The global burden of antimicrobial resistance - urinary tract infections.

Antimicrobial resistance (AMR) has emerged as a significant global healthcare problem. Antibiotic use has accelerated the physiologic process of AMR, particularly in Gram-negative pathogens. Urinary tract infections (UTIs) are predominantly of a Gram-negative nature. Uropathogens are evolutionarily highly adapted and selected strains with specific virulence factors, suggesting common mechanisms in how bacterial cells acquire virulence and AMR factors. The simultaneous increase in resistance and virulence is a complex and context-dependent phenomenon. Among known AMR mechanisms, the plenitude of different ß-lactamases is especially prominent. The risk for AMR in UTIs varies in different patient populations. A history of antibiotic consumption and the physiology of urinary flow are major factors that shape AMR prevalence. The urinary tract is in close crosstalk with the microbiome of other compartments, including the gut and genital tracts. In addition, pharmacokinetic properties and the physiochemical composition of urinary compartments can contribute to the emergence of AMR. Alternatives to antibiotic treatment and a broader approach to address bacterial infections are needed. Among the various alternatives studied, antimicrobial peptides and bacteriophage treatment appear to be highly promising approaches. We herein summarize the present knowledge of clinical and microbiological AMR in UTIs and discuss innovative approaches, namely new risk prediction tools and the use of non-antibiotic approaches to defend against uropathogenic microbes.

TcpC inhibits toll-like receptor signaling pathway by serving as an E3 ubiquitin ligase that promotes degradation of myeloid differentiation factor 88.

TcpC is a virulence factor of uropathogenic E. coli (UPEC). It was found that TIR domain of TcpC impedes TLR signaling by direct association with MyD88. It has been a long-standing question whether bacterial pathogens have evolved a mechanism to manipulate MyD88 degradation by ubiquitin-proteasome pathway. Here, we show that TcpC is a MyD88-targeted E3 ubiquitin ligase. Kidney macrophages from mice with pyelonephritis induced by TcpC-secreting UPEC showed significantly decreased MyD88 protein levels. Recombinant TcpC (rTcpC) dose-dependently inhibited protein but not mRNA levels of MyD88 in macrophages. Moreover, rTcpC significantly promoted MyD88 ubiquitination and accumulation in proteasomes in macrophages. Cys12 and Trp106 in TcpC are crucial amino acids in maintaining its E3 activity. Therefore, TcpC blocks TLR signaling pathway by degradation of MyD88 through ubiquitin-proteasome system. Our findings provide not only a novel biochemical mechanism underlying TcpC-medicated immune evasion, but also the first example that bacterial pathogens inhibit MyD88-mediated signaling pathway by virulence factors that function as E3 ubiquitin ligase.

The Promoter of the Immune-Modulating Gene TIR-Containing Protein C of the Uropathogenic Escherichia coli Strain CFT073 Reacts to the Pathogen's Environment.

The TIR-containing protein C (TcpC) of the uropathogenic Escherichia coli strain CFT073 modulates innate immunity by interfering with the Toll-like receptor and NALP3 inflammasome signaling cascade. During a urinary tract infection the pathogen encounters epithelial and innate immune cells and replicates by several orders of magnitude. We therefore analyzed whether these cell types and also the density of the pathogen would induce the recently defined promoter of the CFT073 tcpC gene to, in time, dampen innate immune responses. Using reporter constructs we found that the uroepithelial cell line T24/83 and the monocytic cell line THP-1 induced the tcpC promoter. Differentiation of monocytic THP-1 cells to macrophages increased their potential to switch on the promoter. Cell-associated CFT073 displayed the highest promoter activity. Since potassium represents the most abundant intracellular ion and is secreted to induce the NLRP3 inflammasome, we tested its ability to activate the tcpC promoter. Potassium induced the promoter with high efficiency. Sodium, which is enriched in the renal cortex generating an antibacterial hypersalinity, also induced the tcpC promoter. Finally, the bacterial density modulated the tcpC promoter activity. In the search for promoter-regulating proteins, we found that the DNA-binding protein H-NS dampens the promoter activity. Taken together, different cell types and salts, present in the kidney, are able to induce the tcpC promoter and might explain the mechanism of TcpC induction during a kidney infection with uropathogenic E. coli strains.

