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International audience; The domesticated marine microalga Diacronema lutheri is of great interest for producing various highly valuable molecules like lipids, particularly long‐chain polyunsaturated fatty acids (LC‐PUFA). In this study, we investigated the impact of phosphorus (P) and nitrogen (N) starvation on growth, carbon fixation (photosynthetic activity) and partitioning, and membrane lipid remodeling in this alga during batch culture. Our results show that the photosynthetic machinery was similarly affected by P and N stress. Under N starvation, we observed a much lower photosynthetic rate and biomass productivity. The degradation and re‐use of cellular N‐containing compounds contributed to triacylglycerol (TAG) accumulation. On the other hand, P‐starved cells maintained pigment content and a carbon partitioning pattern more similar to the control, ensuring a high biomass. Betaine lipids constitute the major compounds of non‐plastidial membranes, which are rich in eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. Under P and N starvations, EPA was transferred from the recycling of membrane polar lipids, most likely contributing to TAG accumulation.

Triclosan is an antimicrobial chemical used in healthcare settings that can be absorbed through the skin. Exposure to triclosan has been positively associated with food and aeroallergy and asthma exacerbation in humans and, although not directly sensitizing, has been demonstrated to augment the allergic response in a mouse model of asthma. The skin barrier and microbiome are thought to play important roles in regulating inflammation and allergy and disruptions may contribute to development of allergic disease. To investigate potential connections of the skin barrier and microbiome with immune responses to triclosan, SKH1 mice were exposed dermally to triclosan (0.5–2%) or vehicle for up to 7 consecutive days. Exposure to 2% triclosan for 5–7 days on the skin was shown to increase transepidermal water loss levels. Seven days of dermal exposure to triclosan decreased filaggrin 2 and keratin 10 expression, but increased filaggrin and keratin 14 protein along with the danger signal S100a8 and interleukin-4. Dermal exposure to triclosan for 7 days also altered the alpha and beta diversity of the skin and gut microbiome. Specifically, dermal triclosan exposure increased the relative abundance of the Firmicutes family, Lachnospiraceae on the skin but decreased the abundance of Firmicutes family, Ruminococcaceae in the gut. Collectively, these results demonstrate that repeated dermal exposure to the antimicrobial chemical triclosan alters the skin barrier integrity and microbiome in mice, suggesting that these changes may contribute to the increase in allergic immune responses following dermal exposure to triclosan.

Heptafluorobutyric acid (PFBA) is a synthetic chemical belonging to the per- and polyfluoroalkyl substances (PFAS) group that includes over 5000 chemicals incorporated into numerous products. PFBA is a short-chain PFAS (C4) labeled as a safer alternative to legacy PFAS which have been linked to numerous health effects. Despite the high potential for dermal exposure, occupationally and environmentally, dermal exposure studies are lacking. Using a murine model, this study analyzed serum chemistries, histology, immune phenotyping, and gene expression to evaluate the systemic toxicity of sub-chronic dermal PFBA 15-day (15% v/v or 375 mg/kg/dose) or 28-day (3.75–7.5% v/v or 93.8–187.5 mg/kg/dose) exposures. PFBA exposure produced significant increases in liver and kidney weights and altered serum chemistries (all exposure levels). Immune-cell phenotyping identified significant increases in draining lymph node B-cells (15%) and CD11b + cells (3.75–15%) and skin T-cells (3.75–15%) and neutrophils (7.5–15%). Histopathological and gene expression changes were observed in both the liver and skin after dermal PFBA exposure. The findings indicate PFBA induces liver toxicity and alterations of PPAR target genes, suggesting a role of a PPAR pathway. These results demonstrate that sustained dermal exposure to PFBA induces systemic effects and raise concerns of short-chain PFAS being promoted as safer alternatives.

