1. Introduction
Propionibacterium acnes has been recognized as an obligate anaerobic organism which is usually found as a
normal skin commensal. This organism has been implicated over other cutaneous microflora in contributing to the
inflammatory response of acne. It acts as an immunostimulator which can produce a variety of enzymes and
biologically active molecules, which are involved in the development of inflammatory acnes. These products include
lipases, proteases, hyaluronidases, and chemotactic factors [1]. The main components of pilosebaceous unit on the skin,
such as keratinocytes and sebocytes can be activated by P. acnes leading to the production of pro-inflammatory
cytokines [2]. It has been reported that a secreted peptidoglycan of P. acnes can stimulate the production of the
proinflammatory cytokines such as IL-1, IL-8, and tumor necrosis factor-alpha (TNF-α) by human monocytic cell lines
and freshly isolated peripheral blood mononuclear cells from acne patients [3].
Moreover, P. acnes significantly induces the interleukin-8 (IL-8) mRNA expression and selectively stimulates the
expression of human beta-defensin-2 mRNA in keratinocytes [4]. Previous findings suggest that P. acnes has a major