Selective neutralization of a bacterial enterotoxin by serum immunoglobulin A in response to mucosal disease

A Streamlined Method to Obtain Biologically Active TcdA and TcdB Toxins from Clostridioides difficile

The major virulence factors of Clostridioides difficile (C. difficile) are enterotoxins A (TcdA) and B (TcdB). The study of toxins is a crucial step in exploring the virulence of this pathogen. Currently, the toxin purification process is either laborious and time-consuming in C. difficile or performed in heterologous hosts. Therefore, we propose a streamlined method to obtain functional toxins in C. difficile. Two C. difficile strains were generated, each harboring a sequence encoding a His-tag at the 3' end of C. difficile 630∆erm tcdA or tcdB genes. Each toxin gene is expressed using the Ptet promoter, which is inducible by anhydro-tetracycline. The obtained purification yields were 0.28 mg and 0.1 mg per liter for rTcdA and rTcdB, respectively. In this study, we successfully developed a simple routine method that allows the production and purification of biologically active rTcdA and rTcdB toxins with similar activities compared to native toxins.

Translational Aspects of the Immunology of Clostridioides difficile Infection: Implications for Pediatric Populations

Clostridioides difficile has become the most common healthcare-associated pathogen in the United States, leading the US Centers for Disease Control and Prevention (CDC) to classify C. difficile as an "urgent" public health threat that requires "urgent and aggressive action." This call to action has led to new discoveries that have advanced our understanding of Clostridioides difficile infection (CDI) immunology and clinical development of immunologic-based therapies for CDI prevention. However, CDI immunology research has been limited in pediatric populations, and several unanswered questions remain regarding the function of host immune response in pediatric CDI pathogenesis and the potential role of immunologic-based therapies in children. This review summarizes the innate and adaptive immune responses previously characterized in animals and humans and provides a current update on clinical development of immunologic-based therapies for CDI prevention in adults and children. These data inform the future research needs for children.

Understanding host immune responses to pneumococcal proteins in the upper respiratory tract to develop serotype-independent pneumococcal vaccines

Introduction: Nasopharyngeal colonization is a precondition for mucosal and invasive pneumococcal disease. Prevention of colonization may reduce pneumococcal transmission and disease incidence. Therefore, several protein-based pneumococcal vaccines are currently under investigation. Areas covered: We aimed to better understand the host immune responses to pneumococcal proteins in the upper respiratory tract (URT) that could facilitate the development of serotype-independent pneumococcal vaccines. English peer-reviewed papers reporting immunological mechanisms involved in host immune response to pneumococcal proteins in the URT were retrieved through a PubMed search using the terms 'pneumococcal proteins,' 'nasopharyngeal colonization' and/or 'cellular/humoral host immune response.' Expert opinion: Although pneumococcal protein antigens induce humoral immune responses, as well as IL-17A-mediated immunity, none of them, when used as single antigen, is sufficient to control and broadly protect against pneumococcal colonization. Novel vaccines should contain multiple conserved protein antigens to activate both arms of the immune system and evoke protection against the whole spectrum of pneumococcal variants by reducing, rather than eradicating, pneumococcal carriage. The highest efficacy would likely be achieved when the vaccine is intranasally applied, inducing mucosal immunity and enhancing the first line of defense by restricting pneumococcal density in the URT, which in turn will lead to reduced transmission and protection against disease.

Age-related changes in intestinal immunity and the microbiome

The gastrointestinal (GI) tract is a vitally important site for the adsorption of nutrients as well as the education of immune cells. Homeostasis of the gut is maintained by the interplay of the intestinal epithelium, immune cells, luminal Ags, and the intestinal microbiota. The well-being of the gut is intrinsically linked to the overall health of the host, and perturbations to this homeostasis can have severe impacts on local and systemic health. One factor that causes disruptions in gut homeostasis is age, and recent research has elucidated how critical systems within the gut are altered during the aging process. Intestinal stem cell proliferation, epithelial barrier function, the gut microbiota, and the composition of innate and adaptive immune responses are all altered in advanced age. The aging population continues to expand worldwide, a phenomenon referred to as the "Silver Tsunami," and every effort must be made to understand how best to prevent and treat age-related maladies. Here, recent research about changes observed in the intestinal epithelium, the intestinal immune system, the microbiota, and how the aging gut interacts with and influences other organs such as the liver, lung, and brain are reviewed. Better understanding of these age-related changes and their impact on multi-organ interactions will aid the development of therapies to increase the quality of life for all aged individuals.

Intranasal Vaccination With Lipoproteins Confers Protection Against Pneumococcal Colonisation

Streptococcus pneumoniae is endowed with a variety of surface-exposed proteins representing putative vaccine candidates. Lipoproteins are covalently anchored to the cell membrane and highly conserved among pneumococcal serotypes. Here, we evaluated these lipoproteins for their immunogenicity and protective potential against pneumococcal colonisation. A multiplex-based immunoproteomics approach revealed the immunogenicity of selected lipoproteins. High antibody titres were measured in sera from mice immunised with the lipoproteins MetQ, PnrA, PsaA, and DacB. An analysis of convalescent patient sera confirmed the immunogenicity of these lipoproteins. Examining the surface localisation and accessibility of the lipoproteins using flow cytometry indicated that PnrA and DacB were highly abundant on the surface of the bacteria. Mice were immunised intranasally with PnrA, DacB, and MetQ using cholera toxin subunit B (CTB) as an adjuvant, followed by an intranasal challenge with S. pneumoniae D39. PnrA protected the mice from pneumococcal colonisation. For the immunisation with DacB and MetQ, a trend in reducing the bacterial load could be observed, although this effect was not statistically significant. The reduction in bacterial colonisation was correlated with the increased production of antigen-specific IL-17A in the nasal cavity. Immunisation induced high systemic IgG levels with a predominance for the IgG1 isotype, except for DacB, where IgG levels were substantially lower compared to MetQ and PnrA. Our results indicate that lipoproteins are interesting targets for future vaccine strategies as they are highly conserved, abundant, and immunogenic.

