Guardians of immunity: NK cell-mediated defense in COVID-19 and post-COVID scenarios

The COVID-19 pandemic has left a lasting impact on global health, challenging communities, healthcare systems, and researchers worldwide. As we navigate this unprecedented crisis, this paper embarks on a multifaceted exploration of the pivotal role played by natural killer (NK) cells in the context of COVID-19. A significant portion of this paper is devoted to dissecting the nuanced role that NK cells assume in the context of COVID-19. From the initial acute infection to post-recovery immunity, NK cells emerge as critical players. We scrutinize the activation and dysregulation of NK cells during SARS-CoV-2 infection, shedding light on their potential contribution to disease severity. Moreover, we explore the fascinating landscape of post-COVID immunity, where NK cells are known to interact with adaptive immune responses, providing a foundation for long-term protection. In light of their central role, we investigate therapeutic strategies targeting NK cells in COVID-19 management, presenting an overview of current research efforts and their promise in mitigating disease progression. Lastly, we draw attention to research gaps, emphasizing the need for further investigation into NK cell dynamics during COVID-19. These gaps represent opportunities for advancing our understanding of NK cell biology and, by extension, enhancing our strategies for combating this global health crisis. This comprehensive exploration not only highlights the intricate interplay between NK cells and the COVID-19 pandemic but also underscores the importance of these innate immune warriors in shaping both the acute response and long-term immunity, ultimately contributing to the broader discourse surrounding the pandemic's pathophysiology and therapeutic approaches.

Potential value of a rapid syndromic multiplex PCR for the diagnosis of native and prosthetic joint infections: a real-world evidence study

Introduction: The BIOFIRE Joint Infection (JI) Panel is a diagnostic tool that uses multiplex-PCR testing to detect microorganisms in synovial fluid specimens from patients suspected of having septic arthritis (SA) on native joints or prosthetic joint infections (PJIs). Methods: A study was conducted across 34 clinical sites in 19 European and Middle Eastern countries from March 2021 to June 2022 to assess the effectiveness of the BIOFIRE JI Panel. Results: A total of 1527 samples were collected from patients suspected of SA or PJI, with an overall agreement of 88.4 % and 85 % respectively between the JI Panel and synovial fluid cultures (SFCs). The JI Panel detected more positive samples and microorganisms than SFC, with a notable difference on Staphylococcus aureus, Streptococcus species, Enterococcus faecalis, Kingella kingae, Neisseria gonorrhoeae, and anaerobic bacteria. The study found that the BIOFIRE JI Panel has a high utility in the real-world clinical setting for suspected SA and PJI, providing diagnostic results in approximately 1 h. The user experience was positive, implying a potential benefit of rapidity of results' turnover in optimising patient management strategies. Conclusion: The study suggests that the BIOFIRE JI Panel could potentially optimise patient management and antimicrobial therapy, thus highlighting its importance in the clinical setting.

Cannabidiol improves memory and decreases IL-1β serum levels in rats with lipopolysaccharide-induced inflammation

AIM

Memory improving and anti-inflammatory properties of cannabidiol (CBD) were investigated in an experimental model of lipopolysaccharide (LPS)-induced inflammation.

Yersinia enterocolitica Bacteremia Associated with a Ruptured Abdominal Aortic Aneurysm: A Case Report with Literature Review

Yersinia enterocolitica is a foodborne pathogen, mainly associated with disorders involving the gastrointestinal tract, including diarrhea, ileitis, and mesenteric lymphadenitis. Extraintestinal presentation is uncommon in healthy individuals, but bacteremia is reported in immunocompromised hosts. We present a 74-year-old male with Y. enterocolitica serogroup O:3 bacteremia who complicated to rupture of an abdominal aortic aneurysm. With the current case report, we aimed to emphasize the association of Y. enterocolitica bacteremia with abdominal aortic aneurysm rupture. Better surveillance is needed, not only to reduce morbidity and mortality but also to update current epidemiological data on the incidence of such associations.

Cytokine profile in patients with acute bacterial meningitis

BACKGROUND

Bacterial meningitis is a life-threatening disease with high mortality and common long-term sequelae. The inflammatory response in the subarachnoid space, modulated by different cytokines, plays a major role in the pathogenesis of acute central nervous system infections. We aimed to examine correlations of interleukin (IL)-6, IL-8, IL-10, IL-12(p40), and tumor necrosis factor (TNF)-α levels with disease severity, complications, and outcome in patients with acute bacterial meningitis.

METHODS

The study involved 30 patients with bacterial meningitis/meningoencephalitis admitted to the University Hospital St. George, Plovdiv over a period of 4 years. Patients were selected based on clinical presentation and laboratory abnormalities, consistent with a neuroinfection. Enzyme-linked immunosorbent assay was used to measure the studied cytokines in both cerebrospinal fluid (CSF) and serum in parallel. For microbiological diagnosis multiplex, polymerase chain reaction, and CSF culture were used.

RESULTS

In patients with acute bacterial meningitis CSF levels of IL-6, IL-8, IL-10, and TNF-α are significantly increased than in serum. CSF TNF-α, CSF IL-8, and CSF IL-10 had a moderate negative correlation to CSF glucose. It was found that serum IL-8 is significantly elevated in patients who experienced neurological complications, have severe clinical course, and in deceased patients. CSF IL-10 is increased only in patients with severe acute bacterial meningitis.

CONCLUSION

Among patients with acute bacterial meningitis serum IL-8 could delineate these with increased risk of neurological complications, severe clinical course, and fatal outcome. Serum IL-8 and CSF IL-10 could be used as indicators of disease severity.

Fucoidan from Ericaria crinita Alleviates Inflammation in Rat Paw Edema, Downregulates Pro-Inflammatory Cytokine Levels, and Shows Antioxidant Activity

Fucoidans are sulfated polysaccharides detected mainly in the cell walls of brown seaweeds. Here, we examined the effects of single doses of fucoidan derived from Ericaria crinita (formerly Cystoseira crinita) on carrageenan-induced paw inflammation in rats. The serum levels of TNF-α, IL-1β, IL-6, and IL-10 of rats with LPS-induced systemic inflammation after 14 days of treatment were also evaluated. Subchronic treatment with fucoidan from E. crinita attenuated the inflammation during the late phase of the degraded carrageenan-induced paw edema (3rd to 5th hour after carrageenan injection) with peak activity at the 3rd hour after the application. Both doses of fucoidan from E. crinita (25 and 50 mg/kg bw) significantly decreased the levels of all tested pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6) in the serum of rats with a model of system inflammation but had no effect on the anti-inflammatory cytokine IL-10. The results showed that the repeated application of fucoidan has a more prominent effect on the levels of some pro-inflammatory cytokines in serum in comparison to a single dose of the sulfated polysaccharide. This reveals the potential of E. crinita fucoidan as an anti-inflammatory agent. Furthermore, E. crinita fucoidan exhibited in vitro antioxidant capacity, determined by 2,2-diphenyl-1-picryl-hydrazyl radical scavenging and ferric reducing antioxidant power assays as follows: IC50 = 412 µg/mL and 118.72 μM Trolox equivalent/g, respectively.

