Supplementary Material for: Susceptibility to Vaccinia Virus Infection and Spread in Mice Is Determined by Age at Infection, Allergen Sensitization and Mast Cell Status

Background: Patients, especially young children, with atopic dermatitis are at an increased risk of developing eczema vaccinatum, a severe reaction to the smallpox vaccine, either through direct vaccination or indirect contact with a person recently vaccinated. Methods: Using a mouse model of infection, the severity of vaccinia-induced lesions was assessed from their appearance and viral DNA content. The response to vaccinia inoculation was assessed in young and adult mice, allergen-sensitized mice, and in mast cell-deficient mice. Results: Young age, sensitization to an allergen prior to infection, and a mast cell deficit, accomplished by using mast cell-deficient mice, resulted in more severe viral lesions at the site of inoculation, according to lesion appearance and viral DNA content. All three factors combined demonstrated maximal susceptibility, characterized by the severity of primary lesions and the development of secondary (satellite) lesions, as occurs in eczema vaccinatum in humans. Resistance to the appearance of satellite lesions could be restored by adoptive transfer of bone marrow-derived mast cells from either wild-type or cathelicidin-related antimicrobial peptide-deficient mice. Primary lesions were more severe following the latter transfer, indicating that cathelicidin-related antimicrobial peptide does contribute to the protective activity of mast cells against infection. Conclusions: The combination of young age, allergen sensitization and a mast cell deficit resulted in the most severe lesions, including satellite lesions. Understanding the factors determining the relative resistance/sensitivity to vaccinia virus will aid in the development of strategies for preventing and treating adverse reactions which can occur after smallpox vaccination.

背景：特应性皮炎（atopic dermatitis）患者，尤其是幼儿，无论通过直接接种天花疫苗（smallpox vaccine）还是间接接触近期接种过天花疫苗的人群，均面临更高的牛痘湿疹（eczema vaccinatum）发病风险——牛痘湿疹是一种对天花疫苗的严重不良反应。
方法：本研究采用感染小鼠模型，通过皮损外观及病毒DNA载量评估牛痘病毒诱导皮损的严重程度。分别对幼鼠、成年小鼠、过敏原致敏小鼠以及肥大细胞缺陷（mast cell-deficient）小鼠的牛痘病毒接种应答情况进行检测。
结果：从皮损外观及病毒DNA载量来看，幼龄状态、感染前过敏原致敏以及通过肥大细胞缺陷小鼠模型实现的肥大细胞缺失，均可导致接种部位的病毒皮损更为严重。当上述三种因素联合存在时，小鼠会表现出最高的易感性，其特征为原发皮损严重程度升高以及继发（卫星病灶，satellite lesions）的形成，这与人类牛痘湿疹的发病表现一致。通过过继转移（adoptive transfer）野生型（wild-type）或cathelicidin相关抗菌肽（cathelicidin-related antimicrobial peptide）缺陷小鼠的骨髓来源肥大细胞（bone marrow-derived mast cells），可恢复其对卫星病灶形成的抵抗能力。而采用后者进行转移后，原发皮损更为严重，这表明cathelicidin相关抗菌肽确实参与了肥大细胞对抗感染的保护活性。
结论：幼龄状态、过敏原致敏与肥大细胞缺失三者联合，可引发最为严重的皮损，包括卫星病灶。明确影响牛痘病毒感染相对抵抗性/易感性的相关因素，将有助于开发预防和治疗天花疫苗接种后可能出现的不良反应的策略。