strains of L. casei exert differential prophylactic effects on asthma through various immunoregulatory mechanisms.
Consistent with the results of alpha diversity analysis, L. casei increased the total number of gut microbiota. The most abundant phylum in the L. casei-supplemented groups was Firmicutes. L. casei2, L. casei3, L. casei4, and L. casei5 significantly increased the abundances of Proteobacteria, Actinobacteria, Bacteroidetes and Proteobacteria, and Deferribacteres respectively.
HDM-induced asthma is a well-established mixed chronic airway inflammatory model in female mice (the female is more sensitive than male in this model). Especially, L.casei3 (CCFM1073) strain-dependent improved the composition and metabolite production of gut microbiota, and regulated immune response related to infiltration of eosinophils and neutrophils, which might facilitate the highest prophylactic effect on asthma through the gut-lung axis. The supplementation of L. casei2, L.casei4, and L. casei5 increased the levels of sIgA in the BALF. To our knowledge, we firstly demonstrated the ability of probiotics to enhance sIgA levels under asthmatic conditions, which might be beneficial for asthma prophylaxis. L. casei2, L. casei3, and L. casei5 promoted the metabolism of carbohydrate and lipid and the growth of Firmicutes. SCFA, as an end-product of carbohydrate and lipid metabolisms, is a potential immunomodulator that decreases the susceptibility to asthma by modulating airway inflammation and regulating Treg cell expansion. The decreased levels of acetate and propionate in the model group were mitigated upon supplementation of L. casei3.