Streptococcus zooepidemicus Meningitis in an HIV-Positive Horse Breeder Patient: A Case Study and Literature Review

Streptococcus equi subsp. zooepidemicus is a rare etiologic agent of bacterial meningitis in humans. The disease is a zoonotic infection and is transmitted through close contact with domestic animals, mainly horses. Only 37 cases of Streptococcus zooepidemicus meningitis have been reported in the literature until July 2023. The aim of this study is to present a rare clinical case of S. zooepidemicus-related meningitis in a human immunodeficiency virus (HIV)-positive patient and analyze the literature. We present a 23-year-old horse breeder patient with advanced immunosuppression due to acquired immunodeficiency syndrome (AIDS) and S. zooepidemicus meningitis, admitted at the Clinic of Infectious Diseases, St. George University Hospital, Plovdiv. The course of meningitis was severe since the beginning, with significant cerebral edema, disturbances in consciousness, persistent fever, and the development of complications against the background of AIDS-related conditions. S. zooepidemicus was microbiologically detected from cerebrospinal fluid culture. After prolonged treatment and a long hospital stay, the patient's condition improved, and eventually he was discharged and recovered from the acute neuroinfection. Although extremely rare, S. zooepidemicus should be considered in patients with clinical and laboratory evidence of bacterial meningitis who have contact with animals, especially horses, other domestic animals, and their dairy products, as well as in immunocompromised patients. To the best of our knowledge, the current clinical case is the first report of S. zooepidemicus-related meningitis in a patient with HIV/AIDS.

Gordonia sputi as an Arising Causative Agent of Bacteremia in Immunocompromised Comorbid Dialysis Patients-A Case Report

Improvements in medical care have turned severe diseases into chronic conditions, but often their treatment and the use of medical devices are related to specific complications. Here, we present a clinical case of a long-term dialysis patient who was infected with a rare opportunistic infectious agent-Gordonia sputi. In recent years, the incidence of Gordonia spp. infections in immunocompromised patients with central venous catheters (CVC) has appeared to rise. The isolation and identification of Gordonia spp. are challenging and require modern techniques. In addition, the treatment is usually persistent and often results in CVC extraction, which is associated with further risk and costs for the patient. We also studied the alterations in the immune status of the patient caused by long-term renal replacement therapy and persistent hepatitis C virus infection. Antibiotic therapy and immunostimulation with Inosine pranobex lead to successful eradication of the infection without the need for CVC replacement.

Extraction, Structural Characterization, and In Vivo Anti-Inflammatory Effect of Alginate from Cystoseira crinita (Desf.) Borry Harvested in the Bulgarian Black Sea

The aim of this study was to identify the chemical composition and sequential structure of alginate isolated from C. crinita harvested in the Bulgarian Black Sea, as well as its effects in histamine-induced paw inflammation in rats. The serum levels of TNF-α, IL-1β, IL-6, and IL-10 in rats with systemic inflammation, and the levels of TNF-α in a model of acute peritonitis in rats were also investigated. The structural characterization of the polysaccharide was obtained by FTIR, SEC-MALS, and 1H NMR. The extracted alginate had an M/G ratio of 1.018, a molecular weight of 7.31 × 104 g/mol, and a polydispersity index of 1.38. C. crinita alginate in doses of 25 and 100 mg/kg showed well-defined anti-inflammatory activity in the model of paw edema. A significant decrease in serum levels of IL-1β was observed only in animals treated with C. crinita alginate in a dose of 25 mg/kg bw. The concentrations of TNF-α and IL-6 in serum were significantly reduced in rats treated with both doses of the polysaccharide, but no statistical significance was observed in the levels of the anti-inflammatory cytokine IL-10. A single dose of alginate did not significantly alter the levels of the pro-inflammatory cytokine TNF-α in the peritoneal fluid of rats with a model of peritonitis.

Improvement and Validation of a Multi-Locus Variable Number of Tandem Repeats Analysis (MLVA8+) for Klebsiella pneumoniae, Klebsiella variicola, and Klebsiella quasipneumoniae

The genotyping of the multidrug-resistant Klebsiella pneumoniae species complex is essential to identify outbreaks and to track their source and spread. The aim of this study was to improve and extend the typeability, availability, cost and time efficiency of an existing multi-locus VNTR analysis (MLVA). A modified scheme (MLVA8+) was adopted and validated for strain-level differentiation of the three Klebsiella species involved in human pathology. A diverse set of 465 K. pneumoniae clinical isolates from 22 hospitals and 3 outpatient laboratories in Bulgaria were studied, where 315 were carbapenem-resistant. The MLVA8+ typeability was significantly improved and the typing data were validated against 158 isolates which were previously typed by WGS. The MLVA8+ results were highly concordant with the classic 7-locus MLST and the novel K. variicola MLST, but had greater congruency coefficients (adjusted Wallace). A major advantage was the differentiation of the hybrid cluster ST258 into its corresponding clades. Furthermore, the applicability of MLVA8+ was demonstrated by conducting a retrospective investigation of the intra-hospital spread of blaKPC-, blaNDM- and blaOXA-48-like producers. The MLVA8+ has improved utility and extended typing scope to K. variicola and K. quasipneumoniae, while its cost and time-to-result were reduced.

Care of patients with inborn errors of immunity in thirty J Project countries between 2004 and 2021

Introduction

The J Project (JP) physician education and clinical research collaboration program was started in 2004 and includes by now 32 countries mostly in Eastern and Central Europe (ECE). Until the end of 2021, 344 inborn errors of immunity (IEI)-focused meetings were organized by the JP to raise awareness and facilitate the diagnosis and treatment of patients with IEI.

Results

In this study, meeting profiles and major diagnostic and treatment parameters were studied. JP center leaders reported patients' data from 30 countries representing a total population of 506 567 565. Two countries reported patients from JP centers (Konya, Turkey and Cairo University, Egypt). Diagnostic criteria were based on the 2020 update of classification by the IUIS Expert Committee on IEI. The number of JP meetings increased from 6 per year in 2004 and 2005 to 44 and 63 in 2020 and 2021, respectively. The cumulative number of meetings per country varied from 1 to 59 in various countries reflecting partly but not entirely the population of the respective countries. Altogether, 24,879 patients were reported giving an average prevalence of 4.9. Most of the patients had predominantly antibody deficiency (46,32%) followed by patients with combined immunodeficiencies (14.3%). The percentages of patients with bone marrow failure and phenocopies of IEI were less than 1 each. The number of patients was remarkably higher that those reported to the ESID Registry in 13 countries. Immunoglobulin (IgG) substitution was provided to 7,572 patients (5,693 intravenously) and 1,480 patients received hematopoietic stem cell therapy (HSCT). Searching for basic diagnostic parameters revealed the availability of immunochemistry and flow cytometry in 27 and 28 countries, respectively, and targeted gene sequencing and new generation sequencing was available in 21 and 18 countries. The number of IEI centers and experts in the field were 260 and 690, respectively. We found high correlation between the number of IEI centers and patients treated with intravenous IgG (IVIG) (correlation coefficient, cc, 0,916) and with those who were treated with HSCT (cc, 0,905). Similar correlation was found when the number of experts was compared with those treated with HSCT. However, the number of patients treated with subcutaneous Ig (SCIG) only slightly correlated with the number of experts (cc, 0,489) and no correlation was found between the number of centers and patients on SCIG (cc, 0,174).

