Cryptosporidium parvum infection stimulates the secretion of TGF-beta, IL-8 and RANTES by Caco-2 cell line

Gene expression profile of HCT-8 cells following single or co-infections with Cryptosporidium parvum and bovine coronavirus

Among the causative agents of neonatal diarrhoea in calves, two of the most prevalent are bovine coronavirus (BCoV) and the intracellular parasite Cryptosporidium parvum. Although several studies indicate that co-infections are associated with greater symptom severity, the host-pathogen interplay remains unresolved. Here, our main objective was to investigate the modulation of the transcriptome of HCT-8 cells during single and co-infections with BCoV and C. parvum. For this, HCT-8 cells were inoculated with (1) BCoV alone, (2) C. parvum alone, (3) BCoV and C. parvum simultaneously. After 24 and 72 h, cells were harvested and analyzed using high-throughput RNA sequencing. Following differential expression analysis, over 6000 differentially expressed genes (DEGs) were identified in virus-infected and co-exposed cells at 72 hpi, whereas only 52 DEGs were found in C. parvum-infected cells at the same time point. Pathway (KEGG) and gene ontology (GO) analysis showed that DEGs in the virus-infected and co-exposed cells were mostly associated with immune pathways (such as NF-κB, TNF-α or, IL-17), apoptosis and regulation of transcription, with a more limited effect exerted by C. parvum. Although the modulation observed in the co-infection was apparently dominated by the virus, over 800 DEGs were uniquely expressed in co-exposed cells at 72 hpi. Our findings provide insights on possible biomarkers associated with co-infection, which could be further explored using in vivo models.

The Effect of Short-Chain Fatty Acids on Growth of Cryptosporidium parvum In Vitro

In a previous study, we observed an increase in the severity of cryptosporidial infection corresponding to decreased levels of short-chain fatty acids (SCFAs). Therefore, we decided to examine the effect of SCFAs on Cryptosporidium growth in human ileocecal adenocarcinoma (HTC-8) cells. HTC-8 cells were infected with 1 × 105 C. parvum oocysts. After 48 h of incubation with selected SCFAs, cells were fixed and labeled with monoclonal antibody directed to all intracellular stages, and the number of parasites was quantitated using a fluorescent microscope. Acetate, butyrate, propionate and valproate significantly inhibited growth, with an EC50 between 4 and 10 mM. Additionally, when combined, butyrate, acetate and propionate showed increased efficacy. Butyrate also inhibited growth when incubated with sporozoites prior to infection of host cell monolayers. In addition, we looked at possible mechanisms of action of inhibition. A combination of C. parvum infection and butyrate treatment led to increases in apoptosis and certain inflammatory cytokines. We conclude that acetate, propionate and butyrate have direct inhibitory activities in host cells against C. parvum, and butyrate can also affect sporozoite infectivity directly. While not preventing infection, SCFAs may help in keeping the infection low or in check.

A genetic screen identifies a protective type III interferon response to Cryptosporidium that requires TLR3 dependent recognition

Cryptosporidium is a leading cause of severe diarrhea and diarrheal-related death in children worldwide. As an obligate intracellular parasite, Cryptosporidium relies on intestinal epithelial cells to provide a niche for its growth and survival, but little is known about the contributions that the infected cell makes to this relationship. Here we conducted a genome wide CRISPR/Cas9 knockout screen to discover host genes that influence Cryptosporidium parvum infection and/or host cell survival. Gene enrichment analysis indicated that the host interferon response, glycosaminoglycan (GAG) and glycosylphosphatidylinositol (GPI) anchor biosynthesis are important determinants of susceptibility to C. parvum infection and impact on the viability of host cells in the context of parasite infection. Several of these pathways are linked to parasite attachment and invasion and C-type lectins on the surface of the parasite. Evaluation of transcript and protein induction of innate interferons revealed a pronounced type III interferon response to Cryptosporidium in human cells as well as in mice. Treatment of mice with IFNλ reduced infection burden and protected immunocompromised mice from severe outcomes including death, with effects that required STAT1 signaling in the enterocyte. Initiation of this type III interferon response was dependent on sustained intracellular growth and mediated by the pattern recognition receptor TLR3. We conclude that host cell intrinsic recognition of Cryptosporidium results in IFNλ production critical to early protection against this infection.

