Canine Atopic Dermatitis: Prevalence, Impact, and Management Strategies.

Atopic dermatitis (AD) is a common inflammatory and pruritic allergic skin disease in humans and dogs worldwide. The pathogenesis of AD is multifactorial, immunologically complex, and may involve genetic factors, epidermal barrier dysfunction, microbiome changes, immune dysregulation, and allergic sensitization. Across species, prevalence of AD is on the rise. At present, there is no cure for canine AD (CAD). The treatment for CAD is multifaceted and aimed at controlling the pruritus, associated inflammation, and infections, repairing the skin barrier function, and dietary management. This review presents data on prevalence, impact, and complex immunological interactions in AD with a focus on subsequent management of the disease in the canine population. A multimodal approach for management of CAD to address varying clinical signs and responses to therapies is discussed.

Immunoglobulin-like receptors in chickens: identification, functional characterization, and renaming to cluster homolog of immunoglobulin-like receptors.

The cluster homolog of immunoglobulin-like receptors (CHIRs), previously known as the "chicken homolog of immunogloublin-like receptors," represents is a large group of transmembrane glycoproteins that direct the immune response. However, the full repertoire of putatively activating, inhibitory, or dual function CHIRA, CHIRB, and CHIRAB on chickens' immune responses is poorly understood. Herein, the study objective was to determine the genes encoding CHIR proteins and predict their function by searching canonical protein structure. A bioinformatics pipeline based on previous work was employed to search for the CHIRs from the newly updated broiler and layer genomes. The categorization into CHIRA, CHIRB, and CHIRAB types was assigned through motif searches, multiple sequence alignment, and phylogeny. In total, 150 protein-encoding genes on Chromosome 31 were identified as CHIRs. Gene members of each functional group (CHIRA, CHIRB, CHIRAB) were classified in accordance with previously recognized proteins. The genes were renamed to "cluster homolog of immunoglobulin-like receptors" (CHIRs) to allow for the naming of orthologous genes in other avian species. Additionally, expression analysis of the classified CHIRs across various reinforces their importance as immune regulators and activation in inflammatory tissues. Furthermore, over 1,000 diverse and rare CHIRs variants associated with differential Marek's disease response (P < 0.05) emphasize the impact of CHIRs on shaping avian immune responses in diverse contexts. The practical applications of these findings encompass advancing immunology, improving poultry health management, optimizing breeding programs for disease resistance, and enhancing overall animal health through a deeper understanding of the roles and functions of CHIRA, CHIRB, and CHIRAB types in avian immune responses.

Unique Cell Subpopulations and Disease Progression Markers in Canines with Atopic Dermatitis.

Atopic dermatitis (AD) is a common pruritic inflammatory skin disease with unclear molecular and cellular contributions behind the complex etiology. To unravel these differences between healthy control and AD skin we employed single-cell transcriptomics, utilizing the canine AD model for its resemblance to human clinical and molecular phenotypes. In this study, we show that there are overall increases in keratinocytes and T cells and decreases in fibroblast populations in AD dogs. Within immune cell types, we identified an enriched γδ T cell population in AD, which may contribute to cutaneous inflammation. A prominent IL26-positive fibroblast subpopulation in AD was detected, which may activate neighboring cells in the dermal-epidermal niche. Lastly, by comparing dogs with different disease severities, we found genes that follow disease progression and may serve as potential biomarkers. In this study, we characterized key AD cell types and cellular processes that can be further leveraged in diagnosis and treatment.

Transcriptomes of an Array of Chicken Ovary, Intestinal, and Immune Cells and Tissues.

While the chicken (Gallus gallus) is the most consumed agricultural animal worldwide, the chicken transcriptome remains understudied. We have characterized the transcriptome of 10 cell and tissue types from the chicken using RNA-seq, spanning intestinal tissues (ileum, jejunum, proximal cecum), immune cells (B cells, bursa, macrophages, monocytes, spleen T cells, thymus), and reproductive tissue (ovary). We detected 17,872 genes and 24,812 transcripts across all cell and tissue types, representing 73% and 63% of the current gene annotation, respectively. Further quantification of RNA transcript biotypes revealed protein-coding and lncRNAs specific to an individual cell/tissue type. Each cell/tissue type also has an average of around 1.2 isoforms per gene, however, they all have at least one gene with at least 11 isoforms. Differential expression analysis revealed a large number of differentially expressed genes between tissues of the same category (immune and intestinal). Many of these differentially expressed genes in immune cells were involved in cellular processes relating to differentiation and cell metabolism as well as basic functions of immune cells such as cell adhesion and signal transduction. The differential expressed genes of the different segments of the chicken intestine (jejunum, ileum, proximal cecum) correlated to the metabolic processes in nutrient digestion and absorption. These data should provide a valuable resource in understanding the chicken genome.