Conclusions

1) this is the first study describing major diagnostic and treatment parameters of IEI care in countries of the JP; 2) the data suggest that the JP had tremendous impact on the development of IEI care in ECE; 3) our data help to define major future targets of JP activity in various countries; 4) we suggest that the number of IEI centers and IEI experts closely correlate to the most important treatment parameters; 5) we propose that specialist education among medical professionals plays pivotal role in increasing levels of diagnostics and adequate care of this vulnerable and still highly neglected patient population; 6) this study also provides the basis for further analysis of more specific aspects of IEI care including genetic diagnostics, disease specific prevalence, newborn screening and professional collaboration in JP countries.

Structural Characterization and In Vivo Anti-Inflammatory Activity of Fucoidan from Cystoseira crinita (Desf.) Borry

The aim of this study was to evaluate the effects of fucoidan isolated from C. crinita on histamine-induced paw inflammation in rats, and on the serum levels of TNF-α, IL-1β, IL-6, and IL-10 in rats during systemic inflammation response. The levels of TNF-α in a model of acute peritonitis in rats were also investigated. The isolated crude fucoidan was identified as a sulfated xylogalactofucan with high, medium, and low molecular weight fractions and a content of fucose of 39.74%, xylose of 20.75%, and galactose of 15.51%. Fucoidan from C. crinita showed better anti-inflammatory effects in the rat paw edema model, and this effect was present during all stages of the experiment. When compared to controls, a commercial fucoidan from F. vesiculosus, the results also displayed anti-inflammatory activity on the 60th, 90th, and 120th minute of the experiment. A significant decrease in serum levels of IL-1β in rats treated with both doses of C. crinita fucoidan was observed in comparison to controls, whereas TNF-α concentrations were reduced only in the group treated with fucoidan from C. crinita at the dose of 25 mg/kg bw. In the model of carrageenan-induced peritonitis, we observed a tendency of decrease in the levels of the pro-inflammatory cytokine TNF-α in peritoneal fluid after a single dose of C. crinita fucoidan, but this did not reach the statistical significance margin. Single doses of C. crinita fucoidan did not alter serum levels of the anti-inflammatory cytokine IL-10 in animals with lipopolysaccharide-induced systemic inflammation.

Vitamin D3 exerts immunomodulatory and memory improving properties in rats with lipopolysaccharide-induced inflammation

INTRODUCTION

Vitamin D is a fat-soluble secosteroid, its primary function being regulation of calcium-phosphate homeostasis and maintenance of bone integrity and mineralization. Recently, pleotropic effects of this vitamin have been recognized, including an immunomodulatory role and involvement in normal brain development and functioning.

Current methods for microbiological diagnosis of acute central nervous system infections

The incidence of infections affecting the central nervous system has increased in recent years, making neuroinfections a current global health problem. The central nervous system is quite well protected from the external and internal environments, although it is susceptible to infection by a wide variety of pathogens. The etiological diversity further complicates the management of such infections because it is important to identify correctly the specific cause in order to choose the most appropriate antimicrobial therapy. Diagnosis is made not only based on clinical and epidemiological data but also on the results of clinical laboratory and microbiological examination of cerebrospinal fluid. This article aims to review current microbiological methods in the diagnosis of acute central nervous system infections and help healthcare providers to recognize their advantages and limitations in order to manage their patients appropriately.

Primary immunodeficiencies in Bulgaria - achievements and challenges of the PID National Expert Center

Tremendous progress has been made in the recognition of primary immune deficiencies (PIDs) in Bulgaria since in 2005 we have joined the J Project Central-Eastern European collaborative program. Ten years later an Expert Centre (ExpC) for Rare Diseases - Primary Immune Deficiencies at the University Hospital “Alexandrovska”- Sofia was established. In May 2017 The National Register of Patients with Rare Diseases also became operational as a database containing clinical and genetic information for Bulgarian patients with PID. The transfer of data and information on Bulgarian PID patients to the European Primary Immunodeficiency Database, managed by the European Society for Primary Immunodeficiency (ESID) has started in 2020. The total number of registered patients now is 191 (100 men and 91 women), with more than half of them being children (106; 55.5%). Regular updating of the information in the register showed that 5.2% of patients are deceased and the majority (94.8%) is a subject to continuous monitoring as it has been reported for other European countries as well. With the establishment of the ExpC, the dynamics in the diagnosis and registration of patients with PID significantly intensified. For a period of 5 years (2016-2021) 101 patients were evaluated and registered in comparison with previous period - before ExpC establishment when only 89 patients were diagnosed. The most common pathology was humoral immune deficiency (85 patients; 44.5%). Ninety-six (50.3%) of the patients underwent genetic testing, and 66. 7% had genetically confirmed diagnosis. Three of the variants have not been reported in population databases. Following genetic investigation confirmation of the initial phenotypic diagnosis was achieved in 82.8% of cases and change in the diagnosis - in 17%. Sixty-two patients were on regular replacement or specific therapy, and the rest received symptomatic and supportive treatment. In summary, we present the first epidemiological report of PIDs in Bulgaria, based on the National PID register. Data on the clinical, phenotypic and genetic characteristics of PID patients provided important information about the nature of primary immunodeficiency diseases in our country.

Quantitative system for diagnosis of vulvovaginal candidiasis

INTRODUCTION

Vaginal infections are one of the most common reason for gynecological consultations. Many of them are the result of overgrowth of resident microorganisms. The clinical symptoms of vulvovaginal candidiasis are nonspecific and an accurate diagnosis is a problem that often leads to inadequate treatment or delays in treatment. The lack of an exact and practical diagnostic method is a common cause of misdiagnosis.

AIM

To create a complex, quantitative method for the diagnosis of vulvovaginal candidiasis which to enables differentiation from vaginal fungal colonization.

MATERIAL AND METHODS

A total of 2306 vaginal samples were examined. Clinical, microbiological, epidemiological methods and statistical models are used.

