Specific substance of Maruyama (SSM) suppresses immune responses in atopic dermatitis-like skin lesions in DS-Nh mice by modulating dendritic cell functions.

Background: Specific substance of Maruyama (SSM) is a carcinostatic immunotherapeutic agent extracted from Mycobacterium tuberculosis. The efficacy of SSM induced interleukin(IL)-12 and IFN-γ production, and inhibition of IL-4, resulting in a shift from Th2 to Th1 in vivo.

Objective: The DS-Nh mice are a model of human atopic dermatitis (AD), which spontaneously develop dermatitis under conventional conditions. In this study, to determine whether SSM can prevent the development of skin lesions in a murine model of AD.

Methods: DS-Nh mice were injected with SSM 5 days per week for 11 weeks. Pharmacological, histological and serological studies were performed to investigate the therapeutic effect of SSM for DS-Nh mice. Analysis of cytokines responses to SSM using quantitative RT-PCR and flow cytometry were also performed to evaluate their therapeutic mechanisms in these AD model mice.

Results: Clinically, erythema, erosions, excoriation, and edema were observed in DS-Nh mice at 16 weeks of age, which advanced with age. Histologically, the relative number of mast cells increased in DS-Nh mice. SSM treatment alleviated the clinical and histological findings in accord with reduced serum IgE level, and increased IgG2a level. TSLP expression was not induced, but IL-1β, IL-12, IL-17A, and IFN-γ were induced in SSM-treated DS-Nh mice. Overall, SSM treatments increased the number of activated DCs in lesions. SSM induced CD80, CD86, and MHC class II expression on bone marrow-derived DCs.

Conclusions: SSM enhanced IL-12 production, but suppressed TSLP expression, resulting in a shift from Th2 to Th1 responses. This shift suppressed AD-like skin lesions in a similar fashion as the BCG vaccine. Therefore, SSM may be a useful adjuvant for suppressing skin lesions in AD models.