CRFK and Primary Macrophages Transcriptomes in Response to Feline Coronavirus Infection Differ Significantly.

Coronaviruses are highly infectious and common in many species, including in humans, and agricultural and domestic animals. Host responses play an important role in viral entry, replication, assembly, and pathogenesis, although much is still to be understood, particularly host-virus interactions. Feline coronavirus is highly contagious, and ubiquitous in virtually all cat populations. Host-pathogen interactions have not been studied extensively due to the complex pathogenesis and development of clinical disease. Few studies have investigated cellular host responses to feline coronavirus infection, particularly at early time points. Transcriptome studies based on next-generation sequencing have the potential to elucidate the early responses of cells after viral infection and, consequently, give further insight into the pathogenesis of viruses. The current study aims to characterize and compare the viral- and immune-related differentially expressed genes in response to the coronavirus FIPV across different time points in a cell line which is permissive for productive replication versus primary cells implicated in pathogenesis. When comparing host responses in Crandell-Rees Feline Kidney (CRFK) cells to primary macrophages, many differences were observed with regards to expressed genes and their enrichments for both KEGG pathways and GO terms. CRFK cells which are permissive for productive replication of feline infectious peritonitis virus, showed induction of a large network of immunological and virally induced pathways. In contrast, Macrophages did not show similar host responses, with stronger pathway enrichment in downregulated transcripts. This study provides insights to better understand gene transcription in immune cells compared to epithelial cells discerning pathways relevant to pathogenesis in the early stages of infection.

Broiler chickens and early life programming: Microbiome transplant-induced cecal community dynamics and phenotypic effects.

The concept of successional trajectories describes how small differences in initial community composition can magnify through time and lead to significant differences in mature communities. For many animals, the types and sources of early-life exposures to microbes have been shown to have significant and long-lasting effects on the community structure and/or function of the microbiome. In modern commercial poultry production, chicks are reared as a single age cohort and do not directly encounter adult birds. This scenario is likely to initiate a trajectory of microbial community development that is significantly different than non-industrial settings where chicks are exposed to a much broader range of environmental and fecal inocula; however, the comparative effects of these two scenarios on microbiome development and function remain largely unknown. In this work, we performed serial transfers of cecal material through multiple generations of birds to first determine if serial transfers exploiting the ceca in vivo, rather than the external environment or artificial incubations, can produce a stable microbial community. Subsequently, we compared microbiome development between chicks receiving this passaged, i.e. host-selected, cecal material orally, versus an environmental inoculum, to test the hypothesis that the first exposure of newly hatched chicks to microbes determines early GI microbiome structure and may have longer-lasting effects on bird health and development. Cecal microbiome dynamics and bird weights were tracked for a two-week period, with half of the birds in each treatment group exposed to a pathogen challenge at 7 days of age. We report that: i) a relatively stable community was derived after a single passage of transplanted cecal material, ii) this cecal inoculum significantly but ephemerally altered community structure relative to the environmental inoculum and PBS controls, and iii) either microbiome transplant administered at day-of-hatch appeared to have some protective effects against pathogen challenge relative to uninoculated controls. Differentially abundant taxa identified across treatment types may inform future studies aimed at identifying strains associated with beneficial phenotypes.

Host Gene Expression of Macrophages in Response to Feline Coronavirus Infection.

Feline coronavirus is a highly contagious virus potentially resulting in feline infectious peritonitis (FIP), while the pathogenesis of FIP remains not well understood, particularly in the events leading to the disease. A predominant theory is that the pathogenic FIPV arises from a mutation, so that it could replicate not only in enterocytes of the intestines but also in monocytes, subsequently systemically transporting the virus. The immune status and genetics of affected cats certainly play an important role in the pathogenesis. Considering the importance of genetics and host immune responses in viral infections, the goal of this study was to elucidate host gene expression in macrophages using RNA sequencing. Macrophages from healthy male cats infected with FIPV 79-1146 ex vivo displayed a differential host gene expression. Despite the virus uptake, aligned viral reads did not increase from 2 to 17 h. The overlap of host gene expression among macrophages from different cats was limited, even though viral transcripts were detected in the cells. Interestingly, some of the downregulated genes in all macrophages were involved in immune signaling, while some upregulated genes common for all cats were found to be inhibiting immune activation. Our results highlight individual host responses playing an important role, consistent with the fact that few cats develop feline infectious peritonitis despite a common presence of enteric FCoV.