Limited Innovations After More Than 65 Years of Immunoglobulin Replacement Therapy: Potential of IgA- and IgM-Enriched Formulations to Prevent Bacterial Respiratory Tract Infections

Patients with primary immunoglobulin deficiency have lower immunoglobulin levels or decreased immunoglobulin function, which makes these patients more susceptible to bacterial infection. Most prevalent are the selective IgA deficiencies (~1:3,000), followed by common variable immune deficiency (~1:25,000). Agammaglobulinemia is less common (~1:400,000) and is characterized by very low or no immunoglobulin production resulting in a more severe disease phenotype. Therapy for patients with agammaglobulinemia mainly relies on prophylactic antibiotics and the use of IgG replacement therapy, which successfully reduces the frequency of invasive bacterial infections. Currently used immunoglobulin preparations contain only IgG. As a result, concurrent IgA and IgM deficiency persist in a large proportion of agammaglobulinemia patients. Especially patients with IgM deficiency remain at risk for recurrent infections at mucosal surfaces, which includes the respiratory tract. IgA and IgM have multiple functions in the protection against bacterial infections at the mucosal surface. Because of their multimeric structure, both IgA and IgM are able to agglutinate bacteria efficiently. Agglutination allows for entrapment of bacteria in mucus that increases clearance from the respiratory tract. IgA is also important for blocking bacterial adhesion by interfering with bacterial adhesion receptors. IgM in its place is very well capable of activating complement, therefore, it is thought to be important in complement-mediated protection at the mucosal surface. The purpose of this Mini Review is to highlight the latest advances regarding IgA- and IgM-enriched immunoglobulin replacement therapy. We describe the different IgA- and IgM-enriched IgG formulations, their possible modes of action and potential to protect against respiratory tract infections in patients with primary immunoglobulin deficiencies.

Adaptive immune education by gut microbiota antigens

Host-microbiota mutualism has been established during long-term co-evolution. A diverse and rich gut microbiota plays an essential role in the development and maturation of the host immune system. Education of the adaptive immune compartment by gut microbiota antigens is important in establishing immune balance. In particular, a critical time frame immediately after birth provides a 'window of opportunity' for the development of lymphoid structures, differentiation and maturation of T and B cells and, most importantly, establishment of immune tolerance to gut commensals. Depending on the colonization niche, antigen type and metabolic property of different gut microbes, CD4 T-cell responses vary greatly, which results in differentiation into distinct subsets. As a consequence, certain bacteria elicit effector-like immune responses by promoting the production of pro-inflammatory cytokines such as interferon-γ and interleukin-17A, whereas other bacteria favour the generation of regulatory CD4 T cells and provide help with gut homeostasis. The microbiota have profound effects on B cells also. Gut microbial exposure leads to a continuous diversification of B-cell repertoire and the production of T-dependent and -independent antibodies, especially IgA. These combined effects of the gut microbes provide an elegant educational process to the adaptive immune network. Contrariwise, failure of this process results in a reduced homeostasis with the gut microbiota, and an increased susceptibility to various immune disorders, both inside and outside the gut. With more definitive microbial-immune relations waiting to be discovered, modulation of the host gut microbiota has a promising future for disease intervention.

No appendix necessary: Fecal transplants and antibiotics can resolve Clostridium difficile infection

The appendix has been hypothesized to protect the colon against Clostridium difficile infection (CDI) by providing a continuous source of commensal bacteria that crowd out the potentially unhealthy bacteria and/or by contributing to defensive immune dynamics. Here, a series of deterministic systems comprised of ordinary differential equations, which treat the system as an ecological community of microorganisms, model the dynamics of colon microbiome. The first model includes migration of commensal bacteria from the appendix to the gut, while the second model expands this to also include immune dynamics. Simulations and simple analytic techniques are used to explore dynamics under biologically relevant parameters values. Both models exhibited bistability with steady states of a healthy state and of fulminant CDI. However, we find that the appendix size was much too small for migration to affect the stability of the system. Both models affirm the use of fecal transplants in conjunction with antibiotic use for CDI treatment, while the second model also suggests that anti-inflammatory drugs may protect against CDI. Ultimately, in general neither the appendiceal migration rate of commensal microbiota nor the boost to antibody production could exert an appreciable impact on the stability of the system, thus failing to support the proposed protective role of the appendix against CDI.

Immunization with Recombinant TcdB-Encapsulated Nanocomplex Induces Protection against Clostridium difficile Challenge in a Mouse Model

Clostridium difficile is considered to be one of the major cause of infectious diarrhea in healthcare systems worldwide. Symptoms of C. difficile infection are caused largely by the production of two cytotoxins: toxin A (TcdA) and toxin B (TcdB). Vaccine development is considered desirable as it would decrease the mounting medical costs and mortality associated with C. difficile infections. Biodegradable nanoparticles composed of poly-γ-glutamic acid (γ-PGA) and chitosan have proven to be a safe and effective antigen delivery system for many viral vaccines. However, few studies have used this efficient antigen carrier for bacterial vaccine development. In this study, we eliminated the toxin activity domain of toxin B by constructing a recombinant protein rTcdB consists of residues 1852-2363 of TcdB receptor binding domain. The rTcdB was encapsulated in nanoparticles composed of γ-PGA and chitosan. Three rounds of intraperitoneal vaccination led to high anti-TcdB antibody responses and afforded mice full protection mice from lethal dose of C. difficile spore challenge. Protection was associated with high levels of toxin-neutralizing antibodies, and the rTcdB-encapsulated NPs elicited a longer-lasting antibody titers than antigen with the conventional adjuvant, aluminum hydroxide. Significant reductions in the level of proinflammatory cytokines and chemokines were observed in vaccinated mouse. These results suggested that polymeric nanocomplex-based vaccine design can be useful in developing vaccine against C. difficile infections.

