In vivo staphylococcal superantigen-driven polyclonal Ig responses in mice: dependence upon CD4(+) cells and human MHC class II

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.

Constitutive overexpression of BAFF in autoimmune-resistant mice drives only some aspects of systemic lupus erythematosus-like autoimmunity

OBJECTIVE

To determine whether overexpression of BAFF can promote systemic lupus erythematosus (SLE)-like autoimmunity in mice that are otherwise autoimmune-resistant.

METHODS

We used class II major histocompatibility complex (MHC)-deficient C57BL/6 (B6) mice as a model of resistance to SLE and Sles1-bearing B6 mice as a model of resistance to the autoantibody-promoting capacity of the Sle1 region. We generated BAFF-transgenic (Tg) counterparts to these respective mice and evaluated lymphocyte phenotype, serologic autoimmunity, renal immunopathology, and clinical disease in the BAFF-Tg and non-Tg mouse sets.

RESULTS

Although constitutive BAFF overexpression did not lead to B cell expansion in class II MHC-deficient B6 mice, it did lead to increased serum IgG autoantibody levels. Nevertheless, renal immunopathology was limited, and clinical disease did not develop. In B6 and B6.Sle1 mice, constitutive BAFF overexpression led to increased numbers of B cells and CD4+ memory cells, as well as increased serum IgG and IgA autoantibody levels. Renal immunopathology was modestly greater in BAFF-Tg mice than in their non-Tg counterparts, but again, clinical disease did not develop. Introduction of the Sles1 region into B6.Sle1.Baff mice abrogated the BAFF-driven increase in CD4+ memory cells and the Sle1-driven, but not the BAFF-driven, increase in serum IgG antichromatin levels. Renal immunopathology was substantially ameliorated.

CONCLUSION

Although constitutive BAFF overexpression in otherwise autoimmune-resistant mice led to humoral autoimmunity, meaningful renal immunopathology and clinical disease did not develop. This raises the possibility that BAFF overexpression, even when present, may not necessarily drive disease in some SLE patients. This may help explain the heterogeneity of the clinical response to BAFF antagonists in human SLE.

[Culture of dendritic cells in vitro and its anti-tumor immunotherapy]

背景与目的

恶性肿瘤患者免疫力低下，缺乏强有力的抗肿瘤免疫应答，其原因是肿瘤细胞的抗原性较弱，而且抗原提呈细胞的功能低下，使肿瘤抗原不能有效地提呈给淋巴细胞。因此如何能有效地诱导出抗肿瘤免疫效应是一个非常关键的问题。本研究通过建立体外培养树突状细胞（dendritic cells, DC）的方法并观察其诱导的抗肺癌作用的研究，为以DC为基础的肺癌免疫瘤苗的临床应用提供实验依据。

方法

3 mol/L氯化钾法提取人肺腺癌细胞GLC-82的可溶性抗原多肽；从人外周血单个核细胞（peripheral blood mononuclear cell, PBMC）中用GMCSF、IL-4和TNF-α体外诱导扩增DC，用流式细胞仪FCM及免疫染色法分析鉴定DC；肺癌肿瘤可溶性抗原（tumor soluble antigen, TSA）和超抗原金黄色葡萄球菌肠毒素A（staphylococcal enterotoxin A, SEA）联合修饰致敏DC；以联合抗原修饰后的DC、单纯肺癌抗原TSA致敏的DC、单纯超抗原SEA修饰的DC和未经抗原修饰的DC分别与外周血T淋巴细胞共同孵育，刺激T淋巴细胞活化增殖，诱导产生具有识别肺癌抗原的特异性CTL（作为效应细胞分别称为TSA-SEA-DCL、TSA-DCL、SEA-DCL、DCL）；采用MT法检测各效应细胞对靶细胞GLC-82、肺癌CALU-6和人红白血病K562细胞的抗癌活性；镜下观察DC、效应细胞形态及对靶细胞的杀伤过程。

