The yeast to hyphal transition following hematogenous candidiasis induces shock and organ injury independent of circulating tumor necrosis factor-alpha

Viral Delivery of IL-7 Is a Potent Immunotherapy Stimulating Innate and Adaptive Immunity and Confers Survival in Sepsis Models

Persistence of an immunosuppressive state plays a role in septic patient morbidity and late mortality. Both innate and adaptive pathways are impaired, pointing toward the need for immune interventions targeting both arms of the immune system. We developed a virotherapy using the nonpropagative modified vaccinia virus Ankara (MVA), which harbors the intrinsic capacity to stimulate innate immunity, to deliver IL-7, a potent activator of adaptive immunity. The rMVA-human IL-7 (hIL-7)-Fc encoding the hIL-7 fused to the human IgG2-Fc was engineered and shown to express a dimeric, glycosylated, and biologically active cytokine. Following a single i.v. injection in naive mice, the MVA-hIL-7-Fc increased the number of total and activated B, T, and NK cells but also myeloid subpopulations (Ly6C^high, Ly6C^int, and Ly6C^neg cells) in both lung and spleen. It triggered differentiation of T cells in central memory, effector memory, and acute effector phenotypes and enhanced polyfunctionality of T cells, notably the number of IFN-γ-producing cells. The MVA vector contributed significantly to immune cell activation, particularly of NK cells. The MVA-hIL-7-Fc conferred a significant survival advantage in the cecal ligation and puncture (CLP) and Candida albicans sepsis models. It significantly increased cell numbers and activation in both spleen and lung of CLP mice. Comparatively, in naive and CLP mice, the rhIL-7-Fc soluble counterpart overall induced less vigorous, shorter lasting, and narrower immune activities than did the MVA-hIL-7-Fc and favored TNF-α-producing cells. The MVA-hIL-7-Fc represents a novel class of immunotherapeutic with clinical potential for treatment of septic patients.

Candida albicans Yeast, Pseudohyphal, and Hyphal Morphogenesis Differentially Affects Immune Recognition

Candida albicans is a human opportunist pathogen that can grow as yeast, pseudohyphae, or true hyphae in vitro and in vivo, depending on environmental conditions. Reversible cellular morphogenesis is an important virulence factor that facilitates invasion of host tissues, escape from phagocytes, and dissemination in the blood stream. The innate immune system is the first line of defense against C. albicans infections and is influenced by recognition of wall components that vary in composition in different morphological forms. However, the relationship between cellular morphogenesis and immune recognition of this fungus is not fully understood. We therefore studied various vegetative cell types of C. albicans, singly and in combination, to assess the consequences of cellular morphogenesis on selected immune cytokine outputs from human monocytes. Hyphae stimulated proportionally lower levels of certain cytokines from monocytes per unit of cell surface area than yeast cells, but did not suppress cytokine response when copresented with yeast cells. Pseudohyphal cells induced intermediate cytokine responses. Yeast monomorphic mutants had elevated cytokine responses under conditions that otherwise supported filamentous growth and mutants of yeast and hyphal cells that were defective in cell wall mannosylation or lacking certain hypha-specific cell wall proteins could variably unmask or deplete the surface of immunostimulatory ligands. These observations underline the critical importance of C. albicans morphology and morphology-associated changes in the cell wall composition that affect both immune recognition and pathogenesis.

