Identifying an indoor air exposure limit for formaldehyde considering both irritation and cancer hazards

Formaldehyde is a well-studied chemical and effects from inhalation exposures have been extensively characterized in numerous controlled studies with human volunteers, including asthmatics and other sensitive individuals, which provide a rich database on exposure concentrations that can reliably produce the symptoms of sensory irritation. Although individuals can differ in their sensitivity to odor and eye irritation, the majority of authoritative reviews of the formaldehyde literature have concluded that an air concentration of 0.3 ppm will provide protection from eye irritation for virtually everyone. A weight of evidence-based formaldehyde exposure limit of 0.1 ppm (100 ppb) is recommended as an indoor air level for all individuals for odor detection and sensory irritation. It has recently been suggested by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and the US Environmental Protection Agency (US EPA) that formaldehyde is causally associated with nasopharyngeal cancer (NPC) and leukemia. This has led US EPA to conclude that irritation is not the most sensitive toxic endpoint and that carcinogenicity should dictate how to establish exposure limits for formaldehyde. In this review, a number of lines of reasoning and substantial scientific evidence are described and discussed, which leads to a conclusion that neither point of contact nor systemic effects of any type, including NPC or leukemia, are causally associated with exposure to formaldehyde. This conclusion supports the view that the equivocal epidemiology studies that suggest otherwise are almost certainly flawed by identified or yet to be unidentified confounding variables. Thus, this assessment concludes that a formaldehyde indoor air limit of 0.1 ppm should protect even particularly susceptible individuals from both irritation effects and any potential cancer hazard

Insights into molecular mechanisms of contact hypersensitivity gained from gene knockout studies

Contact hypersensitivity (CHS), a dendritic-cell (DC)-dependent, T-cell-mediated skin immune response to reactive haptens, has been a subject of intense research for many years. The molecular mechanisms underlying CHS are complicated and are not fully understood. During the past few years, varieties of gene-targeted knockout mice have been used in the study of CHS. Such studies have contributed significantly to our understanding of the mechanisms responsible for the initiation of CHS. This review focuses on insights into molecular requirements for CHS gained from knockout studies

Keratinocytes and cytokine/growth factors

Cytokines are polypeptide growth factors produced by most nucleated cells in the body including epithelial cells, keratinocytes, and Langerhans cells in the skin. Cytokines can be classified into interleukins, tumor necrosis factors, chemokines, colony-stimulating factor interferons, and growth factors. Like classic hormones, cytokines bind to specific receptors to transmit their messages to target cells. Cytokine receptors can be divided into three cytokine receptor superfamilies, the immunoglobulin superfamily, the hematopoietin family, and the tumor necrosis factor family. Following cytokine/cytokine-receptor binding (first messenger), a signal transduction pathway is initiated. Factors affecting homeostasis in the skin and oral mucosa include a delicate balance between cytokines/cytokine-receptors and their antagonists. An imbalance in these variables can influence the development of cutaneous and oral diseases-such as lichen planus, autoimmune disorders, and some neoplastic processes-and can affect wound healing. Potential uses of cytokines include cancer and antiviral therapy

Urokinase plasminogen activator mRNA is induced by IL-1α and TNF-α in in vitro acantholysis

The role of urokinase type plasminogen activator (uPA) has been well documented in the pathogenesis of pemphigus vulgaris (PV). Activation of plasminogen into active serine protease plasmin initiates extracellular proteolysis leading to acantholysis but the mechanisms underlying this process are not clearly understood. We have previously shown that keratinocyte derived cytokines IL-1α and TNF-α are involved in PV-induced acantholysis. In the present study we sought to examine whether keratinocyte-derived IL-1α and TNF-α are correlated with uPA induction in keratinocytes during acantholysis. Normal human keratinocytes were incubated with diluted PV serum. mRNAs for IL-1α, TNF-α and uPA were examined with RT-PCR at various time points and acantholysis was measured. IL-1α, TNF-α and uPA mRNAs were all induced in keratinocytes following PV serum stimulation; IL-1α/TNF-α mRNAs' expression was earlier than the expression of uPA mRNA. To further examine the role of IL-1α, TNF-α and uPA in acantholysis, we performed antibody blocking studies. Anti-IL-la, anti-TNF-a and anti-uPA antibodies suppressed acantholysis by 76%, 80% and 90%, respectively. In addition, anti-IL-1α and anti-TNF-α antibodies inhibited uPA mRNA induction, whereas anti-uPA antibodies did not alter IL-1α/TNF-α mRNAs' expression. Our results confirm the role of uPA in acantholysis and suggest an involvement of IL-1α/TNF-α in uPA induction. © Blackwell Munksgaard, 2003