Immune responses induced by Clostridium difficile

The spectrum of Clostridium difficile infections is highly variable, ranging from asymptomatic carriage to fatal colitis depending on the strain virulence and on the host, its gut microbiota and its immune response. After disruption of the gut microbiota, C. difficile pathogenesis can be divided into three steps: 1) contamination by spores and their germination; 2) multiplication of vegetative cells and intestinal colonization using colonization factors; 3) production of the toxins TcdA and TcdB, and for some strains, the binary toxin, which are responsible for the clinical signs. Three lines of defense counteract C. difficile. The first line is the epithelial barrier, which is breached by the toxins. Then, a rapid innate immune response follows, which forms the second line of defense. It provides very quick defense reactions against C. difficile but is non-specific and does not confer memory. C. difficile and its virulence factors, the toxins and colonization factors, induce a highly pro-inflammatory response, which can be either beneficial or harmful, but triggers the adaptive immunity as the third line of defense required to control the infectious process. Adaptive immunity provides a highly specific immune response against C. difficile with memory and long lasting immunity. The innate and adaptive immune responses against the toxins and surface components are analyzed as well as their role in disease susceptibility, severity and recurrences.

Host Immune Response to Clostridium difficile Infection in Inflammatory Bowel Disease Patients

BACKGROUND

Clostridium difficile infection (CDI) affects patients with inflammatory bowel disease (IBD). The aim of this study was to compare humoral response to C. difficile toxins in IBD patients and control outpatients.

METHODS

We prospectively followed adult IBD patients and control subjects with serum and stool samples obtained at enrollment and during periods of CDI and tested by PCR. Semiquantitative serum levels of IgM, IgG, and IgA to C. difficile toxins A and B were measured.

RESULTS

Overall, 119 stool and 117 serum samples were obtained from 150 subjects. Different levels of IgA to toxin A (P = 0.0016) and toxin B (P = 0.0468) were noted between different IBD groups. Toxin A IgA levels were higher in the Crohn's disease group (P = 0.0321) and ileal pouch anal anastomosis (IPAA) group (P = 0.001) compared with the ulcerative colitis (UC) group, and toxin B IgA levels were higher in the IPAA group compared with the UC group (P = 0.0309). There were lower levels of toxin A IgA in IBD patients compared with those in subjects without new CDI (P = 0.0488) and higher levels in IBD patients with compared with those in subjects without CDI history before enrollment (P = 0.016). There were nonsignificant lower toxin A IgG levels in IBD patients compared with those in subjects without prior CDI (P = 0.095) and higher levels in control subjects with a history of CDI compared with IBD patients with prior CDI (P = 0.049).

CONCLUSIONS

Patients with UC have lower IgA levels to C. difficile toxins compared with those with Crohn's disease and those after IPAA. Patients with IBD with prior CDI failed to demonstrate any increase in antitoxin IgG. Our findings suggest that IBD patients may benefit from immunization strategies targeting C. difficile toxins.

Protection from Clostridium difficile infection in CD4 T Cell- and polymeric immunoglobulin receptor-deficient mice

Clostridium difficile rivals methicillin-resistant Staphylococcus aureus as the primary hospital-acquired infection. C. difficile infection (CDI) caused by toxins A and/or B can manifest as mild diarrhea to life-threatening pseudomembranous colitis. Although most patients recover fully from CDI, ~20% undergo recurrent disease. Several studies have demonstrated a correlation between anti-toxin antibody (Ab) and decreased recurrence; however, the contributions of the systemic and mucosal Ab responses remain unclear. Our goal was to use the CDI mouse model to characterize the protective immune response to C. difficile. C57BL/6 mice infected with epidemic C. difficile strain BI17 developed protective immunity against CDI and did not develop CDI upon rechallenge; they generated systemic IgG and IgA as well as mucosal IgA Ab to toxin. To determine if protective immunity to C. difficile could be generated in immunodeficient individuals, we infected CD4(-/-) mice and found that they generated both mucosal and serum IgA anti-toxin Abs and were protected from CDI upon rechallenge, with protection dependent on major histocompatibility complex class II (MHCII) expression; no IgG anti-toxin Ab was found. We found that protection was likely due to neutralizing mucosal IgA Ab. In contrast, pIgR(-/-) mice, which lack the receptor to transcytose polymeric Ab across the epithelium, were also protected from CDI, suggesting that although mucosal anti-toxin Ab may contribute to protection, it is not required. We conclude that protection from CDI can occur by several mechanisms and that the mechanism of protection is determined by the state of immunocompetence of the host.

Carbohydrate-based Clostridium difficile vaccines

Clostridium difficile is responsible for thousands of deaths each year and a vaccine would be welcomed, especially one that would disrupt bacterial maintenance, colonization and persistence in carriers and convalescent patients. Structural explorations at the University of Guelph (ON, Canada) discovered that C. difficile may express three phosphorylated polysaccharides, named PSI, PSII and PSIII; this review captures our recent efforts to create vaccines based on these glycans, especially PSII, the common antigen that has precipitated immediate attention. The authors describe the design and immunogenicity of vaccines composed of raw polysaccharides and conjugates thereof. So far, it has been observed that anti-PSII antibodies can be raised in farm animals, mice and hamster models; humans and horses carry anti-PSII IgA and IgG antibodies from natural exposure to C. difficile, respectively; phosphate is an indispensable immunogenic epitope and vaccine-induced PSII antibodies recognize PSII on C. difficile outer surface.

Immunization strategies for Clostridium difficile infections

Clostridium difficile infection is a major cause of nosocomial disease in Western countries. The recent emergence of hypervirulent strains resistant to most antibiotics correlates with increasing disease incidence, severity and lethal outcomes. Current treatments rely on metronidazol and vancomycin, but the limited ability of these antibiotics to cure infection and prevent relapse highlights the need for new strategies. A better knowledge of the molecular mechanisms of the disease, the host immune response and identification of key virulence factors of Clostridium difficile now permits the development of new products specifically targeting the pathogen. Immune-based strategies relying on active vaccination or passive administration of antibody products are the focus of intense research and, today, the efficacy of monoclonal antibodies and of two vaccines are evaluated clinically. This review presents recent data, discusses the different strategies and highlights the challenges linked to the development of immunization strategies against this emerging threat.

The appendix may protect against Clostridium difficile recurrence

BACKGROUND & AIMS

Several risk factors have been identified for the development of recurrent Clostridium difficile infection (CDI) that alter host immunity and disrupt colonic flora. Although the function of the appendix has been debated, its active, gut-associated lymphoid tissue and biofilm production indicate potential roles in recovery from initial CDI and protection against recurrent CDI. We investigated whether the presence or absence of an appendix is associated with CDI recurrence.