RESULTS AND DISCUSSION

The proposed score system is a specific, sensitive and inexpensive method to routinely diagnose vulvovaginal candidiasis. Statistical processing of the obtained data shows the impact of the individual components on which the method is based: the presence of vaginal discharge, pruritus, direct microscopy and assessment of the fungal growth. The data analysis reveals good sensitivity (71%) and high specificity (98%) of the method. This allows accurate interpretation of the result of the clinical and microbiological examination of each patient.

CONCLUSION

The system for diagnosing vulvovaginal candidiasis is complex and based on quantitative indicators. The method can be used to differentiate vulvovaginal candidiasis from vaginal fungal colonization (the cut-off value is 5.5 points) and to more accurately interpret a Candida positive result from quantitative real-time PCR in asymptomatic patients or in women with mixed vaginal infection.

Application of Fluorescent In Situ Hybridization for Quick Identification of Microorganisms from Positive Blood Cultures

AIM: The aim of this study was to evaluate the diagnostic potential of the fluorescent in situ hybridization (FISH) method for quick identification of microorganisms from positive blood cultures. MATERIALS AND METHODS: QuickFISH BC is a multicolor, qualitative nucleic acid hybridization assay using specific fluorescent-labeled probes for identification of Gram-positive bacteria (S. aureus, Coagulase-negative Staphylococcus spp. – CoNS, E. faecalis, and E. faecium); Gram-negative bacteria (E. coli, P. aeruginosa, and K. pneumoniaе), and fungi (C. albicans, C. tropicalis, and C. glabrata). This method applied to 72 positive blood cultures obtained from patients admitted at the University Hospital St. George – Plovdiv. A preliminary selection based on Gram staining was performed before the application of the FISH test. All microorganisms were subject to identification by routine biochemical tests, semi-automated and automated systems as well. Statistical data processing included descriptive statistics, nonparametric analysis for testing hypotheses by SPSS v. 22.0, and Microsoft Excel software. p < 0.05 was considered statistically significant. RESULTS: FISH detected microorganisms in 63 (87.5%) positive blood cultures, whereas no fluorescent signal was observed in 9 (12.5%). The latter was because not all the microorganisms we identified are included in the test spectrum, for example – Enterobacter spp. and Acinetobacter spp. By FISH, we found S. aureus in 10 (15.9%) cases, CoNS in 20 (31.6%), E. faecalis in 4 (6.4%), and E. faecium in 4 (6.4%). E. coli (n = 7; 11.1%) was the leading cause of bacteremia among Gram-negative bacteria, whereas C. albicans predominated (n = 4; 6.4%) among fungi. CONCLUSION: QuickFISH BC is a rapid and accurate screening method for the identification of some of the most frequent pathogens causing bacteremia. This enables the initiation of the early and adequate antimicrobial therapy. The lack of pathogen identification from positive blood cultures using this method implies the need to continue identification with other tests.

Coinfection of the intestinal tract with Aeromonas hydrophila, Clostridium difficile and Rotavirus - a case report

Most cases of acute diarrhea in adults are of infectious etiology, likely viral and self-limited. Among those with severe diarrhea, however, bacterial causes are responsible for most cases.

Apart from the standard stool cultures, to increase the positive yield a novel multiplex molecular test can be performed simultaneously. The authors present a patient with recurrent diarrhea and detection of Aeromonas hydrophila by culturing and Rotavirus and Clostridioides difficile by multiplex molecular test. They discuss and justify which is the most likely actionable pathogen. Good communication between the physicians and interpretation on the multiple positive results in the context of clinical picture and the test employed were important for a better management and favourable outcome of the patient.

Combined testing of cerebrospinal fluid IL-12 (p40) and serum C-reactive protein as a possible discriminator of acute bacterial neuroinfections

INTRODUCTION

Central nervous system infections (CNS) are life-threatening diseases, with meningitis being the most common. Viral infections are usually self-limiting diseases but bacterial pathogens are associated with higher mortality rates and persistent neurological sequelae. We aimed to study the role of IL-6, IL-8, IL-10, IL-12(p40), TNF-α cytokines, classical cerebrospinal fluid (CSF) parameters, and serum C-reactive protein levels (CRP) for discriminating bacterial from viral central nervous system infections.

MATERIAL AND METHODS

This prospective study included 80 patients with clinical signs and abnormal cerebrospinal fluid laboratory findings typical for neuroinfection admitted to St. George University Hospital-Plovdiv. Routine methods such as direct microscopy, culturing and identification were used for microbiological analysis as well as latex-agglutination test and multiplex PCR. Cytokines' concentrations were measured by ELISA. CRP and CSF parameters were collected from the patients' medical records.

RESULTS

We observed the highest discriminatory power among cytokines for cerebrospinal IL-12(p40) (AUC = 0.925; p = 0.000). CSF protein levels were the best predictor for bacterial neuroinfection (AUC = 0.973; p = 0.000). The AUC for the serum CRP as a stand-alone biomarker was estimated to be 0.943. The discriminatory power can be increased up to 0.995 (p = 0.000) when combining cerebrospinal fluid IL-12(p40) and serum CRP, with an optimal cut-off value of 144 (Sensitivity 100%; Specificity 90.9%).

CONCLUSION

The combined testing of CSF IL-12(p40) and serum CRP is associated with the highest diagnostic accuracy.

Serum Procalcitonin Levels in Patients with Acute Central Nervous System Infections

BACKGROUND: Bacterial infections of the brain are associated with high mortality and neurological sequelae, whereas viral diseases are usually self-limiting. A fast and easy-to-perform biomarker is needed to improve management in these patients. AIM: Procalcitonin (PCT) testing has already been implemented in many laboratories for evaluating septic patients and it is an easily accessible biomarker, so we aimed to examine its role specifically in discriminating acute bacterial from viral infections of the central nervous system (CNS). MATERIALS AND METHODS: This prospective study included 80 patients with both clinical symptoms and laboratory findings suggesting acute CNS infection. The microbiological analysis included direct microscopy, culturing, latex-agglutination test, and multiplex polymerase chain reaction. PCT levels were measured by enzyme-linked fluorescent assay technology. RESULTS: Following the results of the microbiological analysis, the cases were divided into three groups – bacterial 26.3% (n = 21), viral 17.5% (n = 14), and unidentified neuroinfections – 56.2% (n = 45). A statistically significant difference in the median serum PCT was observed between the bacterial and viral neuroinfections (p = 0.004) as well as between bacterial and unidentified infections of the brain (p = 0.000). No significant difference was found (p = 1.000) when comparing viral and unidentified neuroinfection. The area under the receiver operating characteristic curve for serum PCT was 0.823 but could be increased to 0.929 when combining serum PCT and C-reactive protein (CRP). CONCLUSION: Serum PCT levels are significantly higher in patients with acute bacterial infections of the brain. As a stand-alone biomarker, its discriminatory power is not superior to the classical laboratory parameters in the cerebrospinal fluid and serum CRP. However, when combined with serum CRP, excellent discriminatory power is observed.

