Hereditary auto-inflammatory disorders and biologics

The term auto-inflammatory disorders has been coined to describe a group of conditions characterized by spontaneously relapsing and remitting bouts of systemic inflammation without apparent involvement of antigen-specific T cells or significant production of auto-antibodies. The hereditary periodic fever syndromes are considered as the prototypic auto-inflammatory diseases, and genetic studies have yielded important new insights into innate immunity. DNA analysis has greatly enhanced the clinical characterization of these conditions, and elucidation of their molecular aetiopathogenesis has suggested that therapies may be aimed at specific targets within the immune cascade. The availability of biologic response modifiers such as inhibitors of tumour necrosis factor (TNF) and interleukin-1beta has greatly improved the outlook for some of these disorders, although effective therapies remain elusive in patients with certain conditions, including hyperimmunoglobulinaemia-D with periodic fever syndrome (HIDS) and a proportion of those with TNF-receptor associated periodic syndrome (TRAPS). Indeed, outstanding challenges and the unique potential to further elucidate molecular mechanisms in innate immunity are illustrated by the dashed early hope that TNF blockade would be a panacea for TRAPS: not only is etanercept (Enbrel) ineffective in some cases, but there are anecdotal reports of this condition being greatly exacerbated by infliximab (Remicade).

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.

Enzymes involved in the biosynthesis of leukotriene B4 and prostaglandin E2 are active in sebaceous glands

The expression of enzymes involved in leukotriene and prostaglandin signalling pathways, of interleukins 6 and 8 and of peroxisome proliferator-activated receptors in sebaceous glands of acne-involved facial skin was compared with those of non-involved skin of acne patients and of healthy individuals. Moreover, 5-lipoxygenase and leukotriene A(4) hydrolase were expressed at mRNA and protein levels in vivo and in SZ95 sebocytes in vitro (leukotriene A(4) hydrolase > 5-lipoxygenase), while 15-lipoxygenase-1 was only detected in cultured sebocytes. Cyclooxygenase-1 and cyclooxygenase-2 were also present. Peroxisome proliferator-activated receptors were constitutively expressed. Enhanced 5-lipoxygenase, cyclooxygenase 2 and interleukin 6 expression was detected in acne-involved facial skin. Arachidonic acid stimulated leukotriene B(4) and interleukin 6 release as well as prostaglandin E(2) biosynthesis in SZ95 sebocytes, induced abundant increase in neutral lipids and down-regulated peroxisome proliferator-activated receptor-alpha, but not receptor-gamma1 mRNA levels, which were the predominant peroxisome proliferator-activated receptor isotypes in SZ95 sebocytes. In conclusion, human sebocytes possess the enzyme machinery for functional leukotriene and prostaglandin pathways. A comprehensive link between inflammation and sebaceous lipid synthesis is provided.

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.

Induction of a chemoattractive proinflammatory cytokine response after stimulation of keratinocytes with Propionibacterium acnes and coproporphyrin III

BACKGROUND

The inflammation in acne vulgaris is widely thought to be induced by an immunological reaction, but the role of Propionibacterium acnes is unclear.

OBJECTIVES

To examine the local host response mechanism of a keratinocyte cell line 3 h and 6 h after stimulation with viable and heat-killed P. acnes.

METHODS

The quantitative expression of cytokines was measured at the mRNA level by real-time reverse transcription-polymerase chain reaction.

RESULTS

The coincubation of a keratinocyte cell line with viable, but not heat-killed, P. acnes modulated an adequate cytokine response for interleukin (IL)-1beta, granulocyte/macrophage colony-stimulating factor and IL-8. High-performance liquid chromatographic analysis of the in vivo porphyrin pattern secreted by P. acnes revealed a predominance of coproporphyrin III in acne lesions. This same porphyrin fraction also modestly induced IL-8 expression by keratinocytes.

CONCLUSIONS

This cytokine pattern may favour a chemotactic response and implicates P. acnes and coproporphyrin III in the recruitment of inflammatory cells to the site of infection and in the development of acne lesions.

Granulysin-derived peptides demonstrate antimicrobial and anti-inflammatory effects against Propionibacterium acnes

Propionibacterium acnes is a key therapeutic target in acne, yet this bacterium has become resistant to standard antibiotic agents. We investigated whether the human antimicrobial protein granulysin is a potential candidate for the treatment of acne. Granulysin and synthetic granulysin-derived peptides possessing a helix-loop-helix motif killed P. acnes in vitro. Modification of a helix-loop-helix peptide, 31-50, by substitution of a tryptophan for the valine at amino acid 44 (peptide 31-50v44w) to increase its interaction with bacterial surfaces also increased its antimicrobial activity. Moreover, when synthesized with D- rather than L-type amino acids, this peptide (D-31-50v44w) became less susceptible to degradation by proteases and more effective in killing P. acnes. Granulysin peptides were bactericidal, demonstrating an advantage over standard bacteriostatic antibiotics in their control of P. acnes. Moreover, peptide D-31-50v44w killed P. acnes in isolated human microcomedone preparations. Importantly, peptides 31-50, 31-50v44w, and D-31-50v44w also have potential anti-inflammatory effects, as demonstrated by suppression of P. acnes-stimulated cytokine release. Taken together, these data suggest that granulysin peptides may be useful as topical therapeutic agents, providing alternatives to current acne therapies.