Health-care workers have an increased incidence of allergic disease compared with the general public and are exposed to a variety of high-level disinfectants. Although exposure to these agents has been associated with allergic disease, findings between epidemiology and animal studies often conflict respecting immunological mechanisms. Therefore, we hypothesized that previous exposure to a representative IgE-mediated sensitizer (ortho-phthalaldehyde [OPA]) alters immune responses to a representative T-cell-mediated sensitizer (didecyldimethlyammonium chloride [DDAC]). Here, BALB/c mice were topically exposed to OPA (0.5%) for 3 days, rested, then topically exposed to DDAC (0.0625%, 0.125%, and 0.25%) for 14 days. Coexposure resulted in phenotypic changes in draining lymph node (dLN) cells, including a decreased frequency of CD8+ T cells and increased frequency and number of B cells compared with DDAC-only treated mice. The coexposed mice also had enhanced Th2 responses, including significant alterations in: dLN Il4 (increased), B-cell activation (increased), CD8+ T-cell activation (decreased), and local and systemic IgE production (increased). These changes were not observed if mice were exposed to DDAC prior to OPA. Exposure to OPA alone shows Th2 skewing, indicated by increased activation of skin type 2 innate lymphoid cells, increased frequency and activation of draining lymph node B cells, and increased levels of type 2 cytokines. These findings suggest that the OPA-induced immune environment may alter the response to DDAC, resulting in increased IgE-mediated immune responses. This data may partially explain the discordance between epidemiological and laboratory studies regarding disinfectants and provide insight into the potential immunological implications of mixed chemical exposures.

5-Chloro-2-(2,4-dichlorophenoxy)phenol (triclosan) is an antimicrobial chemical widely used in consumer household and clinical healthcare products. Human and animal studies have associated triclosan exposure with allergic disease. Mechanistic studies have identified triclosan as a mitochondrial uncoupler; recent studies suggest that mitochondria play an important role in immune cell function and are involved in activation of the NLRP3 inflammasome. In this study, early immunological effects were evaluated via NLRP3 activation following dermal triclosan application in a BALB/c murine model. These investigations revealed rapid caspase-1 activation and mature IL-1β secretion in the skin and draining lymph nodes (dLNs) after 1.5% and 3% triclosan exposure. Correspondingly, pro-Il-1b and S100a8 gene expression increased along with extracellular ATP in the skin. Peak gene expression of chemokines associated with caspase-1 activation occurred after 2 days of exposure in both skin tissue and dLNs. Phenotypic analysis showed an increase in neutrophils and macrophages in the dLN and myeloid and inflammatory monocytes in the skin tissue. Triclosan also caused mitochondrial dysfunction shown through effects on mitochondrial reactive oxygen species, mass, mitochondrial membrane potential, and mitochondrial morphology. These results indicate that following triclosan exposure, activation of the NLRP3 inflammasome occurs in both the skin tissue and dLNs, providing a possible mechanism for triclosan’s effects on allergic disease and further support a connection between mitochondrial involvements in immunological responses.

Perfluorooctanoic acid (PFOA) is a per- and polyfluoroalkyl substance (PFAS) once used as a surfactant in the polymerization of chemicals. Because of its ubiquitous nature and long half-life, PFOA is commonly detected in the environment, wildlife, and humans. While skin exposure to PFOA is of concern, studies evaluating the immunotoxicity of dermal exposure are lacking. These studies evaluated the immunotoxicity of PFOA (0.5–2% w/v, or 12.5–50 mg/kg/dose) following dermal exposure using a murine model. PFOA (0.5–2%) was not identified to be an irritant or sensitizer using the local lymph node assay. The IgM antibody response to sheep red blood cell. was significantly reduced in the spleen following 4-days of dermal exposure (2%). PFOA exposure produced a significant decrease in thymus (1 and 2%) and spleen (0.5–2%) weight along with an increase in liver weight (0.5–2%). Immune cell phenotyping identified a reduction in the frequency (1 and 2%) and number (0.5–2%) of splenic B-cells. To further define the mechanism of immunotoxicity, gene expression was also evaluated in the skin. The findings support a potential involvement of the nuclear receptor PPARα. These results demonstrate that dermal exposure to PFOA is immunotoxic and raise concern about potential adverse effects from dermal exposure.