结果

诱导出高表达CD1a、HLADR、CD80具有典型树突状细胞特性的DC；TSA-SEA-DCL对靶细胞GLC-82的杀伤率明显高于TSA-DCL、SEA-DCL及DCL，亦明显高于对K562细胞的杀伤率；与靶细胞共育时镜下发现效应细胞CTL靠近并聚集在肿瘤细胞周围，致使肿瘤细胞发生变性坏死及凋亡。

结论

本实验方法能成功诱导出具有典型特征的成熟DC，肺癌TSA联合超抗原SEA诱导的DC疫苗对肺癌细胞有高效特异杀伤作用。

Attenuation of massive cytokine response to the staphylococcal enterotoxin B superantigen by the innate immunomodulatory protein lactoferrin

Staphylococcal enterotoxin B (SEB) is a pyrogenic exotoxin and a potent superantigen which causes massive T cell activation and cytokine secretion, leading to profound immunosuppression and morbidity. The inhibition of SEB-induced responses is thus considered a goal in the management of certain types of staphylococcal infections. Lactoferrin (LF) is a multi-functional glycoprotein with both bacteriostatic and bactericidal activities. In addition, LF is known to have potent immunomodulatory properties. Given the anti-microbial and anti-inflammatory properties of this protein, we hypothesized that LF can modulate T cell responses to SEB. Here, we report that bovine LF (bLF) was indeed able to attenuate SEB-induced proliferation, interleukin-2 production and CD25 expression by human leucocyte antigen (HLA)-DR4 transgenic mouse T cells. This inhibition was not due to bLF's iron-binding capacity, and could be mimicked by the bLF-derived peptide lactoferricin. Cytokine secretion by an engineered SEB-responsive human Jurkat T cell line and by peripheral blood mononuclear cells from healthy donors was also inhibited by bLF. These findings reveal a previously unrecognized property of LF in modulation of SEB-triggered immune activation and suggest a therapeutic potential for this naturally occurring protein during toxic shock syndrome.

Triggering of T cell activation via CD4 dimers

The onset of activation in Th cells is triggered by localized co-engagement of TCRs and the coreceptor CD4. A CD4 crystal suggested that CD4 may form dimers in some circumstances. In this study, we use live-cell fluorescence resonance energy transfer imaging to demonstrate that CD4 dimers are present at a basal level on the cell surface and accumulate at the synapse. Mechanistically, we reveal two conditions under which dimers are highly relevant. First, CD4 dimers are more proficient in mediating prolonged cell contacts with APCs in the presence or absence of Ag. This is consistent with a model whereby the dimer functions to increase T-APC avidity. Second, we show that dimer mutations result in an increased level of an inactive lckTyr(505) bound to the CD4 molecule relative to dimer-competent CD4. We also find a consistent defect in signaling onset in these cells. This supports a role for CD4 dimerization in maintaining active signaling machinery. We suggest that modulation of the dimer/monomer ratio may permit tuning of activation thresholds during initial engagement.

Community-Acquired Pneumonia and Sepsis Caused by a Multiresistant Staphylococcus Aureus Strain Resulting in a Severe and Long-Lasting Multiple Organ Inflammatory Involvement

An exceptional case report of community-acquired, disseminated infection caused by a methicillin-resistant Staphylococcus aureus strain, responsible for pneumonia, sepsis, and scattered septic embolism, and accompanied by diffuse polyvisceritis and thrombophlebitis as signs of an overwhelming extensive activation of the immune system, is reported and discussed on the grounds of the most recent evidence in literature. The striking features of a severe, multiresistant S. aureus polyvisceral disease associated with multiple immune-mediated focal manifestations are in contrast with the community-acquired origin of infection and the apparent absence of supporting factors for both antimicrobial resistance and the unexpected, exaggerated immune activation occurred in an otherwise healthy man. The extensive immune activation status (as demonstrated by a proportionally maintained absolute lymphocyte cont and a T-cell subset study pointing out an increased quote of CD4+, CD34+, and CD4-CD8- cells, compared with a proportional decrease of CD8+ T-lymphocytes) probably had a prominent role in prompting several focal clinical features of our patient, which apparently were not directly related to bacterial invasion, such as the polyvisceritis, the massive pleuric and pericardial effusion, the myocarditis-pericarditis, and the thrombophlebitis occurring in multiple and remote body sites, as compared with to the initial respiratory localization. This case report raises multiple questions regarding the epidemiology, pathogenesis, clinical manifestations, and management of complicated S. aureus infection, including the role of novel antimicrobial agents and corticosteroids.

