Distinct strains of Propionibacterium acnes induce selective human beta-defensin-2 and interleukin-8 expression in human keratinocytes through toll-like receptors

Acne is a chronic inflammatory disease of the pilosebaceous follicle. One of the main pathogenetic factors in acne is the increased proliferation of Propionibacterium acnes (P. acnes) in the pilosebaceous unit. We investigated whether direct interaction of P. acnes with keratinocytes might be involved in the inflammation and ductal hypercornification in acne. The capacities of different P. acnes strains to activate the innate immune response and the growth of cultured keratinocytes were investigated. We have found that two clinical isolates of P. acnes significantly induced human beta-defensin-2 (hBD2) messenger RNA (mRNA) expression; in contrast a third clinical isolate and the reference strain (ATCC11828) had no effect on hBD2 mRNA expression. In contrast, all four strains significantly induced the interleukin-8 (IL-8) mRNA expression. The P. acnes-induced increase in hBD2 and IL-8 gene expression could be inhibited by anti-Toll-like receptor 2 (TLR2) and anti-TLR4 neutralizing antibodies, suggesting that P. acnes-induced secretion of soluble factors in keratinocytes are both TLR2 and TLR4 dependent. In addition, the clinical isolate P. acnes (889) was capable of inducing keratinocyte cell growth in vitro. Our findings suggest that P. acnes modulates the antimicrobial peptide and chemokine expression of keratinocytes and thereby contributes to the recruitment of inflammatory cells to the sites of infections.     

Induction of toll-like receptors by Propionibacterium acnes

BACKGROUND: The bacterium Propionibacterium acnes is involved in the induction and maintenance of the inflammatory phase of acne. Recent studies have found that keratinocytes express toll-like receptors (TLRs) implicated in immediate immunity. No studies have, to date, been carried out on the action of P. acnes upon TLR activation in keratinocytes. OBJECTIVES: Focusing on the inflammatory phase of acne, to clarify the role of P. acnes in immediate immunity by inducing expression of TLR-2 and TLR-4 by keratinocytes. We also studied how the secretion and expression of matrix metalloproteinase (MMP)-9 is induced by P. acnes. METHODS: The work was carried out on two levels: in vivo with the study of the expression of TLR-2 and TLR-4 proteins in biopsies of acne lesions and in vitro on cultured keratinocyte monolayers to study the modulating effects of P. acnes on the expression of TLR-2 and TLR-4 and also on the expression and secretion of MMP-9. RESULTS: Our findings reveal that in vivo TLR-2 and TLR-4 expression is increased in the epidermis of acne lesions. In vitro, an increase in TLR-2 and TLR-4 expression by human keratinocytes occurred in the first hours of incubation with bacterial fractions as well as an increase of the expression and secretion by the keratinocytes of MMP-9, which plays a role in inflammation. CONCLUSIONS: This work demonstrates that P. acnes induces TLR expression and that this mechanism could play an essential role in acne-linked inflammation. These receptors could be involved notably in acute acne.     

Glucocorticoids enhance Toll-like receptor 2 expression in human keratinocytes stimulated with Propionibacterium acnes or proinflammatory cytokines

Toll-like receptors (TLRs) on keratinocytes are important cell surface receptors involved in the innate and acquired immune response to invading microorganisms. In acne vulgaris, TLR2 activation by Propionibacterium acnes (P. acnes) may induce skin inflammation via induction of various proinflammatory molecules that stimulate the invasion of inflammatory cells. Although corticosteroids themselves exert immunosuppressive or anti-inflammatory effects, it is well known clinically that systemic or topical glucocorticoid treatment provokes an acneiform reaction. Nevertheless, the effect of steroids on TLR2 expression in human keratinocytes remains unknown. Here, we found that the addition of glucocorticoids, such as dexamethasone and cortisol, to cultured human keratinocytes increased their TLR2 gene expression. Moreover, these glucocorticoids markedly enhanced TLR2 gene expression, which was further stimulated by P. acnes, tumor necrosis factor-alpha, and IL-1alpha. Gene expression of mitogen-activated protein kinase (MAPK) phosphatase-1 was also increased by the addition of dexamethasone. By using several inhibitors and activators, we found that TLR2 gene induction by glucocorticoids was mediated by the suppression of p38 MAPK activity following induction of MAPK phosphatase-1. These findings strongly suggest that steroid-induced TLR2 together with P. acnes existing as normal resident flora plays an important role in the exacerbation of acne vulgaris as well as in possible induction of corticosteroid-induced acne or in that of rosacea-like dermatitis.     