Construction of a nitro-oxidative stress-driven, mechanistic model of mood disorders: A nomothetic network approach

Major depression is accompanied by increased IgM-mediated autoimmune responses to oxidative specific epitopes (OSEs) and nitric oxide (NO)-adducts. These responses were not examined in bipolar disorder type 1 (BP1) and BP2. IgM responses to malondialdehyde (MDA), phosphatidinylinositol, oleic acid, azelaic acid, and NO-adducts were determined in 35 healthy controls, and 47 major depressed (MDD), 29 BP1, and 25 BP2 patients. We also measured serum peroxides, IgG to oxidized LDL (oxLDL), and IgM/IgA directed to lipopolysaccharides (LPS). IgM responses to OSEs and NO-adducts (OSENO) were significantly higher in MDD and BP1 as compared with controls, and IgM to OSEs higher in MDD than in BP2. Partial Least Squares (PLS) analysis showed that 57.7% of the variance in the clinical phenome of mood disorders was explained by number of episodes, a latent vector extracted from IgM to OSENO, IgG to oxLDL, and peroxides. There were significant specific indirect effects of IgA/IgM to LPS on the clinical phenome, which were mediated by peroxides, IgM OSENO, and IgG oxLDL. Using PLS we have constructed a data-driven nomothetic network which ensembled causome (increased plasma LPS load), adverse outcome pathways (namely neuro-affective toxicity), and clinical phenome features of mood disorders in a data-driven model. Based on those feature sets, cluster analysis discovered a new diagnostic class characterized by increased plasma LPS load, peroxides, autoimmune responses to OSENO, and increased phenome scores. Using the new nomothetic network approach, we constructed a mechanistically transdiagnostic diagnostic class indicating neuro-affective toxicity in 74.3% of the mood disorder patients.

Increased Serum Immunoglobulin Responses to Gut Commensal Gram-Negative Bacteria in Unipolar Major Depression and Bipolar Disorder Type 1, Especially When Melancholia Is Present

Major depressive disorder (MDD) is accompanied by higher serum IgM/IgA responses to LPS of Gram-negative bacteria, suggesting increased bacterial translocation and gut dysbiosis while the latter may occur in bipolar disorder (BD). There are differences between MDD and BD type 1 (BP1) and 2 (BP2) in nitro-oxidative stress biomarkers associated with leaky gut. This study examines serum IgM/IgA responses directed to LPS of 6 Gram-negative bacteria as well as IgG responses to oxidized LDL (oxLDL) in 29 BP1, 37 BP2, 44 MDD, and 30 healthy individuals. Increased IgM/IgA responses to Pseudomonas aeruginosa significantly discriminated patients with affective disorders (MDD plus BD) from controls. BP1 patients showed higher IgM responses to Morganella morganii as compared with MDD and BP2 patients. Patients with melancholia showed higher IgA responses to Citrobacter koseri as compared to controls and non-melancholic depression. The total score on the Hamilton Depression Rating Scale was significantly associated with IgA responses to C. koseri. IgG to oxLDL was significantly associated with increased bacterial translocation. In conclusion, MDD, BP1, and BP2 are accompanied by an immune response due to the increased load of LPS while these aberrations in the gut-brain axis are most pronounced in BP1 and melancholia. Activated oxidative stress pathways and autoimmune responses to oxidative specific epitopes in mood disorders may be driven by a breakdown in gut paracellular, transcellular, and/or vascular pathways. If replicated, drugs that protect the integrity of the gut barrier may offer novel therapeutic opportunities for BP1 and MDD.

Multicentre investigation of carbapenemase-producing Klebsiella pneumoniae and Escherichia coli in Bulgarian hospitals - Interregional spread of ST11 NDM-1-producing K. pneumoniae

AIM

The aim of this study was to investigate the mechanisms of beta-lactam-resistance and the clonal relatedness of carbapenem-nonsusceptible Klebsiella pneumoniae and Escherichia coli isolates, collected consecutively in eight centers in five Bulgarian cities from November 2014 to March 2018. Carbapenemase-producing enterobacteria were detected in all but one centers. Overall, 104 K. pneumoniae and one E. coli were analysed.

MATERIALS AND METHODS

Antimicrobial susceptibility and beta-lactamases were analysed. Conjugation experiments, plasmid fingerprinting and replicon typing, as well as MLST and ERIC-PCR were carried out.

RESULTS

KPC-2 (51%) and NDM-1 (47%) were the main carbapenemases identified. KPC-2 producing K. pneumoniae were classified into 10 MLST-types. The four dominating MLST-types ST29, ST15, ST336 and ST902 comprised 79% of the KPC-2 producers. All but one of the NDM-1 producing isolates belonged to the MLST-type ST11 and were found in seven centers. Furthermore, single K. pneumoniae isolates producing VIM-1 (ST147) and OXA-48 (ST15) were identified. In addition to the carbapenemases, the ESBLs CTX-M-15, CTX-M-3, and SHV-12 as well as AmpC enzyme CMY-4 were found. The FIIAs-replicon-type was found in all KPC-2 producers while the A/C-replicons dominated in NDM-1 producing isolates. The single NDM-1 producing E. coli was determined as MLST-Type ST10 (Warwick scheme).

CONCLUSION

The interregional clonal expansion of NDM-1 producing ST11 K. pneumoniae and the dissemination of bla_KPC-2 carrying plasmids were responsible for the spread of carbapenemase-producing K. pneumoniae in Bulgaria. Our findings highlight the urgency to prevent dissemination of these highly transmissible and dangerous lineages.

Do Human Endogenous Retroviruses Contribute to Multiple Sclerosis, and if So, How?

The gammaretroviral human endogenous retrovirus (HERV) families MRSV/HERV-W and HERV-H (including the closely related HERV-Fc1) are associated with an increased risk of multiple sclerosis (MS). Complete HERV sequences betray their endogenous retroviral origin, with open reading frames in gag, pro, pol and env being flanked by two long terminal repeats containing promoter and enhancer sequences with the capacity to regulate HERV transactivation and the activity of host genes in spite of endogenous epigenetic repression mechanisms. HERV virions, RNA, cDNA, Gag and Env, and antibodies to HERV transcriptional products, have variously been found in the blood and/or brain and/or cerebrospinal fluid of MS patients, with the HERV expression level being associated with disease status. Furthermore, some HERV-associated single nucleotide polymorphisms (SNPs), such as rs662139 T/C in a 3-kb region of Xq22.3 containing a HERV-W env locus, and rs391745, upstream of the HERV-Fc1 locus on the X chromosome, are associated with MS susceptibility, while a negative association has been reported with SNPs in the tripartite motif-containing (TRIM) protein-encoding genes TRIM5 and TRIM22. Factors affecting HERV transcription include immune activation and inflammation, since HERV promoter regions possess binding sites for related transcription factors; oxidative stress, with oxidation of guanine to 8-oxoguanine and conversion of cytosine to 5-hydroxymethylcytosine preventing binding of methyl groups transferred by DNA methyltransferases; oxidative stress also inhibits the activity of deacetylases, thereby favouring the acetylation of histone lysine residues favouring gene expression; interferon beta; natalizumab treatment; impaired epigenetic regulation; and the sex of patients.

