Intranasal exposure to bacterial superantigens induces airway inflammation in HLA class II transgenic mice

Characterization of genetic humanized mice with transgenic HLA DP401 or DRA but deficient in endogenous murine MHC class II genes upon Staphylococcus aureus pneumonia

BACKGROUND

Staphylococcus aureus can cause serious infections by secreting many superantigen exotoxins in "carrier" or "pathogenic" states. HLA DQ and HLA DR humanized mice have been used as a small animal model to study the role of two molecules during S. aureus infection. However, the contribution of HLA DP to S. aureus infection is unknown yet.

METHODS

In this study, we have produced HLA DP401 and HLA DRA0101 humanized mice by microinjection of C57BL/6J zygotes. Neo-floxed IAβ+/- mice were crossbred with Ella-Cre and further crossbred with HLA DP401 or HLA-DRA0101 humanized mice. After several rounds of traditional crossbreeding, we finally obtained HLA DP401-IAβ-/- and HLA DRA-IAβ-/- humanized mice, in which human DP401 or DRA0101 molecule was introduced into IAβ-/- mice deficient in endogenous murine MHC class II molecules. A transnasal infection murine model of S. aureus pneumonia was induced in the humanized mice by administering 2 × 108  CFU of S. aureus Newman dropwise into the nasal cavity. The immune responses and histopathology changes were further assessed in lungs in these infected mice.

RESULTS

We evaluated the local and systemic effects of S. aureus delivered intranasally in HLA DP401-IAβ-/- and HLA DRA-IAβ-/- transgenic mice. S. aureus Newman infection significantly increased the mRNA level of IL 12p40 in lungs in humanized mice. An increase in IFN-γ and IL-6 protein was observed in HLA DRA-IAβ-/- mice. We observed a declining trend in the percentage of F4/80+ macrophages in lungs in HLA DP401-IAβ-/- mice and a decreasing ratio of CD4+ to CD8+ T cells in lungs in IAβ-/- mice and HLA DP401-IAβ-/- mice. A decreasing ratio of Vβ3+ to Vβ8+ T cells was also found in the lymph node of IAβ-/- mice and HLA DP401-IAβ-/- mice. S. aureus Newman infection resulted in a weaker pathological injury in lungs in IAβ-/- genetic background mice.

CONCLUSION

These humanized mice will be an invaluable mouse model to resolve the pathological mechanism of S. aureus pneumonia and study what role DP molecule plays in S. aureus infection.

IFN- Is Protective in Cytokine Release Syndrome-associated Extrapulmonary Acute Lung Injury

The mechanisms by which excessive systemic activation of adaptive T lymphocytes, as in cytokine release syndrome (CRS), leads to innate immune cell-mediated acute lung injury (ALI) or acute respiratory distress syndrome, often in the absence of any infection, remains unknown. Here, we investigated the roles of IFN-γ and IL-17A, key T-cell cytokines significantly elevated in patients with CRS, in the immunopathogenesis of CRS-induced extrapulmonary ALI. CRS was induced in wild-type (WT), IL-17A- and IFN-γ knockout (KO) human leukocyte antigen-DR3 transgenic mice with 10 μg of the superantigen, staphylococcal enterotoxin B, given intraperitoneally. Several ALI parameters, including gene expression profiling in the lungs, were studied 4, 24, or 48 hours later. Systemic T-cell activation with staphylococcal enterotoxin B resulted in robust upregulation of several chemokines, S100A8/A9, matrix metalloproteases, and other molecules implicated in tissue damage, granulocyte as well as agranulocyte adhesion, and diapedesis in the lungs as early as 4 hours, which was accompanied by subsequent neutrophil/eosinophil lung infiltration and severe ALI in IFN-γ KO mice. These pathways were significantly underexpressed in IL-17A KO mice, which manifested mildest ALI and intermediate in WT mice. Neutralization of IFN-γ worsened ALI in WT and IL-17A KO mice, whereas neutralizing IL-17A did not mitigate lung injury in IFN-γ KO mice, suggesting a dominant protective role for IFN-γ in ALI and that IL-17A is dispensable. Ruxolitinib, a Janus kinase inhibitor, increased ALI severity in WT mice. Thus, our study identified novel mechanisms of ALI in CRS and its differential modulation by IFN-γ and IL-17A.

The Role of Staphylococcus aureus and Its Toxins in the Pathogenesis of Allergic Asthma

Bronchial asthma is one of the most common chronic diseases worldwide and affects more than 300 million patients. Allergic asthma affects the majority of asthmatic children as well as approximately 50% of adult asthmatics. It is characterized by a Th2-mediated immune response against aeroallergens. Many aspects of the overall pathophysiology are known, while the underlying mechanisms and predisposing factors remain largely elusive today. Over the last decade, respiratory colonization with Staphylococcus aureus (S. aureus), a Gram-positive facultative bacterial pathogen, came into focus as a risk factor for the development of atopic respiratory diseases. More than 30% of the world’s population is constantly colonized with S. aureus in their nasopharynx. This colonization is mostly asymptomatic, but in immunocompromised patients, it can lead to serious complications including pneumonia, sepsis, or even death. S. aureus is known for its ability to produce a wide range of proteins including toxins, serine-protease-like proteins, and protein A. In this review, we provide an overview of the current knowledge about the pathophysiology of allergic asthma and to what extent it can be affected by different toxins produced by S. aureus. Intensifying this knowledge might lead to new preventive strategies for atopic respiratory diseases.

Safety and Immunogenicity of a 4-Component Toxoid-Based Staphylococcus aureus Vaccine in Rhesus Macaques

Staphylococcus aureus is a leading cause of significant morbidity and mortality and an enormous economic burden to public health worldwide. Infections caused by methicillin-resistant S. aureus (MRSA) pose a major threat as MRSA strains are becoming increasingly prevalent and multi-drug resistant. To this date, vaccines targeting surface-bound antigens demonstrated promising results in preclinical testing but have failed in clinical trials. S. aureus pathogenesis is in large part driven by immune destructive and immune modulating toxins and thus represent promising vaccine targets. Hence, the objective of this study was to evaluate the safety and immunogenicity of a staphylococcal 4-component vaccine targeting secreted bi-component pore-forming toxins (BCPFTs) and superantigens (SAgs) in non-human primates (NHPs). The 4-component vaccine proved to be safe, even when repeated vaccinations were given at a dose that is 5 to 10- fold higher than the proposed human dose. Vaccinated rhesus macaques did not exhibit clinical signs, weight loss, or changes in hematology or serum chemistry parameters related to the administration of the vaccine. No acute, vaccine-related elevation of serum cytokine levels was observed after vaccine administration, confirming the toxoid components lacked superantigenicity. Immunized animals demonstrated high level of toxin-specific total and neutralizing antibodies toward target antigens of the 4-component vaccine as well as cross-neutralizing activity toward staphylococcal BCPFTs and SAgs that are not direct targets of the vaccine. Cross-neutralization was also observed toward the heterologous streptococcal pyogenic exotoxin B. Ex vivo stimulation of PBMCs with individual vaccine components demonstrated an overall increase in several T cell cytokines measured in supernatants. Immunophenotyping of CD4 T cells ex vivo showed an increase in Ag-specific polyfunctional CD4 T cells in response to antigen stimulation. Taken together, we demonstrate that the 4-component vaccine is well-tolerated and immunogenic in NHPs generating both humoral and cellular immune responses. Targeting secreted toxin antigens could be the next-generation vaccine approach for staphylococcal vaccines if also proven to provide efficacy in humans.

