[Show abstract][Hide abstract] ABSTRACT: Proof of the Germ theory of disease and acceptance of Koch's postulates in the late 1890's launched the fields of microbial pathogenesis and infectious diseases and provided the conceptual framework that has guided thought and research in these fields. A central tenet that emerged from studies with microbes that fulfilled Koch's postulates was that microbes that caused disease had characteristics that allowed them to do so, with the corollary that microbes that did not cause disease lacked disease-causing determinants. This observation, which held true for many diseases that were known to cause disease in the late 19th century, such as toxin-producing and encapsulated bacteria, led to the view that the ability to cause disease rested with microbes and reflected the activity of specific determinants, or virulence factors. With the dawn of the 20th century, efforts to neutralize virulence factors were under development and ultimately translated into anti-microbial therapy in the form of antibodies targeted to toxins and polysaccharide capsules. However, the 20th century progressed, antibiotics were identified and developed as therapy for infectious diseases while other medical advances, such as specialized surgeries, intensive care units, intravenous catheters, and cytotoxic chemotherapy became commonplace in resourced nations. An unintended consequence of many of these advances was that they resulted in immune impairment. Similarly, HIV/AIDS, which emerged in the late 1970's also produced profound immune impairment. Unexpectedly, the prevailing view that microbes were the sole perpetrators of virulence was untenable. Microbes that were rarely if ever associated with disease emerged as major causes of disease in people with impaired immunity. This phenomenon revealed that available explanations for microbial infectiveness and virulence were flawed. In this review, we discuss the question 'what is infectiveness' based on the tenets of the Damage-response framework.
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT Cryptococcosis is caused by the fungal genus Cryptococcus. Cryptococcosis, predominantly meningoencephalitis, emerged with the HIV pandemic, primarily afflicting HIV-infected patients with profound T-cell deficiency. Where in use, combination antiretroviral therapy has markedly reduced the incidence of and risk for disease, but cryptococcosis continues to afflict those without access to therapy, particularly in sub-Saharan Africa and Asia. However, cryptococcosis also occurs in solid organ transplant recipients and patients with other immunodeficiencies as well as those with no known immunodeficiency. This article reviews innate and adaptive immune responses to C. neoformans, with an emphasis on recent studies on the role of B cells, natural IgM and Fc gamma receptor polymorphisms in resistance to cryptococcosis.
No preview · Article · Apr 2015 · Future Microbiology
[Show abstract][Hide abstract] ABSTRACT: Disease is as much about the host as it is the infectious agent — the focus on microbes is hindering research into treatments, say Arturo Casadevall and Liise-anne Pirofski.
[Show abstract][Hide abstract] ABSTRACT: Since proof of the germ theory of disease in the late 19(th) century a major focus of the fields of microbiology and infectious diseases has been to seek differences between pathogenic and non-pathogenic microbes and the role that the host plays in microbial pathogenesis. Remarkably, despite the increasing recognition that host immunity plays a role in microbial pathogenesis, there has been little discussion about what constitutes a host. Historically, hosts have been viewed in the context of their fitness or immunological status, and characterized by adjectives such as immune, immunocompetent, immunosuppressed, immunocompromised, or immunologically impaired. However, in recent years it has become apparent that the microbiota has profound effects on host homeostasis and susceptibility to microbial diseases in addition to its effects on host immunity. This raises the question of how to incorporate the microbiota into defining a host. This definitional problem is further complicated because neither host nor microbial properties are adequate to predict the outcome of host-microbe interaction because this outcome exhibits emergent properties. In this essay we revisit the 'damage-response framework' (DRF) of microbial pathogenesis and demonstrate how it can incorporate the rapidly accumulating information being generated by the microbiome revolution. We use the tenets of the DRF to put forth the following definition of a host: a host is an entity that houses an associated microbiome/microbiota and interacts with microbes such that the outcome results in damage, benefit, or indifference thus resulting in the states of symbiosis, colonization, commensalism, latency and disease.
Preview · Article · Nov 2014 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Journal names are important because they often define the scope of the publication. A journal’s name must be sufficiently specific to define the major interest of the publication but not too narrow to prevent its rapid obsolescence as fields evolve. In naming this journal ‘Virulence’ the creators of this scientific publishing venue have staked a remarkably broad scope and it is worthwhile to reflect on the choice of the word and what this could mean for the future of the journal.