Polyphenon-60 displays a therapeutic effect on acne by suppression of TLR2 and IL-8 expression via down-regulating the ERK1/2 pathway

Propionibacterium acnes (P. acnes) is a well-known acne-inducing factor which causes inflammatory skin lesions by enhancing cytokine production through toll-like receptor 2 (TLR2). Green tea extract catechin has been documented to possess anti-inflammatory effects. However, little is known about the mechanisms involved or any direct effect of green tea catechin on acne. The present study investigated the therapeutic effects and mechanism of polyphenon-60, also known as green tea catechin compound, on acne in vitro and in vivo. In a clinical study using topical polyphenon-60 treatment, acne patients showed symptomatic improvement with decrease in the number of comedos and pustules. To investigate the mechanism underlying the activity of polyphenon-60 in acne therapy, an in vitro study was performed. We found that polyphenon-60 reduced the levels of P. acnes-enhanced TLR2 and interleukin-8 (IL-8) in THP-1 cells, human monocyte cell line and human primary monocytes. Taken together, these data demonstrate that polyphenon-60 has a therapeutic effect on acne by suppressing inflammation, specifically by inhibiting TLR2 expression and IL-8 secretion via down-regulation of extracellular signal-regulated kinases 1/2 (ERK1/2) pathway and activator protein-1 (AP-1) pathway.     

In vitro modulation of TLR-2, CD1d and IL-10 by adapalene on normal human skin and acne inflammatory lesions

The anti-inflammatory mechanisms of adapalene, a synthetic retinoid used for the treatment of acne patients, are partially understood. They seem particularly related to the modulation of the non-specific immunity. Recent studies have shown that Toll-like receptor (TLR)-2 expression, a receptor of the innate immune system, was increased in acne lesions and could play an essential role in acne-linked inflammation. The aim of our study was to investigate the new mechanisms of the anti-inflammatory activity of adapalene in vitro, and more specifically the modulatory effect of adapalene on the expression of TLR-2, CD1d, a cell surface glycoprotein that plays a role as antigen-presenting molecules and is responsible for the development of cutaneous inflammation, and also on the expression and the secretion of the anti-inflammatory interleukin (IL)-10 cytokine. Both explants of normal human skin and explants of acne patients were incubated with adapalene (10(-7) or 10(-6) M) or the control medium for 24 h. Evaluation of epidermal expression by immunohistochemistry showed a decreased expression of TLR-2 and IL-10 in explants of normal skin and explants of acne with adapalene. On the contrary, adapalene increased CD1d expression in explants of acne patients. Thus, adapalene can modulate the epidermal immune system by increasing the CD1d expression and by decreasing the IL-10 expression by keratinocytes. Moreover, these modulations could increase the interactions between dendritic cells and T lymphocytes and could strengthen the antimicrobial activity against Propionibacterium acnes. The decreased expression of TLR-2 by the keratinocytes can contribute to explain the anti-inflammatory activity of adapalene observed in clinical practice.     

Review of the innate immune response in acne vulgaris: activation of Toll-like receptor 2 in acne triggers inflammatory cytokine responses

Acne vulgaris is a common disorder that affects 40-50 million people in the USA alone. The pathogenesis of acne is multifactorial, including hormonal, microbiological and immunological mechanisms. One of the factors that contributes to the pathogenesis of acne is Propionibacterium acnes; yet, the molecular mechanism by which P. acnes induces inflammation is not known. Recent studies have demonstrated that microbial agents trigger cytokine responses via Toll-like receptors (TLRs). TLRs are pattern recognition receptors that recognize pathogen-associated molecular patterns conserved among microorganisms and elicit immune responses. We investigated whether TLR2 mediates P. acnes-induced cytokine production in acne. Using transfectant cells we found that TLR2 was sufficient for NF-kappaB activation in response to P. acnes. In addition, peritoneal macrophages from wild-type, TLR6 knockout and TLR1 knockout mice, but not TLR2 knockout mice, produced IL-6 in response to P. acnes.P. acnes induced activation of IL-12 and IL-8 production by primary human monocytes, and this cytokine production was inhibited by anti-TLR2-blocking antibody. Finally, in acne lesions, TLR2 was expressed on the cell surface of macrophages surrounding pilosebaceous follicles. These data suggest that P. acnes triggers inflammatory cytokine responses in acne by activation of TLR2. As such, TLR2 may provide a novel target for the treatment of this common skin disease.     