Healthcare workers concurrently may be at a higher risk of developing respiratory infections and allergic disease, such as asthma, than the general public. Increased incidence of allergic diseases is thought to be caused, in part, due to occupational exposure to chemicals that induce or augment Th2 immune responses. However, whether exposure to these chemical antimicrobials can influence immune responses to respiratory pathogens is unknown. Here, we use a BALB/c murine model to test if the Th2-promoting antimicrobial chemical triclosan influences immune responses to influenza A virus. Mice were dermally exposed to 2% triclosan for 7 days prior to infection with a sub-lethal dose of mouse adapted PR8 A(H1N1) virus (50 pfu); triclosan exposure continued until 10 days post infection (dpi). Infected mice exposed to triclosan did not show an increase in morbidity or mortality, and viral titers were unchanged. Assessment of T cell responses at 10 dpi showed a decrease in the number of total and activated (CD44hi) CD4+ and CD8+ T cells at the site of infection (BAL and lung) in triclosan exposed mice compared to controls. Influenza-specific CD4+ and CD8+ T cells were assessed using MHCI and MHCII tetramers, with reduced populations, although not reaching statistical significance at these sites following triclosan exposure. Reductions in the Th1 transcription factor T-bet were seen in both activated and tetramer+ CD4+ and CD8+ T cells in the lungs of triclosan exposed infected mice, indicating reduced Th1 polarization and providing a potential mechanism for numerical reduction in T cells. Overall, these results indicate that the immune environment induced by triclosan exposure has the potential to influence the developing immune response to a respiratory viral infection and may have implications for healthcare workers who may be at an increased risk for developing infectious diseases.

The anti-microbial compound triclosan is incorporated into numerous consumer products and is detectable in the urine of 75% of the general United States population. Recent epidemiological studies report positive associations with urinary triclosan levels and allergic disease. Although not sensitizing, earlier studies previously found that repeated topical application of triclosan augments the allergic response to ovalbumin (OVA) though a thymic stromal lymphopoietin (TSLP) pathway in mice. In the present study, early immunological effects following triclosan exposure were further evaluated following topical application in a murine model. These investigations revealed abundant expression of S100A8/A9, which reportedly acts as an endogenous ligand for Toll-like Receptor 4 (TLR4), in skin tissues and in infiltrating leukocytes during topical application of 0.75–3.0% triclosan. Expression of Tlr4 along with Tlr1, Tlr2 and Tlr6 increased in skin tissues over time with triclosan exposure; high levels of TLR4 were expressed on skin-infiltrating leukocytes. In vivo antibody blockade of the TLR4/MD-2 receptor complex impaired local inflammatory responses after four days, as evidenced by decreased Il6, Tnfα, S100a8, S100a9, Tlr1, Tlr2, Tlr4 and Tlr6 expression in the skin and decreased lymph node cellularity and production of IL-4 and IL-13 by lymph node T-cells. After nine days of triclosan exposure with TLR4/MD-2 blockade, impaired T-helper cell type 2 (TH2) cytokine responses were sustained, but other early effects on skin and lymph node cellularity were lost; this suggested alternative ligands/receptors compensated for the loss of TLR4 signaling. Taken together, these data suggest the S100A8/A9-TLR4 pathway plays an early role in augmenting immunomodulatory responses with triclosan exposure and support a role for the innate immune system in chemical adjuvancy.