METHODS

We reviewed the medical records of adult inpatients with CDI who were admitted to a tertiary-care teaching hospital from 2005 to 2007 to identify those with and without an appendix. The primary dependent variable for statistical analysis was CDI recurrence.

RESULTS

In a multivariate analysis of 11 clinical variables, the presence of an appendix was associated inversely with CDI recurrence (P < .0001; adjusted relative risk, .398). Age older than 60 years also was associated with CDI recurrence (P = .0280; adjusted relative risk, 2.44).

CONCLUSIONS

The presence of an appendix has a significant and independent, inverse association with CDI recurrence, but this finding requires validation in a prospective study. Assessing the presence or absence of an appendix might be useful in predicting CDI recurrence.

Immunization with Bacillus spores expressing toxin A peptide repeats protects against infection with Clostridium difficile strains producing toxins A and B

Clostridium difficile is a leading cause of nosocomial infection in the developed world. Two toxins, A and B, produced by most strains of C. difficile are implicated as virulence factors, yet only recently has the requirement of these for infection been investigated by genetic manipulation. Current vaccine strategies are focused mostly on parenteral delivery of toxoids. In this work, we have used bacterial spores (Bacillus subtilis) as a delivery vehicle to evaluate the carboxy-terminal repeat domains of toxins A and B as protective antigens. Our findings are important and show that oral immunization of the repeat domain of toxin A is sufficient to confer protection in a hamster model of infection designed to closely mimic the human course of infection. Importantly, neutralizing antibodies to the toxin A repeat domain were shown to be cross-reactive with the analogous domain of toxin B and, being of high avidity, provided protection against challenge with a C. difficile strain producing toxins A and B (A(+)B(+)). Thus, although many strains produce both toxins, antibodies to only toxin A can mediate protection. Animals vaccinated with recombinant spores were fully able to survive reinfection, a property that is particularly important for a disease with which patients are prone to relapse. We show that mucosal immunization, not parenteral delivery, is required to generate secretory IgA and that production of these neutralizing polymeric antibodies correlates with protection. This work demonstrates that an effective vaccine against C. difficile can be designed around two attributes, mucosal delivery and the repeat domain of toxin A.

Intravenous immunoglobulin for the treatment of Clostridium difficile infection: a review

Clostridium difficile infection (CDI) has increased sharply in incidence, mortality rate, and burden on the healthcare system over the past decade. Therefore, novel treatment modalities have been developed, including intravenous immunoglobulin (IVIG). The level of immune response to Clostridium difficile colonization is the major determinant of the magnitude and duration of clinical manifestations. This effect is mediated predominantly by serum IgG anti-toxin A antibodies. Based on this finding, anti-toxin A and B antibodies were successfully used in multiple in vitro and in vivo experimental settings to passively immunize hamsters in CDI models. In humans, IVIG was used as the source of those antibodies. Fifteen small, mostly retrospective and non-randomized reports documented IVIG's success in the treatment of protracted, recurrent, or severe CDI. Diarrhea resolution rates were higher in the former patient group, but the recurrence rates were similar. IVIG mechanism of action is neutralization of mainly toxin A through IgG anti-toxin A antibodies. Purified anti-toxin A and B antibodies were successfully used to decrease CDI recurrence rates among patients with no or one previous CDI episodes. In conclusion, the efficacy of IVIG for CDI treatment in animal models has been convincingly demonstrated. However, only few small non-randomized, mostly uncontrolled reports have been published on human subjects. A phase II trial results support the use of purified anti-toxin A and B antibodies to decrease CDI recurrence rates. Therefore, IVIG should currently only be used as adjunct therapy until results from large, randomized controlled trials are available.

Toxin-specific antibodies for the treatment of Clostridium difficile: current status and future perspectives

Therapeutic agents targeting bacterial virulence factors are gaining interest as non-antibiotic alternatives for the treatment of infectious diseases. Clostridium difficile is a Gram-positive pathogen that produces two primary virulence factors, enterotoxins A and B (TcdA and TcdB), which are responsible for Clostridium difficile-associated disease (CDAD) and are targets for CDAD therapy. Antibodies specific for TcdA and TcdB have been shown to effectively treat CDAD and prevent disease relapse in animal models and in humans. This review summarizes the various toxin-specific antibody formats and strategies under development, and discusses future directions for CDAD immunotherapy, including the use of engineered antibody fragments with robust biophysical properties for systemic and oral delivery.

Clostridium difficile and the disease it causes

Clostridium difficile is a spore-forming, toxin-producing, anaerobic bacterium abundant in soils and water. Frequent and early colonization of the human intestinal flora is common and often asymptomatic. Antimicrobials given commonly disrupt the intestinal microflora and through proliferation in colon and production of toxin A and B it precipitates C. difficile infection (CDI). The enterocytic detachment and bowel inflammation provoke C. difficile-associated diarrhoea (CDAD) sometimes developing into severe pseudomembranous colitis (PMC) and paralytic ileus. Infection is acquired from an endogenous source or from spores in the environment, most easily facilitated during hospital stay. In the elderly, comorbidity, hospitalization and antimicrobial treatment present as major risk factors and the slow recolonization of the normal flora likely responsible for single or multiple recurrences of CDI (25-50%) post therapy. The key procedure for diagnosis is toxin detection from stool specimens and sometimes in combination with culture to increase sensitivity. In mild cases stopping the offending antimicrobial will lead to resolution (25%) but standard therapy still consist of either oral metronidazole or vancomycin. Alternative agents are presently being developed and fidaxomicin, as well as nitrothiazolide are promising. Furthermore, host factors like low antitoxin A levels in serum relates to increased risk of recurrence and small numbers of patients have received immunoglobulin with good results. An immunogenic toxoid vaccine has been developed and human colostrum rich in specific secretory Ig A also support the future use of immunotherapy. Today we experience a tenfold increase of CDI incidence in the western world and both epidemics and therapeutic failure of metronidazole is contributing to morbidity and mortality. The current epidemic of the C. difficile strain NAP1/027 emerging in 2002 in Canada and the USA has now spread to most parts of Europe and virulence factors like high toxin production and sporulation challenge the therapeutic situation and cause great concern among infection control workers. Excessive use of modern fluoroquinolones is thought to play an important role in facilitating this epidemic since NAP1/027 was shown to have acquired moxifloxacin resistance compared to historical strains of the same genotype. Both the current epidemic like this and other local outbreaks from resistant or virulent strains warrant culture to be routinely performed enabling susceptibility testing and typing of the pathogen. Genotyping is most commonly done today by pulse-field gel electrophoresis (PFGE) or PCR ribotyping but multilocus variable-number tandem-repeat analysis (MLVA) seems promising. Epidemiological surveillance using all these tools will help us to better understand the global spread of C. difficile.