The pathophysiology of acne

Acne is a multifactorial inflammatory disease affecting pilosebaceous follicles. The initial event in the development of an acne lesion is abnormal desquamation of the keratinocytes that line the sebaceous follicle, which creates a microplug or microcomedo. An increase in circulating androgens at the onset of puberty stimulates the production of sebum into the pilosebaceous unit. These events combine to create an environment within the pilosebaceous unit that is favorable for the colonization of the commensal bacteria, Propionibacterium acnes. With proliferation, P acnes secretes various inflammatory molecules and chemotactic factors that initiate and perpetuate the local inflammatory response and possibly induce keratinocyte hyperproliferation as well.

The Role of Toll-Like Receptors in the Pathophysiology of Acne

Acne vulgaris is a common cutaneous disorder of the pilosebaceous follicle, affecting more than 45 million people in the United States alone. The pathogenesis of acne is multifactorial, involving abnormal hyperkeratinization, increased sebum production, hormones, cutaneous microbes, and immunological mechanisms. Many of the immunological processes that contribute to the formation of acne lesions take place at the very site of disease, the skin. Skin is an important component of the innate immune system, providing both physical barriers and rapid cellular responses by keratinocytes, Langerhans cells, and other infiltrating inflammatory cells. In this review, we discuss the ability of the innate immune system to use Toll-like receptors (TLRs) to recognize microbial patterns and initiate immune responses in cutaneous disorders. Because TLRs are vital players in infectious and inflammatory diseases, they are potential therapeutic targets. Indeed, the ability of TLRs to combat disease already has been harnessed through the development of drugs that act as TLR agonists. A better understanding of TLRs will allow for the development of new therapeutic options for cutaneous inflammatory diseases such as acne.

The Role of Inflammation in the Pathogenesis of Acne and Acne Scarring

Evidence now supports a pivotal role for cellular inflammatory events at all stages of acne lesion development, from preclinical initiation to clinical presentation of active lesions through to resolution. The emphasis has moved from acne as a primarily hyperproliferative disorder of the sebaceous follicle to that of an inflammatory skin disorder. However, although the sequence of events leading to lesion formation has become clearer, the triggers for initiation remain speculative. The development of noninvasive techniques to detect preclinical "acne-prone" follicles is essential before triggers for initiation can be defined. Finally, the differences highlighted in the inflammatory profiles of inflamed lesions from patients who scar, as compared with other nonscarring acne patients reinforces the view that acne is a disorder, which embraces a number of pathologies.

Acne: inflammation

The inflammatory stage of acne vulgaris is usually of greatest concern to the patient. A number of morphologically different inflammatory lesions may form that can be painful and unsightly. In 30% of patients, such lesions lead to scarring(1). Inflammatory acne and acne scarring can have significant psychological effects on the patient, including depression, anxiety, and poor self-image(2). Although inflammatory acne has been well characterized clinically, the mechanisms by which inflammatory lesions arise are still poorly understood. The human skin commensal bacterium, Propionibacterium acnes, has long been associated with inflammatory acne. This organism has been implicated over and above all of the other cutaneous microflora in contributing to the inflammatory response characteristic of acne. However, its precise role in the disease and its interaction with the human immune system remain to be elucidated.

The potential immunomodulatory effects of topical retinoids

New research has refined our understanding of the immunopathophysiology of acne. Various immune factors, including both innate and adaptive immune responses, have been implicated in the pathophysiology of inflammatory acne. Topical retinoids such as tretinoin, adapalene, and tazarotene, exhibit immunomodulatory effects that may help to explain their efficacy in the resolution of inflammatory lesions.

Cutting Edge: All-transRetinoic Acid Down-Regulates TLR2 Expression and Function

A major consequence of microbial infection is the tissue injury that results from the host inflammatory response. In acne, inflammation is due in part to the ability of Propionibacterium acnes to activate TLR2. Because all-trans retinoic acid (ATRA) decreases inflammation in acne, we investigated whether it regulates TLR2 expression and function. Treatment of primary human monocytes with ATRA led to the down-regulation of TLR2 as well as its coreceptor CD14, but not TLR1 or TLR4. The ability of a TLR2/1 ligand to trigger monocyte cytokine release was inhibited by pre- and cotreatment with ATRA; however, TLR4 activation was affected by cotreatment only. ATRA also down-regulated monocyte cytokine induction by P. acnes. These data indicate that ATRA exerts an anti-inflammatory effect on monocytes via two pathways, one specifically affecting TLR2/1 and CD14 expression and one independent of TLR expression. Agents that target TLR expression and function represent a novel strategy to treat inflammation in humans.

