Background Keratinocytes form the first line of defence in the skin and alert the host to danger by the production of a number of cytokines and chemokines. However, the interaction of commensal microorganisms with keratinocytes has not been well studied.
Objectives To investigate the effect of viable and nonviable cells of Propionibacterium acnes in both exponential and stationary growth phases, and of P. acnes GroEL on cytokine production by human primary keratinocytes.
Methods Actively proliferating or contact-inhibited keratinocytes were cocultured with viable or formaldehyde-killed P. acnes cells in either the exponential or stationary phase of growth. Culture supernatants were assayed by enzyme-linked immunosorbent assay for the cytokines interleukin (IL)-1α, tumour necrosis factor (TNF)-α and granulocyte/macrophage colony-stimulating factor (GM-CSF). Keratinocytes were also stimulated with different concentrations of P. acnes GroEL and supernatants assayed for cytokines.
Results Viable P. acnes in the stationary phase of growth stimulated keratinocyte monolayers to produce significantly higher amounts of IL-1α, TNF-α and GM-CSF than unstimulated keratinocytes. Viable exponential-phase bacteria stimulated production of significantly higher amounts of TNF-α and GM-CSF but these levels were significantly lower than those for stimulation with stationary-phase bacteria. Nonviable P. acnes from either growth phase was not able to stimulate cytokine production. P. acnes GroEL at concentrations in the range 0·05–1·0 µg mL−1 was able to induce increased production of cytokines by keratinocytes in a dose-dependent manner. This was analogous to stimulation with Escherichia coli GroEL.
Conclusions Stimulation of cytokine production by P. acnes and P. acnes GroEL may be important in the pathogenesis of inflammatory acne vulgaris and may have wider implications for the immunomodulation of the human immune system by commensal skin microorganisms.