Expression of tumor necrosis factor alpha and interleukin 1 beta in jejuna of volunteers after experimental challenge with Cryptosporidium parvum correlates with exposure but not with symptoms

Regulatory Functions of Hypoxia in Host-Parasite Interactions: A Focus on Enteric, Tissue, and Blood Protozoa

Body tissues are subjected to various oxygenic gradients and fluctuations and hence can become transiently hypoxic. Hypoxia-inducible factor (HIF) is the master transcriptional regulator of the cellular hypoxic response and is capable of modulating cellular metabolism, immune responses, epithelial barrier integrity, and local microbiota. Recent reports have characterized the hypoxic response to various infections. However, little is known about the role of HIF activation in the context of protozoan parasitic infections. Growing evidence suggests that tissue and blood protozoa can activate HIF and subsequent HIF target genes in the host, helping or hindering their pathogenicity. In the gut, enteric protozoa are adapted to steep longitudinal and radial oxygen gradients to complete their life cycle, yet the role of HIF during these protozoan infections remains unclear. This review focuses on the hypoxic response to protozoa and its role in the pathophysiology of parasitic infections. We also discuss how hypoxia modulates host immune responses in the context of protozoan infections.

The Efficacy of Citrus maxima Peels Aqueous Extract Against Cryptosporidiosis in Immunecompromised Mice

INTRODUCTION

 Cryptosporidiosis is an opportunistic globally distributed parasitic disease caused by protozoan Cryptosporidium where its development is closely related to the host's immune status. New therapeutic agents are a high priority as chemotherapeutics are impractical and vaccines are unavailable for young as well as immune-compromised patients or animals. The current study was designed to evaluate the therapeutic effect of the internal white (albedo) and external yellow (flavedo) peels of Citrus maxima (C. maxima) as an alternative medicinal plant. MATERIALS AND METHODS : Parasitological examination for oocysts in the stool was determined. Histopathological alterations and immunohistochemical expression of APC and cyclin D1 as well as an assessment of interferon-γ (IFN-γ) and interleukin 1β (IL-1β) in ileal tissues was carried out. In addition, the biochemical examination of serum albumin, globulin and liver enzymes were evaluated. Results revealed a significant decrease of oocysts count correlated with an amelioration of histopathological and immunohistochemical changes in ileal tissue with an enhancement of liver enzymes and inflammatory cytokines levels.

CONCLUSION

 It could be concluded that treatment with C. maxima peel extracts have a potential therapeutic and an immunoregulatory efficacy against Cryptosporidiosis. Obtained results showed that the white peel was found to have more immunological effect that could significantly enhance inflammatory cytokines response towards normal status. Hence, it can be used in the daily animal diet to give protective effects against infection.

Inflammasome components caspase-1 and adaptor protein apoptosis-associated speck-like proteins are important in resistance to Cryptosporidium parvum

Cryptosporidium spp. are opportunistic protozoan parasites that infect epithelial cells in the intestinal tract and cause a flu-like diarrheal illness. Innate immunity is key to limiting the expansion of parasitic stages early in infection. One mechanism in which it does this is through the generation of early cytokines, such as IL-18. The processing and secretion of mature IL-18 (and IL-1β) is mediated by caspase-1 which is activated within an inflammasome following the engagement of inflammasome-initiating sensors. We examined how the absence of caspase-1 and caspase-11, the adapter protein Asc, and other inflammasome components affects susceptibility to cryptosporidial infection by these and other key cytokines in the gut. We found that Casp-11^-/-Casp-1^-/- knockout mice have increased susceptibility to Cryptosporidium parvum infection as demonstrated by the 35-fold higher oocyst production (at peak infection) compared to wild-type mice. Susceptibility correlated with a lack of IL-18 in caspase-1 and caspase1/11 knockout mice, whereas IL-18 is significantly elevated in wildtype mice. IL-1β was not generated in any significant amount following infection nor was any increased susceptibility observed in IL-1β knockout mice. We also show that the adapter protein Asc is important to susceptibility, and that the caspase-1 canonical inflammasome signaling pathway is the dominant pathway in C. parvum resistance.