Systems Genetics Approaches in Mouse Models of Group A Streptococcal Necrotizing Soft-Tissue Infections

Mouse models are invaluable resources for studying the pathogenesis and preclinical evaluation of therapeutics and vaccines against many human pathogens. Infections caused by group A streptococcus (GAS, Streptococcus pyogenes) are heterogeneous ranging from mild pharyngitis to severe invasive necrotizing fasciitis, a subgroup of necrotizing soft-tissue infections (NSTIs). While several strains of mice including BALB/c, C3H/HeN, CBA/J, and C57BL/10 offered significant insights, the human specificity and the interindividual variations on susceptibility or resistance to GAS infections limit their ability to mirror responses as seen in humans. In this chapter, we discuss the advanced recombinant inbred (ARI) BXD mouse model that mimics the genetic diversity as seen in humans and underpins the feasibility to map multiple genes (genetic loci) modulating GAS NSTI. GAS produces a myriad of virulence factors, including superantigens (SAg). Superantigens are potent immune toxins that activate T cells by cross-linking T cell receptors with human leukocyte antigen class-II (HLA-II) molecules expressed on antigen-presenting cells. This leads to a pro-inflammatory cytokine storm and the subsequent multiple organ damage and shock. Inbred mice are innately refractive to SAg-mediated responses. In this chapter, we discuss the versatility of the HLA-II transgenic mouse model that allowed the biological validation of known genetic associations to GAS NSTI. The combined utility of ARI-BXD and HLA-II mice as complementary approaches that offer clinically translatable insights into pathomechanisms driven by complex traits and host genetic context and novel means to evaluate the in vivo efficiency of therapies to improve outcomes of GAS NSTI are also discussed.

Discordant rearrangement of primary and anamnestic CD8+ T cell responses to influenza A viral epitopes upon exposure to bacterial superantigens: Implications for prophylactic vaccination, heterosubtypic immunity and superinfections

Infection with (SAg)-producing bacteria may precede or follow infection with or vaccination against influenza A viruses (IAVs). However, how SAgs alter the breadth of IAV-specific CD8⁺ T cell (T_CD8) responses is unknown. Moreover, whether recall responses mediating heterosubtypic immunity to IAVs are manipulated by SAgs remains unexplored. We employed wild-type (WT) and mutant bacterial SAgs, SAg-sufficient/deficient Staphylococcus aureus strains, and WT, mouse-adapted and reassortant IAV strains in multiple in vivo settings to address the above questions. Contrary to the popular view that SAgs delete or anergize T cells, systemic administration of staphylococcal enterotoxin B (SEB) or Mycoplasma arthritidis mitogen before intraperitoneal IAV immunization enlarged the clonal size of ‘select’ IAV-specific T_CD8 and reshuffled the hierarchical pattern of primary T_CD8 responses. This was mechanistically linked to the TCR Vβ makeup of the impacted clones rather than their immunodominance status. Importantly, SAg-expanded T_CD8 retained their IFN-γ production and cognate cytolytic capacities. The enhancing effect of SEB on immunodominant T_CD8 was also evident in primary responses to vaccination with heat-inactivated and live attenuated IAV strains administered intramuscularly and intranasally, respectively. Interestingly, in prime-boost immunization settings, the outcome of SEB administration depended strictly upon the time point at which this SAg was introduced. Accordingly, SEB injection before priming raised CD127^highKLRG1^low memory precursor frequencies and augmented the anamnestic responses of SEB-binding T_CD8. By comparison, introducing SEB before boosting diminished recall responses to IAV-derived epitopes drastically and indiscriminately. This was accompanied by lower Ki67 and higher Fas, LAG-3 and PD-1 levels consistent with a pro-apoptotic and/or exhausted phenotype. Therefore, SAgs can have contrasting impacts on anti-IAV immunity depending on the naïve/memory status and the TCR composition of exposed T_CD8. Finally, local administration of SEB or infection with SEB-producing S. aureus enhanced pulmonary T_CD8 responses to IAV. Our findings have clear implications for superinfections and prophylactic vaccination.

Exposure to bacterial superantigens (SAgs) is often a consequence of infection with common Gram-positive bacteria causing septic and toxic shock or food poisoning. How SAgs affect the magnitude, breadth and quality of infection/vaccine-elicited CD8⁺ T cell (T_CD8) responses to respiratory viral pathogens, including influenza A viruses (IAVs), is far from clear. Also importantly, superinfections with IAVs and SAg-producing bacteria are serious clinical occurrences during seasonal and pandemic flu and require urgent attention. We demonstrate that two structurally distinct SAgs, including staphylococcal enterotoxin B (SEB), unexpectedly enhance primary T_CD8 responses to ‘select’ IAV-derived epitopes depending on the TCR makeup of the responding clones. Intriguingly, the timing of exposure to SEB dictates the outcome of prime-boost immunization. Seeing a SAg before priming raises memory precursor frequencies and augments anamnestic T_CD8 responses. Conversely, a SAg encounter before boosting renders T_CD8 prone to death or exhaustion and impedes recall responses, thus likely compromising heterosubtypic immunity to IAVs. Finally, local exposure to SEB increases the pulmonary response of immunodominant IAV-specific T_CD8. These findings shed new light on how bacterial infections and SAgs influence the effectiveness of anti-IAV T_CD8 responses, and have, as such, wide-ranging implications for preventative vaccination and infection control.

Nature of T cell epitopes in lupus antigens and HLA-DR determines autoantibody initiation and diversification

OBJECTIVES

The generation of systemic lupus erythematosus (SLE)-related autoantibodies have been shown to be T cell dependent and antigen driven with HLA-DR restriction. In this study, the initiating antigen(s) and the mechanism of autoantibody diversification were investigated.

METHODS

T cell epitopes (T-epitopes) of SmD1 (SmD) were mapped by T-T hybridomas generated from DR3+AE0 mice immunised with SmD and with SmD overlapping peptides. TCRs from the reactive hybridomas were sequenced. The core epitopes were determined. Bacterial mimics were identified by bioinformatics. Sera from DR3+AE0 mice immunised with SmD peptides and their mimics were analysed for their reactivity by ELISA and immunohistochemistry. Samples of blood donors were analysed for HLA-DR and autoantibody specificities.

RESULTS

Multiple HLA-DR3 restricted T-epitopes within SmD were identified. Many T-T hybridomas reacted with more than one epitope. Some of them were cross-reactive with other snRNP peptides and with proteins in the Ro60/La/Ro52 complex. The reactive hybridomas used unique TCRs. Multiple T-epitope mimics were identified in commensal and environmental bacteria. Certain bacterial mimics shared both T and B cell epitopes with the related SmD peptide. Bacterial mimics induced autoantibodies to lupus-related antigens and to different tissues. HLA-DR3+ blood donors made significantly more SLE-related autoantibodies.

CONCLUSIONS

The unique antigenic structures of the lupus-related autoantigens provide the basis for being targeted and for T and B cell epitope spreading and autoantibody diversification with unique patterns. SLE-related autoantibodies are likely generated from responses to commensal and/or environmental microbes due to incomplete negative selection for autoreactive T cells. The production of SLE-related antibodies is inevitable in normal individuals. The findings in this investigation have significant implications in autoimmunity in general.

Leaf-Encapsulated Vaccines: Agroinfiltration and Transient Expression of the Antigen Staphylococcal Endotoxin B in Radish Leaves

Transgene introgression is a major concern associated with transgenic plant-based vaccines. Agroinfiltration can be used to selectively transform nonreproductive organs and avoid introgression. Here, we introduce a new vaccine modality in which Staphylococcal enterotoxin B (SEB) genes are agroinfiltrated into radishes (Raphanw sativus L.), resulting in transient expression and accumulation of SEB in planta. This approach can simultaneously express multiple antigens in a single leaf. Furthermore, the potential of high-throughput vaccine production was demonstrated by simultaneously agroinfiltrating multiple radish leaves using a multichannel pipette. The expression of SEB was detectable in two leaf cell types (epidermal and guard cells) in agroinfiltrated leaves. ICR mice intranasally immunized with homogenized leaves agroinfiltrated with SEB elicited detectable antibody to SEB and displayed protection against SEB-induced interferon-gamma (IFN-γ) production. The concept of encapsulating antigens in leaves rather than purifying them for immunization may facilitate rapid vaccine production during an epidemic disease.

