The Effects of Heat-Killed Wild-Type Lactobacillus casei Shirota on Allergic Immune Responses in an Allergy Mouse Model

Abstract

Background: Probiotics are used as a management strategy for allergic diseases, but their effects on allergic responses in sensitized allergic individuals remain unclear. This study explored the immunomodulatory effects of probiotics on allergen-specific allergic reactions in an allergy mouse model. Methods: C57BL/6 mice were presensitized by epicutaneous patching with recombinant Der p 2, and were subsequently administered orally with either heat-killed wild-type Lactobacillus casei or NaHCO₃ buffer for 5 weeks (n = 6 per group). All mice then received 2 subcutaneous immunizations of Der p 2 to mimic allergen immunotherapy, followed by aerosol challenge with Der p 2 a week later. Results: The Der p 2-sensitized mice fed L. casei showed significantly lower Der p 2-specific IgE and IgG1 after subcutaneous immunizations and airway challenge with Der p 2 compared to the control, unfed group. Splenic T cells of mice fed L. casei showed suppression of Th-2 (IL-5, IL-13, IL-10 and IL-4) and proinflammatory (TNF-α, IFN-γ) cytokines. Following airway allergen challenge, the mice fed L. casei showed histological evidence of attenuation of lung inflammation, as well as reductions in the total cell count and Th2 and proinflammatory cytokines in bronchoalveolar lavage fluid, compared to controls. Taken together, these results suggest that the oral administration of heat-killed L. casei could effectively downregulate the pre-existing Th-2 allergic responses and pulmonary inflammatory responses upon subcutaneous and airway allergen challenge. Conclusions:L. casei has intrinsic adjuvant and immunomodulatory properties that could potentially be exploited for secondary prevention or treatment of allergic respiratory diseases.