Serotype changes and antimicrobial nonsusceptibility rates of invasive and non-invasive Streptococcus pneumoniae isolates after implementation of 10-valent pneumococcal nontypeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) in Bulgaria

The 10-valent pneumococcal conjugate vaccine (PCV10) has been included in Bulgarian Childhood Immunization Program since 2010. This study aimed to assess serotype distribution and antimicrobial resistance of 198 invasive and non-invasive Streptococcus pneumoniae strains that had been isolated in Bulgaria during 2011-2016 from patients with invasive (IPD) and non-invasive (NIPD) pneumococcal diseases. The most common invasive serotypes were 3 (10.1%), 19F (4.0%), and 7F (3.0%). A significant decrease in the proportion of invasive vaccine types (VTs) from 64.2% to 35.2% was found in comparison with pre-vaccine era. The most common serotypes among middle ear fluids were 3, 19A and 19F (5.6% each), and VTs fell down from 66.4% to 40.0% in post-PCV10 period. Among respiratory isolates, the most prevalent serotypes were some emergent serotypes such as 15A/B/C (5.0%), 19A, and 6C (4.0% each). VTs decreased significantly (16.3%) among vaccinated children compared to unvaccinated children and adults (44.0%). Two non-VTs (19A and 6C) have increased significantly more (p<0.05) in vaccinated children than in unvaccinated patients. The rates of antibiotic nonsusceptible S. pneumoniae in Bulgaria remained high in post-PCV10 era. Among all source of isolates, antimicrobial nonsusceptibility rates were: oral penicillin - 46.5%, trimethoprim-sulfamethoxazole - 45.4%, erythromycin - 43.9%, tetracycline - 37.4%, and multidrug-resistance (MDR) was 44%. The most common MDR serotypes were 19F, 19A, 6A/C, 15A/B/C and 23A. Our results proved that PCV10 vaccination substantially reduced VTs pneumococcal IPD and NIPD. There has been a shift in the distribution of S. pneumoniae serotypes mostly in vaccinated children but also in the whole population and strong serotype-specific antibiotic resistance was observed after vaccine implementation. Therefore, it is important to continue monitoring serotype changes and pneumococcal resistance among all patient ages in addition to aid in determining the long-term effectiveness of PCV10 interventions.

Evaluation of antimicrobial resistance among Salmonella and Shigella isolates in the University Hospital "St. George," Plovdiv, Bulgaria

The aim of this work is to study the epidemiology and antimicrobial resistance to the most commonly used antibiotics for the treatment of acute gastroenteritis caused by Salmonella and Shigella at the largest Bulgarian hospital-University Hospital "St. George," Plovdiv-for the period 2009-2013. Two hundred ninety strains were in vitro tested for resistance to 15 antimicrobial agents. The presence of extended-spectrum beta-lactamases (ESBLs) was demonstrated by a variety of specialized tests. For comparison, a collection of 28 strains submitted by the National Reference Laboratory (NRL) "Enteric Infections" at the National Center of Infectious and Parasitic Diseases (NCIPD), Sofia, was also tested for the production of ESBLs. In isolates, phenotypically demonstrated as ESBL producers, polymerase chain reaction (PCR) detection of the genes bla-CTX-M, bla-SHV, and bla-TEM was performed. Among the 290 tested isolates, only two- Salmonella serotype Livingstone and Shigella flexneri-were phenotypically proven to be ESBL producers. Only 4 strains from the collection of 28, submitted from the NRL "Intestinal Infections" in NCIPD, Sofia, were phenotypically confirmed as ESBL producers. The presence of the bla-CTX-M gene was detected in all of the tested strains (4 from NRL, NCIPD, Sofia, and 2 from the University Hospital St. George, Plovdiv), the bla-SHV gene only in strain S. Livingstone from Plovdiv, and the bla-TEM gene in two from Sofia and one (again S. Livingstone) from Plovdiv. In conclusion, Salmonella and Shigella isolates from patients hospitalized at the University Hospital St. George, Plovdiv, with acute gastroenteritis demonstrate good susceptibility to the most commonly used antibiotic agents, including azithromycin.

Study on anti-inflammatory and immunomodulatory effects of fluoxetine in rat models of inflammation

The aim of the present study was to evaluate the anti-inflammatory effect of fluoxetine in carrageenan- and lipoplysaccharide-induced models of inflammation by investigating the changes in serum levels of pro-inflammatory cytokine TNF-α and anti-inflammatory cytokines IL-10 and TGF-β after single and repeated administration of the drug. To study the effect of a single and repeated dose fluoxetine on carrageenan-induced paw edema male Wistar rats were divided into five groups (n = 8): control group; positive control group; and three experimental groups treated with 5, 10, and 20 mg/kg bodyweight (bw) fluoxetine, respectively. To study the effect of a single and repeated dose of fluoxetine on serum cytokine levels, the animals were divided in four groups (n = 8): two control groups treated with saline and two experimental groups treated with fluoxetine 20 mg/kg bw. Carrageenan and LPS were injected immediately after fluoxetine or saline injection. Serum cytokine concentrations were tested by enzyme immunoassay. In single administration only the highest dose used inhibited carrageenan-induced inflammation. Edema inhibition was seen with 10 and 20 mg/kg bw fluoxetine after repeated administration. At 24 h a statistically significant effect on inhibition of carrageenan edema was found only in rats treated with 20 mg/kg bw fluoxetine In carrageenan-induced inflammation, fluoxetine significantly increased Il-10 and decreased TNF-α after repeated administration. Surprisingly, in single-dose treated animals an increase in TNF-α values upon fluoxetine administration was observed in this model of inflammation. In LPS-induced inflammation, fluoxetine significantly decreased TNF-α after single and repeated treatment. Fluoxetine has anti-inflammatory and immunomodulatory effect in the carrageenan-induced model of exudative inflammation. In LPS-induced inflammation it showed an immunomodulatory effect manifested with a decrease in pro-inflammatory cytokine TNF-α.

Study on anti-inflammatory and immunomodulatory effects of clomipramine in carrageenan- and lipopolysaccharide-induced rat models of inflammation

The aim of the present study was to evaluate the anti-inflammatory effect of clomipramine in carrageenan- and lipopolysaccharide-induced (LPS-induced) models of inflammation by investigating the changes in serum levels of the pro-inflammatory cytokine TNF-α and the anti-inflammatory cytokines IL-10 and TGF-β after single and repeated administration of the drug.