Treatment of Experimental Candida Sepsis with a Janus Kinase Inhibitor Controls Inflammation and Prolongs Survival

Janus kinases (JAK) are intracellular tyrosine kinases that transduce cytokine-mediated signals to the nucleus, promoting gene expression. Cytokines play a major role in microbial sepsis, which is often associated with uncontrolled inflammation leading to death. JAK inhibitors have been used for the treatment of several autoimmune diseases by modulating immune response, but they have never been tested against microbial sepsis. Ruxolitinib is a small-molecule inhibitor of JAK1/2 proteins, which are involved in the downstream signaling pathway of the vast majority of proinflammatory and anti-inflammatory cytokines. We therefore studied the effect of ruxolitinib in a mouse model of sepsis due to Candida albicans. When ruxolitinib therapy (50 mg/kg [of body weight]/day) was started 1 day before infection, the median survival time was reduced by 3 days, the fungal loads in all organs were higher, the inflammation was significantly less, and serum tumor necrosis factor alpha (TNF-α) and interleukin 10 (IL-10) levels and IL-10/TNF-α ratios were higher than in controls. When ruxolitinib therapy (50 to 1.5 mg/kg/day) was started 1 day after infection, an inverted-U relationship was found, with 6.25 mg/kg/day prolonging median survival time by 6 days, resulting in similar fungal loads, less inflammation, and similar cytokine levels but higher IL-10/TNF-α ratios than the controls. The optimal dose of ruxolitinib controlled infection and prolonged survival with less inflammation than in control animals. Administration of JAK inhibitors may be a promising therapeutic adjunct that needs further investigation.

Alterations of serum cytokine levels and their relation with inflammatory markers in candidemia

The roles of CRP, PCT, serum amyloid A (SAA), and cytokines in the diagnosis of fungal infections have not yet been clearly demonstrated. This study aims to measure the serum levels of interleukin (IL)-23, IL-17, IL-1β, tumor necrosis factor (TNF)-α, IL-10, transforming growth factor (TGF)-β, C-reactive protein (CRP), procalcitonin (PCT), and serum amyloid A (SAA) in cases of candidemia and to compare them with those observed in cases of bacteremia. For this purpose, the serum cytokine levels from 50 patients with candidemia were compared with those of 14 patients with polymicrobial sepsis, 30 patients with bacteremia, and 27 healthy control subjects. The cytokine levels were studied using sandwich ELISAs according to the manufacturer protocol. The serum levels of TGF-β, IL-23, and IL-17 were found to be significantly higher in the candidemia group in comparison with the samples from those with bacteremia and healthy controls. The PCT and SAA levels were higher in samples from the group with bacteremia those from individuals with candidemia and the healthy control group. Assuming an IL-17 level threshold of >38.79 pg/ml, the sensitivity and specificity were 38% and 96.6%, respectively but considering an IL-23 threshold of >59.97 pg/ml, the sensitivity and specificity values were found to be 72% and 60%, respectively. The sensitivity and the specificity of the TGF-ß levels were found to be 85.71% and 53.33%, respectively, when the TGF-ß threshold is >560 pg/ml. PCT and SAA demonstrated a superior performance for the differentiation of candidemia and bacteremia. Our study demonstrates that IL-17, IL-23, TGF-ß, PCT, and SAA levels could be a diagnostic marker for candidemia.

Pathophysiology of unilateral pulmonary aspergillosis in an experimental rat model

Because little is known about the pathophysiology of invasive pulmonary aspergillosis (IPA), we examined changes in pulmonary and general physiology during this disease in an animal model. In a model of fatal left-sided IPA, 19 persistently neutropenic rats were monitored for clinical signs including body temperature, body weight and respiratory distress. A separate group of nine rats with IPA was used for measurements of arterial blood pressure, arterial O2 and CO2 pressure, lung compliance and surfactant function. Body temperature and body weight decreased, whereas respiratory distress increased during progression of the disease. Compared to uninfected controls, in rats with IPA arterial blood pressure and lung compliance were significantly lower, and left lung minimal surface tension was significantly higher. Right lung surfactant function was not affected. Arterial O2 and CO2 pressures were not different between rats with IPA and uninfected controls. Infection with Aspergillus fumigatus in neutropenic rats resulted in hypothermia, body weight loss and respiratory distress. Loss of left lung function was probably compensated by the uninfected right lung, even in a late stage of the disease. Circulatory failure was a major feature in the terminal phase of the infection.