Nadifloxacin, an antiacne quinolone antimicrobial, inhibits the production of proinflammatory cytokines by human peripheral blood mononuclear cells and normal human keratinocytes

BACKGROUND: Acne vulgaris is a chronic inflammatory disease involving colonization of Propionibacterium acnes (P. acnes), activation of neutrophils and lymphocytes. Circumstantial evidence suggests that antigen-independent and -dependent immune responses against P. acnes are involved in the pathogenesis of inflammatory acne. Epidermal keratinocytes are also suggested to be involved in initiation and progression of cutaneous inflammation. Nadifloxacin, a fluorinated quinolone, has potent antimicrobial activities against Gram-negative and -positive microbes and is used to treat multiple inflamed acne lesions. However, its effect on immune conferring cells such as mononuclear cells and keratinocytes has not been examined. OBJECTIVE: To evaluate the possible involvement of potential anti-inflammatory activity of nadifloxacin in its therapeutic effect on inflammatory acne, we examined the effects of nadifloxacin, in comparison with other antibiotics used to treat acne vulgaris, on cytokine production by human peripheral blood mononuclear cells (PBMC) and keratinocytes. METHODS: Cytokine production by PBMC was determined after treatment with heat-killed P. acnes in the presence or absence of antimicrobials using a real-time PCR and ELISA. Cultured human epidermal keratinocytes were stimulated by IFN-gamma plus IL-1beta and the effects of antimicrobials were examined by using ELISA. RESULTS: Nadifloxacin as well as macrolide antibiotics and clindamycin inhibited IL-12 and IFN-gamma production by PBMC stimulated by heat-killed P. acnes. The drug also inhibited the IL-1alpha, Il-6, IL-8 and GM-CMS production by keratinocytes treated with IFN-gamma plus IL-1beta. CONCLUSIONS: Inhibitory effects of nadifloxacin to activate T cells and keratinocytes may be involved at least in part in the mechanism of its therapeutic effect against inflammatory acne.     

Propionibacterium acnes activates the IGF-1/IGF-1R system in the epidermis and induces keratinocyte proliferation

Propionibacterium acnes has a major role in the development of acne lesions. IGF-1 stimulates the proliferation of keratinocytes via an activation of the IGF-1 receptor (IGF-1R). Zinc has been proven to work efficiently against inflammatory acne and to modulate the IGF-1 system. Our objectives were to study the modulation of IGF-1 and IGF-1R expression by P. acnes extracts and to determine their modulation by zinc gluconate. In vivo, we analyzed biopsies of acne lesions and healthy skin, and in vitro we used skin explants incubated with two P. acnes extracts--membrane fraction (MF) and cytosolic proteins--with or without zinc. IGF-1 and IGF-1R expression was evaluated using immunohistochemistry, and the IGF-1 production in supernatants was measured by ELISA. Then, IGF-1 and IGF-1R mRNA levels were analyzed using quantitative PCR on normal human epidermal keratinocytes (NHEKs). IGF-1 and IGF-1R were overexpressed in acne lesions. MF increased IGF-1 and IGF-1R expression in the epidermis of explants and was associated with an overexpression of both Ki-67 and filaggrin. Zinc had the effect of downregulating IGF-1 and IGF-1R levels. These observations were confirmed at the mRNA level for IGF-1R in NHEKs. These results demonstrate that P. acnes can induce the formation of comedones by stimulating the IGF/IGF-1R system. Moreover, zinc downregulates this pathway.     