Didecyldimethylammonium bromide (DDAB) is a fourth generation dialkyl-quaternary ammonium compound (QAC) that is used in numerous products for its antimicrobial properties. While many QACs have been associated with allergic disease, the toxicity and sensitization of DDAB have not been thoroughly investigated. The purpose of these studies was to evaluate the irritancy and sensitization potential of DDAB following dermal application in a murine model. DDAB induced significant irritancy (0.0625–2%), evaluated by ear swelling in female BALB/c mice. Initial evaluation of the sensitization potential was conducted using the local lymph node assay (LLNA) at concentrations ranging from 0.0625% to 2%. A concentration-dependent increase in lymphocyte proliferation was observed with a calculated EC3 value of 0.057%. Immune cell phenotyping along with local and systemic IgE levels were evaluated following 4 and 14 days of dermal application. Phenotypic analyses revealed significant and dose-responsive increases in the absolute number of B-cells, CD4+ T-cells, CD8+ T-cells, and dendritic cells in the draining lymph nodes (DLNs) following 4 and 14 days of dermal exposure with significant increases in the number of activated B-cells and dendritic cells. However, increased activation of CD4+ T-cell and CD8+ T-cells was only observed following four days of DDAB exposure. Exposure to DDAB also induced increased production of IgE as evaluated by phenotypic analysis of DLN B-cells (IgE+ B-cells) and measurement of total serum IgE levels following 14 days but not four days of dermal application. Significant increases in gene expression were observed in the DLN (Il-4, Il-10, and ox40l) and ear (tslp) following 4 and 14 days of DDAB exposure. These results demonstrate the potential for development of irritation and hypersensitivity responses to DDAB following dermal exposure and raise concerns about the effects of exposure duration on hypersensitivity responses.

Diatoms adapt to changing environmental conditions in very efficient ways. Among the mechanisms that can be activated, the reorientation of carbon metabolism is crucial because it allows the storage of energy into energy-dense molecules, typically lipids. Beside their roles in physiology, lipids are commercially interesting compounds. Therefore studies dealing with this topic are relevant for both basic and applied science. Although the molecular mechanisms involved in the reorientation of carbon metabolism as a response to a deficiency in nutrients such as nitrogen or phosphorus has been partially elucidated, the impacts of carbon availability on the implementation of the reorientation mechanisms remain unclear. Indeed, it has not been determined if the same types of mechanisms are activated under carbon and other nutrient deficiencies or limitations. The first aim of this work was to get insights into the physiological, biological and molecular processes triggered by progressive carbon starvation in the model diatom Phaeodactylum tricornutum. The second aim was to investigate the effects of the growth light intensity on these processes. For such a purpose three different photon flux densities 30, 300, and 1000 μmol photons m-2 s-1 were used. The results presented here demonstrate that under carbon limitation, diatom cells still reorient carbon metabolism toward either phosphoenolpyruvate or pyruvate, which serves as a hub for the production of more complex molecules. The distribution of carbon atoms between the different pathways was partially affected by the growth photon flux density because low light (LL) provides conditions for the accumulation of chrysolaminarin, while medium light mostly stimulated lipid synthesis. A significant increase in the amount of proteins was observed under high light (HL).

Didecyldimethylammonium chloride (DDAC) is a dialkyl-quaternary ammonium compound that is used in numerous products for its bactericidal, virucidal and fungicidal properties. There have been clinical reports of immediate and delayed hypersensitivity reactions in exposed individuals; however, the sensitization potential of DDAC has not been thoroughly investigated. The purpose of these studies was to evaluate the irritancy and sensitization potential of DDAC following dermal exposure in a murine model. DDAC induced significant irritancy (0.5 and 1%), evaluated by ear swelling in female Balb/c mice. Initial evaluation of the sensitization potential was conducted using the local lymph node assay (LLNA) at concentrations ranging from 0.0625-1%. A concentration-dependent increase in lymphocyte proliferation was observed with a calculated EC3 value of 0.17%. Dermal exposure to DDAC did not induce increased production of IgE as evaluated by phenotypic analysis of draining lymph node B-cells (IgE (+) B220(+)) and measurement of total serum IgE levels. Additional phenotypic analyses revealed significant and dose-responsive increases in the absolute number of B-cells, CD4 (+) T-cells, CD8 (+) T-cells and dendritic cells in the draining lymph nodes, along with significant increases in the percentage of B-cells (0.25% and 1% DDAC) at Day 10 following 4 days of dermal exposure. There was also a significant and dose-responsive increase in the number of activated CD44 (+) CD4 (+) and CD8 (+) T-cells and CD86 (+) B-cells and dendritic cells following exposure to all concentrations of DDAC. These results demonstrate the potential for development of irritation and hypersensitivity responses to DDAC following dermal exposure and raise concerns about the use of this chemical and other quaternary ammonium compounds that may elicit similar effects.