In order to study the effect of single and repeated doses of clomipramine on carrageenan-induced paw oedema, male Wistar rats were divided in five groups (n = 8): control, positive control group and three experimental groups treated with 5, 10 and 20 mg/kg bw clomipramine, respectively. The effect of single and repeated doses of clomipramine on serum cytokine levels was studied as animals were divided in four groups: two control groups treated with saline and two experimental groups treated with clomipramine 20 mg/kg bw. Carrageenan and LPS were injected immediately after clomipramine or saline injection. Serum cytokine concentrations were tested by enzyme immunoassay.

Following acute administration only the highest dose that was used inhibited the carrageenan-induced inflammation. Oedema inhibition was observed with 5, 10 and 20 mg/kg bw clomipramine after repeated administration. Single and repeated administration of clomipramine at a dose of 20 mg/kg bw did not significantly change the serum levels of TGF-1β, IL-10 and TNF-α when compared to the controls in carrageenan-induced inflammation. Following LPS-induced inflammation clomipramine significantly increased the serum levels of TGF-1β after repeated administration and decreased TNF-α in rats after single-dose and repeated pretreatment with 20 mg/kg bw clomipramine. A significant increase in the levels of IL-10 in relation to this inflammatory model was observed only in single dose treated animals.

Clomipramine possesses an anti-inflammatory effect in the carrageenan-induced model of exudative inflammation. In LPS-induced inflammation, clomipramine showed an immunomodulatory effect, decreasing TNF-α and increasing TGF-1β after repeated administration, and increasing IL-10 after a single dose.

Diagnosis of spontaneous and secondary bacterial peritonitis in patients with hepatic cirrhosis and ascites

Spontaneous bacterial peritonitis (SBP) is an infection that is not caused by intra-abdominal source requiring surgery. Nowadays SBP is the main cause of death in patients with cirrhosis. Treatment is carried out with third generation cephalosporins and albumin infusions. The aim of the study is to identify patients with SBP and to be distinguished from the cases with secondary bacterial peritonitis (SecBP) in patients with cirrhosis and ascites. We studied 167 patients with cirrhosis and ascites and SBP was observed in 25 of them, while SecBP--in 22. The diagnosis of SBP is set in neutrophilic leukocytes in ascites > or = 250 cells/mm3 as bacterial cultures are positive in only 16% of them. Completely asymptomatic course had 16% of patients with SBP. Diagnosis of SecBP (according to Runyon's criteria) is based on increased total protein in ascitic fluid > 10 g/l (in 63.7% of patients > 30 g/l), elevated lactate dehydrogenase in ascites (LDH is > 240 U/l in all patients) and glucose < 2,7 mmol/l (only 4.5% of cases with secondary bacterial peritonitis). In support of SecBP are the polymicrobial flora, the isolation of anaerobes, enterococci, fungi, and the very high number of neutrophilic leukocytes in the peritoneal effusion and the refractoriness from conservative treatment. The examination of ascites with Multistix is more informative in secondary than in spontaneous bacterial peritonitis. In suspected secondary bacterial peritonitis CT is indicated.

Serum levels of interferon-γ, interleukin-12, tumour necrosis factor-α, and interleukin-10, and bacterial clearance in patients with gastroenteric Salmonella infection

Cytokines as intercellular signal molecules are responsible to a great extent for the pathological processes in Salmonella infection, as well as for the development of protective mechanisms in the disease. The present study aimed to reveal the correlation between serum levels of IFN-gamma, IL-12, TNF-alpha and IL-10, measured by enzyme-immunoassay, and clearance of bacteria in stool of patients with gastroenteric Salmonella infection. The study included 36 patients with culture confirmed gastroenteric Salmonella infection. At discharge from hospital, 20 patients recovered with bacteriological negative stool culture for Salmonella and 16 were Salmonella excretors. Mean serum concentrations of IFN-gamma, IL-12, TNF-alpha and IL-10 in the acute stage were compared between the 2 groups of patients and with those of healthy controls. Serum levels of examined cytokines were increased (p<0.001) in the patients in comparison with the healthy controls. In patients with early bacterial clearance mean serum concentrations of IFN-gamma, IL-12 and TNF-alpha in the acute stage were significantly (p<0.05) higher than in the non-clearance group. IL-10 serum level showed an opposite correlation (p<0.01) and higher values in Salmonella excretors. The accumulated data imply that Th1 type cytokines probably participate in protective immunity and early bacterial clearance in patients with gastroenteric Salmonella infection.

In vitro study on cytotoxic effect of some chemicals on serum McCoy and serum-free McCoy-Plovdiv cell culture systems

The cytotoxicity of test agents on serum-free McCoy cultures has not been studied at all. The cytotoxic effect of EDTA, methanol, DMSO, and cycloheximide on serum-free McCoy-Plovdiv cell culture (SF) was detected visually on inverted microscope and quantitatively by tests for viability (NR) and total protein (KBP). The IC50 values for the tested chemicals were calculated. SF showed the lowest IC50 values for cycloheximide, DMSO and EDTA and the highest for methanol according to both tests. EDTA, methanol, DMSO and cycloheximide had dose-effect relationship in the cell test systems after treatment. The data indicate that McCoy-Plovdiv cell line is a suitable serum-free cell system for in vitro cytotoxic studies.

Study on proinflammatory cytokines (IL-1 beta, IL-6, TNF-alpha) and IL-2 in patients with acute hepatitis B

Cytokine production in patients with hepatitis B may be related either to multiple immune abnormalities or to favourable outcome of the disease. Serum levels of IL-1 beta, IL-2, IL-6 and TNF-alpha were determined dynamically by ELISA kits in patients with self-limited form of acute hepatitis B infection (A-HBV) during the first, second and third decade after icterus appearance. IL-1 beta, IL-6 and TNF-alpha had characteristically high levels in patients measured in all decades, but these were the highest during the first. Then they gradually decreased, reaching normal values at the stage of convalescence. Serum IL-2 levels were found to be most significantly elevated during the second decade and also dropped to normal values in the course of the disease. Patients who cleared HBsAg on the third month after dehospitalisation had higher mean values of IL-2, IL-6 and TNF-alpha in comparison with those who were still HBsAg carriers, thus indicating that proinflammatory cytokine production in self-limited HBV may be important for viral clearance.

