Role of mast cells in Staphylococcus aureus enterotoxin Binduced atopic dermatitis-like skin inflammation in mice

Objective To investigate the role of mast cells in Staphylococcus aureus enterotoxin B (SEB) -induced atopic dermatitis (AD) -like skin inflammation in BALB/c mice. Methods A total of 24 BALB/c mice were randomly and equally divided into 4 groups to be topically treated with ovalbumin (OVA group) , SEB (SEB group) , OVA+ SEB (OVA+ SEB group) and sodium chloride physiological solution (control group) respectively, so as to establish mouse models of epicutaneously induced AD-like skin inflammation. The AD-like skin lesions were evaluated by clinical observation and eczema area and severity index (EASI) . Biopsy specimens were obtained from lesional skin of mice and then subjected to toluidine blue staining and immunohistochemical staining to count the mast cells, observe the morphology and distribution of mast cells, and calculate the percentage of degranulated mast cells. Results After 7-week treatment, the OVA group, SEB group and OVA+ SEB group all showed severer local skin inflammation, higher EASI scores and denser infiltration of inflammatory cells compared with the control group. Moreover, the OVA+ SEB group showed significantly severer local skin inflammation, skin lesions and degree of infiltration of inflammatory cells compared with the OVA group and SEB group (all P < 0.05) . The number of mast cells in the dermis of AD-like skin lesions per high-power field (× 400) was significantly higher in the OVA group (median[quartile range]: 10.625[3.675]) , SEB group (11.000[4.163]) and OVA+ SEB group (13.875[8.813]) than that in the control group (5.925[2.088], all P < 0.05) . The SEB group (71.083% ± 14.519%) and OVA+ SEB group (58.767% ± 16.978%) both showed significantly higher percentage of degranulated mast cells compared with the OVA group (24.050% ± 11.161%, both P < 0.05) and control group (23.617% ± 8.132%, both P < 0.05) . Bivariate correlation analysis showed that the number of mast cells in the skin lesions was positively linearly correlated with the EASI scores (P < 0.05) . Conclusions Epicutaneous application of SEB can induce AD-like skin lesions in mice, and can exacerbate the severity of OVA-induced AD-like skin lesions. Mast cell proliferation, activation/degranulation and tryptase release may participate in the inflammation. Key words: Dermatitis, atopic; Mast cells; Staphylococcus aureus; Enterotoxins; Tryptases; Ovalbumin