Therapeutic blockade of CD54 attenuates pulmonary barrier damage in T cell-induced acute lung injury

Acute respiratory distress syndrome (ARDS) is a serious, often fatal condition without available pharmacotherapy. Although the role of innate cells in ARDS has been studied extensively, emerging evidence suggests that T cells may be involved in disease etiology. Staphylococcus aureus enterotoxins are potent T-cell mitogens capable of triggering life-threatening shock. We demonstrate that 2 days after inhalation of S. aureus enterotoxin A, mice developed T cell-mediated increases in vascular permeability, as well as expression of injury markers and caspases in the lung. Pulmonary endothelial cells underwent sequential phenotypic changes marked by rapid activation coinciding with inflammatory events secondary to T-cell priming, followed by reductions in endothelial cell number juxtaposing simultaneous T-cell expansion and cytotoxic differentiation. Although initial T-cell activation influenced the extent of lung injury, CD54 (ICAM-1) blocking antibody administered well after enterotoxin exposure substantially attenuated pulmonary barrier damage. Thus CD54-targeted therapy may be a promising candidate for further exploration into its potential utility in treating ARDS patients.

Intra-tracheal Administration of Haemophilus influenzae in Mouse Models to Study Airway Inflammation

Here, we describe a detailed procedure to efficiently and directly deliver Haemophilus influenzae into the lower respiratory tracts of mice. We demonstrate the procedure for preparing H. influenzae inoculum, intra-tracheal instillation of H. influenzae into the lung, collection of broncho-alveolar lavage fluid (BALF), analysis of immune cells in the BALF, and RNA isolation for differential gene expression analysis. This procedure can be used to study the lung inflammatory response to any bacteria, virus or fungi. Direct tracheal instillation is mostly preferred over intranasal or aerosol inhalation procedures because it more efficiently delivers the bacterial inoculum into the lower respiratory tract with less ambiguity.

Trace Levels of Staphylococcal Enterotoxin Bioactivity Are Concealed in a Mucosal Niche during Pulmonary Inflammation

Pathogen and cellular by-products released during infection or trauma are critical for initiating mucosal inflammation. The localization of these factors, their bioactivity and natural countermeasures remain unclear. This concept was studied in mice undergoing pulmonary inflammation after Staphylococcal enterotoxin A (SEA) inhalation. Highly purified bronchoalveolar lavage fluid (BALF) fractions obtained by sequential chromatography were screened for bioactivity and subjected to mass spectrometry. The Inflammatory and inhibitory potentials of the identified proteins were measured using T cells assays. A potent pro-inflammatory factor was detected in BALF, and we hypothesized SEA could be recovered with its biological activity. Highly purified BALF fractions with bioactivity were subjected to mass spectrometry. SEA was the only identified protein with known inflammatory potential, and unexpectedly, it co-purified with immunosuppressive proteins. Among them was lactoferrin, which inhibited SEA and anti-CD3/-CD28 stimulation by promoting T cell death and reducing TNF synthesis. Higher doses of lactoferrin were required to inhibit effector compared to resting T cells. Inhibition relied on the continual presence of lactoferrin rather than a programming event. The data show a fraction of bioactive SEA resided in a mucosal niche within BALF even after the initiation of inflammation. These results may have clinical value in human diagnostic since traces levels of SEA can be detected using a sensitive bioassay, and may help pinpoint potential mediators of lung inflammation when molecular approaches fail.

Staphylococcal enterotoxin burden determines the type of T helper cell response and pathology of the maxillary sinus mucosa in rabbits

Staphylococcal enterotoxin (SE) induces T lymphocyte activation along with nasal allergic inflammation during rhinosinusitis, but it is under debate on which types of T helper (Th) cells respond exclusively or whether they respond synergically. We hypothesize that their responses may vary based on dose of SE. To test this hypothesis, we initiated to determine the nature of the T cell response and pathological feature upon repeated exposure to staphylococcal enterotoxin A (SEA) at different doses in the maxillary sinus of rabbits. SEA (0.6 or 60 ng) was instilled daily into the left maxillary sinus of rabbits for 28 days. The right maxillary sinus receiving normal saline was used as control. Mucosal histological changes were examined by hematoxylin-eosin and toluidine blue staining. Tissue expression of myeloperoxidase (MPO), eosinophil cationic protein (ECP), T-box expressed in T cells (T-bet), and GATA binding protein 3 (GATA-3) were examined using immunohistochemistry. Mucosal levels of representative pro-inflammatory cytokines were measured using ELISA. SEA at 60 ng/day induced acute rhinosinusitis, as confirmed by CT scan. Histopathologic examination revealed epithelial disruption, subepithelial edema, and inflammatory cell infiltration. MPO and T-bet expression, as well as interleukin (IL)-2 and interferon (IFN)-γ levels, were up-regulated. However, 0.6 ng/day SEA did not cause discharge. Histological examination revealed prominent eosinophilic infiltration. ECP and GATA-3 expression, as well as IL-4 and IL-5 levels, were increased at this lower dose. In conclusion, SEA induces acute rhinosinusitis associated with a Th1-type immune response at high dose, and a predominantly Th2-biased allergic inflammation at low dose.

A study of the association of childhood asthma with HLA alleles in the population of Siliguri, West Bengal, India

Asthma is a heterogeneous disease for which a strong genetic basis is firmly established. It is a complex disorder influenced by gene-environment interaction. Human leukocyte antigen (HLA) genes have been shown to be consistently associated with asthma and its related phenotypes in various populations. The aim of this study was to determine the frequency of the selected HLA classes I and II allelic groups in asthmatic and control groups. HLA typing was performed using polymerase chain reaction-sequence-specific typing (PCR-SSP) method. The allele frequency was estimated by direct counting. Frequency of each HLA allelic group was compared between asthmatic group and control group using χ(2) test. P-value was corrected by multiplying with the number of the allelic groups studied. Odds ratio (OR) and its corresponding 95% confidence interval (CI) for each allelic group were calculated using graphpad instat 3.10. The results of this study showed a significantly higher frequency of HLA-DRB1*03 in asthmatics than in controls (11.43% vs 3.64%, OR = 3.78, 95% CI = 1.61-8.85, P = 0.0025, Pcorr  < 0.05). Analysis of HLA alleles in low and high total serum immunoglobulin E (IgE) level in asthmatics revealed no significant association. HLA-DRB1*03 may be implicated in the susceptibility to asthma in the pediatric population.

Late multiple organ surge in interferon-regulated target genes characterizes staphylococcal enterotoxin B lethality

Background

Bacterial superantigens are virulence factors that cause toxic shock syndrome. Here, the genome-wide, temporal response of mice to lethal intranasal staphylococcal enterotoxin B (SEB) challenge was investigated in six tissues.

Results

The earliest responses and largest number of affected genes occurred in peripheral blood mononuclear cells (PBMC), spleen, and lung tissues with the highest content of both T-cells and monocyte/macrophages, the direct cellular targets of SEB. In contrast, the response of liver, kidney, and heart was delayed and involved fewer genes, but revealed a dominant genetic program that was seen in all 6 tissues. Many of the 85 uniquely annotated transcripts participating in this shared genomic response have not been previously linked to SEB. Nine of the 85 genes were subsequently confirmed by RT-PCR in every tissue/organ at 24 h. These 85 transcripts, up-regulated in all tissues, annotated to the interferon (IFN)/antiviral-response and included genes belonging to the DNA/RNA sensing system, DNA damage repair, the immunoproteasome, and the ER/metabolic stress-response and apoptosis pathways. Overall, this shared program was identified as a type I and II interferon (IFN)-response and the promoters of these genes were highly enriched for IFN regulatory matrices. Several genes whose secreted products induce the IFN pathway were up-regulated at early time points in PBMCs, spleen, and/or lung. Furthermore, IFN regulatory factors including Irf1, Irf7 and Irf8, and Zbp1, a DNA sensor/transcription factor that can directly elicit an IFN innate immune response, participated in this host-wide SEB signature.

Conclusion

Global gene-expression changes across multiple organs implicated a host-wide IFN-response in SEB-induced death. Therapies aimed at IFN-associated innate immunity may improve outcome in toxic shock syndromes.

