Demodex mites modulate sebocyte immune reaction: Possible role in the pathogenesis of rosacea

Abstract

Rosacea is a common facial skin disorder affecting middle-aged adults. Its aetiology is unknown and pathogenesis uncertain. Activation of the host innate immune response has been identified as important. The Demodex mite population in the skin of these patients is significantly higher than in subjects with normal skin suggesting they may be of etiological importance in this disorder. Little is known of the role of these mites in human skin and their potential to interact with the host immune system has not been elucidated.

Live Demodex mites were extracted from normal facial skin of control subjects and used in cell stimulation experiments with the immortalised SZ95 sebocyte line. Time and mite dose dependent experiments were performed. Direct Demodex effects and the effects of medium in which Demodex had been cultured were evaluated on the TLR-signalling pathway on both a gene and protein expression level.

Mites modulated TLR signalling events on both mRNA and protein levels in SZ95 sebocytes. An initial trend towards down modulation of genes in this pathway was observed. A subsequent switch to positive gene up-regulation was recorded after 48 hours of co-culture. Demodex secreted bioactive molecules that affected TLR2 receptor expression by sebocytes. High numbers of Demodex induced pro-inflammatory cytokine secretion whereas lower numbers did not.

Demodex mites have the capacity to modulate the TLR signalling pathway of an immortalised human sebocyte line. Mites have the capacity to secrete bioactive molecules that affect the immune reactivity of sebocytes. Increasing mite numbers influenced IL8 secretion by these cells.

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