[Show abstract][Hide abstract] ABSTRACT: Background: Emergency room utilization in the US has increased over the last decade. Little is known about antibiotic utilization and its appropriateness in the Emergency Department (ED). Published data indicate that over 50% of patients presenting with viral upper respiratory tract infections receive inappropriate antibiotics during an ED visit. Thus, opportunities exist to improve prescribing.
Methods: We implemented an antibiotic stewardship (ASP) and infectious diseases (ID) management pilot program, designed in collaboration with the ED at the Einstein Campus of Montefiore Medical Center (a 424 bed non-profit teaching facility with over 72,000 ED visits a year and 16,000 admissions), the University Hospital of Albert Einstein College of Medicine in Bronx, NY. For 17 consecutive weeks an ID physician was notified about patients presenting with infectious conditions by ED providers or ASP staff (during antibiotic auditing and approval calls). An ID physician formally evaluated the patient and offered recommendations for antibiotic selection, dosing, duration, additional testing, and when appropriate, outpatient management. Patients who were hospitalized were offered follow up with an ID specialist.
Results: During the intervention period, 230 patients were evaluated. Of those patients, 138 (60%) were initially prescribed ‘inappropriate’ antimicrobial regimens. Outpatient management with discharge from the ED was recommended in 28 (12%) patients, and 28 (12%) were recommended to stop antimicrobial therapy completely. Acceptability of ASP/ID consultation was high, with 92% of ED physicians prescribing the recommended antibiotic regimen.
Number of Consults
Antibiotics prescribing inappropriate
Reasons, N (%):
No antibiotics needed: 28 (12)
Coverage too broad: 37 (16)
Coverage too narrow: 27 (12)
Able to switch to oral: 17 (7)
Other (e.g., incorrect drug due to allergy or prior cultures, incorrect dosing) 29 (13)
Conclusion: Our pilot data suggests that a collaborative approach with early ASP and ID consultation in the ED is a feasible and acceptable model that can improve initial antibiotic prescribing, reduce unnecessary antibiotic use, improve patient safety, avert unnecessary hospital admissions and build relationships with ED staff.
[Show abstract][Hide abstract] ABSTRACT: Background:
Some Streptococcus pneumoniae serotypes express an ahemolytic pneumolysin (PLYa). Serotypes that commonly express PLYa, including serotype 8 (ST8) and ST1, are often associated with a low prevalence during colonization but a higher propensity to cause invasive disease. We sought to study the host response to ST8 PLYa in a homologous and heterologous capsular background.
We genetically exchanged the PLYa of ST8 strain 6308 with the hemolytic PLY (PLYh) of ST3 A66.1 and vice versa and determined the impact of the exchange on nasopharyngeal colonization in mice. Then, to compare the response of human cells to PLYa-expressing and PLYh-expressing strains, we infected human peripheral blood mononuclear cells (PBMCs) with PLY-switched strains and assessed dendritic cell and CD4(+) T-cell responses by intracellular cytokine staining.
Mice colonized with PLYa-expressing strains had significantly higher colonization densities than those colonized with PLYh-expressing strains, irrespective of capsular background. Compared with infection of PBMCs with PLYh-expressing strains, infection with PLYa-expressing strains induced diminished innate (dendritic cell cytokines, costimulatory receptor, and apoptotic) and adaptive (CD4(+) T-cell proliferative and memory interleukin 17A) responses.
Our findings demonstrate that PLYa has the potential to manipulate host immunity irrespective of capsule type. PLY exchange between STs expressing PLYa and PLYh could lead to unexpected colonization or invasion phenotypes.
No preview · Article · Jun 2014 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: Extracellular vesicles are produced by many pathogenic microorganisms and have varied functions that include secretion and release of microbial factors, which contribute to virulence. Very little is known about vesicle production by Gram-positive bacteria, as well as their biogenesis and release mechanisms. In this work, we demonstrate the active production of vesicles by Streptococcus pneumoniae from the plasma membrane, rather than being a product from cell lysis. We biochemically characterized them by proteomics and fatty acid analysis, showing that these vesicles and the plasma membrane resemble in essential aspects, but have some differences: vesicles are more enriched in lipoproteins and short-chain fatty acids. We also demonstrate that these vesicles act as carriers of surface proteins and virulence factors. They are also highly immunoreactive against human sera and induce immune responses that protect against infection. Overall, this work provides insights into the biology of this important Gram-positive human pathogen and the role of extracellular vesicles in clinical applications.