Intravenous immunoglobulin for the treatment of severe Clostridium difficile colitis: an observational study and review of the literature

BACKGROUND

Clostridium difficile colitis (CDC) is the most common cause of hospital-acquired diarrhea. The increase in the incidence and fatality rate of CDC over the past decade has stimulated a search for new therapies, including intravenous immunoglobulin (IVIG). We report our experience with IVIG for the treatment of 21 patients with severe CDC.

METHOD

Retrospective review of patients with severe CDC who received IVIG between July 2002 and April 2006 at a teaching hospital. The existing literature on IVIG infusion for severe CDC was also reviewed.

RESULTS

Twenty-one of 1230 patients with CDC were treated with IVIG. The mean age was 68 (range, 35-98) years, with mean hospital stay of 23 (range, 9-64) days. Conventional treatment was used for an average of 8 (range, 1-25) days before IVIG infusion. All patients had evidence of pancolitis (radiologically) or ileus (clinically). The mean Acute Physiological Assessment and Chronic Health Evaluation (APACHE II) score was 25 (range, 6-39) at day 1 of IVIG infusion. Nine patients (43%) survived their hospitalization with colitis resolution while 12 (57%) died. One patient developed pulmonary edema after IVIG infusion. Symptoms resolved after an average of 10 (range, 2-20) days for survivors. Two patients underwent urgent colectomy.

CONCLUSIONS

This is the largest case series describing IVIG use for patients with severe CDC and the one with the highest mortality rate to date. The use of IVIG in this setting does not seem to benefit all patients. Benefit appears to depend on the extent of systemic involvement. Further studies are needed before adopting IVIG as routine treatment for severe CDC.

Probiotics and Gastrointestinal Disease: Clinical Evidence and Basic Science

Our intestinal microbiota serve many roles vital to the normal daily function of the human gastrointestinal tract. Many probiotics are derived from our intestinal bacteria, and have been shown to provide clinical benefit in a variety of gastrointestinal conditions. Current evidence indicates that probiotic effects are strain-specific, they do not act through the same mechanisms, and nor are all probiotics indicated for the same health conditions. However, they do share several common features in that they exert anti-inflammatory effects, they employ different strategies to antagonize competing microorganisms, and they induce cytoprotective changes in the host either through enhancement of barrier function, or through the upregulation of cytoprotective host proteins. In this review we focus on a few selected probiotics - a bacterial mixture (VSL#3), a Gram-negative probiotic (E. coli Nissle 1917), two Gram-positive probiotic bacteria (LGG, L. reuteri), and a yeast probiotic (S. boulardii) - for which sound clinical and mechanistic data is available. Safety of probiotic formulations is also discussed.

Pharmacological action of tick saliva upon haemostasis and the neutralization ability of sera from repeatedly infested hosts

Ticks are blood-feeding arthropods widely distributed in the world and vectors of several diseases. As haematophagy demands evasion strategies and repeatedly infested hosts develop protective immune responses, we investigated the mechanisms of the Rhipicephalus (Boophilus) microplus saliva anti-haemostatic activity and the possible relationship between the acquired natural anti-tick host resistance and anti-haemostatic action. For this purpose, we studied the effects of R. microplus saliva on different pathways of haemostasis and tested whether repeated infested bovine sera (RIBS) are able to abolish salivary anti-haemostatic activities. R. microplus saliva (i) displays inhibitory activity upon collagen-induced platelet aggregation; (ii) inhibits the induction of endothelial pro-coagulant state; and (iii) reduces thrombogenesis in vivo. RIBS were shown to be able to partially block the delay of coagulation and the anti-thrombotic effect of saliva, and to totally abolish the modulation of endothelium activation. Conversely, RIBS has no effect on the inhibition of platelet aggregation. These results show, for the first time, the neutralization ability of sera from acquired resistance hosts against tick anti-haemostatics. Moreover, this is the first report of a haematophagous parasite able to modulate endothelial cell pro-coagulant state, and addresses the presence of anti-platelet and anti-thrombotic activity in R. microplus saliva.

Severity of Clostridium difficile-associated diarrhea in solid organ transplant patients

Clostridium difficile-associated diarrhea (CDAD) has a wide spectrum of disease severity. Studies have implicated immunosuppressants as a risk factor for severe disease. We hypothesized that solid organ transplant (SOT) patients with CDAD would be at greater risk for severe disease because of their profound immunosuppression. Adult SOT patients with CDAD seen at Duke University Medical Center between 1999 and 2003 were compared with a reference group of non-transplant patients with CDAD. The primary outcome was the development of complicated colitis defined as death, intensive care unit admission, or urgent colectomy within 30 days of diagnosis. A secondary outcome was relapse within 60 days. Eighty transplant and 86 non-transplant cases were reviewed. There was no significant difference in the development of complicated colitis (13.8% vs. 7.0%) or relapse rates (6.2% vs. 7.0%) between the 2 groups. In the entire sample, 18.5% of patients receiving corticosteroids unrelated to transplantation relapsed as compared with 4.5% not receiving corticosteroids (risk ratio 4.3, P=0.02). In conclusion, no significant difference was found in severity of CDAD between SOT patients and non-transplant patients. Exposure to corticosteroids was significantly associated with an increased risk of relapse and may warrant a longer treatment course.