Toluene diisocyanate (TDI) is a leading cause of chemical-induced occupational asthma which impacts workers in a variety of industries worldwide. Recently, the robust regulatory potential of regulatory T cells (Tregs) has become apparent, including their functional role in the regulation of allergic disease; however, their function in TDI-induced sensitization has not been explored. To elucidate the kinetics, phenotype, and function of Tregs during TDI sensitization, BALB/c mice were dermally exposed (on each ear) to a single application of TDI (0.5-4% v/v) or acetone vehicle and endpoints were evaluated via RT-PCR and flow cytometry. The draining lymph node (dLN) Treg population expanded significantly 4, 7, and 9 days after single 4% TDI exposure. This population was identified using a variety of surface and intracellular markers and was found to be phenotypically heterogeneous based on increased expression of markers including CD103, CCR6, CTLA4, ICOS, and Neuropilin-1 during TDI sensitization. Tregs isolated from TDI-sensitized mice were significantly more suppressive compared with their control counterparts, further supporting a functional role for Tregs during TDI sensitization. Last, Tregs were depleted prior to TDI sensitization and an intensified sensitization response was observed. Collectively, these data indicate that Tregs exhibit a functional role during TDI sensitization. Because the role of Tregs in TDI sensitization has not been previously elucidated, these data contribute to the understanding of the immunologic mechanisms of chemical induced allergic disease.

Triclosan is an antimicrobial chemical commonly used occupationally and by the general public. Using select immune function assays, the purpose of these studies was to evaluate the immunotoxicity of triclosan following dermal exposure using a murine model. Triclosan was not identified to be a sensitizer in the murine local lymph node assay (LLNA) when tested at concentrations ranging from 0.75-3.0%. Following a 28-day exposure, triclosan produced a significant increase in liver weight at concentrations of ≥ 1.5%. Exposure to the high dose (3.0%) also produced a significant increase in spleen weights and number of platelets. The absolute number of B-cells, T-cells, dendritic cells and NK cells were significantly increased in the skin draining lymph node, but not the spleen. An increase in the frequency of dendritic cells was also observed in the lymph node following exposure to 3.0% triclosan. The IgM antibody response to sheep red blood cells (SRBC) was significantly increased at 0.75% - but not at the higher concentrations - in the spleen and serum. These results demonstrate that dermal exposure to triclosan induces stimulation of the immune system in a murine model and raise concerns about potential human exposure.

Nitrogen (N) and phosphorus (P) limitations induce neutral lipid accumulation and membrane lipid remodeling in the domesticated oleaginous microalga Tisochrysis lutea. This study compared growth, photosynthetic activity, biochemical and transcriptional responses of T. lutea throughout batch cultures under N or P limitation compared with non-limiting nutrient condition (NP). The results show that, under N limitation, the breakdown and re-use of cellular N-containing compounds contributed to carbohydrates and further triacylglycerol (TAG) accumulation, where the accumulation of docosahexaenoic acid (DHA) in neutral lipids might mainly be derived from the recycling of membrane polar lipids. Conversely, P limitation did not hinder the photosynthetic capacity; a higher efficiency of carbon fixation fueled the allocation of carbon fluxes to the reserves of carbohydrates and neutral lipids. These latter accumulated without massive degradation of essential cellular compounds. Betaine lipids constitute the major compounds of non-plastidial membranes in T. lutea. Given an extremely low constitutive phospholipid level, phospholipids might not be involved in the regulation of P storage. However, transfer of P from non-plastidial to chloroplast membranes might occur, keeping a stable lipid composition of thylakoid membranes and maintaining a relatively high photosynthetic capacity under P deprivation.