Host genotype, intestinal microbiota and inflammatory disorders

Intestinal microbiota may influence human physiology and disease risk due to the role it plays in mediating appropriate immune responses to harmful and innocuous antigens. Colonisation of the intestine in early life seems particularly important as it is the main environmental stimulus for immune system maturation. This is a dynamic process, which depends on both environmental and genetic factors. The pathogenesis of inflammatory bowel disease, such as Crohn's disease, involves genetic polymorphisms (e.g. CARD15/nucleotide-binding oligomerisation domain 2) related to an excessive inflammatory response to commensal microbiota and to its unbalanced composition. Atopic diseases have also been linked to imbalances in microbiota and to related genetic factors (e.g. TLR4 and CD14 genes), although these associations are still controversial. Research into the relationship between the genetic risk of developing celiac disease (human leukocyte antigen (HLA)-DQ2/DQ8) and the early colonisation process in infants at family risk of the disease has also reported that the HLA-DQ genotype could influence staphylococcal colonisation. Future observational studies considering both host genetics and microbiota could be critical in defining the complex host-microbe interactions and the respective role each plays in inflammatory disorders.

Evaluation of a recombinant double mutant of staphylococcal enterotoxin B (SEB-H32Q/K173E) with enhanced antitumor activity effects and decreased pyrexia

BACKGROUND

Immunotherapy has been used to improve patient immune function, inhibit tumor growth and has become a highly promising method of cancer treatment. Highly agglutinative staphylococcin (HAS), a mixture of Staphylococcus aureus culture filtrates, which include staphylococcal enterotoxin (SE) C as the active ingredient, has been used clinically as an immunomodifier in the treatment of a number of tumors for many years. However, the use of HAS has been associated with some unavoidable side-effects such as fever. Previous studies have shown that SEB stimulates a more potent activation of T lymphocytes than SEC3, and mutations of the histidine residues eliminated the toxicity of SEB. SE mutants with decreased side-effects and/or more potent antitumor activities are required.

METHODOLOGY/PRINCIPAL FINDINGS

We built a structural model of the MHC II-SEB-TCR complex and found that a mutation of SEB at Lys173 might decrease the repulsion force between the SEB-TCR, which would facilitate their interaction. From the above results, we designed SEB-H32Q/K173E (mSEB). Analysis of in vitro stimulation of the proliferation of human peripheral blood mononuclear cells (PBMCs), IFN-γ secretion and inhibition of the growth of various tumor cell lines demonstrated that mSEB exhibited higher antitumor activity compared with wild-type SEB (wtSEB). Notably, mSEB inhibited the growth of various tumors at an extremely low concentration with little cytotoxicity against normal cells. Three animal tumor models (C57BL/6 mouse, New Zealand rabbit and a humanized NOD/SCID mouse) were used to evaluate the in vivo immunotherapeutic effects. Compared with wtSEB, mSEB significantly enhanced antitumor effect in more than one animal model with reduced pyrexia toxicity and prolonged the survival of tumor-bearing mice.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that SEB-H32Q/K173E retains superantigen (SAg) characteristics and enhances the host immune response to neoplastic diseases while reducing associated pyrogenic toxicity.

Chronic exposure to staphylococcal superantigen elicits a systemic inflammatory disease mimicking lupus

Chronic nasal and skin colonization with superantigen (SAg)-producing Staphylococcus aureus is well documented in humans. Given that trans-mucosal and trans-cutaneous absorption of SAgs can occur, we determined whether chronic exposure to small amounts of SAg per se could activate autoreactive CD4(+) and CD8(+) T cells and precipitate any autoimmune disease without further external autoantigenic stimulation. Because HLA class II molecules present SAg more efficiently than do mouse MHC class II molecules, HLA-DQ8 transgenic mice were implanted s.c. with mini-osmotic pumps capable of continuously delivering the SAg, staphylococcal enterotoxin B (total of 10 μg/mouse), or PBS over 4 wk. Chronic exposure to staphylococcal enterotoxin B resulted in a multisystem autoimmune inflammatory disease with features similar to systemic lupus erythematosus. The disease was characterized by mononuclear cell infiltration of lungs, liver, and kidneys, accompanied by the production of anti-nuclear Abs and deposition of immune complexes in the renal glomeruli. The inflammatory infiltrates in various organs predominantly consisted of CD4(+) T cells bearing TCR Vβ8. The extent of immunopathology was markedly reduced in mice lacking CD4(+) T cells and CD28, indicating that the disease is CD4(+) T cell mediated and CD28 dependent. The absence of disease in STAT4-deficient, as well as IFN-γ-deficient, HLA-DQ8 mice suggested the pathogenic role of Th1-type cytokines, IL-12 and IFN-γ. In conclusion, our study suggests that chronic exposure to extremely small amounts of bacterial SAg could be an etiological factor for systemic lupus erythematosus.

Staphylococcus aureus enterotoxin B contributes to induction of nasal polypoid lesions in an allergic rhinosinusitis murine model

BACKGROUND

Studies on the pathophysiology of nasal polyps in human subjects have been limited; thus an animal model is needed. There is increasing evidence supporting the role of Staphylococcus aureus enterotoxin B (SEB) in the pathogenesis of nasal polyposis. The aim of this study was to investigate the histological and immunologic effects of SEB on the formation of nasal polypoid lesions in an allergic rhinosinusitis murine model.

METHODS

After induction of an ovalbumin (OVA)-induced allergic rhinosinusitis, OVA with SEB (5 or 500 ng) was instilled into the nasal cavity of mice for 8 weeks. Control mice did not receive SEB or OVA instillation. Histopathological changes were observed using hematoxylin and eosin, Sirius red, Giemsa, Masson's trichrome, and Alcian blue stains. The levels of interleukin (IL)-4, IL-5, IL-8, IL-13, eotaxin, interferon gamma, total IgE, and OVA-specific IgE from serum or nasal lavage fluid were measured using enzyme-linked immunosorbent assay.

RESULTS

The group treated with OVA plus 5 ng of SEB had significantly more mucosal lesions with epithelial disruption and nasal polypoid lesions than mice treated with OVA only, showing a significant increase in the infiltration of total inflammatory cells, eosinophils, and lymphocytes than the other groups. Levels of IL-5, eotaxin, and OVA-specific IgE in nasal lavage fluid were increased in the group treated with OVA plus 5 ng of SEB than in the other groups. A higher number of secretory cells in the groups treated with OVA plus SEB was observed than in other groups.

CONCLUSION

Low-dose SEB induced nasal polypoid lesions with an increased eosinophilic infiltration in an allergic rhinosinusitis murine model.

Infection, eosinophilia and childhood asthma

There is a growing list of viruses and bacteria associated with wheezing illness and asthma. It is well known that a few of these pathogens are strongly associated with wheezing illness and asthma exacerbations. What is not known is if early childhood infections with these pathogens cause asthma, and, if so, exactly what are the pathophysiologic mechanisms behind its development. The current consensus is respiratory infection works together with allergy to produce the immune and physiologic conditions necessary for asthma diasthesis. One link between respiratory infection and asthma may be the eosinophil, a cell that plays prominently in asthma and allergy, but can also be found in the body in response to infection. In turn, the eosinophil and its associated products may be novel therapeutic targets, or at the very least used to elucidate the complex pathophysiologic pathways of asthma and other respiratory illnesses. Together or separately, they can also be used for diagnosis, treatment and monitoring. The optimal care of a patient must take into consideration not only symptoms, but also the underlying disease mechanisms.