Stem cell-derived enteroid cultures as a tool for dissecting host-parasite interactions in the small intestinal epithelium

Toxoplasma gondii and Cryptosporidium spp. can cause devastating pathological effects in humans and livestock, and in particular to young or immunocompromised individuals. The current treatment plans for these enteric parasites are limited due to long drug courses, severe side effects or simply a lack of efficacy. The study of the early interactions between the parasites and the site of infection in the small intestinal epithelium has been thwarted by the lack of accessible, physiologically relevant and species-specific models. Increasingly, 3D stem cell-derived enteroid models are being refined and developed into sophisticated models of infectious disease. In this review, we shall illustrate the use of enteroids to spearhead research into enteric parasitic infections, bridging the gap between cell line cultures and in vivo experiments.

The role of chemokines and their receptors during protist parasite infections

Protists are a diverse collection of eukaryotic organisms that account for a significant global infection burden. Often, the immune responses mounted against these parasites cause excessive inflammation and therefore pathology in the host. Elucidating the mechanisms of both protective and harmful immune responses is complex, and often relies of the use of animal models. In any immune response, leucocyte trafficking to the site of infection, or inflammation, is paramount, and this involves the production of chemokines, small chemotactic cytokines of approximately 8–10 kDa in size, which bind to specific chemokine receptors to induce leucocyte movement. Herein, the scientific literature investigating the role of chemokines in the propagation of immune responses against key protist infections will be reviewed, focussing onPlasmodiumspecies,Toxoplasma gondii, Leishmaniaspecies andCryptosporidiumspecies. Interestingly, many studies find that chemokines can in fact, promote parasite survival in the host, by drawing in leucocytes for spread and further replication. Recent developments in drug targeting against chemokine receptors highlights the need for further understanding of the role played by these proteins and their receptors in many different diseases.

Cryptosporidium Priming Is More Effective than Vaccine for Protection against Cryptosporidiosis in a Murine Protein Malnutrition Model

Cryptosporidium is a major cause of severe diarrhea, especially in malnourished children. Using a murine model of C. parvum oocyst challenge that recapitulates clinical features of severe cryptosporidiosis during malnutrition, we interrogated the effect of protein malnutrition (PM) on primary and secondary responses to C. parvum challenge, and tested the differential ability of mucosal priming strategies to overcome the PM-induced susceptibility. We determined that while PM fundamentally alters systemic and mucosal primary immune responses to Cryptosporidium, priming with C. parvum (10⁶ oocysts) provides robust protective immunity against re-challenge despite ongoing PM. C. parvum priming restores mucosal Th1-type effectors (CD3⁺CD8⁺CD103⁺ T-cells) and cytokines (IFNγ, and IL12p40) that otherwise decrease with ongoing PM. Vaccination strategies with Cryptosporidium antigens expressed in the S. Typhi vector 908htr, however, do not enhance Th1-type responses to C. parvum challenge during PM, even though vaccination strongly boosts immunity in challenged fully nourished hosts. Remote non-specific exposures to the attenuated S. Typhi vector alone or the TLR9 agonist CpG ODN-1668 can partially attenuate C. parvum severity during PM, but neither as effectively as viable C. parvum priming. We conclude that although PM interferes with basal and vaccine-boosted immune responses to C. parvum, sustained reductions in disease severity are possible through mucosal activators of host defenses, and specifically C. parvum priming can elicit impressively robust Th1-type protective immunity despite ongoing protein malnutrition. These findings add insight into potential correlates of Cryptosporidium immunity and future vaccine strategies in malnourished children.

Cryptosporidium attributable morbidities in malnourished children are increasingly recognized. Exactly how malnutrition interferes with host mucosal immunity to diarrheal pathogens and mucosal vaccine responses remains unclear. Dissecting these interactions in an experimental model of cryptosporidiosis can uncover new insights into novel therapeutic approaches against a pathogen for which effective therapies and vaccines are currently unavailable. We demonstrate that although malnutrition diminishes baseline (primary) Th1-type mucosal immunity these deficits can be partially overcome via non-specific mucosal strategies (S. Typhi and CpG) and completely restored after a sub-clinical (low-dose) exposure to viable C. parvum. These results add insight into preventive strategies to help alleviate Cryptosporidium-specific diarrhea in children in low-resource settings and abrogate prolonged post-infection sequelae.