Phosphodiesterase 4D, miR-203 and selected cytokines in the peripheral blood are associated with canine atopic dermatitis.

Canine Atopic Dermatitis (AD) is a common complex and multifactorial disease involving immune dysregulation, genetic predisposition, skin barrier defects, environmental factors and allergic sensitization. To date, diagnosis of canine AD relies on a combination of patient history, clinical examination, allergy testing and response to diet trials/therapies with no reliable biomarkers available to distinguish AD from other diseases with similar clinical presentations. A handful of studies to identify potential biomarkers in the peripheral blood of AD dogs and healthy controls have been performed with some showing inconsistent and contradictory results. In this study, we, for the first time, report statistically significant increases in expression of phosphodiesterase 4D (PDE4D) gene in peripheral blood mononuclear cells (PBMCs) and miR-203 in plasma from AD dogs compared to healthy controls. In addition, we report a statistically non-significant change of the CD4+/CD8+ ratio, a dramatic decrease of three gene markers (PIAS1, RORA and SH2B1) as well as a panel of differential expression of cytokines in AD dogs in comparison to the healthy controls. Our study provides important insight into the complexities of canine AD, and further studies to verify the specificity of these findings for canine AD at a larger-scale are warranted.

Cross-sectional quantitative RT-PCR study of feline coronavirus viremia and replication in peripheral blood of healthy shelter cats in Southern California.

Objectives The objectives of this study were to determine the prevalence of feline coronavirus (FCoV) viremia, and its replication in peripheral blood using quantitative RT-PCR (qRT-PCR) methodology in a population of 205 healthy shelter cats in Southern California, as well as to assess any possible connection to longitudinal development of feline infectious peritonitis (FIP). Methods The study was performed on buffy-coat samples from EDTA-anticoagulated whole blood samples of 205 healthy shelter cats. From 50 of these cats, fecal samples were also examined. FCoV genomic and subgenomic RNA in the buffy coats was amplified by a total FCoV RNA qRT-PCR. Evidence for FCoV replication in peripheral blood and feces was obtained by M gene mRNA qRT-PCR. Results Nine of 205 cats (4.4%) were viremic by the total FCoV RNA qRT-PCR, and one of these cats had evidence of peripheral FCoV blood replication by an FCoV mRNA qRT-PCR. The single cat with peripheral blood replication had a unique partial M gene sequence distinct from positive controls and previously published FCoV sequences. Neither seven of the nine viremic cats with follow-up nor the single cat with replicating FCoV with positive qRT-PCR results developed signs compatible with FIP within 6 months of sample collection. Conclusions and relevance FCoV viremia and peripheral blood replication in healthy shelter cats have a low prevalence and do not correlate with later development of FIP in this study population, but larger case-control studies evaluating the prognostic accuracy of the qRT-PCR assays are needed.

RNA sequencing demonstrates large-scale temporal dysregulation of gene expression in stimulated macrophages derived from MHC-defined chicken haplotypes.

Discovering genetic biomarkers associated with disease resistance and enhanced immunity is critical to developing advanced strategies for controlling viral and bacterial infections in different species. Macrophages, important cells of innate immunity, are directly involved in cellular interactions with pathogens, the release of cytokines activating other immune cells and antigen presentation to cells of the adaptive immune response. IFNγ is a potent activator of macrophages and increased production has been associated with disease resistance in several species. This study characterizes the molecular basis for dramatically different nitric oxide production and immune function between the B2 and the B19 haplotype chicken macrophages.A large-scale RNA sequencing approach was employed to sequence the RNA of purified macrophages from each haplotype group (B2 vs. B19) during differentiation and after stimulation. Our results demonstrate that a large number of genes exhibit divergent expression between B2 and B19 haplotype cells both prior and after stimulation. These differences in gene expression appear to be regulated by complex epigenetic mechanisms that need further investigation.

Bioinformatics Analysis of Chicken miRNAs Associated with Monocyte to Macrophage Differentiation and Subsequent IFNγ Stimulated Activation.