Co-Medication and Nutrition in Hepatocellular Carcinoma: Potentially Preventative Strategies in Hepatocellular Carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide, with about 841,000 new cases and 782,000 deaths annually. Given the clearly defined population at risk, mostly patients with liver cirrhosis, prevention of HCC could be highly effective. SUMMARY: Besides regular ultrasound surveillance, numerous publications have suggested protective effects of diverse drugs and nutrients. However, none of those preventive options has made it into clinical routine or practice guidelines. We therefore summarize the current status of preventive effects of drugs such as statins, acetylsalicylic acid (ASA), and metformin, but also dietary aspects and nutrients such as coffee, tea, and vitamin D supplementation. A successful implementation of some of these strategies may potentially lead to improved prevention of HCC development in patients with liver cirrhosis. Key Messages: Accumulating data suggest that particularly ASA, antidiabetic therapies, and statins may substantially decrease HCC incidence in patients at risk.

Presence of gustatory and olfactory dysfunction in the time of the COVID-19 pandemic.

BACKGROUND: The unexpected outbreak of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused more than 49 million cases and an estimated 2,000,000 associated deaths worldwide. In Germany, there are currently more than 2,000,000 laboratory-confirmed coronavirus disease 2019 (COVID-19) cases including 51,800 deaths. However, regional differences also became apparent and with the second wave of infections, the detailed characterization of COVID-19 patients is crucial to early diagnosis and disruption of chains of infections. METHODS: Handing out detailed questionnaires to all individuals tested for COVID-19, we evaluated the clinical characteristics of negative and positive tested individuals. Expression of symptoms, symptom duration and association between predictor variables (i.e. age, gender) and a binary outcome (olfactory and gustatory dysfunction) were assessed. RESULTS: Overall, the most common symptoms among individuals who tested positive for SARS-CoV-2 were fatigue, headache, and cough. Olfactory and gustatory dysfunction were also reported by many SARS-CoV-2 negative individuals, more than 20% of SARS-CoV-2 negative tested individuals in our study reported olfactory and gustatory dysfunction. Independent of SARS-CoV-2 status, more females displayed symptoms of gustatory (29.8%, p = 0.0041) and olfactory dysfunction (22.9%, p = 0.0174) compared to men. CONCLUSIONS: Bringing early SARS-CoV-2 tests to the populations at risk must be a main focus for the upcoming months. The reliability of olfactory and gustatory dysfunction in COVID-19 negative tested individuals requires deeper investigation in the future.

Emergence of carbapenem-resistant ST131 Escherichia coli carrying blaOXA-244 in Germany, 2019 to 2020.

The dissemination of carbapenem-producing Gram-negative bacteria is a major public health concern. We report the first detection of OXA-244-producing ST131 O16:H5 Escherichia coli in three patients from two tertiary hospitals in the south-west of Germany. OXA-244 is emerging in Europe. Because of detection challenges, OXA-244-producing E. coli may be under-reported. The emergence of carbapenem resistance in a globally circulating high-risk clone, such as ST131 E. coli is of clinical relevance and should be monitored closely.

Rapid susceptibility testing of multi-drug resistant Escherichia coli and Klebsiella by glucose metabolization monitoring.

Background The increasing number of multi-drug resistant (MDR) bacteria provides enormous challenges for choosing an appropriate antibiotic therapy in the early phase of sepsis. While bacterial identification has been greatly accelerated by the introduction of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), the antibiotic susceptibility testing (AST) remains time-consuming. Here, we present a rapid susceptibility testing method for testing Gram-negative bacteria, exemplarily validated for Escherichia coli and Klebsiella spp. Methods Gram-negative isolates (E. coli and Klebsiella spp.) were either taken as single colonies from agar plates (n=136) or directly extracted and identified from positive blood cultures (n=42) using MALDI-TOF MS. Bacteria were incubated in glucose-supplemented Luria broths (LBs) each containing one antibiotic (ceftazidime, piperacillin, imipenem and ciprofloxacin), routinely used to classify Gram-negative bacteria in Germany. To determine susceptibility the dynamics of glucose utilization in bacterial suspensions were quantitatively measured in the presence or absence of antibiotics designated liquid-AST (L-AST). Results The L-AST can be run on clinical-chemistry analyzers and integrated into laboratory routines. It yields critical resistance information within 90-150 min downstream of a MS-based identification. The results showed a high concordance with routine susceptibility testing, with less than 1% very major errors (VME) and 3.51% major errors (ME) for 178 assessed isolates. Analysis of turnaround time (TAT) for 42 clinical samples indicated that L-AST results could be obtained 34 h earlier than the routine results. Conclusions As exemplified for E. coli and Klebsiella spp., L-AST provides substantial acceleration of susceptibility testing following MALDI-TOF MS identification. The assay is a simple and low-cost method that can be integrated into clinical laboratory to allow for 24/7 AST. This approach could improve antibiotic therapy.