The impact of tacrolimus on the immunopathogenesis of staphylococcal enterotoxin-induced systemic inflammatory response syndrome and pneumonia

Staphylococcal superantigens (SAg) are a family of potent exotoxins produced by Staphylococcus aureus. They play an important role in the pathogenesis of staphylococcal shock and pneumonia by causing a robust activation of the immune system and eliciting a strong surge in systemic cytokine and chemokine levels. Given the biological functions of SAg, we evaluated the efficacy of tacrolimus, a potent immunosuppressive agent, in the prophylaxis and therapy of staphylococcal TSS and pneumonia using human leukocyte antigen (HLA)-DR3 transgenic mice. Tacrolimus significantly inhibited staphylococcal SAg induced T cell activation in vitro. In vivo, tacrolimus significantly suppressed the SAg-induced elevation in serum cytokine and chemokine levels when given prophylactically, when administered immediately or even 2 h following systemic SAg challenge. Paradoxically, neither the prophylactic nor post-exposure treatment with tacrolimus protected mice from lethal SAg-induced TSS. A closer examination revealed that tacrolimus failed to suppress SAg-induced T cell proliferation and systemic pathology, including gut dysfunction. Tacrolimus also failed to protect from lethal pneumonia induced by a SAg-producing S. aureus strain. Thus, our study showed that even though T cell activation by SAg plays a major role in the immunopathogenesis of TSS and pneumonia, tacrolimus alone has no beneficial effect.

Chimeric anti-staphylococcal enterotoxin B antibodies and lovastatin act synergistically to provide in vivo protection against lethal doses of SEB

Staphylococcal enterotoxin B (SEB) is one of a family of toxins secreted by Staphylococcus aureus that act as superantigens, activating a large fraction of the T-cell population and inducing production of high levels of inflammatory cytokines that can cause toxic shock syndrome (TSS) and death. Extracellular engagement of the TCR of T-cells and class II MHC of antigen presenting cells by SEB triggers the activation of many intracellular signaling processes. We engineered chimeric antibodies to block the extracellular engagement of cellular receptors by SEB and used a statin to inhibit intracellular signaling. Chimeric human-mouse antibodies directed against different neutralizing epitopes of SEB synergistically inhibited its activation of human T-cells in vitro. In the in vivo model of lethal toxic shock syndrome (TSS) in HLA-DR3 transgenic mice, two of these antibodies conferred significant partial protection when administered individually, but offered complete protection in a synergistic manner when given together. Similarly, in vivo, lovastatin alone conferred only partial protection from TSS similar to single anti-SEB antibodies. However, used in combination with one chimeric neutralizing anti-SEB antibody, lovastatin provided complete protection against lethal TSS in HLA-DR3 transgenic mice. These experiments demonstrate that in vivo protection against lethal doses of SEB can be achieved by a statin of proven clinical safety and chimeric human-mouse antibodies, agents now widely used and known to be of low immunogenicity in human hosts.

Immunopathogenesis of Staphylococcus aureus pulmonary infection

Staphylococcus aureus is a common human pathogen highly evolved as both a component of the commensal flora and as a major cause of invasive infection. Severe respiratory infection due to staphylococci has been increasing due to the prevalence of more virulent USA300 CA-MRSA strains in the general population. The ability of S. aureus to adapt to the milieu of the respiratory tract has facilitated its emergence as a respiratory pathogen. Its metabolic versatility, the ability to scavenge iron, coordinate gene expression, and the horizontal acquisition of useful genetic elements have all contributed to its success as a component of the respiratory flora, in hospitalized patients, as a complication of influenza and in normal hosts. The expression of surface adhesins facilitates its persistence in the airways. In addition, the highly sophisticated interactions of the multiple S. aureus virulence factors, particularly the α-hemolysin and protein A, with diverse immune effectors in the lung such as ADAM10, TNFR1, EGFR, immunoglobulin, and complement all contribute to the pathogenesis of staphylococcal pneumonia.

Human leukocyte antigen class II transgenic mouse model unmasks the significant extrahepatic pathology in toxic shock syndrome

Among the exotoxins produced by Staphylococcus aureus and Streptococcus pyogenes, the superantigens (SAgs) are the most potent T-cell activators known to date. SAgs are implicated in several serious diseases including toxic shock syndrome (TSS), Kawasaki disease, and sepsis. However, the immunopathogenesis of TSS and other diseases involving SAgs are still not completely understood. The commonly used conventional laboratory mouse strains do not respond robustly to SAgs in vivo. Therefore, they must be artificially rendered susceptible to TSS by using sensitizing agents such as d-galactosamine (d-galN), which skews the disease exclusively to the liver and, hence, is not representative of the disease in humans. SAg-induced TSS was characterized using transgenic mice expressing HLA class II molecules that are extremely susceptible to TSS without d-galN. HLA-DR3 transgenic mice recapitulated TSS in humans with extensive multiple-organ inflammation affecting the lung, liver, kidneys, heart, and small intestines. Heavy infiltration with T lymphocytes (both CD4(+) and CD8+), neutrophils, and macrophages was noted. In particular, the pathologic changes in the small intestines were extensive and accompanied by significantly altered absorptive functions of the enterocytes. In contrast to massive liver failure alone in the d-galN sensitization model of TSS, findings of the present study suggest that gut dysfunction might be a key pathogenic event that leads to high morbidity and mortality in humans with TSS.

HLA-DR3 restricted T cell epitope mimicry in induction of autoimmune response to lupus-associated antigen SmD

Although systemic lupus erythematosus (SLE) is a multigenic autoimmune disorder, HLA-D is the most dominant genetic susceptibility locus. This study was undertaken to investigate the hypothesis that microbial peptides bind HLA-DR3 and activate T cells reactive with lupus autoantigens. Using HLA-DR3 transgenic mice and lupus-associated autoantigen SmD protein, SmD(79-93) was identified to contain a dominant HLA-DR3 restricted T cell epitope. This T cell epitope was characterized by using a T-T hybridoma, C1P2, generated from SmD immunized HLA-DR3 transgenic mouse. By pattern search analysis, 20 putative mimicry peptides (P2-P21) of SmD(79-93,) from microbial and human origin were identified. C1P2 cells responded to SmD, SmD(79-93) and a peptide (P20) from Vibro cholerae. Immunization of HLA-DR3 mice with P20 induced T cell responses and IgG antibodies to SmD that were not cross-reactive with the immunogen. A T-T hybridoma, P20P1, generated from P20 immunized mice, not only responded to P20 and SmD(79-93), but also to peptides from Streptococcus agalactiae (P17) and human-La related protein (P11). These three T cell mimics (P20, P11 and P17) induced diverse and different autoantibody response profiles. Our data demonstrates for the first time molecular mimicry at T cell epitope level between lupus-associated autoantigen SmD and microbial peptides. Considering that distinct autoreactive T cell clones were activated by different microbial peptides, molecular mimicry at T cell epitope level can be an important pathway for the activation of autoreactive T cells resulting in the production of autoantibodies. In addition, the novel findings reported herein may have significant implications in the pathogenesis of SLE.

Gram-positive bacterial superantigen outside-in signaling causes toxic shock syndrome

Staphylococcus aureus and Streptococcus pyogenes (group A streptococci) are Gram-positive pathogens capable of producing a variety of bacterial exotoxins known as superantigens. Superantigens interact with antigen-presenting cells (APCs) and T cells to induce T cell proliferation and massive cytokine production, which leads to fever, rash, capillary leak and subsequent hypotension, the major symptoms of toxic shock syndrome. Both S. aureus and group A streptococci colonize mucosal surfaces, including the anterior nares and vagina for S. aureus, and the oropharynx and less commonly the vagina for group A streptococci. However, due to their abilities to secrete a variety of virulence factors, the organisms can also cause illnesses from the mucosa. This review provides an updated discussion of the biochemical and structural features of one group of secreted virulence factors, the staphylococcal and group A streptococcal superantigens, and their abilities to cause toxic shock syndrome from a mucosal surface. The main focus of this review, however, is the abilities of superantigens to induce cytokines and chemokines from epithelial cells, which has been linked to a dodecapeptide region that is relatively conserved among all superantigens and is distinct from the binding sites required for interactions with APCs and T cells. This phenomenon, termed outside-in signaling, acts to recruit adaptive immune cells to the submucosa, where the superantigens can then interact with those cells to initiate the final cytokine cascades that lead to toxic shock syndrome.