A rapid IL-17 response to Cryptosporidium parvum in the bovine intestine

Cryptosporidium parvum causes diarrhoea, due to villi damage, in livestock and humans globally. Immunity develops after repeated infections but initial infections can be severe, highlighting the importance of early infection dynamics. We have modelled early C. parvum infection in bovine jejunum biopsies. IL-17A accumulated over time peaking at 9 h post-infection, with no effect of infection on IL-1β; antibiotics positively influenced IL-17A as higher levels were found in cultures with antibiotics. Infection of primary fibroblasts resulted in lower plaque formation when fibroblasts were primed with IL-17A. Our results indicate a role for IL-17A in reducing C. parvum-dependent host cell damage.

Cryptosporidiosis-an overview

Apicomplexan protozoan parasites of the genus Cryptosporidium infect the gastrointestinal tract and lungs of a wide variety of animals, including humans. The majority of human infections are due to either Cryptosporidium hominis (C. hominis) and/or Cryptosporidium parvum (C. parvum). The parasite has a complex life cycle that includes both asexual and sexual stages. While there are invasive free living stages, proliferation and differentiation take place within a unique parasitrophorous vacuole under the host cell brush border but outside the host cell cytoplasm. Infection is spread by environmentally resistant spores that primarily contaminate drinking water and occasionally food sources, which may cause significant outbreaks of diarrhea that generally lasts less than 2 w in immunocompetent individuals. In immunodeficient or immunosuppressed individuals, diarrhea may be copious and can result in significant morbidity and mortality, particularly in AIDS patients. Although diagnosis is relatively simple, effective drug treatment, particulary for infections in immunodeficient patients, has not been uniformly successful. This overview summarizes the species known to infect humans, aspects of the parasite life cycle, sources of infection, the pathophysiology of cryptosporidiosis, the immune response to infection, diagnosis, treatment and some aspects of cryptosporidiosis in China.

Identification and immunological characterization of three potential vaccinogens against Cryptosporidium species

Cryptosporidiosis is a ubiquitous infectious disease, caused by the protozoan parasites Cryptosporidium hominis and Cryptosporidium parvum, leading to acute, persistent, and chronic diarrhea with life-threatening consequences in immunocompromised individuals. In developing countries, cryptosporidiosis in early childhood has been associated with subsequent significant impairment in growth, physical fitness, and intellectual abilities. Currently, vaccines are unavailable and chemotherapeutics are toxic and impractical, and agents for immunoprophylaxis or treatment of cryptosporidiosis are a high priority. Availability of the genome sequences for C. hominis and C. parvum provides new opportunities to procure and examine novel vaccine candidates. Using the novel approach of "reverse vaccinology," we identified several new potential vaccine candidates. Three of these antigens--Cp15, profilin, and a Cryptosporidium apyrase--were delivered in heterologous prime-boost regimens as fusions with cytolysin A (ClyA) in a Salmonella live vaccine vector and as purified recombinant antigens, and they were found to induce specific and potent humoral and cellular immune responses, suggesting their potential as new vaccinogens against Cryptosporidium infection.

The cell biology of cryptosporidium infection

Cryptosporidiosis remains a significant cause of enteric disease worldwide. Basic investigations of host: pathogen interactions have revealed the intricate processes mediating infection. The following summarizes the interactions that mediate infection and the host responses that both permit and ultimately clear the infection.

Host immune response to Cryptosporidium parvum infection

Species of the genus Cryptosporidium are protozoan parasites (Apicomplexa) that cause gastroenteritis in animals and humans. Of these Cryptosporidium parvum and Cryptosporidium hominis are the major causative agents of human cryptosporidiosis. Whereas infection is self-limiting in the immunocompetent hosts, immunocompromised individuals develop a chronic, life-threatening disease. As specific therapeutic or preventive interventions are not yet available, better understanding of the immune response to the parasite is required. This minireview briefly summarizes the factors involved in the innate and acquired immune response in this pathogen-host interaction with an emphasis on more recent data from mouse models of infection.

Human immune responses in cryptosporidiosis

Immune responses play a critical role in protection from, and resolution of, cryptosporidiosis. However, the nature of these responses, particularly in humans, is not completely understood. Both innate and adaptive immune responses are important. Innate immune responses may be mediated by Toll-like receptor pathways, antimicrobial peptides, prostaglandins, mannose-binding lectin, cytokines and chemokines. Cell-mediated responses, particularly those involving CD4(+) T cells and IFN-gamma play a dominant role. Mucosal antibody responses may also be involved. Proteins mediating attachment and invasion may serve as putative protective antigens. Further knowledge of human immune responses in cryptosporidiosis is essential in order to develop targeted prophylactic and therapeutic interventions. This review focuses on recent advances and future prospects in the understanding of human immune responses to Cryptosporidium infection.