Molecular Basis of Acute Cystitis Reveals Susceptibility Genes and Immunotherapeutic Targets.

Tissue damage is usually regarded as a necessary price to pay for successful elimination of pathogens by the innate immune defense. Yet, it is possible to distinguish protective from destructive effects of innate immune activation and selectively attenuate molecular nodes that create pathology. Here, we identify acute cystitis as an Interleukin-1 beta (IL-1ß)-driven, hyper-inflammatory condition of the infected urinary bladder and IL-1 receptor blockade as a novel therapeutic strategy. Disease severity was controlled by the mechanism of IL-1ß processing and mice with intact inflammasome function developed a moderate, self-limiting form of cystitis. The most severe form of acute cystitis was detected in mice lacking the inflammasome constituents ASC or NLRP-3. IL-1ß processing was hyperactive in these mice, due to a new, non-canonical mechanism involving the matrix metalloproteinase 7- (MMP-7). ASC and NLRP-3 served as transcriptional repressors of MMP7 and as a result, Mmp7 was markedly overexpressed in the bladder epithelium of Asc-/- and Nlrp3-/- mice. The resulting IL-1ß hyper-activation loop included a large number of IL-1ß-dependent pro-inflammatory genes and the IL-1 receptor antagonist Anakinra inhibited their expression and rescued susceptible Asc-/- mice from bladder pathology. An MMP inhibitor had a similar therapeutic effect. Finally, elevated levels of IL-1ß and MMP-7 were detected in patients with acute cystitis, suggesting a potential role as biomarkers and immunotherapeutic targets. The results reproduce important aspects of human acute cystitis in the murine model and provide a comprehensive molecular framework for the pathogenesis and immunotherapy of acute cystitis, one of the most common infections in man. TRIAL REGISTRATION: The clinical studies were approved by the Human Ethics Committee at Lund University (approval numbers LU106-02, LU236-99 and Clinical Trial Registration RTP-A2003, International Committee of Medical Journal Editors, www.clinicaltrials.gov).

Multidrug-resistant organisms in allogeneic hematopoietic cell transplantation.

OBJECTIVE: Multidrug-resistant organisms (MDRO) are a challenge in allogeneic hematopoietic cell transplantation (HCT). However, in the literature there is no comprehensive analysis on MDRO in HCT. In this retrospective, single-center analysis, we appraised prevalence and clinical impact of MDRO in 98 consecutive allogeneic HCT patients. METHOD: Prior to the conditioning (baseline) and whenever clinically indicated patients underwent a full screening for MDRO (stool and urine cultures, swabs from several body regions). RESULTS: It turned out that 26 patients were colonized by 33 MDRO, either at baseline (n=16) or at any other time until day 100 post-transplantation. Of these 26 patients, eight developed an infection with MDRO, four of them by 4MRGN Pseudomonas aeruginosa, and three of them died MDRO-related. However, there was no significant difference between MDRO-colonized and non-colonized patients regarding overall survival (OS) and non-relapse-mortality (NRM). There was only a trend toward a higher NRM in patients already colonized by MDRO at baseline. This was due to the high NRM in multidrug-resistant P. aeruginosa-colonized patients. CONCLUSION: In summary, colonization with MDRO other than P. aeruginosa had no negative impact on NRM and OS. Patients colonized by multidrug-resistant P. aeruginosa had a dismal outcome. HCT of these patients should be considered with care. Screening for MDRO in the pretransplant work-up is suggested.

Direct comparison of galactomannan performance in concurrent serum and bronchoalveolar lavage samples in immunocompromised patients at risk for invasive pulmonary aspergillosis.