Full-text · Article · Apr 2014 · Journal of proteomics
[Show abstract][Hide abstract] ABSTRACT: Unlabelled:
Cryptococcus neoformans is one of the most common causes of fungal disease in HIV-infected persons, but not all of those who are infected develop cryptococcal disease (CD). Although CD4(+) T cell deficiency is a risk factor for HIV-associated CD, polymorphisms of phagocytic Fc gamma receptors (FCGRs) have been linked to CD risk in HIV-uninfected persons. To investigate associations between FCGR2A 131 H/R and FCGR3A 158 F/V polymorphisms and CD risk in HIV-infected persons, we performed PCR-based genotyping on banked samples from 164 men enrolled in the Multicenter AIDS Cohort Study (MACS): 55 who were HIV infected and developed CD and a matched control group of 54 who were HIV infected and 55 who were HIV uninfected. Using additive and allelic statistical models for analysis, the high-affinity FCGR3A 158V allele was significantly associated with CD status after adjusting for race/ethnicity (odds ratio [OR], 2.1; P = 0.005), as was the FCGR3A 158 VV homozygous genotype after adjusting for race/ethnicity, rate of CD4(+) T cell decline, and nadir CD4(+) T cell count (OR, 21; P = 0.005). No associations between CD and FCGR2A 131 H/R polymorphism were identified. In binding studies, human IgG (hIgG)-C. neoformans complexes exhibited more binding to CHO-K1 cells expressing FCGR3A 158V than to those expressing FCGR3A 158F, and in cytotoxicity assays, natural killer (NK) cells expressing FCGR3A 158V induced more C. neoformans-infected monocyte cytotoxicity than those expressing FCGR3A 158F. Together, these results show an association between the FCGR3A 158V allele and risk for HIV-associated CD and suggest that this polymorphism could promote C. neoformans pathogenesis via increased binding of C. neoformans immune complexes, resulting in increased phagocyte cargo and/or immune activation.
HIV-associated CD4(+) T cell deficiency is a sine qua non for HIV-associated cryptococcal disease (CD), but not all patients with CD4(+) T cell deficiency develop CD despite serological evidence of previous infection. At present, there are no biomarkers that predict HIV-associated CD risk. The goal of our study was to understand whether Fc gamma receptor (FCGR) polymorphisms that have been shown to portend CD risk in HIV-uninfected people are associated with CD risk in HIV-infected people. Such biomarkers could identify those who would benefit most from targeted prophylaxis and/or earlier treatment, particularly in sub-Saharan Africa, where there are nearly a million cases of HIV-associated CD annually. A biomarker of risk could also identify potential candidates for immunization, should there be a vaccine for Cryptococcus neoformans.
[Show abstract][Hide abstract] ABSTRACT: Bruton’s tyrosine kinase (Btk) is a signaling molecule that plays important roles in B-1 B cell development and innate myeloid cell functions and has recently been identified as a target for therapy of B cell lymphomas. We examined the contribution of B-1 B cells to resistance to Cryptococcus neoformans infection by utilizing X-linked immunodeficient (XID) mice (CBA-CaHN-XID), which possess a mutation in Btk. XID mice had significantly higher brain fungal burdens than the controls 6 weeks after infection with C. neoformans strain 52D (CN52D); however, consistent with the propensity for greater virulence of C. neoformans strain H99 (CNH99), CNH99-infected XID mice had higher lung and brain fungal burdens than the controls 3 weeks after infection. Further studies in a chronic CN52D model revealed markedly lower levels of total and C. neoformans-specific serum IgM in XID mice than in the control mice 1 and 6 weeks after infection. Alveolar macrophage phagocytosis was markedly impaired in CN52D-infected XID mice compared to the controls, with XID mice exhibiting a disorganized lung inflammatory pattern in which Gomori silver staining revealed significantly more enlarged, extracellular C. neoformans cells than the controls. Adoptive transfer of B-1 B cells to XID mice restored peritoneal B-1 B cells but did not restore IgM levels to those of the controls and had no effect on the brain fungal burden at 6 weeks. Taken together, our data support the hypothesis that IgM promotes fungal containment in the lungs by enhancing C. neoformans phagocytosis and restricting C. neoformans enlargement. However, peritoneal B-1 B cells are insufficient to reconstitute a protective effect in the lungs.