Development of serum IgM antibodies against superantigens of Staphylococcus aureus and Streptococcus pyogenes in Kawasaki disease

To serologically determine the association of microbial superantigens and the pathogenesis of Kawasaki disease (KD), we conducted a case-control study. Serum IgG and IgM antibodies against staphylococcal enterotoxin A (SEA), SEB, SEC, toxic shock syndrome toxin-1 (TSST-1), and streptococcal pyrogenic exotoxin A (SPEA) were measured by an enzyme-linked immunosorbent assay in 293 serum samples from 65 KD patients on clinical days 1-28 and 120 control samples. The administration of immunoglobulin products, which contain high concentrations of IgG antibodies against all the superantigens, directly elevated antitoxin IgG antibodies in KD patients. In contrast, antitoxin IgM antibodies were not detected in immunoglobulin products. Actually, we found a significant elevation of IgM antibodies against SEA in KD patients in the first (median titre: 0.020, P < 0.01 versus control), second (0.024, P < 0.001), third (0.030, P < 0.001) and fourth (0.038, P < 0.001) weeks, compared to the controls (0.015). Significant differences of IgM antibodies were also true for SEB, TSST-1, and SPEA throughout the first to fourth weeks, and for SEC throughout the second to fourth weeks. The prevalence of KD patients having high IgM titres (> mean + 2SD of control values) to the 5 superantigens was increased with the clinical weeks, and reached 29-43% of KD subjects at the fourth week. This is the first study that describes kinetics of IgM antibodies against superantigens and clarifies the serological significance throughout the clinical course of KD. Our results suggest that multiple superantigens involve in the pathogenesis of KD.

HIV-1 Viral Protein-R (VPR) Protects against Lethal Superantigen Challenge While Maintaining Homeostatic T Cell Levels in Vivo

The HIV-1 accessory protein Vpr exhibits many interesting features related to macrophage and T cell biology. As a viral protein or as a soluble molecule it can suppress immune cell activation and cytokine production in vitro in part by targeted inhibition of NF-kappaB. In this regard we sought to test its effects in vivo on an NF-kappaB-dependent immune pathway. We examined the activity of Vpr in a lethal toxin-mediated challenge model in mice. Intravenous delivery of Vpr was sufficient to protect mice from lethal challenge with staphylococcal endotoxin B (SEB). Furthermore, Vpr protected host CD4+ T cells from in vivo depletion likely by preventing induction of AICD of SEB-exposed cells in a post-toxin-binding fashion. Understanding the biology of Vpr's activities in this model may allow for new insight into potential mechanisms of hyperinflammatory disease and into Vpr pathobiology in the context of HIV infection.

Dichotomous effects of complete versus partial class II major histocompatibility complex deficiency on circulating autoantibody levels in autoimmune-prone mice

OBJECTIVE

To assess the effects of altered class II major histocompatibility complex (MHCII) expression on circulating autoantibody levels in C57BL/6 (B6) mice congenic for the Sle1 (B6.Sle1 mice) or Nba2 (B6.Nba2 mice) regions.

METHODS

H-2Ab(+/+) (MHCII-intact), H-2Ab(+/-) (MHCII-intermediate), and H-2Ab(-/-) (MHCII-deficient) littermate B6.Sle1 and B6.Nba2 mice were evaluated for spleen cell phenotype, numbers of splenic Ig-secreting cells, and serum levels of total IgM, total IgG, IgG antichromatin, IgG antihistone, and IgG anti-double-stranded DNA (anti-dsDNA).

RESULTS

Compared with their MHCII-intact littermates, MHCII-deficient B6.Sle1 and B6.Nba2 mice developed markedly decreased circulating levels of IgG autoantibodies, along with decreased circulating levels of total IgG. In sharp contrast, MHCII-intermediate mice developed increased circulating levels of IgG autoantibodies. This was associated with increased numbers of splenic Ig-secreting cells and serum levels of total IgG in B6.Sle1 mice, but it occurred without concomitant increases in the numbers of splenic Ig-secreting cells or serum total IgG levels in B6.Nba2 mice.