HLA-DR polymorphism modulates response to house dust mites in a transgenic mouse model of airway inflammation

We and others have reported that HLA-DRB1*03 is associated with childhood asthma. To extend this observation and to prove this association, we sensitized and challenged either HLA-DR2 (HLA-DRB1*1502) or HLA-DR3 (HLA-DRB1*0301) transgenic mice with house-dust mite extract. Inflammatory cell counts and cytokine levels in the bronchoalveolar lavage (BAL) fluid between HLA-DR3 and DR2 mice were compared. HLA-DR3 transgenic mice had significantly elevated eosinophil counts, Interleukin-4 and Interleukin-13 levels in the BAL fluid but not interferron gamma-γ. Thus, our study suggests that HLA-DRB1*0301 plays an important role in mounting a Th2-predominant immune response to house dust mite and Th2-type inflammation in the lung.

Interferon gamma-dependent intestinal pathology contributes to the lethality in bacterial superantigen-induced toxic shock syndrome

Toxic shock syndrome (TSS) caused by the superantigen exotoxins of Staphylococcus aureus and Streptococcus pyogenes is characterized by robust T cell activation, profound elevation in systemic levels of multiple cytokines, including interferon-γ (IFN-γ), followed by multiple organ dysfunction and often death. As IFN-γ possesses pro- as well as anti-inflammatory properties, we delineated its role in the pathogenesis of TSS. Antibody-mediated in vivo neutralization of IFN-γ or targeted disruption of IFN-γ gene conferred significant protection from lethal TSS in HLA-DR3 transgenic mice. Following systemic high dose SEB challenge, whereas the HLA-DR3.IFN-γ^+/+ mice became sick and succumbed to TSS, HLA-DR3.IFN-γ^−/− mice appeared healthy and were significantly protected from SEB-induced lethality. SEB-induced systemic cytokine storm was significantly blunted in HLA-DR3.IFN-γ^−/− transgenic mice. Serum concentrations of several cytokines (IL-4, IL-10, IL-12p40 and IL-17) and chemokines (KC, rantes, eotaxin and MCP-1) were significantly lower in HLA-DR3.IFN-γ^−/− transgenic mice. However, SEB-induced T cell expansion in the spleens was unaffected and expansion of SEB-reactive TCR Vβ8⁺ CD4⁺ and CD8⁺ T cells was even more pronounced in HLA-DR3.IFN-γ^−/− transgenic mice when compared to HLA-DR3.IFN-γ^+/+ mice. A systematic histopathological examination of several vital organs revealed that both HLA-DR3.IFN-γ^+/+ and HLA-DR3.IFN-γ^−/− transgenic mice displayed comparable severe inflammatory changes in lungs, and liver during TSS. Remarkably, whereas the small intestines from HLA-DR3.IFN-γ^+/+ transgenic mice displayed significant pathological changes during TSS, the architecture of small intestines in HLA-DR3.IFN-γ^−/− transgenic mice was preserved. In concordance with these histopathological changes, the gut permeability to macromolecules was dramatically increased in HLA-DR3.IFN-γ^+/+ but not HLA-DR3.IFN-γ^−/− mice during TSS. Overall, IFN-γ seemed to play a lethal role in the immunopathogenesis of TSS by inflicting fatal small bowel pathology. Our study thus identifies the important role for IFN-γ in TSS.

The systemic and pulmonary immune response to staphylococcal enterotoxins

In response to environmental cues the human pathogen Staphylococcus aureus synthesizes and releases proteinaceous enterotoxins. These enterotoxins are natural etiologic entities of severe food poisoning, toxic shock syndrome, and acute diseases. Staphylococcal enterotoxins are currently listed as Category B Bioterrorism Agents by the Center for Disease Control and Prevention. They are associated with respiratory illnesses, and may contribute to exacerbation of pulmonary disease. This likely stems from the ability of Staphylococcal enterotoxins to elicit powerful episodes of T cell stimulation resulting in release of pro-inflammatory cytokines. Here, we discuss the role of the immune system and potential mechanisms of disease initiation and progression.

Potent neutralization of staphylococcal enterotoxin B by synergistic action of chimeric antibodies

Staphylococcal enterotoxin B (SEB), a shock-inducing exotoxin synthesized by Staphylococcus aureus, is an important cause of food poisoning and is a class B bioterrorism agent. SEB mediates antigen-independent activation of a major subset of the T-cell population by cross-linking T-cell receptors (TCRs) with class II major histocompatibility complex (MHC-II) molecules of antigen-presenting cells, resulting in the induction of antigen independent proliferation and cytokine secretion by a significant fraction of the T-cell population. Neutralizing antibodies inhibit SEB-mediated T-cell activation by blocking the toxin's interaction with the TCR or MHC-II and provide protection against the debilitating effects of this superantigen. We derived and searched a set of monoclonal mouse anti-SEB antibodies to identify neutralizing anti-SEB antibodies that bind to different sites on the toxin. A pair of non-cross-reactive, neutralizing anti-SEB monoclonal antibodies (MAbs) was found, and a combination of these antibodies inhibited SEB-induced T-cell proliferation in a synergistic rather than merely additive manner. In order to engineer antibodies more suitable than mouse MAbs for use in humans, the genes encoding the VL and VH gene segments of a synergistically acting pair of mouse MAbs were grafted, respectively, onto genes encoding the constant regions of human Igkappa and human IgG1, transfected into mammalian cells, and used to generate chimeric versions of these antibodies that had affinity and neutralization profiles essentially identical to their mouse counterparts. When tested in cultures of human peripheral blood mononuclear cells or splenocytes derived from HLA-DR3 transgenic mice, the chimeric human-mouse antibodies synergistically neutralized SEB-induced T-cell activation and cytokine production.

Critical timing, location and duration of glucocorticoid administration rescue mice from superantigen-induced shock and attenuate lung injury

Bacterial superantigens, such as staphylococcal enterotoxin B (SEB), are major virulence factors implicated in the pathogenesis of toxic shock. In this study we investigated the efficacy of glucocorticoid therapy in preventing SEB-induced lethal shock initiated through the respiratory route in mice. Dexamethasone, a potent anti-inflammatory steroid, administrated intranasally on the first day, followed by intraperitoneal doses on the subsequent 4 days, was effective in attenuating SEB-induced hypothermia, and reduction in systemic and pulmonary proinflammatory mediator release. This optimal dosing and schedule of glucocorticoid treatment mitigated lung inflammation and resulted in 100% survival in this intranasal mouse model of SEB-mediated shock.

Early gene expression changes induced by the bacterial superantigen staphylococcal enterotoxin B and its modulation by a proteasome inhibitor

Toxic shock syndrome (TSS) is an acute, serious systemic illness caused by bacterial superantigens. Nonavailability of a suitable animal model until recently has hampered an in-depth understanding of the pathogenesis of TSS. In the current study, we characterized the early molecular events underlying TSS using our HLA-DR3 transgenic mouse model. Gene expression profiling using DNA microarrays identified a rapid and significant upregulation of several pro- as well as anti-inflammatory mediators, many of which have never been previously described in TSS. In vivo administration of staphylococcal enterotoxin B (SEB) led to an increase in the expression of Th0- (IL-2, 240-fold); Th1- (IFN-gamma, 360-fold; IL-12, 8-fold); Th2- (IL-4, 53-fold; IL-5, 4-fold) as well as Th17-type cytokines (IL-21, 19-fold; IL-17, 5-fold). The immunoregulatory cytokines (IL-6, 700-fold; IL-10, 18-fold); CC chemokines (such as CCL 2, 11, 3, 24, 17, 12, 7), CXC chemokines (such as CXCL 1, 2, 5, 11, 10, 19); and several proteases (matrix metalloproteinases 13, 8, 3, and 9) were also upregulated. Serum levels of several of these cytokines/chemokines were also significantly elevated. Pathway analyses revealed significant modulation in a variety of biochemical and cellular functions, providing molecular insights into the pathogenesis of TSS. Administration of bortezomib, a clinically approved proteasome inhibitor capable of blocking NF-kappaB pathway, was able to significantly modulate the expression of a variety of genes induced by SEB. Thus, our study showed that TSS is a complex process and emphasized the potential of use of bortezomib in the therapy of superantigen-induced TSS.

