Comparative Effects of Live and Heat-Killed Lactobacillus Formulations on DNCB-Induced Dermatitis-like Skin Inflammation in Mice

Background/Objectives: Atopic dermatitis (AD) is a chronic inflammatory skin disease involving barrier dysfunction, pruritus, and immune dysregulation, and microbial-based interventions are being explored as supportive approaches. This study first conducted an exploratory pilot model-development experiment to characterize DNCB-induced dermatitis-like inflammation and subsequently compared oral live Lactobacillus, heat-killed Lactobacillus (paraprobiotics), and a combined live/heat-killed formulation after disease induction. Methods: Male BALB/c mice received repeated topical DNCB exposure followed by 21 days of oral intervention. Outcomes included gross lesion scores, cumulative scratching time, ear and spleen indices, histopathology, qualitative mast-cell staining in the therapeutic experiment, and serum IgE, IL-4, and IFN-γ. Longitudinal gross scores were reanalyzed using generalized estimating equations with group, time, and group-by-time interaction. Results: After Holm correction, the mixed formulation showed a lower left-ear erythema score than placebo at Week 2, whereas no other intervention-versus-placebo gross-score comparison remained significant. Paraprobiotic and mixed formulations reduced spleen weight, but histopathological and serum biomarker responses were variable. Conclusions: These findings indicate partial, endpoint-dependent effects of live and heat-killed Lactobacillus formulations in DNCB-induced dermatitis-like inflammation.