Pulmonary cryptosporidiosis: role of COX2 and NF-kB

In the present study we investigated whether the pathological changes induced by Cryptosporidium in the lungs are mediated through the activation of COX-2, and whether the pathway employed for this activation involves NF-kB. 70 albino rats were submitted for this work. They were categorized into 3 groups: 30 immunocompetent (IC) rats infected with Cryptosporidium oocysts, 30 immunosuppressed (IS) rats infected with Cryptosporidium oocysts, and 10 IC, non-infected rats. Immunohistochemical expression of COX2 and NF-kB in lung tissues of the rats was examined. 43.3% of IC rats showed chronic pneumonia and fibrosis, 40% COX2 positivity, and 36.67% NF-kB positivity. 96.7% of IS rats showed chronic pneumonia and fibrosis, 56.7% non-caseating granuloma with Cryptosporidium oocysts, and 66.7% positivity for both COX2 and NF-kB. Density of inflammatory infiltration was statistically correlated with quickscore of both COX2 and NF-kB in both IC and IS groups. An association between quickscores of COX2 and NF-kB was found in our studied material. These data could demonstrate that Cryptosporidium infection induces upregulation of COX2 possibly through the NF-kB pathway, which suggests the events that contribute to the pathogenesis of Cryptosporidium. These findings could indicate potential therapeutic pharmacological target-mediating treatment of lesions caused by Cryptosporidium.

Role of tumor necrosis factor alpha in development of immunity against Cryptosporidium parvum infection

Tumor necrosis factor (TNF-alpha) significantly reduced Cryptosporidium parvum development in a murine enterocyte cell line, and a key mechanism of action appeared to be inhibition of parasite invasion. However, TNF-alpha-deficient mice controlled infection as effectively as wild-type mice. This suggests that TNF-alpha might have only a redundant role for establishing immunity against C. parvum.

Childhood cryptosporidiosis is associated with a persistent systemic inflammatory response

Cryptosporidiosis in young children prompts local inflammation in the intestinal tract. We studied a cohort of young children with cryptosporidiosis to determine whether systemic inflammatory responses occur and, if so, to evaluate whether inflammation persists after infection. Cryptosporidiosis was associated with increased levels of interleukin-8 and tumor necrosis factor- alpha systemically, which persisted at 6 months after enrollment. The level of intestinal tumor necrosis factor- alpha was elevated at enrollment, but elevated levels did not persist. Worsening of malnutrition, particularly stunting, was observed after infection. The association of cryptosporidiosis, inflammation, and stunting in children with cryptosporidiosis warrants further evaluation.

An updated review on Cryptosporidium and Giardia

Cryptosporidium and Giardia are two of the most commonly occurring enteric protozoans. They are responsible for diarrheal diseases that may lead to nutritional deficiencies and significant morbidity and mortality, especially among children in developing countries and patients who have immune defects. Both are difficult to diagnose with microscopic techniques. This article provides an updated review of the epidemiology, pathogenesis, clinical manifestations, and treatment of Cryptosporidium and Giardia.

Mucosal cytokine and antigen-specific responses to Cryptosporidium parvum in IL-12p40 KO mice

Studies of cellular immune responses to Cryptosporidium parvum have been limited in part by lack of suitable animal models. IL-12p40(-/-)mice are susceptible to initial infection with C. parvum but recover within 2 weeks, rendering the animals resistant to reinfection. Because the host responses that determine duration and severity of primary infection are not yet understood, we studied the cellular immune response to primary infection with C. parvum in IL-12p40(-/-)mice and also explored possible mechanisms for this response. Female IL-12p40(-/-)mice were inoculated with 10,000 oocysts. Uninfected age-matched mice served as controls. At different time intervals following exposure to oocysts, mice were sacrificed and their intestine, spleen, and mesenteric lymph node tissues were harvested. Cellular immune responses to C. parvum were characterized. Infection of IL-12p40(-/-)mice induced changes in the gene expression of the cytokines IFN-gamma, IL-4, IL-15, IL-18, TNF-alpha and TGF-beta during primary infection. There was also a significant increase in total numbers of lymphocytes and CD19/CD62L-expressing cells in mesenteric lymph nodes. These MLN cells exhibited increased antigen-specific proliferation and cytokine production (IL-6 and IFN-gamma) levels when stimulated in vitro. These observations delineate the cellular immune responses during acute C. parvum infection of the IL-12p40(-/-)mouse model.

