Golden Stap (Staphylococcus aureus) secretes a factor that causes mast cell (the so-called allergy cell) degranulation and activation of (Th2-type) allergic inflammation in the skin of atopic dermatitis.
Atopic dermatitis is caused by abnormal immunoglobulin-E–mediated Th2 immune responses (a type of immune reaction) in settings of barrier dysfunction. Defective barrier function is the reason why application of moisturiser is an important part of eczema management. Colonization of lesional skin by Staphylococcus aureus is a hallmark of active disease. S. aureus species produce exotoxins that can act as super antigens in disease models, but the precise mechanism by which S. aureus aggravates atopic dermatitis has been unclear.
Nakamura et al. have now identified the major mechanism by which S. aureus engages allergic-type Th2 T-cell responses in skin. Given the established role of IgE-mediated mast cell activation in atopic dermatitis, the researchers hypothesized that S. aureus secretes a factor that causes mast cell degranulation. Painstakingly, they identified δ-toxin as the mast cell degranulation–inducing factor produced by S. aureus in culture and in mouse skin. Using an antigen-driven mouse model of atopic dermatitis, they showed that colonization by normal S. aureus caused erythema and crusting, with interleukin 4 and IgE production, whereas a mutant S. aureus lacking δ toxin did not. Conversely, mice lacking mast cells were resistant to δ toxin–mediated inflammation and IgE production. Finally, they showed that S. aureus strains cultured from lesional skin of 26 patients with atopic dermatitis all expressed δ toxin.
COMMENT
These findings identify δ toxin as the critical factor elaborated by S. aureus that causes mast cell degranulation and activation of Th2-type allergic inflammation in the lesional skin of atopic dermatitis. The normal function of δ toxin is unknown, but it may contribute to the ability of S. aureus to kill competing bacteria. These results identify an important mechanism of pathogenesis in atopic dermatitis and perhaps identify another target for treating this common disease.
In other words, golden Stap makes eczema worse and eczema allows more golden Stap to colonise the skin. So treating golden Stap is another essential component of eczema management.
modified from NEJM Journal Watch