Biological Functions of IgA

Immunoglobulin A (IgA) is the most enigmatic of immunoglobulins. It is by far the most abundant of human Igs, being present in the blood plasma at concentrations approximating 2–3mg/mL, as well as the dominant isotype in most secretions where its output amounts to some 5–8g/day in adults. Furthermore, its evolutionary origins appear to precede the synapsid– diapsid divergence in tetrapod phylogeny (>300 million years ago) because it is present in both mammals and birds and therefore possibly also in reptiles (reviewed in Peppard et al., 2005); an IgA-like molecule has now been identified in a lizard (Deza et al., 2007).

Recombinant cholera toxin B subunit (rCTB) as a mucosal adjuvant enhances induction of diphtheria and tetanus antitoxin antibodies in mice by intranasal administration with diphtheria-pertussis-tetanus (DPT) combination vaccine

Recombinant cholera toxin B subunit (rCTB) which is produced by Bacillus brevis carrying pNU212-CTB acts as a mucosal adjuvant capable of enhancing host immune responses specific to unrelated, mucosally co-administered vaccine antigens. When mice were administered intranasally with diphtheria-pertussis-tetanus (DPT) combination vaccine consisting of diphtheria toxoid (DTd), tetanus toxoid (TTd), pertussis toxoid (PTd), and formalin-treated filamentous hemagglutinin (fFHA), the presence of rCTB elevated constantly high values of DTd- and TTd-specific serum ELISA IgG antibody titres, and protective levels of diphtheria and tetanus toxin-neutralizing antibodies but the absence of rCTB did not. Moreover, the addition of rCTB protected all mice against tetanic symptoms and deaths. DPT combination vaccine raised high levels of serum anti-PT IgG antibody titres regardless of rCTB and protected mice from Bordetella pertussis challenge. These results suggest that co-administration of rCTB as an adjuvant is necessary for induction of diphtheria and tetanus antitoxin antibodies on the occasion of intranasal administration of DPT combination vaccine.

Active and passive immunization against Clostridium difficile diarrhea and colitis

Clostridium difficile, a gram-positive bacterium, is the major cause of hospital-acquired infectious diarrhea and colitis in industrialized nations. C. difficile colonization results from antibiotic administration and subsequent loss of protection provided by intestinal flora. C. difficile induced-colitis is caused by the release of two exotoxins, toxin A and B. Host factors including advanced age, pre-existing severe illness and weakened immune defenses predispose individuals to symptomatic infection. The generation of antibody responses to toxin A through natural exposure is associated with protection from disease. In addition, an inability to acquire immunity to toxin A puts individuals at risk for recurrent and/or severe disease. Immunological approaches for the management of this disease are being developed which could reduce the reliance on antibiotics for treatment and allow for re-establishment of the natural barrier provided by an intact commensal flora. An active vaccine and various immunotherapeutic strategies under evaluation may prove to be effective against severe or relapsing C. difficile infection.

Toxin gene analysis of a variant strain of Clostridium difficile that causes human clinical disease

A toxin variant strain of Clostridium difficile was isolated from two patients with C. difficile-associated disease (CDAD), one of whom died from extensive pseudomembranous colitis. This strain, identified by restriction endonuclease analysis (REA) as type CF2, was not detected by an immunoassay for C. difficile toxin A. Culture supernatants of CF2 failed to elicit significant enterotoxic activity in the rabbit ileal loop assay but did produce atypical cytopathic effects in cell culture assay. Southern hybridization, PCR amplification, and DNA sequence analyses were performed on the toxin A (tcdA) and toxin B (tcdB) genes of type CF2 isolate 5340. Type CF2 5340 tcdA exhibited a 1,821-bp truncation, due to three deletions in the 3' end of the gene, and a point mutation in the 5' end of the gene, resulting in a premature stop codon at tcdA position 139. Type CF2 5340 tcdB exhibited multiple nucleotide base substitutions in the 5' end of the gene compared to tcdB of the standard toxigenic strain VPI 10463. Type CF2 5340 toxin gene nucleotide sequences and deduced amino acid sequences showed a strong resemblance to those of the previously described variant C. difficile strain 1470, a strain reported to have reduced pathogenicity and no association with clinical illness in humans. REA of strain 1470 identified this strain as a distinct type (CF1) within the same REA group as the closely related type CF2. A review of our clinical-isolate collection identified five additional patients infected with type CF2, three of whom had documented CDAD. PCR amplification of the 3' end of tcdA demonstrated identical 1. 8-kb deletions in all seven type CF2 isolates. REA type CF2 is a toxin variant strain of C. difficile that retains the ability to cause disease in humans but is not detected in clinical immunoassays for toxin A.

Polymeric IgA is superior to monomeric IgA and IgG carrying the same variable domain in preventing Clostridium difficile toxin A damaging of T84 monolayers

The two exotoxins A and B produced by Clostridium difficile are responsible for antibiotic-associated enterocolitis in human and animals. When added apically to human colonic carcinoma-derived T84 cell monolayers, toxin A, but not toxin B, abolished the transepithelial electrical resistance and altered the morphological integrity. Apical addition of suboptimal concentration of toxin A made the cell monolayer sensitive to toxin B. Both toxins induced drastic and rapid epithelial alterations when applied basolaterally with a complete disorganization of tight junctions and vacuolization of the cells. Toxin A-specific IgG2a from hybridoma PCG-4 added apically with toxin A alone or in combination with toxin B abolished the toxin-induced epithelial alterations for up to 8 h. The Ab neutralized basolateral toxin A for 4 h, but not the mixture of the two toxins. Using an identical Ab:Ag ratio, we found that recombinant polymeric IgA (IgAd/p) with the same Fv fragments extended protection against toxin A for at least 24 h in both compartments. In contrast, the recombinant monomeric IgA counterpart behaved as the PCG-4 IgG2a Ab. The direct comparison between different Ig isotype and molecular forms, but of unique specificity, demonstrates that IgAd/p Ab is more efficient in neutralizing toxin A than monomeric IgG and IgA. We conclude that immune protection against C. difficile toxins requires toxin A-specific secretory Abs in the intestinal lumen and IgAd/p specific for both toxins in the lamina propria.