Toll样受体2与痤疮相关性研究进展

痤疮是一种累及毛囊皮脂腺的慢性炎症性皮肤疾病。尽管痤疮的确切病因及发病机制尚不明确,但炎症反应是其发病的重要因素之一,其中痤疮丙酸杆菌是主要致病菌。痤疮丙酸杆菌可通过激活Toll样受体2(Toll-like receptors 2,TLR2)介导的信号传导通路诱导炎症级联反应,从而形成炎症性痤疮。一些药物可以通过调节TLR2受体的功能与表达,发挥抗炎及治疗痤疮的作用。该文就TLR2在痤疮发病中的作用及与之相关的治疗方法做一综述。     

New developments in our understanding of acne pathogenesis and treatment

Abstract:  Interest in sebaceous gland physiology and its diseases is rapidly increasing. We provide a summarized update of the current knowledge of the pathobiology of acne vulgaris and new treatment concepts that have emerged in the last 3 years (2005–2008). We have tried to answer questions arising from the exploration of sebaceous gland biology, hormonal factors, hyperkeratinization, role of bacteria, sebum, nutrition, cytokines and toll-like receptors (TLRs). Sebaceous glands play an important role as active participants in the innate immunity of the skin. They produce neuropeptides, excrete antimicrobial peptides and exhibit characteristics of stem cells. Androgens affect sebocytes and infundibular keratinocytes in a complex manner influencing cellular differentiation, proliferation, lipogenesis and comedogenesis. Retention hyperkeratosis in closed comedones and inflammatory papules is attributable to a disorder of terminal keratinocyte differentiation. Propionibacterium acnes, by acting on TLR-2, may stimulate the secretion of cytokines, such as interleukin (IL)-6 and IL-8 by follicular keratinocytes and IL-8 and -12 in macrophages, giving rise to inflammation. Certain P. acnes species may induce an immunological reaction by stimulating the production of sebocyte and keratinocyte antimicrobial peptides, which play an important role in the innate immunity of the follicle. Qualitative changes of sebum lipids induce alteration of keratinocyte differentiation and induce IL-1 secretion, contributing to the development of follicular hyperkeratosis. High glycemic load food and milk may induce increased tissue levels of 5α-dihydrotestosterone. These new aspects of acne pathogenesis lead to the considerations of possible customized therapeutic regimens. Current research is expected to lead to innovative treatments in the near future.     

Involvement of adenosine triphosphate‐binding cassette subfamily B member 1 in the augmentation of triacylglycerol excretion by Propionibacterium acnes in differentiated hamster sebocytes

An onset of acne, a common inflammatory skin disease, is associated with excess sebum production and secretion in sebaceous glands. Because Propionibacterium acnes has been reported to augment intracellular sebum accumulation in sebaceous glands in hamsters, it remains unclear whether P. acnes influences sebum secretion from differentiated sebocytes. Both P. acnes culture media (Acnes73‐CM ) and formalin‐killed P. acnes (F‐Acnes73) dose‐dependently increased the extracellular levels of triacylglycerol (TG ), a major sebum component, and Rhodamine 123, a substrate of adenosine triphosphate‐binding cassette (ABC ) transporter, from differentiated hamster sebocytes (DHS ). In addition, the gene expression of the ABC subfamily B member 1 (ABCB 1) was dose‐dependently augmented by adding Acnes73‐CM and F‐Acnes73 into DHS . Furthermore, the F‐Acnes73‐induced increase of TG excretion was suppressed by PSC 833, a selective ABCB 1 inhibitor. On the other hand, peptidoglycan (PGN ), which is a Toll‐like receptor 2 (TLR 2) ligand in P. acnes , increased extracellular TG levels, transporter activity and ABCB 1 mRNA expression in DHS . The PGN ‐augmented TG excretion was suppressed by PSC 833. Thus, these results provide novel evidence that P. acnes facilitates sebum secretion due to the activation of ABCB 1 concomitantly with the increased ABCB 1 expression, which may result from the activation of the TLR 2 pathway in DHS . Therefore, the ABCB 1 inhibitor is likely to become a candidate as a possible therapeutic for the treatment of acne.     