Cytolysins augment superantigen penetration of stratified mucosa

Staphylococcus aureus and Streptococcus pyogenes colonize mucosal surfaces of the human body to cause disease. A group of virulence factors known as superantigens are produced by both of these organisms that allows them to cause serious diseases from the vaginal (staphylococci) or oral mucosa (streptococci) of the body. Superantigens interact with T cells and APCs to cause massive cytokine release to mediate the symptoms collectively known as toxic shock syndrome. In this study we demonstrate that another group of virulence factors, cytolysins, aid in the penetration of superantigens across vaginal mucosa as a representative nonkeratinized stratified squamous epithelial surface. The staphylococcal cytolysin alpha-toxin and the streptococcal cytolysin streptolysin O enhanced penetration of toxic shock syndrome toxin-1 and streptococcal pyrogenic exotoxin A, respectively, across porcine vaginal mucosa in an ex vivo model of superantigen penetration. Upon histological examination, both cytolysins caused damage to the uppermost layers of the vaginal tissue. In vitro evidence using immortalized human vaginal epithelial cells demonstrated that although both superantigens were proinflammatory, only the staphylococcal cytolysin alpha-toxin induced a strong immune response from the cells. Streptolysin O damaged and killed the cells quickly, allowing only a small release of IL-1beta. Two separate models of superantigen penetration are proposed: staphylococcal alpha-toxin induces a strong proinflammatory response from epithelial cells to disrupt the mucosa enough to allow for enhanced penetration of toxic shock syndrome toxin-1, whereas streptolysin O directly damages the mucosa to allow for penetration of streptococcal pyrogenic exotoxin A and possibly viable streptococci.

Inhalation of Staphylococcus aureus enterotoxin A induces IFN-gamma and CD8 T cell-dependent airway and interstitial lung pathology in mice

Staphylococcus aureus, a primary source of bacterial superantigen (SAg), is known to colonize the human respiratory tract and has been implicated in airway inflammation. Studies have documented a role for SAgs in respiratory disorders, such as nasal polyps, chronic obstructive pulmonary disease, chronic rhinosinusitis, and asthma. However, cellular and molecular mediators involved in SAg-mediated pulmonary disease have not been clearly identified. In this study, we investigated the effect of intranasal staphylococcal enterotoxin A (SEA) exposure on murine lung. The pathological features in the lung resulting from SEA exposure had characteristics of both obstructive and restrictive pulmonary disorders. There was also an increase in bronchoalveolar lavage protein concentration and cellularity following SEA challenge. Massive CD8(+)Vbeta3(+) T cell accumulation observed in the lung was dependent on CD4 T cell help, both for recruitment and for IFN-gamma synthesis. The primary source of IFN-gamma synthesis was CD8 T cells, and depletion of these cells abrogated disease. IFN-gamma deficiency also prevented SEA-mediated disease, and this was by enhancing early recruitment of neutrophils as detected in the bronchoalveolar lavage. Thus, IFN-gamma appeared to selectively aid the recruitment of T cells to the lungs while preventing the neutrophil accumulation. Therefore, our results show that IFN-gamma-producing CD8 T cells mediated pulmonary alveolitis and inflammation, which were dependent upon CD4 T cells for their recruitment to the lung.

Central roles for IL-2 and MCP-1 following intranasal exposure to SEB: a new mouse model

Murine models for bacterial superantigens like staphylococcal enterotoxin B (SEB) have to date been rather cumbersome. The reasons include: (1) necessary use of potentiating agents such as actinomycin D, d-galactosamine, lipopolysaccharide (LPS), or viruses; (2) high toxin amounts required to elicit effects; and/or (3) generation of phenotypic-stable transgenic animals. Our study employed readily available C3H/HeJ (TLR4 negative, LPS-nonresponsive) mice with intranasal and intraperitoneal administration of low microgram quantities of SEB. These animals responded to SEB with severe lung inflammation and hypothermia, culminating in death. A survey of cytokines/chemokines in sera and lungs after lethal intoxication revealed that monocyte chemoattractant protein-1 and interleukin-2 were associated with effects in this model. In contrast, SEB had minimal effects upon congenic (TLR4 positive, LPS-responsive) C3H/OuJ mice. Lethality of SEB in C3H/HeJ mice was neutralized with SEB-specific antibodies, suggesting potential utility of this model for future therapeutic studies.

Recruitment and in situ renewal regulate rapid accumulation of CD11c+ cells in the lung following intranasal superantigen challenge

BACKGROUND

Staphylococcusaureus, a primary source of bacterial superantigen, is known to colonize the human respiratory tract and has been implicated in airway inflammation. The potential pathological effect of staphylococcal enterotoxins on the respiratory tract necessitates a detailed understanding of how they regulate innate immune cells, particularly CD11c-expressing dendritic cells (DCs).

METHODS

C57BL/6 mice were challenged intranasally with staphylococcal enterotoxin A (SEA) and at indicated time points lung tissue was perfused, digested and analyzed for CD11c+ expressing cells.

RESULTS

The pulmonary CD11c+ cells can be divided into two major populations based on their MHC II expression. One day following intranasal SEA challenge, there was rapid accumulation of CD11c+ cells expressing medium to high levels of MHC II. The peak accumulation of CD11c+ MHC II- population was observed 2 days after SEA challenge; however, careful examination of this cell population revealed that they were heterogeneous, being comprised of cells bearing CD3, CD19, NK1.1 and F4/80 along with varying levels of CD11c. Nevertheless, there was a 2-fold increase of CD11c+ MHC II- (CD3- CD19- NK1.1- F4/80-) cells in the lungs.

CONCLUSION

The mechanism of increase in the CD11c+ MHC II- immune progenitor population was mainly due to cellular division rather than migration from blood to lung. In contrast, the early and rapid accumulation of CD11c+ MHC II(hi) cells, conventionally known as DCs, in the lung on day 1 was mostly due to migration from blood. Thus this study examines the pulmonary innate immune response to a powerful immune stimulus.

Rat model of staphylococcal enterotoxin B-induced rhinosinusitis

Objectives

It has been proposed that microbial persistence, superantigen (SA) production, and host T-cell response may be involved in the development of chronic rhinosinusitis. According to the SA hypothesis, a single intranasal application of SA such as staphylococcal enterotoxin B (SEB) may induce chronic eosinophilic rhinosinusitis. This study aimed to develop a rat model of rhinosinusitis induced by intranasally applied SEB.

Methods

Forty µL of SEB (100 µg/mL) or phosphate buffered saline was applied intranasally through each naris in 4 week-old Sprague-Dawley test rats (N=36) and controls (N=16), respectively. Following sacrifice at 1, 5, 14, and 28 days, the obtained nasal cavity and sinuses were prepared for histologic investigation. The histologic sections were examined in a blind manner for the ratio of the sinus spaces occupied by inflammatory cell clusters and the number of inflammatory cells in the lamina propria.

Results

Infiltration of neutrophils in the lamina propria and appearance of neutrophil clusters in the sinus spaces were observed in the SEB-applied rats. The ratio of the sinus spaces occupied by neutrophil clusters and the number of neutrophils infiltrated in the lamina propria increased significantly at day 1 as compared with the control rats.

Conclusion

Intranasally applied SEB induces acute neutrophilic rhinosinusitis in rats. Eosinophilic inflammation was not demonstrated. The mere presence of SA in the nose does not necessarily induce SA-induced inflammation, as suggested by the SA hypothesis.

Phase I trial of sirolimus combined with radiation and cisplatin in non-small cell lung cancer

PURPOSE

The safety and tolerability of sirolimus combined with thoracic radiation and cisplatin was evaluated in patients with lung cancer. In parallel, the effects of sirolimus were studied in a murine model of radiation pneumonitis.