Killing of Streptococcus pneumoniae by capsular polysaccharide-specific polymeric IgA, complement, and phagocytes

The role of IgA in the control of invasive mucosal pathogens such as Streptococcus pneumoniae is poorly understood. We demonstrate that human pneumococcal capsular polysaccharide-specific IgA initiated dose-dependent killing of S. pneumoniae with complement and phagocytes. The majority of specific IgA in serum was of the polymeric form (pIgA), and the efficiency of pIgA-initiated killing exceeded that of monomeric IgA-initiated killing. In the absence of complement, specific IgA induced minimal bacterial adherence, uptake, and killing. Killing of S. pneumoniae by resting phagocytes with immune IgA required complement, predominantly via the C2-independent alternative pathway, which requires factor B, but not calcium. Both S. pneumoniae-bound IgA and complement were involved, as demonstrated by a 50% decrease in killing with blocking of Fcalpha receptor (CD89) and CR1/CR3 (CD35/CD11b). However, IgA-mediated killing by phagocytes could be reproduced in the absence of opsonic complement by pre-activating phagocytes with the inflammatory products C5a and TNF-alpha. Thus, S. pneumoniae capsule-specific IgA may show distinct roles in effecting clearance of S. pneumoniae in the presence or absence of inflammation. These data suggest mechanisms whereby pIgA may serve to control pneumococcal infections locally and upon the pathogen's entry into the bloodstream.

Local and systemic neutralizing antibody responses induced by intranasal immunization with the nontoxic binding domain of toxin A from Clostridium difficile

Fourteen of the 38 C-terminal repeats from Clostridium difficile toxin A (14CDTA) were cloned and expressed either with an N-terminal polyhistidine tag (14CDTA-HIS) or fused to the nontoxic binding domain from tetanus toxin (14CDTA-TETC). The recombinant proteins were successfully purified by bovine thyroglobulin affinity chromatography. Both C. difficile toxin A fusion proteins bound to known toxin A ligands present on the surface of rabbit erythrocytes. Intranasal immunization of BALB/c mice with three separate 10-microg doses of 14CDTA-HIS or -TETC generated significant levels of anti-toxin A serum antibodies compared to control animals. The coadministration of the mucosal adjuvant heat labile toxin (LT) from Escherichia coli (1 microg) significantly increased the anti-toxin A response in the serum and at the mucosal surface. Importantly, the local and systemic antibodies generated neutralized toxin A cytotoxicity. Impressive systemic and mucosal anti-toxin A responses were also seen following coadministration of 14CDTA-TETC with LTR72, an LT derivative with reduced toxicity which shows potential as a mucosal adjuvant for humans.

Serum antitoxin antibodies mediate systemic and mucosal protection from Clostridium difficile disease in hamsters

Clostridium difficile is the bacterial pathogen identified as the cause of pseudomembranous colitis and is principally responsible for nosocomial antibiotic-associated diarrhea and colitis. The pathologic findings associated with this infection are believed to be caused by two large (approximately 300-kDa) exotoxins, toxins A and B. Because of the mucosal nature of this infection, vaccination strategies aimed at providing prophylactic or therapeutic immune protection have included immunization by mucosal routes. Using the hamster model of C. difficile infection, we examined the protective efficacy of inactivated toxin (toxoid) vaccine formulations prepared as either culture filtrate or partially purified toxoid. We compared combination parenteral and mucosal vaccination regimens involving intranasal, intragastric, or rectal routes of immunization and found that rectal immunization in conjunction with intramuscular (i.m.) vaccination provided full protection of hamsters from death and diarrhea while the other mucosal routes did not. Protection was associated with high levels of toxin-neutralizing antibodies in serum. The requirement for adjuvants for protection was assessed by using sequential i.m. and rectal or i.m. vaccination regimens. Unexpectedly, i.m. immunization without adjuvant conferred the highest protection from death and diarrhea; this regimen elicited the highest serum anti-toxin B titers as well as toxin B neutralizing titers. Passive transfer of mouse antitoxin antibodies protected hamsters in a dose-dependent manner, demonstrating the principal role of circulating antitoxin antibodies in immunity from this toxin-mediated mucosal disease. These results suggest that prophylactic parenteral vaccination or intravenous immunotherapy could provide protection from C. difficile disease in humans.

Characteristics of IgA anti-HIV antibodies in plasma from patients with HIV infection

The concentration of total IgA and the specificity and molecular size of IgA anti-human immunodeficiency virus (HIV) type-1 antibodies in plasma obtained from individuals at different stages of HIV infection were analyzed. The concentration of total IgA in the plasma was not decreased even in the late stage of HIV infection, in contrast with those of total IgG and IgM. The IgA anti-HIV antibodies differed to the IgG anti-HIV antibodies in their specificity as determined by Western blotting. The IgA antibodies mainly bind to Env glycoproteins. The IgA anti-HIV antibodies in plasma were detected between IgG and IgM by gel filtration, suggesting the presence of polymeric IgA anti-HIV antibodies. These results indicate that the production of non-specific IgA in plasma is enhanced by unknown mechanisms in every stages of HIV infection, and suggest that IgA anti-HIV antibodies in plasma which are possibly polymeric and have unique specificity may play an important role in HIV infection.

Evaluation of a new enzyme immunoassay for Clostridium difficile toxin A

AIM

To evaluate a new enzyme immunoassay (EIA) method for detection of Clostridium difficile toxin by comparing it to cytotoxicity assay. To investigate the nature of false negative and false positive EIA results by evaluating clinical and therapeutic parameters.

METHODS

737 consecutive diarrhoeal specimens collected from patients clinically suspected of having C difficile colitis were tested for the presence of C difficile toxin by EIA for toxin A and by cytotoxicity assay. Clinical data were evaluated in all cases positive by either method.

RESULTS

With the cytotoxicity assay as a gold standard, the specificity of EIA for toxin detection was 99.3% and the sensitivity was 62.2%. No false negative EIA specimens were obtained from patients already being treated for C difficile colitis. Among patients with cytotoxicity positive specimens, those with EIA positive samples had no clinical features distinguishing them from patients with EIA negative samples.