Invasive pulmonary aspergillosis (IPA) is a life-threatening infection mainly affecting immunocompromised patients. Early diagnosis is critical, but the diagnostic gold standard (histopathology and culture) is time consuming and cannot offer early confirmation of IPA. Fungal biomarkers like galactomannan (GM) are a promising extension to the diagnostic repertoire. However, it still remains under discussion if biomarker analysis from the site of the infection is superior to testing blood samples. We retrospectively evaluated the diagnostic performance of concurrent serum GM and bronchoalveolar lavage (BAL) GM (obtained within 24 h) of immunocompromised patients at high risk of IPA. Twenty-six proven/probable patients and eight patients with no IPA according to the EORTC/MSG 2008 criteria were included in this study. Sensitivity, specificity, positive predictive value, negative predictive value and diagnostic odds ratio were for BAL GM: 85%, 88%, 96%, 64% and 38.5, and for serum GM: 23%, 88%, 88%, 26% and 2.1 respectively. BAL GM proved to be significantly more sensitive for the detection of IPA compared to same-day serum GM in patients at high risk of IPA (P < 0.0001). Our data show that BAL GM testing is significantly superior to serum GM implying that diagnostic efforts should focus on specimens from the site of infection.

Molecular mechanisms for the subversion of MyD88 signaling by TcpC from virulent uropathogenic Escherichia coli.

The Toll/IL-1 receptor (TIR) domains are crucial signaling modules during innate immune responses involving the Toll-like receptors (TLRs) and IL-1 receptor (IL-1R). Myeloid differential factor 88 (MyD88) is a central TIR domain-containing adapter molecule responsible for nearly all TLR-mediated signaling and is targeted by a TIR domain-containing protein C (TcpC) from virulent uropathogenic Escherichia coli, a common human pathogen. The mechanism of such molecular antagonism has remained elusive. We present the crystal structure of the MyD88 TIR domain with distinct loop conformations that underscore the functional specialization of the adapter, receptor, and microbial TIR domains. Our structural analyses shed light on the genetic mutations at these loops as well as the Poc site. We demonstrate that TcpC directly associates with MyD88 and TLR4 through its predicted DD and BB loops to impair the TLR-induced cytokine induction. Furthermore, NMR titration experiments identify the unique CD, DE, and EE loops from MyD88 at the TcpC-interacting surface, suggesting that TcpC specifically engages these MyD88 structural elements for immune suppression. These findings thus provide a molecular basis for the subversion of TLR signaling by the uropathogenic E. coli virulence factor TcpC and furnish a framework for the design of novel therapeutic agents that modulate immune activation.

Crystal structures of the Toll/Interleukin-1 receptor (TIR) domains from the Brucella protein TcpB and host adaptor TIRAP reveal mechanisms of molecular mimicry.

The Toll/IL-1 receptor (TIR) domains are crucial innate immune signaling modules. Microbial TIR domain-containing proteins inhibit Toll-like receptor (TLR) signaling through molecular mimicry. The TIR domain-containing protein TcpB from Brucella inhibits TLR signaling through interaction with host adaptor proteins TIRAP/Mal and MyD88. To characterize the microbial mimicry of host proteins, we have determined the X-ray crystal structures of the TIR domains from the Brucella protein TcpB and the host adaptor protein TIRAP. We have further characterized homotypic interactions of TcpB using hydrogen/deuterium exchange mass spectrometry and heterotypic TcpB and TIRAP interaction by co-immunoprecipitation and NF-κB reporter assays. The crystal structure of the TcpB TIR domain reveals the microtubule-binding site encompassing the BB loop as well as a symmetrical dimer mediated by the DD and EE loops. This dimerization interface is validated by peptide mapping through hydrogen/deuterium exchange mass spectrometry. The human TIRAP TIR domain crystal structure reveals a unique N-terminal TIR domain fold containing a disulfide bond formed by Cys(89) and Cys(134). A comparison between the TcpB and TIRAP crystal structures reveals substantial conformational differences in the region that encompasses the BB loop. These findings underscore the similarities and differences in the molecular features found in the microbial and host TIR domains, which suggests mechanisms of bacterial mimicry of host signaling adaptor proteins, such as TIRAP.

Guanine modification of inhibitory oligonucleotides potentiates their suppressive function.