CONCLUSION

In 2 clinically healthy strains of mice with a genetic proclivity for developing autoantibodies, the effects of class II MHC expression on levels of circulating IgG autoantibodies were found to be complex. In the absence of MHCII expression, circulating IgG autoantibody levels were minimal. With full MHCII expression, circulating IgG autoantibody levels were considerable. With intermediate MHCII expression, circulating IgG autoantibody levels were even greater. These last findings may help explain why heterozygosity at the H-2 locus is associated with increased autoantibody titers and aggravated disease in certain lupus-prone mice.

In vitro and in vivo T cell oligoclonality following chronic stimulation with staphylococcal superantigens

Microbial superantigens (SAg), including SEB and TSST-1, polyclonally activate T cells belonging to specific TCR BV families. A pathogenic role for SAg in various human diseases has been suggested, but enthusiasm for this view has been tempered by the T cell oligoclonality in these disorders. To assess whether T cell oligoclonality can emerge following protracted SAg stimulation, human PBMC were stimulated with SEB, TSST-1, or anti-CD3 mAb and maintained in culture with exogenous IL-2. Oligoclonality was appreciated by day 14 among CD4(+) and CD8(+) T cells. In addition, mice transgenic for human DR2 and DQ8 were injected weekly with SEB, and splenic CD4(+) and CD8(+) T cells were analyzed for oligoclonality. In mice that received one or three such injections, little-to-no oligoclonality was detected. In contrast, considerable oligoclonality was detected in mice that received eight weekly SEB injections. Many of these T cell oligoclones were identical to "spontaneously" arising oligoclones detected in SEB-naive mice. Thus, T cell oligoclonality can emerge following chronic SAg stimulation. In hosts who have lost tolerance to self Ag, chronic exposure to SAg may preferentially promote expansion of autoreactive T cells and facilitate development of clinical disease.

Toxicity of the staphylococcal enterotoxin B mutants with histidine-to-tyrosine substitutions

In this study we made a series of site-directed mutants of staphylococcal enterotoxin B (SEB), in which histidine residues in the molecule were replaced by tyrosine. The mutant genes were cloned and expressed, and the corresponding proteins were purified. These mutant proteins were tested for binding to human HLA-DR4 and for mitogenetic activity in mouse splenocyte culture. Toxicity of the proteins in vivo was evaluated in the actinomycin D-primed C3H/HeJ mouse model. We found that SEB mutant proteins with fewer than four histidine-to-tyrosine (his-to-tyr) substitutions retained toxic properties similar to wild-type SEB. However, studies showed that his-to-tyr substitution of four consecutive histidine residues eliminated SEB toxicity. Our results clearly show that this genetically modified SEB protein is non-toxic and justifies its further development as a component of a new, safer vaccine to prevent SEB intoxication.

So many ways of getting in the way: diversity in the molecular architecture of superantigen-dependent T-cell signaling complexes

Superantigens (SAGs) elicit massive T-cell proliferation through simultaneous interaction with MHC and TCR molecules. SAGs have been implicated in toxic shock syndrome and food poisoning, and they may also play a pathogenic role in autoimmune diseases. The best-characterized group of SAGs are the pyrogenic bacterial SAGs, which utilize a high degree of genetic variation on a common structural scaffold to achieve a wide range of MHC-binding and T-cell-stimulating effects while assisting pathogen evasion of the adaptive immune response. Several new structures of SAG-MHC and SAG-TCR complexes have significantly increased understanding of the molecular bases for high-affinity peptide/MHC binding by SAGs and for TCR Vbeta domain specificity of SAGs. Using the currently available SAG-MHC and SAG-TCR complex structures, models of various trimolecular MHC-SAG-TCR complexes may be constructed that reveal wide diversity in the architecture of SAG-dependent T-cell signaling complexes, which nevertheless may result in similar signaling outcomes.