BACKGROUND: The goal of this project was to characterize the molecular and cellular roles of various gene targets regulated by miRNAs identified in differentiating and stimulating avian macrophages. Once a monocyte arrives to a site of infection, local signals induce a redistribution of resources into a macrophage phenotype. This may involve upregulating pathogen pattern recognizing receptors and increasing the efficiency of lysosomal biogenesis, while simultaneously recycling components involved in circulatory migration and leukocyte extravasation. a monocyte tooled with chemokine surface receptors and an internal cytoskeletal structure geared towards mobility may efficiently sense, react, and migrate toward a site of infection. METHODS: Peripheral blood derived monocytes were purified and cultured from young chickens. RNA sequencing was performed on both peripheral blood monocytes during differentiation into macrophages and on mature macrophages following stimulation with interferon gamma. A set of microRNAs were identified and investigated using bioinformatics methods to ascertain their potential role in avian macrophage biology. RESULTS: Among a number of miRNAs that are found to be expressed in avian macrophages, we focused on eight specific miRNAs (miR-1618, miR-1586, miR-1633, miR-1627, miR-1646, miR-1649, miR-1610, miR-1647) associated with macrophage differentiation and activation. Expression profiles of microRNAs were characterized during differentiation and activation. Candidate miRNA targets were implicated in processes including Wnt signaling, ubiquitination, PPAR mediated macrophage function, vesicle mediated cytokine trafficking, and WD40 domain protein functions. CONCLUSION: A global theme for macrophage function that may be modulated by microRNAs is the comprehensive redistribution of the cell's protein repertoire. This redistribution involves two processes: 1) the degradation and recycling of unneeded cytoplasmic and membrane components and 2) the mobilization of newly synthesized cellular components via vesicular trafficking. Generally, it appears that macrophages need to closely regulate gene expression for differentiation to be able to activate successfully in response to a pathogen. This is a process in which miRNAs participate by affecting several pathways critical for both, differentiation and activation.

Macrophages from disease resistant B2 haplotype chickens activate T lymphocytes more effectively than macrophages from disease susceptible B19 birds.

Resistance to respiratory pathogens, including coronavirus-induced infection and clinical illness in chickens has been correlated with the B (MHC) complex and differential ex vivo macrophage responses. In the current study, in vitro T lymphocyte activation measured by IFNγ release was significantly higher in B2 versus B19 haplotypes. AIV infection of macrophages was required to activate T lymphocytes and prior in vivo exposure of chickens to NP AIV plasmid enhanced responses to infected macrophages. This study suggests that the demonstrated T lymphocyte activation is in part due to antigen presentation by the macrophages as well as cytokine release by the infected macrophages, with B2 haplotypes showing stronger activation. These responses were present both in CD4 and CD8 T lymphocytes. In contrast, T lymphocytes stimulated by ConA showed greater IFNγ release of B19 haplotype cells, further indicating the greater responses in B2 haplotypes to infection is due to macrophages, but not T cells. In summary, resistance of B2 haplotype chickens appears to be directly linked to a more vigorous innate immune response and the role macrophages play in activating adaptive immunity.

Dramatic differences in the response of macrophages from B2 and B19 MHC-defined haplotypes to interferon gamma and polyinosinic:polycytidylic acid stimulation.

The chicken MHC has been associated with disease resistance, though the mechanisms are not understood. The functions of macrophages, critical to both innate and acquired immunity, were compared between the more infectious bronchitis virus-resistant B2 and the more infectious bronchitis virus-susceptible B19 lines. In vivo peripheral blood concentrations of monocytes were similar in B2 or B19 homozygous haplotypes. Peripheral blood-derived macrophages were stimulated with poly I:C, simulating an RNA virus, or IFNγ, a cytokine at the interface of innate and adaptive immunity. Not only did B2-derived peripheral monocytes differentiate into macrophages more readily than the B19 monocytes, but as determined by NO production, macrophages from B2 and B2 on B19 genetic background chicks were also significantly more responsive to either stimulant. In conclusion, the correlation with resistance to illness following viral infection may be directly linked to a more vigorous innate immune response.

A DNA vaccine expressing ENV and GAG offers partial protection against reticuloendotheliosis virus in the prairie chicken (Tympanicus cupido).

