Abstract
OBJECTIVES: This study aimed to compare systematically strain-specific immune differences between BALB/c and C57BL/6 mice in a local tolerance model and explore the underlying mechanisms. METHODS: BALB/c and C57BL/6 mice received daily intranasal ovalbumin (OVA; 25 mg/ml, 10μl/nostril) or PBS for 15 weeks. Systemic responses (serum OVA-specific IgE, IgG1, IgG2a; splenocyte cytokine secretion: IL-4, IL-10, IFN-γ) and local nasal responses (symptoms, histopathology: polymorphonuclear/goblet cell infiltration; immunohistochemistry: TGF-β, IL-10, eotaxin; RNA-seq transcriptomics of nasal mucosa) were assessed at the 8th and 15th weeks. RESULTS: BALB/c mice initially exhibited worsening nasal symptoms, which was followed by significant alleviation. In contrast, C57BL/6 mice showed a significant worsening of symptoms. Serum levels of IgE, IgG1, and IgG2a increased significantly over time in BALB/c mice. In C57BL/6 mice, serum IgE and IgG1 levels also increased significantly, while IgG2a levels showed no significant changes. In splenocyte supernatants, BALB/c mice showed IL-4 levels that initially increased significantly but later decreased significantly, whereas IL-10 levels were significantly elevated and sustained. Conversely, C57BL/6 mice exhibited no significant changes in these splenocyte cytokines. Within nasal mucosa, BALB/c mice displayed polymorphonuclear cell infiltration and significantly elevated eotaxin levels, which subsequently stabilized, alongside significant upregulation of TGF-β and IL-10 expression. At 15th week, C57BL/6 mice demonstrated significantly higher nasal PMN infiltration and eotaxin levels compared to BALB/c mice, but showed no significant increase in TGF-β or IL-10 compared to controls. RNA-seq analysis of nasal mucosa revealed that BALB/c mice at 15th week exhibited significant upregulation of genes involved in biological processes, tolerance-related signaling pathways, and negative regulatory pathways. Conversely, C57BL/6 mice showed significant upregulation of genes associated with cell synthesis- and secretion-related pathways. CONCLUSION: Based on the criteria defining "local tolerance" in this model-significant symptom attenuation despite allergen escalation coupled with downregulation of nasal inflammatory markers (eotaxin, polymorphonuclear cell infiltration)-local tolerance was successfully induced in BALB/c mice by long-term OVA stimulation, but not in C57BL/6 mice. The normal function of T regulatory cells is key to establishing local tolerance.