Pathophysiology and impact of enteric bacterial and protozoal infections: new approaches to therapy

Despite numerous scientific advances in the past few years regarding the pathogenesis, diagnostic tools and treatment of infectious enteritis, enteric infections remain a serious threat to health worldwide. With globalization of the food supply, the increase in travel, mass food processing and antibiotic resistance, infectious diarrhea has become a critical concern for both developing and developed countries. Oral rehydration therapy has been cited as the most important medical discovery of the century due to the millions of lives that have been saved. However, statistics concerning diarrhea-induced mortality and the highly underestimated morbidity continue to demonstrate the severity of the problem. A more complete understanding of the pathogenesis of infectious diarrhea and potential new vaccines and effective treatments are badly needed. In addition, public health preventive actions, such as early detection of outbreaks, care with food, water and sanitation and, where relevant, immunization, should be considered a priority. This article provides an overview of the epidemiological impact, pathogenesis and new approaches to the management of enteric infections.

Differential regulation of beta-defensin gene expression during Cryptosporidium parvum infection

Invasion of enterocytes by pathogenic microbes evokes both innate and adaptive immune responses, and microbial pathogens have developed strategies to overcome the initial host immune defense. beta-Defensins are potentially important endogenous antibiotic-like effectors of innate immunity expressed by intestinal epithelia. In this study, the interplay between the enteric protozoan parasite Cryptosporidium parvum and host epithelial beta-defensin expression was investigated. Using human and murine models of infection, we demonstrated that C. parvum infection differentially regulates beta-defensin gene expression. Downregulation of murine beta-defensin-1 mRNA and protein was observed in both in vitro and in vivo models of infection. Infection of the human colonic HT29 cell line with the parasite resulted in differential effects on various members of the defensin gene family. Partial reduction in human beta-defensin-1 (hBD-1), induction of hBD-2, and no effect on hBD-3 gene expression was observed. Recombinant hBD-1 and hBD-2 peptides exhibited significant antimicrobial activity against C. parvum sporozoites in vitro. These findings demonstrate that C. parvum infection of enterocytes may affect the expression of various defensins in different ways and suggest that the overall outcome of the effect of antimicrobial peptides on early survival of the parasite may be complex.

Breaking the species barrier: use of SCID mouse-human chimeras for the study of human infectious diseases

Mouse-human chimeras have become a novel way to model the interactions between microbial pathogens and human cells, tissues or organs. Diseases studied with human xenografts in severe combined immunodeficient (SCID) mice include Pseudomonas aeruginosa infection in cystic fibrosis, group A streptococci and impetigo, bacillary and amoebic dysentery, and AIDS. In many cases, disease in the human xenograft appears to accurately reproduce the disease in humans, providing a powerful model for identifying virulence factors, host responses to infection and the effects of specific interventions on disease. In this review, we summarize recent studies that have used mouse-human chimeras to understand the pathophysiology of specific bacterial and protozoan infections.