Effect of zinc gluconate on propionibacterium acnes resistance to erythromycin in patients with inflammatory acne: in vitro and in vivo study

Tetracyclines and macrolide antibiotics have been in use for acne treatment for more than 20 years. Since 1992 increasing resistance to these antibiotics, and especially to erythromycin, is reported with Propionibacterium acnes. Zinc salts have demonstrated their efficacy in inflammatory acne treatment as well as their bacteriostatic activity against Propionibacterium acnes. The objective of our work was firstly to determine whether the clinical anti-inflammatory efficacy of zinc salts was altered in the presence of erythromycin resistant strains in vivo, and secondly to study the in vitro and in vivo effect of zinc on the sensitivity of Propionibacterium acnes strains to erythromycin. Thirty patients with inflammatory acne were treated by zinc gluconate with a daily dose of 30 mg for two months and bacteriologic samples were taken at D0, D30 and D60. In vivo, this study displayed a reduction in the number of inflammatory lesions after a 2-month treatment whether or not Propionibacterium acnes carriage was present. Concurrently, in vitro addition of zinc salts in the culture media of Propionibacterium acnes reduced resistance of Propionibacterium acnes strains to erythromycin. Thus, association of zinc salts via a systemic route and topical erythromycin treatment seems an interesting option in the light of an increasing number of patients carrying erythromycin resistant Propionibacterium acnes strains.     

Proinflammatory cytokine production by human keratinocytes stimulated with Propionibacterium acnes and P. acnes GroEL

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)-1alpha, tumour necrosis factor (TNF)-alpha 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-1alpha, TNF-alpha and GM-CSF than unstimulated keratinocytes. Viable exponential-phase bacteria stimulated production of significantly higher amounts of TNF-alpha 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 micro g 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.     

Single nucleotide polymorphisms of toll‐like receptor‐4 protect against acne conglobata

Background Former studies have shown that Propionibacterium acnes may stimulate expression of toll‐like receptor 4 (TLR4) in keratinocytes of patients with acne vulgaris. Objective To investigate the impact of single nucleotide polumorphisms (SNPs) of the TLR4 gene in acne vulgaris. Methods Genomic DNA was isolated from 191 patients with acne vulgaris and 75 healthy controls. Asp299Gly and Thr399Ile SNPs were defined after cutting of the PCR products by restriction enzymes. Sebum of lesions was cultured for P. acnes. Results No differences in SNP allele frequencies were found between patients and healthy controls. 46.5% of carriers of wild‐type alleles were suffering from acne conglobata compared with 28.6% of carriers of SNP alleles (P = 0.040). After adjusting for gender, family history of acnes, intake of any therapy and skin isolation of P. acnes, carriage of TLR4 gene SNPs was the only independent variable linked with a protective role against acne conglobata (OR = 0.269, P = 0.014). No differences were found in the amount of pro‐inflammatory cytokines released by peripheral blood mononuclear cells isolated from patients with acne conglobata carrying only wild‐type alleles and SNP alleles. Conclusions Carriage of gene SNPs is protective against the development of acne conglobata even in the presence of P. acnes.     

Propionibacterium acnes stimulates pro-matrix metalloproteinase-2 expression through tumor necrosis factor-alpha in human dermal fibroblasts

Propionibacterium acnes (P. acnes) is a commensal microorganism found in sebum-rich skin and plays a role in acne inflammation by stimulating keratinocyte to produce a number of proinflammatory cytokines. However, the role of P. acnes in the dermis of acne lesions, where tissue remodeling after inflammation eventually takes place, is not known. In this study, we investigated whether P. acnes induces matrix metalloproteinase (MMP), a key enzyme involved in matrix remodeling in human dermal fibroblasts (hDF). We found that P. acnes increased expression of pro-matrix metalloproteinase (proMMP)-2 mRNA/protein in hDF, but not that of proMMP-9. Concomitantly, P. acnes induced tumor necrosis factor-alpha (TNF-alpha) mRNA/protein expression in hDF, which in turn increases both proMMP-2 mRNA and protein expression. P. acnes induced such changes through the activated NF-kappaB pathway. Doxycycline was found to inhibit the expression of proMMP-2 induced either by P. acnes or TNF-alpha. These results suggest that P. acnes stimulates hDF to produce TNF-alpha, which mediates the expression of proMMP-2 through the NF-kappaB pathway. The secretion of proMMP-2 from hDF upon P. acnes stimulation may contribute to the pathogenesis of tissue remodeling in acne skin.     