[Show abstract][Hide abstract] ABSTRACT: Purpose of review:
Infection with Streptococcus pneumoniae (pneumococcus) results in colonization, which can lead to local or invasive disease, of which pneumonia is the most common manifestation. Despite the availability of pneumococcal vaccines, pneumococcal pneumonia is the leading cause of community and inhospital pneumonia in the United States and globally. This article discusses new insights into the pathogenesis of pneumococcal disease.
The host-microbe interactions that determine whether pneumococcal colonization will result in clearance or invasive disease are highly complex. This article focuses on new information in three areas that bear on the pathogenesis of pneumococcal disease: factors that govern colonization, the prelude to invasive disease, including effects on colonization and invasion of capsular serotype, pneumolysin, surface proteins that regulate complement deposition, biofilm formation and agglutination; the effect of coinfection with other bacteria and viruses on pneumococcal growth and virulence, including the synergistic effect of influenza virus; and the contribution of the host inflammatory response to the pathogenesis of pneumococcal pneumonia, including the effects of pattern recognition molecules, cells that enhance and modulate inflammation, and therapies that modulate inflammation, such as statins.
Recent research on pneumococcal pathogenesis reveals new mechanisms by which microbial factors govern the ability of pneumococcus to progress from the state of colonization to disease and host inflammatory responses contribute to the development of pneumonia. These mechanisms suggest that therapies which modulate the inflammatory response could hold promise for ameliorating damage stemming from the host inflammatory response in pneumococcal disease.
No preview · Article · Apr 2013 · Current Opinion in Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: The role of B cells in host defense against fungi has been difficult to establish. We quantified and determined the molecular derivation of B-1a, B-1b, and B-2 B cell populations in C57BL/6 mice after pulmonary infection with Cryptococcus neoformans. Total B-1 and B-2 cell numbers increased in lungs and peritoneal cavity as early as day 1 postinfection, but lacked signs of clonal expansion. Labeled capsular (24067) and acapsular (Cap67) C. neoformans strains were used to identify C. neoformans-binding B cell subsets by flow cytometry. Peritoneal cavity B-1a B cells exhibited the most acapsular and capsular C. neoformans binding in C. neoformans-infected mice, and C. neoformans-selected B-1 B cells secreted laminarin- and C. neoformans-binding IgM. Single-cell PCR-based sequence analysis of B-1a, B-1b, and B-2 cell IgH V region H chain (V(H)) genes revealed increased usage of V(H)11 and V(H)12, respectively, in acapsular and capsular C. neoformans-selected B-1a cells. Germline V(H) segments were used, with capsular C. neoformans-selected cells having less junctional diversity than acapsular C. neoformans-selected cells. Further studies in B-1 B cell-depleted mice showed that these mice had higher brain and lung fungal burdens and less alveolar macrophage phagocytosis of C. neoformans than did control and B-1a B cell-reconstituted mice. Taken together, these results establish a mechanistic role for B-1 B cells in the innate B cell response to pulmonary infection with C. neoformans and reveal that IgM-producing B-1a cells, which express germline V(H) genes, bind C. neoformans and contribute to early fungal clearance. Thus, B-1a B cells provide a first line of defense during pulmonary C. neoformans infection in mice.
Full-text · Article · Nov 2012 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Background:
Pneumococcal vaccination is recommended for human immunodeficiency virus-infected (HIV+) persons; the best timing for immunization with respect to initiation of antiretroviral therapy (ART) is unknown.
Double-blind, placebo-controlled trial in HIV+ with CD4(+) T cells/µL (CD4) ≥ 200 randomized to receive the 23-valent pneumococcal polysaccharide vaccine (PPV23) or placebo at enrollment, followed by placebo or PPV23, respectively, 9-12 months later (after ≥6 months of ART). Capsular polysaccharide-specific immunoglobin (Ig) G and IgM levels to serotypes 1, 3, 4, 6B, and 23F, and opsonophagocytic killing activity (OPA) to serotypes 6B and 23F were evaluated 1 month postvaccination.
One hundred seven subjects were enrolled, 72 (67.3%) were evaluable (36/group). Both groups had significant increases in pre- to 1-month postvaccination IgG levels, but negligible to IgM, and significant increases in OPA titers to serotype 6B but not to 23F. There were no significant differences between groups in serotype-specific IgM or IgG levels or OPA titers. For the combined groups, there was a significant correlation between serotype-specific IgG and OPA titers to 23F but not to 6B. There was no correlation between CD4, viral load and IgG responses.
