Staphylococcus aureus (S. aureus) is frequently detected in patients with atopic dermatitis (AD). Decreased diversity of bacterial flora on the skin surface (dysbiosis) has been considered as an important pathogenic factor of AD. We previously demonstrated that the skin immune responses induced by AD skin-derived strains of S. aureus (AD strain) was altered, compared to those by standard strains of S. aureus. However, detailed mechanisms have not been elucidated.
To investigate how the colonization of S. aureus is controlled by the skin barrier and cytokine milieu, we quantitated the number of AD strain internalized into keratinocyte (KC, HaCaT). Fluorescent labeled S. aureus was detected using a cell imaging system (Opera Phenix^TM), KC was stimulated by heat-inactivated AD strain or standard strain, with or without Th1 cytokine (IFN-γ, 100ng/ml) and Th2 cytokines (IL-4 and IL-13, 10ng/ml respectively) for 24hr.Time course study revealed that only AD strain could adhere to KC within 15 minutes, and was rapidly internalized into KC within 3 hr. The number of AD strain internalized to KC was significantly higher than that of standard strain. The treatment with Th1 cytokine significantly decreased the number of AD strain internalized into KC, while Th2 cytokines exerted no effect on the internalization. When filaggrin (FLG) in KC was knocked down by using specific siRNA, AD strain was significantly accumulated in KC. These characters of AD strain may promote the long-term retention of S. aureus in AD skin.