Recurring infection of reticuloendotheliosis virus (REV), an avian oncogenic gammaretrovirus, has been a major obstacle in attempts to breed and release the endangered Attwater's prairie chicken (Tympanicus cupido attwateri). The aim of this study was to develop a DNA vaccine that protects the birds against REV infection. A plasmid was constructed expressing fusion proteins of REV envelope (env) and VP22 of Gallid herpesvirus 2 or REV gag and VP22. Birds vaccinated with these recombinant plasmids developed neutralizing antibodies; showed delayed replication of virus; and had significantly less infection of lymphocytes, specifically CD4+ lymphocytes. Although the vaccine did not prevent infection, it offered partial protection. Birds in field conditions and breeding facilities could potentially benefit from increased immunity when vaccinated.

Feline coronavirus in multicat environments.

Feline infectious peritonitis (FIP), a fatal disease in cats worldwide, is caused by FCoV infection, which commonly occurs in multicat environments. The enteric FCoV, referred to as feline enteric virus (FECV), is considered a mostly benign biotype infecting the gut, whereas the FIP virus biotype is considered the highly pathogenic etiologic agent for FIP. Current laboratory tests are unable to distinguish between virus biotypes of FCoV. FECV is highly contagious and easily spreads in multicat environments; therefore, the challenges to animal shelters are tremendous. This review summarizes interdisciplinary current knowledge in regard to virology, immunology, pathology, diagnostics, and treatment options in the context of multicat environments.

An avian, oncogenic retrovirus replicates in vivo in more than 50% of CD4+ and CD8+ T lymphocytes from an endangered grouse.

Reoccurring infection of reticuloendotheliosis virus (REV), an avian oncogenic retrovirus, has been a major obstacle in attempts to breed and release an endangered grouse, the Attwater's prairie chicken (Tympanicus cupido attwateri). REV infection of these birds in breeding facilities was found to result in significant decreases in the CD4(+) and increases in the CD8(+) lymphocyte populations, although experimental infection of birds resulted in only increases in the CD8(+) lymphocytes. Because our indirect immunofluorescent assay readily detected infection of both CD4(+) and CD8(+) lymphocytes, a triple labeling flow cytometric procedure was developed to quantify the individual lymphocytes infected in vivo with REV. Lymphocytes were gated with a biotinylated pan-leukocyte marker bound to streptavidin R-PE-Cy5. Chicken CD4 or CD8 specific mouse MAb directly labeled with R-PE identified the phenotype and with permeabilizing of cells, infection was indirectly labeled with rabbit IgG specific for the REV gag polypeptide and FITC conjugated goat anti-rabbit antibody. More than 50% of the total lymphocytes and of the total CD4(+) or CD8(+) lymphocytes supported in vivo viral expression in all infected birds examined. Remarkably, this level of infection was detected in the absence of visible clinical signs of illness.

Heme oxygenase-1 mediates the anti-inflammatory effects of acute alcohol on IL-10 induction involving p38 MAPK activation in monocytes.

Inflammation and immunoregulatory cytokines play a central role in alcohol-induced liver damage. We previously reported that acute alcohol treatment augments IL-10 and inhibits TNF-alpha production in monocytes. Heme oxygenase-1 (HO-1), a stress-inducible protein, also regulates IL-10 and TNF-alpha production. Here, we report that augmentation of LPS-induced IL-10 production by alcohol was prevented by inhibition of HO-1 activity. Acute ethanol increased LPS-induced enzyme activity and RNA levels of HO-1, and DNA binding of AP-1, a transcription factor essential in HO-1 regulation. LPS-induced phospho-p38 MAPK levels were augmented by ethanol treatment and the p38 inhibitor, SB203580, prevented both the ethanol-induced increase in IL-10 production and the inhibitory effect of ethanol on TNF-alpha production. Ethanol-induced down-regulation of TNF-alpha production was abrogated by inhibition of HO-1. We found that LPS-induced activation of NF-kappaB, a regulator of TNF-alpha, was inhibited by both ethanol treatment and HO-1 activation, but the ethanol-induced inhibition of NF-kappaB was HO-1 independent. In LPS-challenged mice in vivo, both acute alcohol administration and HO-1 activation augmented IL-10 and inhibited TNF-alpha serum levels. These results show that 1) acute alcohol augments HO-1 activation in monocytes, 2) HO-1 activation plays a role in alcohol-induced augmentation of IL-10 production likely via increased p38 MAPK activation, and 3) HO-1 activation is involved in attenuation of TNF-alpha production by alcohol independent of inhibition of NF-kappaB activation by alcohol. Thus, HO-1 activation is a key mediator of the anti-inflammatory effects of acute alcohol on monocytes.