Inhibitory TLR7 and/or TLR9 oligonucleotides (inhibitory oligonucleotide [INH-ODN]) are characterized by a phosphorothioate backbone and a CC(T)XXX3₋5GGG motif, respectively. INH-ODN 2088 is a prototypic member of this class of INH-ODN and acts as a TLR7 and TLR9 antagonist. It contains a G quadruple that leads to higher order structures by the formation of G tetrads. These structures are unfavorable for the prediction of their pharmacological and immunological behavior. We show in this study that modification of Gs within the G quadruple by 7-deaza-guanine or 7-deaza-2'-O-methyl-guanine avoids higher order structures and improves their inhibitory potential. Whereas TLR9-induced TNF-α secretion of bone marrow-derived macrophages and conventional dendritic cells was equally inhibited by INH-ODN 2088 and G-modified INH-ODNs such as INH-ODN 24888, TLR7-induced TNF-α release and TLR7- and TLR9-induced IL-12p40 release were significantly more impaired by G-modified INH-ODNs. Similarly, the IL-6 release of B cells from wild-type and autoimmune MRL/Mp-lpr/lpr mice was more efficiently impaired by G-modified INH-ODNs. Surprisingly, INH-ODN 2088 stimulated B cells to proliferate when used in higher doses. Finally, in vivo, in wild-type and autoimmune MRL/Mp-lpr/lpr mice, G-modified INH-ODN 24888 was significantly more efficient than unmodified INH-ODN 2088. In summary, G modification allows the development of INH-ODNs with superior inhibitory potency for inflammatory diseases with high medical need such as systemic lupus erythematosus.

Acute osteomyelitis of the humerus mimicking malignancy: Streptococcus pneumoniae as exceptional pathogen in an immunocompetent adult.

BACKGROUND: Chronic osteomyelitis due to direct bone trauma or vascular insufficiency is a frequent problem in orthopaedic surgery. In contrast, acute haematogenous osteomyelitis represents a rare entity that almost exclusively affects prepubescent children or immunodeficient adults. CASE PRESENTATION: In this article, we report the case of acute pneumococcal osteomyelitis of the humerus in an immunocompetent and otherwise healthy 44-year-old male patient presenting with minor inflammation signs and misleading clinical features. CONCLUSIONS: The diagnosis had to be confirmed by open biopsy which allowed the initiation of a targeted therapy. A case of pneumococcal osteomyelitis of a long bone, lacking predisposing factors or trauma, is unique in adults and has not been reported previously.

Bacterial Co- or Superinfection in Patients Treated in Intensive Care Unit with COVID-19- and Influenza-Associated Pneumonia.

Viral pneumonia is frequently complicated by bacterial co- or superinfection (c/s) with adverse effects on patients' outcomes. However, the incidence of c/s and its impact on the outcomes of patients might be dependent on the type of viral pneumonia. We performed a retrospective observational study in patients with confirmed COVID-19 pneumonia (CP) or influenza pneumonia (IP) from 01/2009 to 04/2022, investigating the incidence of c/s using a competing risk model and its impact on mortality in these patients in a tertiary referral center using multivariate logistic regressions. Co-infection was defined as pulmonary pathogenic bacteria confirmed in tracheal aspirate or bronchoalveolar lavage within 48 h after hospitalization. Superinfection was defined as pulmonary pathogenic bacteria detected in tracheal aspirate or bronchoalveolar lavage 48 h after hospitalization. We examined 114 patients with CP and 76 patients with IP. Pulmonary bacterial co-infection was detected in 15 (13.2%), and superinfection was detected in 50 (43.9%) of CP patients. A total of 5 (6.6%) co-infections (p = 0.2269) and 28 (36.8%) superinfections (p = 0.3687) were detected in IP patients. The overall incidence of c/s did not differ between CP and IP patients, and c/s was not an independent predictor for mortality in a study cohort with a high disease severity. We found a significantly higher probability of superinfection for patients with CP compared to patients with IP (p = 0.0017).

Lightweight Visual Transformers Outperform Convolutional Neural Networks for Gram-Stained Image Classification: An Empirical Study.

We aimed to automate Gram-stain analysis to speed up the detection of bacterial strains in patients suffering from infections. We performed comparative analyses of visual transformers (VT) using various configurations including model size (small vs. large), training epochs (1 vs. 100), and quantization schemes (tensor- or channel-wise) using float32 or int8 on publicly available (DIBaS, n = 660) and locally compiled (n = 8500) datasets. Six VT models (BEiT, DeiT, MobileViT, PoolFormer, Swin and ViT) were evaluated and compared to two convolutional neural networks (CNN), ResNet and ConvNeXT. The overall overview of performances including accuracy, inference time and model size was also visualized. Frames per second (FPS) of small models consistently surpassed their large counterparts by a factor of 1-2×. DeiT small was the fastest VT in int8 configuration (6.0 FPS). In conclusion, VTs consistently outperformed CNNs for Gram-stain classification in most settings even on smaller datasets.