MATERIALS AND METHODS

The phase I trial evaluated standard three-dimensional conformal thoracic radiation therapy (60 Gy) and weekly cisplatin (25 mg/m2 i.v.) in combination with escalating doses of oral sirolimus. Sirolimus drug levels and inhibition of mTOR signaling to ribosomal S6 protein were assessed in blood. The effects of sirolimus administered during and after whole thoracic radiation of C57BL6/J mice were evaluated by monitoring mouse breathing rates and survival.

RESULTS

Seven patients with stage III lung cancer were accrued to the clinical study. None of the four patients treated with 2 mg/day sirolimus developed dose-limiting toxicities. Three patients were treated with 5 mg/day sirolimus, and one patient at this dose level had dose-limiting toxicity of grade 3 dysphagia. However, the maximally tolerated dose of sirolimus in this regimen was not defined because the study was terminated prematurely because of loss of funding. In the mouse experiments, concomitant sirolimus treatment was not associated with an increase in radiation-associated morbidity or mortality.

CONCLUSIONS

Combination therapy with sirolimus, radiation, and cisplatin was well tolerated in patients.

Measurement of staphylococcal enterotoxin B in serum and culture supernatant with a capture enzyme-linked immunosorbent assay

Staphylococcal enterotoxin B (SEB) is a select agent because it is a potent mitogen that elicits life-threatening polyclonal T-cell proliferation and cytokine production at very low concentrations. Efforts are in progress to develop therapeutic reagents and vaccines that neutralize or prevent the devastating effects of this toxin. Because of its rapid binding to in vivo receptors, this toxin is difficult to detect in serum. This rapid binding also constitutes a major challenge for the development of effective therapeutic reagents that can neutralize the effects of the toxin in vivo. We have developed a highly sensitive capture enzyme-linked immunosorbent assay that detects SEB in body fluids at very low levels. With this assay, the peak levels of SEB in serum and renal clearance can be measured in mice. After either oral ingestion or nasal inhalation of SEB by mice, this assay documents the transcytosis of SEB across the mucosal membranes into serum within 2 h. Furthermore, this assay was used to compare the SEB levels in different murine models for SEB-induced lethal shock and demonstrated that the coadministration of toxin-enhancing chemicals, such as D-galactosamine and lipopolysaccharide, can alter the peak serum SEB levels. Hence, this assay is a potentially useful tool for the study of the pharmacokinetics of SEB and the effects of potential therapeutic reagents on serum SEB levels.

Severity of childhood asthma and human leukocyte antigens type

We sought to learn if Class II HLA genes are associated with the severity of asthma in children. We examined a previously recruited cohort of 340 healthy children who had Class II HLA allele data available. We conducted a comprehensive review of their medical records to determine asthma status and, when present, its severity. We found that Class II HLA alleles, which were previously reported to have an association with asthma incidence, appear to have an association as well with asthma severity. These data support our hypothesis that both the incidence and severity of asthma are heritable and that HLA may play an important role in both development and severity of asthma. Because of limited statistical power, our study findings are subject to further investigation.

Childhood asthma and human leukocyte antigen type

Little is known about the relationship between human leukocyte antigen (HLA) class II genes and family history of asthma or atopy in relation to the incidence of childhood asthma. The objective of the study was to determine whether specific HLA class II genes (e.g., DRB1*03) are associated with asthma and whether such association explains the influences of family history of asthma or atopy on asthma incidence. A stratified random sample of 340 children who had HLA data available from the Rochester Family Measles Study cohort (n= 876) and a convenience sample of healthy children aged 5-12 years were the participants. We conducted comprehensive medical record reviews to determine asthma status of these children. The associations between the presence of specific HLA alleles and development of asthma and the role of family history of asthma or atopy in the association were evaluated by fitting Cox models. The cumulative incidence of asthma by 12 years of age among children who carry HLA DRB1*03 was 33%, compared to 24.2% among those who did not carry this allele. Adjusting for family history of asthma or atopy, gender, low birth weight, season of birth, HLA DRB1*04, and HLA DQB1*0302, the hazards ratio for HLA DRB1*03 carriers was 1.8 (95% confidence interval: 1.1-2.9, P= 0.020). We concluded that the HLA DRB1*03 allele is associated with asthma. However, the HLA class II gene does not explain the influences of family history of asthma or atopy on development of asthma. The mechanism underlying the association between asthma and HLA genes needs to be elucidated.

HLA Transgenic Mice Provide Evidence for a Direct and Dominant Role of HLA Class II Variation in Modulating the Severity of Streptococcal Sepsis

Our epidemiologic studies on invasive Group A Streptococci (GAS) infections identified specific HLA class II haplotypes/alleles conferring high-risk or protection from streptococcal toxic shock syndrome with a strong protection conferred by the DRB1*15/DQB1*06 haplotype. We used HLA-transgenic mice to provide an in vitro and in vivo validation for the direct role of HLA class II allelic variation in streptococcal toxic shock syndrome. When splenocytes from mice expressing the protective HLA-DQB1*06 (DQ6) allele were stimulated with a mixture of streptococcal superantigens (SAgs), secreted by the prevalent M1T1 strain, both proliferative and cytokine responses were significantly lower than those of splenocytes from mice expressing the neutral DRB1*0402/DQB1*0302 (DR4/DQ8) alleles (p < 0.001). In crisscross experiments, the presentation of SAgs to pure T cells from either the DQ6 or the DR4/DQ8 mice resulted in significantly different levels of response depending on the HLA type expressed on the APCs. Presentation by HLA-DQ6 APCs elicited significantly lower responses than the presentation by HLA-DR4/DQ8 APCs. Our in vitro data were supported by in vivo findings, as the DQ6 mice showed significantly longer survival post-i.v. infection with live M1T1 GAS (p < 0.001) and lower inflammatory cytokine responses as compared with the DR4/DQ8 mice (p < 0.01). The data presented here provide evidence for a direct role of HLA class II molecules in modulating responses to GAS SAgs and underscore the dominant role of HLA class II allelic variation in potentiating the severity of GAS systemic infections.

Acute systemic immune activation following vaginal exposure to staphylococcal enterotoxin B—Implications for menstrual shock

Menstrual toxic shock syndrome (mTSS) is an acute systemic inflammatory disease associated with the superantigenic exotoxin, toxic shock syndrome toxin (TSST)-1, produced by Staphylococcus aureus and the use of high absorbency tampons. Even though S. aureus is capable of elaborating several other superantigenic exotoxins, only TSST-1 has been implicated in the pathogenesis of mTSS possibly because most other superantigenic exotoxins are known enterotoxins. Nonetheless, we have shown recently that one of the enterotoxigenic staphylococcal superantigens, staphylococcal enterotoxin B (SEB), can cause robust systemic immune activation following exposure through non-enteric mucosa, including nasal or conjunctival routes. In a similar manner, we show here that vaginal administration of SEB in HLA class II transgenic mice can cause robust systemic immune activation characterized by profound elevation of proinflammatory cytokines in the serum, activation and expansion of SEB-reactive CD4(+) and CD8(+) T cells in peripheral lymphoid organs and SEB-induced deletion of immature thymocytes. Vaginal administration of SEB also caused leukocytic infiltration in major organs, such as liver and lung, reminiscent of human toxic shock syndrome. Systemic immune activation following vaginal superantigen delivery was independent of the stage of the estrus cycle in the mouse. Using HLA class II transgenic mice, we have shown that exposure to SEB through the vaginal canal can cause robust systemic immune activation. SEB could thus play a role in the pathogenesis of mTSS.

Acute systemic immune activation following conjunctival exposure to staphylococcal enterotoxin B

Conjunctival exposure to the Staphylococcus aureus superantigen staphylococcal enterotoxin B (SEB) may occur accidentally, as a result of bioterrorism, or during colonization or infection of the external eye. Using human leukocyte antigen class II transgenic mice, we show for the first time that conjunctival exposure to SEB can cause robust systemic immune activation.