Susceptibility and Resistance to Antigen-Induced Apoptosis in the Thymus of Transgenic Mice

Injection of TCR transgenic mice with antigenic peptide results in the deletion of immature thymocytes expressing the transgenic TCR. We have analyzed this process in mice transgenic for a TCR (F5) that recognizes a peptide from the influenza nucleoprotein (NP68). To determine whether deletion of immature thymocytes is the result of specific recognition of the antigenic peptide by the thymocytes or mature T cell activation, bone marrow chimeric mice were generated using a mixture of cells from F5 transgenic and nontransgenic mice. Injection of these mice with antigenic peptide leads to the preferential depletion of F5 transgenic thymocytes, whereas nontransgenic thymocytes remain largely unaffected. Furthermore, exposure of F5 fetal thymic lobes to peptide leads to thymocyte deletion even though no mature single positive T cells are present at this stage. These data suggest that Ag-induced death of immature thymocytes is due to peptide-specific recognition, although activated mature T cells appear to potentiate such deletion. Further administration of antigenic peptide to F5 mice results in the appearance of double-positive thymocytes that are resistant to Ag or anti-CD3-induced apoptosis. These data suggest a change in the ability of the cells to signal through the TCR-CD3 complex, resembling the state of anergy induced in peripheral T cells following chronic exposure to Ag.

Susceptibility and resistance to antigen-induced apoptosis in the thymus of transgenic mice

Injection of TCR transgenic mice with antigenic peptide results in the deletion of immature thymocytes expressing the transgenic TCR. We have analyzed this process in mice transgenic for a TCR (F5) that recognizes a peptide from the influenza nucleoprotein (NP68). To determine whether deletion of immature thymocytes is the result of specific recognition of the antigenic peptide by the thymocytes or mature T cell activation, bone marrow chimeric mice were generated using a mixture of cells from F5 transgenic and nontransgenic mice. Injection of these mice with antigenic peptide leads to the preferential depletion of F5 transgenic thymocytes, whereas nontransgenic thymocytes remain largely unaffected. Furthermore, exposure of F5 fetal thymic lobes to peptide leads to thymocyte deletion even though no mature single positive T cells are present at this stage. These data suggest that Ag-induced death of immature thymocytes is due to peptide-specific recognition, although activated mature T cells appear to potentiate such deletion. Further administration of antigenic peptide to F5 mice results in the appearance of double-positive thymocytes that are resistant to Ag or anti-CD3-induced apoptosis. These data suggest a change in the ability of the cells to signal through the TCR-CD3 complex, resembling the state of anergy induced in peripheral T cells following chronic exposure to Ag.

Inhibition of thymocyte negative selection by T cell receptor antagonist peptides

The T cell receptor (TCR) recognizes antigenic peptide presented by major histocompatibility complex (MHC) molecules. Analogs of antigenic peptides have been shown to inhibit antigen-specific T cell responses, a phenomenon described as TCR antagonism. We have examined the effect of a natural variant of an antigenic peptide and a synthetic peptide analog, on the responses of mature T cells and immature thymocytes from an alpha-beta TCR-transgenic mouse (F5), the TCR of which recognizes a nonamer peptide from the nucleoprotein (NP) of influenza virus in the context of the H-2Db MHC molecule. Both peptides were shown to antagonize specifically the T cells cytolytic response without being able directly to stimulate mature T cells from these transgenic mice. Furthermore, a negative selection assay in vitro was used to demonstrate for the first time that antagonistic peptides are capable of antagonizing thymocyte deletion induced by antigenic peptides. These data suggest that the final selection of a T cell could be the result of a balance between the positive and negative influences of endogenous peptide ligands.

Inhibition of I-Ad-, but not Db-restricted peptide-induced thymic apoptosis by glucocorticoid receptor antagonist RU486 in T cell receptor transgenic mice

Thymocytes differentiate by positive and negative selection of immature CD4+ CD8+ T cells. Negative selection occurs by default or by high-affinity recognition of peptides bound to proteins encoded by the major histocompatibility complex (MHC). MHC class I molecules are expressed on many different cell types, although at different levels, whereas MHC class II molecules are selectively expressed on thymic epithelial cells (TEC) and dendritic cells (DC). We investigated the role of the glucocorticoid receptor (GR) in thymic negative selection using the receptor antagonist RU486. Glucocorticoids (GC) are known to be potent inducers of apoptosis in CD4+ CD8+ thymocytes, and we have earlier shown that anti-CD3-induced thymic apoptosis can be blocked by RU486 in vivo. We now show that anti-CD3 induces thymic apoptosis in mice that have been adrenalectomized (ADX), and that RU486 inhibits anti-CD3 antibody-mediated thymocyte killing in newborn thymic organ cultures. Thymocyte apoptosis induced by ovalbumin peptide OVA323-339 treatment of mice transgenic for the DO11.10T cell receptor (TCR), which recognizes this peptide in the context of I-Ad, was found to be inhibited by RU486. These mice responded to peptide treatment by an extensive activation of the peripheral immune system, which became lethal in 60% of the mice when accompanied by simultaneous RU486 treatment. In contrast, RU486 had no effect on thymic apoptosis induced by the influenza A nucleoprotein NP366-374 peptide, recognized in context of Db, in F5 TCR transgenic mice. We interpret the results to demonstrate that different deletion systems operate in the thymus. We propose that endogenous GC may be important for negative selection by default and by high-affinity recognition of endogenous MHC-presented peptides on TEC.

Tolerance in TCR/cognate antigen double-transgenic mice mediated by incomplete thymic deletion and peripheral receptor downregulation

Influenza nucleoprotein (NP)-specific T-cell receptor transgenic mice (F5) were crossed with transgenic mice expressing the cognate antigenic protein under the control of the H-2Kb promoter. Double-transgenic mice show negative selection of thymocytes at the CD4+8+TCRlo to CD4+8+TCRhi transition stage. A few CD8+ T cells, however, escape clonal deletion, and in the peripheral lymphoid organs of these mice, they exhibit low levels of the transgenic receptor and upregulated levels of the CD44 memory marker. Such cells do not proliferate upon exposure to antigen stimulation in vivo or ex vivo, however, they can develop low but detectable levels of antigen-specific cytotoxic function after stimulation in vitro in the presence of IL-2.

The programmed cell death of an immature thymocyte cell line transgenic for an alpha beta TCR and the c-myc proto-oncogene

The c-myc proto-oncogene linked to the mouse Thy-1 gene transcriptional unit predisposes mice to development of thymic tumors consisting predominantly of immature CD4+ CD8+ cells. In an attempt to immortalize immature T cells expressing a known T-cell antigen receptor (TCR), Thy-1/c-myc transgenic mice were bred to alpha beta TCR transgenic mice (F5), and CD4+ CD8+ cell lines were established from thymic tumors in double-transgenic mice. These cells expressed high-level heat-stable antigen (HSA) and were able to undergo programmed cell death upon induction with steroids and CD3 cross-linking, but not with cognate peptide. In addition, one line had rearranged and transcribed endogenous TCR alpha and beta genes, in spite of the fact that transgenic alpha and beta genes were also expressed. Furthermore, we show that Thy-1/myc transgenic mice deficient in recombination activating gene-1 (RAG-1) do not develop tumors, in contrast to RAG-1-/- mice, which are also transgenic for both Thy-1/myc and the F5 TCR. This indicates that in order for thymocytes to be transformed by the Thy-myc transgene, they need to proceed to the double-positive stage.