Different pro-inflammatory and immunogenic potentials of Propionibacterium acnes and Staphylococcus epidermidis: implications for chronic inflammatory acne

INTRODUCTION

Propionibacterium acnes (PA) and Staphyloccocus epidermidis (SE) are two major bacterial strains isolated from acne lesions. Nevertheless, only PA seems to be implicated in the pathogenesis of inflammatory acne vulgaris. Evidence for this, however, remains indirect and the precise role of PA in inflammatory acne is still a matter for conjecture. The aim of this study was to compare some pro-inflammatory and adjuvant properties of PA and SE.

MATERIAL/METHODS

To determine some of the pathogenic, immunostimulatory, and pro-inflammatory proper of PA and SE, two experimental models of inflammation were used. In vivo; chronic inflammation was induced by intradermal injection of living bacteria into the ear. In vitro; peritoneal macrophages elicited by the bacteria were examined for their ability to generate reactive oxygen species (ROS), nitric oxide (NO), and cytokines.

RESULTS

PA, but not SE, evoked mild local inflammation of infected ears. Macrophages elicited with PA produced more tumor necrosis factor alpha and interleukin IL-12 than those induced with SE, while SE was a stronger inducer of IL-10 production. Both bacteria equally induced the generation of NO and ROS. In contrast, only PA showed adjuvant proper-ties.

CONCLUSIONS

The results of these studies indicate that SE, in contrast to PA, does not exert pro-inflammatory properties. Thus it is unlikely that SE may be implicated in the pathogenesis of inflammatory acne vulgaris.

The pathogenesis of acne

Acne vulgaris is a multifactorial disease of as yet incompletely elucidated etiology and pathogenesis. The following have been identified as the most significant factors: follicular hyperkeratosis, increased sebum secretion, Propionibacterium (P.) acnes, and inflammation. Increased sebum production and follicular hyperkeratosis result in the development of microcomedones, and changes in follicular milieu in intensive growth of P. acnes. P. acnes secretes several proinflammatory products, which play an important role in the development of inflammation. These include lipases, proteases, hyaluronidases, and chemotactic factors. Immune response to P. acnes includes humoral and cell-mediated immunity as well as complement activation. Recent results indicate that keratinocytes and sebocytes, as major components of pilosebaceous unit, may act as immune cells and may be activated by P. acnes via toll-like receptors (TLRs) and CD14, and through CD1 molecules may recognize altered lipid content in sebum, followed by the production of inflammatory cytokines.

The Complete Genome Sequence of Propionibacterium Acnes, a Commensal of Human Skin

Propionibacterium acnes is a major inhabitant of adult human skin, where it resides within sebaceous follicles, usually as a harmless commensal although it has been implicated in acne vulgaris formation. The entire genome sequence of this Gram-positive bacterium encodes 2333 putative genes and revealed numerous gene products involved in degrading host molecules, including sialidases, neuraminidases, endoglycoceramidases, lipases, and pore-forming factors. Surface-associated and other immunogenic factors have been identified, which might be involved in triggering acne inflammation and other P. acnes-associated diseases.

Antibody response to crude cell lysate of propionibacterium acnes and induction of pro-inflammatory cytokines in patients with acne and normal healthy subjects

Propionibacterium acnes (P. acnes) plays an important role in the disease pathogenesis of acne vulgaris, a disorder of pilosebaceous follicles, seen primarily in the adolescent age group. In the present study, the presence of antibodies against P. acnes (MTCC1951) were detected in acne patient (n=50) and disease free controls (n=25) using dot-ELISA and Western blot assay. The ability of P. acnes to induce pro-inflammatory cytokines by human peripheral blood mononuclear cells (PBMCs), obtained from acne patients and healthy subjects, were also analysed. The patients (n=26) who were culture positive for skin swab culture, were found to have a more advanced disease and higher antibody titres (1:4000 to > 1:16000) compared to the P. acnes negative patients (n=24) and normal controls (n=25). An analysis of patients' sera by western blot assay recognized a number of antigenic components of P. acnes, ranging from 29 to 205 kDa. The major reactive component was an approximately 96 kDa polypeptide, which was recognised in 92% (24 of 26) of the patients sera. Further, the P. acnes culture supernatant, crude cell lysate and heat killed P. acnes whole cells, obtained from 72-h incubation culture, were observed to be able to induce significant amounts of IL-8 and tumor necrosis factor alpha (TNF-alpha) by the PBMCs in both the healthy subjects and patients, as analysed by cytokine-ELISA. The levels of cytokines were significantly higher in the patients than the healthy subjects. A major 96 kDa polypeptide reactant was eluted from the gel and was found to cause dose dependent stimulation of the productions of IL-8 and TNF-alpha. Thus, the above results suggest that both humoral and pro-inflammatory responses play major roles in the pathogenesis of acne.