CONCLUSIONS

Although specific, the new EIA method directed against toxin A lacks sensitivity compared to cytotoxicity. False negative EIA tests are not associated with concurrent treatment for C difficile colitis nor with any specific clinical features examined in our study.

Nitric oxide production during Vibrio cholerae infection

Vibrio cholerae induces massive intestinal fluid secretion that continues for the life of the stimulated epithelial cells. Enhanced regional blood flow and peristalsis are required to adapt to this obligatory intestinal secretory challenge. Nitric oxide (NO) is a multifunctional molecule that modulates blood flow and peristalsis and possesses both cytotoxic and antibacterial activity. We demonstrate that, compared with those in asymptomatic control subjects, levels of stable NO metabolites (NO2-/NO3-) are significantly increased in sera from acutely ill Peruvian patients with natural cholera infection as well as from symptomatic volunteers from the United States infected experimentally with V. cholerae. In a rabbit ileal loop model in vivo, cholera toxin (CT) elicited fluid secretion and dose-dependent increases in levels of NO2-/NO3- in the fluid (P < 0.01). In contrast, lipopolysaccharide (LPS) elicited no such effects when applied to the intact mucosa. NO synthase (NOS) catalytic activity also increased in toxin-exposed tissues (P < 0.05), predominantly in epithelial cells. The CT-induced NOS activity was Ca2+ dependent and was not suppressed by dexamethasone. In conclusion, symptomatic V. cholerae infection induces NO production in humans. In the related animal model, CT, but not LPS, stimulated significant production of NO in association with increases in local Ca(2+)-dependent NOS activity in the tissues.

Intranasal booster vaccination against diphtheria and tetanus in man

The booster responses of three different formulations of intranasal (i.n.) diphtheria-tetanus (D-T) vaccines were determined in military recruits and compared with a conventional subcutaneous D-T vaccine. The vaccines for mucosal delivery were sprayed into one nostril and contained D and T toxoids in an enhancer mixture of polysorbate and caprylic/capric glycerides. All of the vaccines gave rise mainly to a systemic IgG response. Among 51 persons with anti-D antibody concentrations in serum below a protective level of 0.01 international units (IU ml-1) before vaccination, all except two attained protective antibody concentrations 4 weeks after vaccination. The median increase in anti-D antibody concentration was 113-fold with the most efficient i.n. formulation. The median increase in anti-T antibody level was 2.4-fold, however, the pre-vaccination levels for this antigen were very high. Within the examined levels, the booster response depended mainly on the dose of the antigen in the vaccine rather than on the concentration of the vehicle mixture. Compared with the parenteral D-T vaccine containing aluminium hydroxide as an adjuvant, all of the tested i.n. formulations showed somewhat lower immunogenicity in man as well as in pre-clinical guinea-pig studies. Among 215 persons immunized i.n., 61% preferred this route of administration rather than a parenteral injection, although the formulations were all associated with varying local symptoms, frequently stinging and pronounced, nasal secretion.

Hepatobiliary transport of IgA in the golden Syrian hamster (Mesocricetus auratus)

Do hamsters, like rats, rabbits and mice, possess an hepatocyte 'IgA pump' whereby circulating plasma polymeric IgA (pIgA) is actively transported into bile, against a concentration gradient, via the polymeric Ig receptor or secretory component (SC)? Precipitating antisera, raised against rat Igs and serum proteins, and crossreacting with their hamster homologues, detected hamster SC by immunoelectrophoresis in bile, but not serum. Gel filtration of hamster bile indicated that free SC eluted between IgG and albumin, as for other mammals. Hamster bile IgA was pIgA, and was true secretory IgA (SIgA) by its reaction with anti-SC antiserum and by SDS-PAGE with reduction. Hamster serum IgA comprised both pIgA and IgA monomers. Mean bile-to-serum concentration ratios (B/S) for IgA, IgG, transferrin and albumin, measured by radial immunodiffusion, were 2.65, 0.019, 0.024, and 0.016, respectively, demonstrating strongly selective enrichment of bile in IgA. Human 125I-labelled dimeric IgA was injected into the circulation of five hamsters with cannulated bile ducts; 20% of the [125I]IgA (> 95% precipitable by trichloroacetic acid) was recovered in bile within 5 h, a figure close to that for mice, but smaller than that for rats and rabbits. The data suggest that bile significantly contributes to hamster intestinal SIgA, as shown for rats, rabbits and mice. This could be relevant to studies where hamsters are used as an experimental model for infection by the human intestinal pathogen, Clostridium difficile.

Prolonged and preferential production of polymeric immunoglobulin A in response to Streptococcus pneumoniae capsular polysaccharides

Streptococcus pneumoniae is an invasive mucosal pathogen for which host defense is dependent on capsular polysaccharide-specific antibody. Capsule-specific immunoglobulin G (IgG), IgM, and IgA are produced following pneumococcal vaccination and infection. Serum IgA has two molecular forms, polymeric and monomeric. These forms may modulate the avidity of antigen binding and evolve over time as the immune response matures. Therefore, we sequentially characterized the molecular forms of serum IgA to three serotypes of pneumococcal capsular polysaccharides (types 8, 12F, and 14) after pneumococcal vaccination and after natural infection with type 14 S. pneumoniae. Although typically the form of IgA in antigen-specific systemic responses to protein antigens is predominantly polymeric in sera of patients shortly after exposure and shifts to the monomeric form in sera obtained several weeks later, the form of IgA in response to each pneumococcal capsular polysaccharide remained predominantly polymeric 1 month after natural infection and up to I year following vaccination. In contrast, IgA to pneumococcal cell wall polysaccharide was both polymeric and monomeric. Moreover, the form of IgA in response to polyribosyl-ribitol-phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b, was predominantly monomeric in the sera of 8 of 10 subjects tested 1 to 3 months after vaccination with either PRP alone or the diphtheria toxoid conjugate of PRP. We conclude that systemic responses to pneumococcal capsular polysaccharides are distinct in the production of predominantly polymeric IgA over time. The persistence of polymeric IgA may facilitate binding and clearance of pneumococci from the systemic circulation or reflect limited maturation of the immune response to pneumococcal capsular polysaccharides.