Increased lipopolysaccharide sensitivity in alcoholic fatty livers is independent of leptin deficiency and toll-like receptor 4 (TLR4) or TLR2 mRNA expression.

BACKGROUND: Both alcoholic (AFL) and nonalcoholic (NAFL) fatty livers show increased sensitivity to endotoxin-induced injury. Lipopolysaccharide (LPS) is recognized by toll-like receptor 4 (TLR4), whereas lipopeptide triggers TLR2 to induce common downstream activation of nuclear factor (NF)-kappaB and pro-inflammatory pathways that are activated in AFL and NAFL. METHODS: Serum alanine aminotransferase (ALT), tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 levels; hepatic NF-kappaB activity; and expression of TLR2, TLR4, inducible nitric oxide synthase (iNOS), and heme oxygenase (HO)-1 mRNAs were investigated in lean and leptin-deficient ob/ob mice after LPS challenge in combination with acute or chronic alcohol feeding. RESULTS: Increased LPS sensitivity in AFL and NAFL was characterized by elevated serum TNF-alpha and IL-6 induction. However, there was no difference in TLR2 and TLR4 mRNA levels between lean and ob/ob livers at baseline and after acute or chronic alcohol treatment. LPS increased TLR2, but not TLR4, mRNA levels in all groups. Chronic alcohol feeding and LPS increased serum ALT and TNF-alpha levels in lean but not in ob/ob mice compared with pair-fed controls. Hepatic NF-kappaB activation was increased in both ob/ob and lean mice after chronic alcohol feeding compared with pair-fed controls. Expression of iNOS, an inducer of oxidative stress, and HO-1, a cytoprotective protein, were higher in ob/ob compared with lean mice after chronic alcohol feeding. However, LPS-induced HO-1, but not iNOS, expression was attenuated in ob/ob compared with lean mice. CONCLUSION: These results imply that the increased sensitivity of AFL to LPS occurs without up-regulation of TLR2 or TLR4 genes and may be related to an imbalance of pro-inflammatory/oxidative and cytoprotective mechanisms.

Selective priming to Toll-like receptor 4 (TLR4), not TLR2, ligands by P. acnes involves up-regulation of MD-2 in mice.

Lipopolysaccharide (LPS) triggers cytokine production through Toll-like receptor 4 (TLR4), which shares downstream signaling pathways with TLR2. We investigated the roles of TLR2 and TLR4 in Propionibacterium acnes (P. acnes)-primed, LPS-induced liver damage using selective TLR ligands. Stock LPS induced interleukin 8 in both TLR4- and TLR2-expressing human embryonic kidney (HEK) 293 cells. Purified LPS (TLR4 ligand) activated HEK/TLR4 cells, while peptidoglycan and lipoteichoic acid (TLR2 ligands) activated HEK/TLR2 cells, respectively. In mice, P. acnes priming resulted in increased liver messenger RNA (mRNA) and serum levels of tumor necrosis factor alpha, interleukin 12, and interferon gamma (IFN-gamma) by both stock LPS and purified LPS challenges compared with nonprimed controls. In contrast, P. acnes failed to sensitize to TLR2 ligands (peptidoglycan + lipoteichoic acid). In the liver, P. acnes-priming was associated with up-regulation of TLR4 and MD-2 proteins, and subsequent LPS challenge further increased MD-2 and CD14 mRNA levels. The lack of sensitization to TLR2 ligands by P. acnes correlated with no increase in hepatic TLR1 or TLR6 mRNA. In vitro, P. acnes pretreatment desensitized RAW macrophages to a secondary stimulation via both TLR2 and TLR4. However, IFN-gamma could selectively prevent desensitization to TLR4 but not to TLR2 ligands. Furthermore, P. acnes induced production of IFN-gamma in vivo as well as in isolated splenocytes. In vitro, P. acnes-primed Hepa 1-6 hepatocytes but not RAW macrophages produced increased MD-2 and CD14 mRNA levels after an LPS challenge. In conclusion, P. acnes priming to selective TLR4-mediated liver injury is associated with up-regulation of TLR4 and MD-2 and is likely to involve IFN-gamma and prevent TLR4 desensitization by P. acnes.