Candida albicans phospholipomannan triggers inflammatory responses of human keratinocytes through Toll-like receptor 2

Abstract:  The Toll-like receptors (TLRs) play an important role in the recognition of Candida albicans components and activation of innate immunity. Phospholipomannan (PLM), a glycolipid, is expressed at the surface of C. albicans cell wall, which acts as a member of the pathogen-associated molecular patterns family. In this study, we sought to clarify whether C. albicans -native PLM could induce an inflammation response in human keratinocytes and to determine the underlying mechanisms. Exposure of cultured human primary keratinocytes to PLM led to the increased gene expression and secretion of proinflammatory cytokines (IL-6) and chemokines (IL-8). PLM hydrolysed with β- d -mannoside mannohydrolase failed to induce gene expression and secretion of IL-6 and IL-8. PLM up-regulated the mRNA and protein levels of TLR2, whereas the mRNA level of TLR4 was not altered. Keratinocytes challenged with PLM resulted in the activation of NF-κB and mitogen-activated protein kinase (MAPKs) including p38. Anti-TLR2 neutralizing antibody, NFκB and p38MAPK inhibitors blocked the PLM-induced secretion of IL-6, IL-8 in keratinocytes, but no such effect was observed in pretreatment with anti-TLR4-neutralizing antibody and lipopolysaccharide inhibitor (polymyxin B). These data suggest C. albicans -native PLM may contribute to the inflammatory responses of cutaneous candidiasis in the TLR2-NF-κB and p38MAPK signalling pathway dependent manner.     

Effects of Propionibacterium acnes on various mRNA expression levels in normal human epidermal keratinocytes in vitro

Propionibacterium acnes is one of the most significant pathogenic factors of acne vulgaris. This bacteria relates to acne by various pathways. It has also been reported that P. acnes influences pro-inflammatory cytokine production in keratinocytes in vitro . However, the influence on the differentiation of keratinocytes by P. acnes has not been studied extensively. We analyzed the expression of keratinocyte differentiation-specific markers, keratins, and pro-inflammatory cytokines in normal human epidermal keratinocytes (NHEK) exposed to P. acnes in vitro . All P. acnes strains used in this study increased transglutaminase (TGase), keratin 17 (K17) and interleukin (IL) mRNA expression levels in NHEK, and decreased K1 and K10 expression levels. Some P. acnes strains increased involucrin and K6 mRNA expression levels in NHEK and decreased filaggrin, K6 and K16 expression levels in vitro . This experiment clarified that P. acnes influences the differentiation of NHEK in vitro . As a result, P. acnes influenced the expression of not only pro-inflammatory cytokines but also some keratinocyte differentiation-specific markers and keratins in NHEK. Our results suggest that P. acnes relates to acne pathogenesis by not only the induction of inflammation but also in the differentiation of keratinocytes. Moreover, it was considered that the reaction of NHEK to P. acnes may be different depending on the type of bacteria.     

Ex vivo demonstration of a synergistic effect of Adapalene and benzoyl peroxide on inflammatory acne lesions

Acne is a chronic inflammatory disease of the pilosebaceous follicle. Thanks to its ability to reduce both comedones and inflammatory lesions, the association of a retinoid and benzoyl peroxide (BPO) is now recommended for the treatment of acne. However, the mechanisms of action of this combined therapy on inflammatory acne lesions are not well understood. In an ex vivo immunohistochemistry study, we investigated the potential synergistic modulator effect of Adapalene associated with BPO on keratinocytes proliferation/differentiation and innate immunity in inflammatory acne lesions. We demonstrated that proliferation (Ki-67), adhesion/differentiation (integrin α(2), α(3) and α(6)) and innate immunity (TLR-2, β-defensin 4, IL-8) markers are overexpressed in inflammatory acne skin compared with uninvolved acne skin. Association of Adapalene and BPO significantly decreased expression of Ki67, α(2) and α(6) integrins, TLR-2, β-defensin 4 and IL-8 in inflammatory acne skin, whereas single treatments with Adapalene or BPO alone were less effective. These results contribute to explain the comedolytic and anti-inflammatory activities of this combined therapy observed in recent clinical trials.