In this study, we investigated the responses of Phaeodactylum tricornutum cells acclimated to 300 µmol m −2 s −1 photon flux density to an increase (1000 µmol m −2 s −1 ) or decrease (30 µmol m −2 s −1 ) in photon flux densities. The light shift occurred abruptly after 5 days of growth and the acclimation to new conditions was followed during the next 6 days at the physiological and molecular levels. The molecular data reflect a rearrangement of carbon metabolism towards the production of phosphoenolpyruvic acid (PEP) and/or pyruvate. These intermediates were used differently by the cell as a function of the photon flux density: under low light, photosynthesis was depressed while respiration was increased. Under high light, lipids and proteins accumulated. Of great interest, under high light, the genes coding for the synthesis of aromatic amino acids and phenolic compounds were upregulated suggesting that the shikimate pathway was activated. This article is part of the themed issue ‘The peculiar carbon metabolism in diatoms’.

Toluene diisocyanate (TDI) is a potent low molecular weight chemical sensitizer and a leading cause of chemical-induced occupational asthma. The regulatory potential of microRNAs (miRNAs) has been recognized in a variety of disease states, including allergic disease; however, the roles of miRNAs in chemical sensitization are largely unknown. In a previous work, increased expression of multiple miRNAs during TDI sensitization was observed and several putative mRNA targets identified for these miRNAs were directly related to regulatory T-cell (Treg) differentiation and function including Foxp3 and Runx3. In this work, we show that miR-210 expression is increased in the mouse draining lymph node (dLN) and Treg subsets following dermal TDI sensitization. Alterations in dLN mRNA and protein expression of Treg related genes/putative miR-210 targets (foxp3, runx3, ctla4, and cd25) were observed at multiple time points following TDI exposure and in ex vivo systems. A Treg suppression assay, including a miR-210 mimic, was utilized to investigate the suppressive ability of Tregs. Cells derived from TDI sensitized mice treated with miR-210 mimic had less expression of miR-210 compared to the acetone control suggesting other factors, such as additional miRNAs, might be involved in the regulation of the functional capabilities of these cells. These novel findings indicate that miR-210 may have an inhibitory role in Treg function during TDI sensitization. Because the functional roles of miRNAs have not been previously elucidated in a model of chemical sensitization, these data contribute to the understanding of the potential immunologic mechanisms of chemical induced allergic disease.

Concern has been raised over the association of diacetyl with lung disease clinically resembling bronchiolitis obliterans in food manufacturing workers. This has resulted in the need for identification of alternative chemicals to be used in the manufacturing process. Structurally similar chemicals, 2,3-pentanedione, 2,3-hexanedione, 3,4-hexanedione and 2,3-heptanedione, used as constituents of synthetic flavoring agents have been suggested as potential alternatives for diacetyl, however, immunotoxicity data on these chemicals are limited. The present study evaluated the dermal irritation and sensitization potential of diacetyl alternatives using a murine model. None of the chemicals were identified as dermal irritants when tested at concentrations up to 50%. Similar to diacetyl (EC3 = 17.9%), concentration-dependent increases in lymphocyte proliferation were observed following exposure to all four chemicals, with calculated EC3 values of 15.4% (2,3-pentanedione), 18.2% (2,3-hexanedione), 15.5% (3,4-hexanedione) and 14.1% (2,3-heptanedione). No biologically significant elevations in local or total serum IgE were identified after exposure to 25–50% concentrations of these chemicals. These results demonstrate the potential for development of hypersensitivity responses to these proposed alternative butter flavorings and raise concern about the use of structurally similar replacement chemicals. Additionally, a contaminant with strong sensitization potential was found in varying concentrations in diacetyl obtained from different producers.