Immune modulation in pemphigus vulgaris: Role of CD28 and IL-10

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease characterized by Abs to the desmosomal cadherin desmoglein-3. Although the autoantibodies have been shown to be pathogenic, the role of the cellular immune system in the pathology of pemphigus-induced acantholysis is unclear. To further delineate the potential role of T cell-signaling pathways in the pathogenesis of PV, we performed passive transfer experiments with PV IgG in gene-targeted mutant mice. Our results demonstrated that CD28-deficient mice (lacking a costimulatory signal for T cell activation) are 5-fold more sensitive to the development of PV than wild-type mice. To evaluate whether the higher incidence of disease was due to an impairment in intercellular adhesion of keratinocytes, we performed an in vitro acantholysis, using CD28(-/-) mice keratinocytes. No alteration in in vitro adhesion was detected in CD28(-/-)-type keratinocytes. Because the CD28 molecule plays a pivotal role in the induction of Th2 cytokines, we examined the levels of a prototypic Th2 cytokine (IL-10) in CD28(-/-) mice. Lower levels of IL-10 mRNA were found in lesions from CD28(-/-) mice. To determine whether pemphigus susceptibility in CD28(-/-) was related to IL-10 deficiency, we performed passive transfer experiments in IL-10(-/-) mice that demonstrated increased blisters compared with controls. To confirm that IL-10 is involved in the pathogenesis, rIL-10 was given with PV IgG. IL-10 significantly suppressed the disease activity. These data suggest a potential role of IL-10 in PV

Inhibition of interleukin-1β mRNA expression and interleukin-1α and β secretion by a specific human recombinant interleukin-1 receptor antagonist in human peripheral blood mononuclear cells

The transcription and translation of interleukin-1 (IL-1) may have a pleiotropic effect on the immune system and inflammatory diseases. Recently it has been reported that human monocytes not only produce IL-1 but also induce, with adherent IgG, the secretion of an IL-1 receptor antagonist (IL-1Ra), which can play an essential in vivo and in vitro role in the regulation of IL-1 activity. Recombinant human (rh) IL-1Ra is structurally similar to IL-1β but with no IL-1-like activity, and specifically binds to the IL-1 receptor. To more fully evaluate and clarify the inhibitory effect of rhIL-1receptor antagonist on IL-1 we have studied the influence of rhIL-1 Ra on IL-1 transcription and translation. In this report we show that IL-1β mRNA from peripheral blood mononuclear cells (PBMC) is strongly inhibited (66%) when rhIL-1Ra (250 ng/ml) was added to cultured cells activated with lipopolysaccharide (LPS) (100 ng/ml) for 4 hr, determined with the slot blot analysis. The addition of exogenous rhIL-1β to the cell culture diminished the inhibitory effect (44%). Moreover, we report that the block of IL-1 mRNA transcription consequently leads to the inhibition of IL-1α and IL-1β secretion in human PBMC, as measured by ELISA method. In fact, herein we show that LPS activates human PBMC to secrete IL-1β and IL-1α, an effect inhibited, in a dose-dependent fashion by rhIL-1Ra (0.025-250 ng/ml) in an overnight incubation. Since IL-1 is a strong inducer of IL-1 synthesis in vivo and in vitro, in our study we used rh IL-1α to stimulate the secretion of IL-1β in human PBMC. This activation, carried out overnight, also provoked the release of IL-1β in a dose-dependent manner, which was strongly inhibited by rhIL-1Ra used at different concentrations (0.025-250 ng/ml). The inhibitory effect exerted by IL-1Ra on human PBMC IL-1 mRNA transcription and the down-regulation of secretion of IL-1β stimulated by IL-1α, may contribute to therapeutic effects in inflammatory diseases such as rheumatoid arthritis and other autoimmune diseases. We conclude that the suppression of IL-1 mRNA occurring in an early stage consequently provokes an inhibition of post-transcriptional formation of IL-1, and may therefore prove that IL-1Ra is probably part of a physiological system for regulating normal and pathological activities of IL-1 and its inducers