In HIV+ with CD4 ≥ 200, delaying PPV23 until ≥6 months of ART does not improve responses and may lead to missed opportunities for immunization.
[Show abstract][Hide abstract] ABSTRACT: B7x (B7-H4 or B7S1), a member of the B7 family, inhibits in vitro T cell proliferation and cytokine production by binding to an unidentified receptor on activated T cells, but its in vivo function remains largely unclear. We show that B7x protein was expressed in epithelial cells of the lung, but not in lymphoid tissues. To investigate the role of B7x in the lung, we determined the susceptibility of B7x-deficient (B7x(-/-)) mice to a lethal pulmonary infection with Streptococcus pneumoniae. B7x(-/-), but not B7-H3-deficient, mice were significantly more resistant to S. pneumoniae pulmonary infection than their wild-type (Wt) counterparts. B7x(-/-) mice had significantly lower bacterial burdens and levels of inflammatory cytokines in lungs as early as 12 h postinfection. They also had milder immunopathology that was localized in alveolar spaces, whereas Wt mice had severe inflammation that was perivascular. Control of infection in B7x(-/-) mice was associated with a marked increase in activated CD4 and CD8 T cells and fewer neutrophils in lungs, whereas the susceptible Wt mice had the opposite cellular profile. In B7x(-/-)Rag1(-/-) mice that lack T cells, reduction in bacterial burden was no longer observed. Control of S. pneumoniae and the increased survival observed was specific to the lung, because systemically infected B7x(-/-) mice were not resistant to infection. These data indicate that lung-expressed B7x negatively regulates T cells, and that in its absence, in B7x(-/-) mice, an enhanced T cell response contributed to reduced lethality in a pulmonary infection model with S. pneumoniae.
Full-text · Article · Aug 2012 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Only two decades ago antibodies to fungi were thought to have little or no role in protection against fungal diseases. However, subsequent research has provided convincing evidence that certain antibodies can modify the course of fungal infection to the benefit or detriment of the host. Hybridoma technology was the breakthrough that enabled the characterization of antibodies to fungi, illuminating some of the requirements for antibody efficacy. As discussed in this review, fungal-specific antibodies mediate protection through direct actions on fungal cells and through classical mechanisms such as phagocytosis and complement activation. Although mechanisms of antibody-mediated protection are often species-specific, numerous fungal antigens can be targeted to generate vaccines and therapeutic immunoglobulins. Furthermore, the study of antibody function against medically important fungi has provided fresh immunological insights into the complexity of humoral immunity that are likely to apply to other pathogens.
[Show abstract][Hide abstract] ABSTRACT: The cytokines IL-23 and IL-17 have been implicated in resistance to cryptococcal disease, but it is not clear whether IL-23-mediated production of IL-17 promotes fungal containment following pulmonary challenge with Cryptococcus neoformans. We used mice lacking IL-23 (IL-23p19(-/-)) or IL-17RA (IL-17RA(-/-)), and wild type (WT) C57BL/6 mice to examine the IL-23/IL-17 axis after intranasal infection with the C. neoformans strain 52D. The absence of IL-23 or IL-17RA had no effect on pulmonary or brain fungal burden at 1 or 6 weeks after infection. However, survival of IL-23p19(-/-) mice was reduced compared to IL-17RA(-/-) mice. IL-I7 production by CD4 T cells and natural killer T (NKT) cells was impaired in IL-23p19(-/-) lungs, but was not completely abolished. Both IL-23p19(-/-) and IL-17RA(-/-) mice exhibited impaired neutrophil recruitment, increased serum levels of IgE and IgG2b, and increased deposition of YM1/YM2 crystals in the lung, but only IL-23p19(-/-) mice developed persistent lung eosinophilia. Although survival of IL-17RA(-/-) and WT mice was similar after 17 weeks of infection, only surviving IL-17RA(-/-) mice exhibited cryptococcal dissemination to the blood. These data demonstrate that IL-23 dampens the allergic response to cryptococcal infection through IL-17-independent suppression of eosinophil recruitment and IL-17-dependent regulation of antibody production and crystal deposition. Furthermore, IL-23, and to a lesser extent IL-17, contribute to disease resistance.
Preview · Article · Feb 2012 · American Journal Of Pathology