International audience; In aquaculture, particularly in bivalve hatcheries, the biochemical composition of algal diets has a strong influence on larval and post-larval development. Biochemical composition is known to be related to culture conditions, among which light represents a major source of variation. The effects of blue light on biochemical composition and photosynthetic rate of Isochrysis sp. (T-iso) CCAP 927/14 were assessed in chemostat at a single irradiance (300 μmol photons m−2 s−1) and compared with white light. Two different dilution (renewal) rates were also tested: 0.7 and 0.2 d−1. Relative carbohydrate content was lower under blue light than under white light at both dilution rates, whereas chlorophyll a and photosynthesis activity were higher. In contrast, carbon quota was lower and protein content higher under blue light than under white light, but only at 0.7 d−1. Despite these metabolic differences, cell productivity was not significantly affected by the spectrum. However, the nitrogen to carbon ratio and photosynthetic activity were higher at 0.7 d−1 than at 0.2 d−1, while carbon quota and carbohydrate content were lower. Our results show that blue light may influence microalgal metabolism without reducing productivity for a given growth rate, a result that should be of great interest for microalgal production in aquaculture.

During the last decade, there has been a remarkable and unexplained increase in the prevalence of asthma. These studies were conducted to investigate the role of dermal exposure to triclosan, an endocrine-disrupting compound, on the hypersensitivity response to ovalbumin (OVA) in a murine model of asthma. Triclosan has had widespread use in the general population as an antibacterial and antifungal agent and is commonly found in consumer products such as soaps, deodorants, toothpastes, shaving creams, mouthwashes, and cleaning supplies. For these studies, BALB/c mice were exposed dermally to concentrations of triclosan ranging from 0.75 to 3% (0.375–1.5 mg/mouse/day) for 28 consecutive days. Concordantly, mice were ip injected with OVA (0.9 μg) and aluminum hydroxide (0.5 mg) on days 1 and 10 and challenged with OVA (125 μg) by pharyngeal aspiration on days 19 and 27. Compared with the animals exposed to OVA alone, increased spleen weights, OVA-specific IgE, interleukin-13 cytokine levels, and numbers of lung eosinophils were demonstrated when mice were coexposed to OVA and triclosan. Statistically significant increases in OVA-specific and nonspecific airway hyperreactivity were observed for all triclosan coexposed groups compared with the vehicle and OVA controls. In these studies, exposure to triclosan alone was not demonstrated to be allergenic; however, coexposure with a known allergen resulted in enhancement of the hypersensitivity response to that allergen, suggesting that triclosan exposure may augment the allergic responses to other environmental allergens.

Several bacterial genera express proteins that contain collagen-like regions, which are associated with variable (V) non-collagenous regions. The streptococcal collagen-like proteins, Scl1 and Scl2, of group A Streptococcus (GAS) are members of this 'prokaryotic collagen' family, and they too contain an amino-terminal non-collagenous V region of unknown function. Here, we use recombinant rScl constructs, derived from several Scl1 and Scl2 variants, and affinity chromatography to identify Scl ligands present in human plasma. First, we show that Scl1, but not Scl2, proteins from different GAS serotypes bind the same ligand identified as apolipoprotein B (ApoB100), which is a major component of the low-density lipoprotein (LDL). Scl1 binding to purified ApoB100 and LDL is specific and concentration-dependent. Furthermore, the non-collagenous V region of the Scl1 protein is responsible for LDL/ApoB100 binding because only those rScls, constructed by domain swapping, which contain the V region from Scl1 proteins, were able to bind to ApoB100 and LDL ligands, and this binding was inhibited by antibodies directed against the Scl1-V region. Electron microscopy images of Scl1-LDL complexes showed that the globular V domain of Scl1 interacted with spherical particles of LDL. Importantly, live M28-type GAS cells absorbed plasma LDL on the cell surface and this binding depended on the surface expression of the Scl1.28, but not Scl2.28, protein. Phylogenetic analysis showed that the non-collagenous globular domains of Scl1 and Scl2 evolved independently to form separate lineages, which differ in amino acid sequence, and these differences may account for the variations in binding patterns of Scl1 and Scl2 proteins. Present studies provide insight into the structure-function relationship of the Scl proteins and also underline the importance of lipoprotein binding by GAS.