Pathogenicity of Cryptosporidium parvum--evaluation of an animal infection model

With the intention of developing a standardised method for assessment of pathogenicity of Cryptosporidium parvum, the CPB-0 isolate was studied by propagation in 1-day-old calves followed by inoculation into specific pathogen free (SPF) piglets. The experiment was repeated. Diarrhoea and shedding of oocysts were seen in all animals infected with the CPB-0 isolate. Clinical signs included depression, inappetence, vomiting (exclusively in the piglets), and death. Histological examination at 17 and 19 days post-infection revealed parasitic stages and microscopic changes primarily restricted to colon and rectum. The unintended presence of rotavirus in some of the experimental animals revealed an additive or synergistic effect between rotavirus and C. parvum as indicated by prolonged diarrhoea, increased oocyst shedding, decreased weight gain and elevated levels of serum haptoglobin and serum amyloid A (SAA) in piglets infected simultaneously with both pathogens. The difference in daily weight gain between infected and control animals was significant only for piglets co-infected with rotavirus. The acute phase response of haptoglobin and SAA was characterised by a large individual variation. In piglets, co-infected with rotavirus, the levels of serum haptoglobin were 3.5 and 4.6 times higher in the infected versus the controls 6 and 9dpi, respectively (mean values: 2411microg/ml+/-S.D. 2023 and 1840 microg/ml+/-S.D. 1697). In the controls infected with rotavirus, peak haptoglobin concentration was seen 3dpi (mean: 1022 microg/ml+/-S.D. 425). Elevated levels of SAA were seen in 1 of 6 piglets infected with C. parvum, and in 5 of 6 piglets co-infected with rotavirus. Tumour necrosis factor alpha (TNFalpha) was undetectable in all serum samples from piglets. The obvious advantages of the SPF pig model are the naturally acquired intestinal microflora, the development of distinct clinical signs similar to cryptosporidiosis in humans and calves, the size of the animals, and the accessibility of individuals born within a short time span. This makes the model ideal for dose-response studies, evaluation of therapeutic agents as well as for assessment of differences in the clinical response to isolates of diverse genetic background. In conclusion, it was shown that the CPB-0 isolate was pathogenic to calves and piglets at a dose of 2.5 x 10(5) oocysts, and that the clinical signs could be replicated during separate experiments. Moreover, diarrhoea, oocyst shedding, body weight changes, histological alterations, and the acute phase response of haptoglobin and SAA were identified as useful parameters for discrimination of isolate-specific differences of pathogenicity.

Recent advances in cryptosporidiosis: the immune response

An increased understanding of host immune responses to Cryptosporidium parvum which are responsible for clearance of primary infection and resistance to reinfection, and characterization of the parasite molecules to which they are directed, are essential for discovery of effective active and passive immunization strategies against cryptosporidiosis. In this article, recent advances in knowledge of humoral and cellular immune responses to C. parvum, their antigen specificities, and mechanisms of protection are briefly reviewed.

The role of cytokines in the pathogenesis of Cryptosporidium infection

First described in 1912, the importance of the coccidian parasite Cryptosporidium parvum as an enteropathogen in humans was not recognized until the early 1980s, when it was found to be a common opportunistic infection in AIDS. Infection with this organism triggers a complex array of innate and cell-mediated immune responses within the intestinal mucosa. How cytokines and chemokines interact to regulate these responses in order to achieve clearance of the parasite yet preserve the integrity of the intestinal mucosa is still being unravelled. T helper type 1 cytokines, and particularly interferon-gamma, have long been considered to be the main orchestrators of the immune response to this infection, but recent studies suggest that T helper type 2 cytokines may also be involved. In addition, transforming growth factor-beta 1, although having little effect on parasite development, is an important modulator of the immune response and plays a role in protecting the epithelial integrity from the effects of the inflammatory process.

Expression of IL-15 and IL-4 in IFN-gamma-independent control of experimental human Cryptosporidium parvum infection

We have previously demonstrated interferon gamma (IFN-gamma) in intestinal mucosa after experimental human Cryptosporidium parvum infection, but expression was limited to sensitized volunteers. To characterize IFN-gamma-independent mechanisms in control of infection, jejunal biopsies from immunocompetent volunteers experimentally challenged with C. parvum were examined by in situ hybridization for interleukin (IL-)15 and IL-4 mRNA with confirmation by immunohistochemistry. Cytokine expression was correlated with prechallenge anti- C. parvum IgG, symptoms, oocyst shedding, and prior IFN-gamma expression data. IL-15 expression was noted only in those without prior sensitization, who did not express IFN-gamma. By contrast, expression of IL-4 was associated with prior sensitization. IL-15 was only detected in those with symptoms (6/14 symptomatic vs 0/3 asymptomatic, P<0.05). Among 14 volunteers who did not express IFN-gamma, oocyst shedding was lower in those expressing IL-15. Overall, 14/15 volunteers who did not shed oocysts expressed either IFN-gamma or IL-15. There was no correlation between expression of IL-4 and symptoms or oocyst shedding. In conclusion, IL-15 expression was associated with control of oocyst shedding in those not expressing IFN-gamma. These data suggest that IL-15 is involved in IFN-gamma independent mechanisms of control of human cryptosporidiosis, perhaps via activation of the innate immune response.