NEUTRALIZATION OF TUMOR NECROSIS FACTOR IN PRECLINICAL MODELS OF SEPSIS

Tumor necrosis factor (TNFalpha), a cardinal early mediator of the innate host inflammatory response, has been an attractive target for therapeutic intervention in human sepsis. However, pooled data from 12 completed randomized controlled trials show only a very modest impact on mortality in a highly heterogeneous population of patients. To gain insight into the preclinical in vivo biology of TNFalpha that might aid in better identifying appropriate patient populations for therapeutic intervention, we undertook a systematic review of published reports of preclinical studies assessing the consequences of neutralization of TNFalpha in models of acute infection or inflammation. We identified 143 reports incorporating 484 unique experimental comparisons in seven different animal species. The effects of neutralization of TNFalpha in these were quite variable. Neutralization of TNFalpha was beneficial in endotoxemia, or after systemic challenge with gram-negative organisms, Staphylococcus aureus, or Group B streptococci. On the other hand, neutralization was detrimental in infections caused by Streptococcus pneumoniae, Candida spp., or intracellular pathogens such as Listeria and Mycobacterium tuberculosis, and in models of pneumonia. Treatment was more efficacious when delivered before infectious challenge, and the therapeutic signal increased as the baseline mortality in the placebo group increased. Evidence of neutralization of TNFalpha bioactivity, and of attenuation of inflammation, was typically accompanied by evidence of impairment of antimicrobial defenses. Multiple specific and nonspecific therapeutic strategies were identified. We conclude that the beneficial effects of TNF in systemic inflammation occur at the cost of impaired antimicrobial defenses, and that a better understanding of the consequences of neutralization of TNFalpha in vivo could aid in better defining optimal patient populations for therapeutic intervention.

IFN-γ primes macrophages for enhanced TNF-α expression in response to stimulatory and non-stimulatory amounts of microparticulate β-glucan

beta-(1-->3)-D-Glucan is an integral cell wall component of a variety of fungi, plants, and bacteria. Like the prototypic inflammatory mediator lipopolysaccharide (LPS), some beta-(1--> 3)-D-glucan-containing preparations have been shown to induce the production of proinflammatory cytokines by macrophages. In the present study, we have tested a new microparticulate form of beta-(1--> 3)-D-glucan (MG) from Saccharomyces cerevisiae for its ability to induce proinflammatory cytokine secretion in mouse peritoneal macrophages in vitro, and we have examined the effect of IFN-gamma. MG was rapidly phagocytized by peritoneal macrophages, and these MG-treated macrophages upregulated TNF-alpha, IL-6, and IL-1beta mRNAs and secreted these proinflammatory cytokines. IFN-gamma treatment alone did not induce unstimulated macrophages to produce TNF-alpha. However, a 4 h IFN-gamma pretreatment augmented TNF-alpha secretion by peritoneal macrophages subsequently treated with an optimally stimulatory dose of MG. IFN-gamma pretreatment for 2 h followed by thorough washing and a further 2 h incubation without IFN-gamma still resulted in enhanced TNF-alpha production in response to MG, suggesting that IFN-gamma can prime macrophages for a subsequent proinflammatory response. Most interestingly, we found that IFN-gamma pretreatment of peritoneal macrophages enhanced the TNF-alpha response to amounts of MG that were poorly stimulatory or non-stimulatory in the absence of IFN-gamma priming. These data suggest that a synergy between IFN-gamma and beta-glucan may have evolved to lower the threshold of sensitivity of the innate immune response to fungal pathogens.