Inhibition of interleukin-1β mRNA expression and interleukin-1α and β secretion by a specific human recombinant interleukin-1 receptor antagonist in human peripheral blood mononuclear cells

The transcription and translation of interleukin-1 (IL-1) may have a pleiotropic effect on the immune system and inflammatory diseases. Recently it has been reported that human monocytes not only produce IL-1 but also induce, with adherent IgG, the secretion of an IL-1 receptor antagonist (IL-1Ra), which can play an essential in vivo and in vitro role in the regulation of IL-1 activity. Recombinant human (rh) IL-1Ra is structurally similar to IL-1β but with no IL-1-like activity, and specifically binds to the IL-1 receptor. To more fully evaluate and clarify the inhibitory effect of rhIL-1receptor antagonist on IL-1 we have studied the influence of rhIL-1 Ra on IL-1 transcription and translation. In this report we show that IL-1β mRNA from peripheral blood mononuclear cells (PBMC) is strongly inhibited (66%) when rhIL-1Ra (250 ng/ml) was added to cultured cells activated with lipopolysaccharide (LPS) (100 ng/ml) for 4 hr, determined with the slot blot analysis. The addition of exogenous rhIL-1β to the cell culture diminished the inhibitory effect (44%). Moreover, we report that the block of IL-1 mRNA transcription consequently leads to the inhibition of IL-1α and IL-1β secretion in human PBMC, as measured by ELISA method. In fact, herein we show that LPS activates human PBMC to secrete IL-1β and IL-1α, an effect inhibited, in a dose-dependent fashion by rhIL-1Ra (0.025-250 ng/ml) in an overnight incubation. Since IL-1 is a strong inducer of IL-1 synthesis in vivo and in vitro, in our study we used rh IL-1α to stimulate the secretion of IL-1β in human PBMC. This activation, carried out overnight, also provoked the release of IL-1β in a dose-dependent manner, which was strongly inhibited by rhIL-1Ra used at different concentrations (0.025-250 ng/ml). The inhibitory effect exerted by IL-1Ra on human PBMC IL-1 mRNA transcription and the down-regulation of secretion of IL-1β stimulated by IL-1α, may contribute to therapeutic effects in inflammatory diseases such as rheumatoid arthritis and other autoimmune diseases. We conclude that the suppression of IL-1 mRNA occurring in an early stage consequently provokes an inhibition of post-transcriptional formation of IL-1, and may therefore prove that IL-1Ra is probably part of a physiological system for regulating normal and pathological activities of IL-1 and its inducers

Immune modulation in pemphigus vulgaris: Role of CD28 and IL-10

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease characterized by Abs to the desmosomal cadherin desmoglein-3. Although the autoantibodies have been shown to be pathogenic, the role of the cellular immune system in the pathology of pemphigus-induced acantholysis is unclear. To further delineate the potential role of T cell-signaling pathways in the pathogenesis of PV, we performed passive transfer experiments with PV IgG in gene-targeted mutant mice. Our results demonstrated that CD28-deficient mice (lacking a costimulatory signal for T cell activation) are 5-fold more sensitive to the development of PV than wild-type mice. To evaluate whether the higher incidence of disease was due to an impairment in intercellular adhesion of keratinocytes, we performed an in vitro acantholysis, using CD28(-/-) mice keratinocytes. No alteration in in vitro adhesion was detected in CD28(-/-)-type keratinocytes. Because the CD28 molecule plays a pivotal role in the induction of Th2 cytokines, we examined the levels of a prototypic Th2 cytokine (IL-10) in CD28(-/-) mice. Lower levels of IL-10 mRNA were found in lesions from CD28(-/-) mice. To determine whether pemphigus susceptibility in CD28(-/-) was related to IL-10 deficiency, we performed passive transfer experiments in IL-10(-/-) mice that demonstrated increased blisters compared with controls. To confirm that IL-10 is involved in the pathogenesis, rIL-10 was given with PV IgG. IL-10 significantly suppressed the disease activity. These data suggest a potential role of IL-10 in PV