Inflammation in acne scarring: a comparison of the responses in lesions from patients prone and not prone to scar

BACKGROUND

Many patients with inflammatory acne suffer from significant scarring, which is disfiguring and difficult to treat. A cell-mediated immune response is considered to be involved in the pathogenesis of acne, although the extent of this response has been found to differ among patients.

OBJECTIVE

To assess whether there were differences in the cell-mediated immune responses at different time points in inflamed lesion development and resolution in patients who were prone (S patients) and those with the same degree of inflamed acne who were not prone (NS patients) to develop scarring.

METHODS

Cellular and vascular markers were investigated using standard immunohistochemical techniques on biopsies of inflamed lesions of known duration, i.e. < 6 h (n = 14), 24 h (n = 14), 48 h (n = 10), 72 h (n = 10) and 6-7 days (n = 11) from the backs of acne patients.

RESULTS

In early lesions from NS patients there was a large influx of CD4+ T cells, macrophages and Langerhans cells with a high number of cells expressing HLA-DR. Also there was significant angiogenesis and vascular adhesion molecule expression. Cell recruitment peaked in 48 h lesions, after which leucocyte numbers decreased and vascular activity returned to normal. Of the T cells, only 50% were memory/effector (CD45RO+) and naive (CD45RA+) cells, while the remainder were unclassified (CD45RO-, CD45RA-). In early lesions from S patients, CD4+ T cell numbers were smaller, although a high proportion were skin homing memory/effector cells. Langerhans cell numbers and cellular HLA-DR expression were low, while numbers of macrophages, blood vessels and vascular adhesion molecules were high. In resolving lesions angiogenesis remained high, with a further influx of macrophages and skin homing memory/effector cells and increased cellular HLA-DR expression.

CONCLUSIONS

The cellular infiltrate was large and active with a greater nonspecific response (few memory T cells) in early lesions of NS patients, which subsided in resolution. In contrast, a predominantly specific immune response was present in S patients, which was initially smaller and ineffective, but was increased and activated in resolving lesions. Such excessive inflammation in healing tissue is conducive to scarring and suggests that the use of topical anti-inflammatory treatments would be appropriate for these patients.

[Immunohistochemical evidence of chronic inflammation in acne vulgaris]

The etiology and pathogenesis of acne vulgaris are not yet completely understood. Therefore we have investigated 5 patients with different clinical forms of disease, including the rare form of acne fulminans. Taking into consideration the four factors that are currently incriminated in the development of acne, sebaceous hypersecretion, hyperkeratosis of the pilosebaceous infundibulum, bacterial colonisation and perifollicular inflammation, we have focused our study on a set of cells involved in the chronic inflammatory process. We have evidenced by immunohistochemistry methods, using appropriate monoclonal antibodies, the presence of T lymphocytes and macrophages, while the B cells could be evidenced only in the severe forms. We were also interested to investigate the occurrence of new capillary formation, as an accompanying phenomenon of the inflammatory process. The presence and histological distribution of these cells highly supports the hypothesis that the mechanisms underlying the development of acne vulgaris belong to the Delayed Type Hypersensitivity.

Is acne really a disease?: a theory of acne as an evolutionarily significant, high-order psychoneuroimmune interaction timed to cortical development with a crucial role in mate choice

Adolescent acne is considered from the perspective of evolutionary psychology with an emphasis on a role in mate choice. The fact that acne, which is almost universal and not a true infection, is (1) initiated at puberty by the action of pubertal hormones on likely distinct, pro-acne follices, and (2) typically resolves in one's early twenties when prefrontal cortex development is complete, suggests that the condition's timeframe is meaningful. Acne's conspicuous localization on the face, and its ability to elicit reflexive disgust and avoidance in observers, suggests a possible role in sexual selection. The pathophysiology of acne is reviewed, and the suggestion made that, far from being a disease, adolescent acne is a normal physiological process - a high-order psychoneuroimmune interaction - that functions to ward off potential mates until the afflicted individual is some years past the age of reproductive maturity, and thus emotionally, intellectually, and physically fit to be a parent.

Physiopathology of acne vulgaris: recent data, new understanding of the treatments

Acne is the most frequent reason for seeing a dermatologist, but its physiopathology is not completely well-known. Yet understanding of the mechanisms of action of the different acne treatments is very important to optimize their use. A lot of new data on the physiopathology have recently been published in the acne field. This paper summarizes the main points of these new facts.