Granulocyte-macrophage colony-stimulating factor responses of oral epithelial cells to Candida albicans

Candida albicans is the principal fungal species responsible for oropharyngeal candidiasis, the most frequent opportunistic infection associated with immune deficiencies. Cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), are important in the generation of effective immunity to C. albicans. The purposes of this investigation were to determine whether C. albicans triggers secretion of GM-CSF by oral epithelial cells in vitro and to investigate mechanisms of host cell-fungal interactions that trigger such responses. Oral epithelial cell lines as well as primary oral mucosal epithelial cells were challenged with stationary phase viable C. albicans, added to human cell cultures at varying yeast:oral cell ratios. Yeast were allowed to germinate for up to 48 h and supernatants were analyzed for GM-CSF by ELISA. Fixed organisms, germination-deficient mutants and separation of yeast from epithelial cells using cell culture inserts were used to assess the effects of viability, germination and physical contact, respectively, on the GM-CSF responses of these cells. Two out of three cell lines and three out of six primary cultures responded to C. albicans with an increase in GM-CSF secretion. GM-CSF responses were contact-dependent, strain-dependent, required yeast viability and were optimal when the yeast germinated into hyphae.

Candida albicans triggers interleukin-8 secretion by oral epithelial cells

Oropharyngeal candidiasis is a frequent opportunistic infection associated with immunocompromised hosts. Candida albicans is the principal species responsible for this infection. Production of interleukin-8 (IL-8), by oral epithelial cells can be expected to play a major role in the recruitment and activation of professional phagocytes at the infected site. The purpose of this study was to determine whether C. albicans triggers secretion of IL-8 by oral epithelial cells in vitro and investigate mechanisms of host cell-fungal interactions that trigger such responses. Oral epithelial cell lines (SCC4, SCC15, and OKF6/TERT-2) as well as primary gingival epithelial cells were used. Epithelial cells were cocultured with C. albicans, strains SC5314, ATCC28366 or ATCC32077, for 24-48 hr, and supernatants were analyzed for IL-8 content by ELISA. A germination-deficient mutant (efg1/efg1 cph1/cph1), otherwise isogenic to strain SC5314, was used to assess the requirement for germination in triggering IL-8 responses. In order to ascertain whether direct contact of yeast with host cells is required to trigger cytokine production, epithelial cells were separated from yeast using cell culture inserts. To test whether IL-8 secretion is dependent on IL-1alpha activity, epithelial cells were challenged with viable C. albicans in the presence or absence of neutralizing anti-IL-1alpha antibody or IL-1ra, and IL-8 secretion was measured in the supernatants. All cell lines and primary cultures responded to C. albicans with an increase in IL-8 secretion. IL-8 responses were contact-dependent, strain-specific, required yeast viability and germination into hyphae, and were in part autoregulated by IL-1alpha.

The Pathophysiology and Treatment of Candida Sepsis

Sepsis can occur during disseminated candidiasis, but its pathogenesis differs from that caused by typical prokaryotic pathogens. Complex interactions between defects in host defense and "relative" virulence factors expressed by Candida lead to dissemination of the saprophyte to parenchymal organs, and subsequently to onset of multiorgan failure. This review focuses first on the pathophysiology of Candida sepsis, detailing current understanding of host-pathogen interactions. We then consider the choice of antifungal and supportive treatments.

Adherence of yeast and filamentous forms of Candida albicans to cultured enterocytes

OBJECTIVE

Systemic candidiasis is a major cause of complicating infections in intensive care units. Morbidity and mortality are high, even in those who receive appropriate antifungal therapy. Because the intestinal tract is considered a major portal of entry for systemic candidiasis, experiments were designed to clarify the ability of yeast and filamentous forms, as well as the INT1 gene product, to influence adherence of Candida albicans to the intestinal epithelium.

DESIGN

Controlled.

SETTING

University teaching hospital research laboratory.

SUBJECTS

Mature Caco-2 and HT-29 cultured enterocytes.