Inhibition of TIR domain signaling by TcpC: MyD88-dependent and independent effects on Escherichia coli virulence.

Toll-like receptor signaling requires functional Toll/interleukin-1 (IL-1) receptor (TIR) domains to activate innate immunity. By producing TIR homologous proteins, microbes inhibit host response induction and improve their own survival. The TIR homologous protein TcpC was recently identified as a virulence factor in uropathogenic Escherichia coli (E. coli), suppressing innate immunity by binding to MyD88. This study examined how the host MyD88 genotype modifies the in vivo effects of TcpC and whether additional, TIR-domain containing proteins might be targeted by TcpC. In wild type mice (wt), TcpC enhanced bacterial virulence, increased acute mortality, bacterial persistence and tissue damage after infection with E. coli CFT073 (TcpC+), compared to a ΔTcpC deletion mutant. These effects were attenuated in Myd88(-/-) and Tlr4(-/-) mice. Transcriptomic analysis confirmed that TcpC inhibits MYD88 dependent gene expression in CFT073 infected human uroepithelial cells but in addition the inhibitory effect included targets in the TRIF and IL-6/IL-1 signaling pathways, where MYD88 dependent and independent signaling may converge. The effects of TcpC on bacterial persistence were attenuated in Trif (-/-) or Il-1ß (-/-) mice and innate immune responses to ΔTcpC were increased, confirming that Trif and Il-1ß dependent targets might be involved in vivo, in addition to Myd88. Furthermore, soluble TcpC inhibited Myd88 and Trif dependent TLR signaling in murine macrophages. Our results suggest that TcpC may promote UTI-associated pathology broadly, through inhibition of TIR domain signaling and downstream pathways. Dysregulation of the host response by microbial TcpC thus appears to impair the protective effects of innate immunity, while promoting inflammation and tissue damage.

Rapid, adaptable and sensitive Cas13-based COVID-19 diagnostics using ADESSO.

During the ongoing COVID-19 pandemic, PCR testing and antigen tests have proven critical for helping to stem the spread of its causative agent, SARS-CoV-2. However, these methods suffer from either general applicability and/or sensitivity. Moreover, the emergence of variant strains creates the need for flexibility to correctly and efficiently diagnose the presence of substrains. To address these needs we developed the diagnostic test ADESSO (Accurate Detection of Evolving SARS-CoV-2 through SHERLOCK (Specific High Sensitivity Enzymatic Reporter UnLOCKing) Optimization) which employs Cas13 to diagnose patients in 1 h without sophisticated equipment. Using an extensive panel of clinical samples, we demonstrate that ADESSO correctly identifies infected individuals at a sensitivity and specificity comparable to RT-qPCR on extracted RNA and higher than antigen tests for unextracted samples. Altogether, ADESSO is a fast, sensitive and cheap method that can be applied in a point of care setting to diagnose COVID-19 and can be quickly adjusted to detect new variants.

Chlamydophila pneumoniae downregulates MHC-class II expression by two cell type-specific mechanisms.

Chlamydophila pneumoniae was shown to prevent IFN gamma-inducible upregulation of MHC-class II molecules by secreting chlamydial protease-like activity factor (CPAF) into the cytosol of those host cells which support the complete bacterial replication cycle. CPAF acts by degrading upstream stimulatory factor 1 (USF-1). However, in cells like bone marrow-derived macrophages (BMM), which restrict chlamydial replication, we show that CPAF expression is barely detectable and the expression of USF-1 is induced upon infection with C. pneumoniae. Nevertheless, the infection still reduced base line and prevented IFN gamma-inducible MHC-class II expression. Similar results were obtained with heat-inactivated C. pneumoniae. In contrast, reduction of MHC-class II molecules was not observed in MyD88-deficient BMM. Reduction of IFN gamma-inducible MHC-class II expression by C. pneumoniae in BMM was mediated in part by the MAP-kinase p38. Infection of murine embryonic fibroblasts (MEF) with C. pneumoniae, which allow chlamydial replication, induced the expression of CPAF and decreased USF-1 and MHC-class II expression. Treatment of these cells with heat-inactivated C. pneumoniae reduced USF-1 and MHC-class II expression to a much lower extent. In summary, C. pneumoniae downregulates MHC-class II expression by two cell type-specific mechanisms which are either CPAF-independent and MyD88-dependent like in BMM or CPAF-dependent like in MEFs.