INTERVENTIONS

C. albicans INT1 mutant strains, defective in filament production, were used to observe the ultrastructural surface interactions of C. albicans with cultured intestinal epithelial cells, namely Caco-2 and HT-29 cells. These mutant strains also were used to quantify the effect of the INT1 gene product on C. albicans adherence (yeast and filamentous forms) to cultured enterocytes. Ultrastructural surface interactions of C. albicans with cultured enterocytes were observed with high resolution scanning electron microscopy. C. albicans adherence to cultured enterocytes was quantified by using a colorimetric enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Both yeast and filamentous forms of C. albicans appeared tightly adherent to the apical surface of cultured enterocytes, and INT1 appeared to have little, if any, effect on these ultrastructural surface interactions. The distal ends of C. albicans filaments appeared to mediate adherence to enterocyte apical microvilli, and thigmotropism (contact guidance) appeared to play a role in C. albicans adherence. The absence of functional INT1 was associated with decreased adherence of C. albicans yeast forms to cultured enterocytes.

CONCLUSIONS

Although functional INT1 appeared to facilitate adherence of C. albicans yeast forms to cultured enterocytes, the role of INT1 in adherence of filamentous forms was unclear, and both yeast and filamentous forms could adhere to, and perhaps invade, the apical surface of cultured enterocytes.

A recombinant tumor necrosis factor-alpha p80 receptor:Fc fusion protein decreases circulating bioactive tumor necrosis factor-alpha but not lung injury or mortality during immunosuppression-related gram-negative bacteremia

PURPOSE

During gram-negative bacteremia (GNB), tumor necrosis factor-alpha (TNF-alpha) is a critical early mediator of host defense, whose overexpression can initiate acute lung injury, multiple organ failure, and death. In this study we evaluated the ability of a chimeric fusion protein containing two extracellular domains of the human p80 TNF-alpha receptor and the Fc region of human IgG1 (TNFR:Fc) to reduce circulating TNF-alpha, and to ameliorate organ injury and improve survival in a rodent model of GNB during immunosuppression-related neutropenia.

MATERIALS AND METHODS

Conscious catheterized male rats (n = 37) with stable cyclophosphamide-induced neutropenia were infected intravenously (i.v.) with 5 x 10(9) live Escherichia coli (EC, serotype O55:B5) ending at t = 0. All animals received antibiotics (penicillin/ amikacin sulfate) at t = 0.5 and t = 8 hours, and 0.9% sodium chloride (normal saline solution (NS), 1 mL/h) from t = 0 to 8 hours. Subgroups were post-treated at t = 0.5 hours with a 1.0 mL i.v. dose of TNFR:Fc (60, 600, or 1,200 micrograms; Immunex), 600 micrograms of human IgG1-kappa or IgG1-lambda (Sigma), or NS alone (controls). A separate TNFR:Fc pretreatment subgroup received 600 micrograms/rat of the fusion protein 5 minutes before starting EC infusion. Hemodynamics were monitored continuously through t = 24 hours, and arterial samples were collected at baseline and at t = 1.5, 4.5, 8, and 24 hours after EC were analyzed for blood gases, quantitative culture, serum endotoxin, bioactive and antigenic TNF-alpha, and formed elements. Postmortem tissues were examined for histopathologic changes.

RESULTS

Compared with antibiotic-treated and fluid-supported controls, TNFR:Fc dose-dependently reduced bioactive but not antigenic TNF-alpha without altering bacterial clearance, serum endotoxin, or 24-hour survival. Of note, 600 micrograms of IgG1-kappa or IgG1-lambda attenuated peak bioactive TNF-alpha to a similar degree as 1,200 micrograms TNFR:Fc, and also significantly reduced serum endotoxin levels. Nevertheless, by t = 8 hours all bacteremic rats were hypothermic with tachypnea-related hypocarbia and hyperoxemia and were thrombocytopenic. At death, all subgroups showed similar hepatic glycogen depletion and pulmonary congestion with perivascular edema and alveolar hemorrhage.

CONCLUSIONS

Although TNFR:Fc and its idiotypic control IgG1 reduced circulating bioactive TNF-alpha, neither treatment prevented progression of lethal shock with attendant organ injury in this conscious, antibiotic-treated and fluid-resuscitated model of immunosuppression-related GNB.