Parasites and malignancies, a review, with emphasis on digestive cancer induced by Cryptosporidium parvum (Alveolata: Apicomplexa)

The International Agency for Research on Cancer (IARC) identifies ten infectious agents (viruses, bacteria, parasites) able to induce cancer disease in humans. Among parasites, a carcinogenic role is currently recognized to the digenetic trematodes Schistosoma haematobium, leading to bladder cancer, and to Clonorchis sinensis or Opisthorchis viverrini, which cause cholangiocarcinoma. Furthermore, several reports suspected the potential association of other parasitic infections (due to Protozoan or Metazoan parasites) with the development of neoplastic changes in the host tissues. The present work shortly reviewed available data on the involvement of parasites in neoplastic processes in humans or animals, and especially focused on the carcinogenic power of Cryptosporidium parvum infection. On the whole, infection seems to play a crucial role in the etiology of cancer.

Human myeloid dendritic cells treated with supernatants of rotavirus infected Caco-2 cells induce a poor Th1 response

We have previously shown that human myeloid dendritic cells treated with purified rotavirus induce an allogenic Th1 response. To determine if rotavirus in the context of an intestinal microenvironment modulates the function of dendritic cells, we treated these cells with supernatants from non-infected or infected Caco-2 cells and studied their capacity to promote Th1 or Th2 responses. Dendritic cells treated with supernatants from rotavirus-infected Caco-2 cells promoted a significantly lower Th1 response, in comparison with those treated with purified rotavirus. We wanted to establish if TGF-β1, induced, or TSLP, not induced, during rotavirus infection, could mediate this effect. Neutralization of TGF-β but not TSLP in the supernatant prior to treatment of dendritic cells increased their capacity to promote a Th1 response. The results suggest that the TGF-β1 induced by rotavirus could be an immune evasion mechanism, and may partially explain the poor rotavirus-specific T cell response we have previously evidenced.

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.

Neutrophils do not mediate the pathophysiological sequelae of Cryptosporidium parvum infection in neonatal piglets

Cryptosporidium parvum is a minimally invasive protozoal pathogen of intestinal epithelium that results in villus atrophy, mucosal lipid peroxidation, diarrhea, and diminished barrier function. Influx of neutrophils is a consistent feature of human and animal cryptosporidiosis, and yet their contribution to the pathological sequelae of infection has not been investigated. Accordingly, we used an established neonatal piglet model of C. parvum infection to examine the role of neutrophils in disease pathogenesis by inhibiting their recruitment and activation in vivo using a monoclonal anti-CD18 antibody. Infected piglets were treated daily with anti-CD18 or isotype control immunoglobulin G and euthanized at peak infection, at which time neutrophil infiltrates, lipid peroxidation, severity of infection, and intestinal barrier function were quantified. C. parvum infection resulted in a significant increase in mucosal neutrophil myeloperoxidase activity that was prevented by treatment of piglets with anti-CD18 antibody. Neutrophil recruitment was dependent on mucosal superoxide formation (prevented by treatment of infected piglets with superoxide dismutase). Neutrophils did not contribute to peroxynitrite formation or peroxidative injury of C. parvum-infected mucosa and had no impact on the severity of epithelial infection, villus atrophy, or diarrhea. The presence of neutrophils in C. parvum-infected mucosa was associated with enhanced barrier function that could not be attributed to mucosal elaboration of prostaglandins or stimulation of their synthesis. These studies are the first to demonstrate that neutrophilic inflammation arising in response to infection by a noninvasive epithelial pathogen results in physiologic rather than pathological effects in vivo.

High levels of CXCL10 are produced by intestinal epithelial cells in AIDS patients with active cryptosporidiosis but not after reconstitution of immunity

Chemokines play key roles in attracting immune cells to sites of infections. However, few data on chemokine expression in the gut during human infections are available. We examined expression of chemokines in intestinal tissues of AIDS patients during active Cryptosporidium infection and during resolution of such an infection. The chemokines and cytokines in cell lysates from jejunal biopsy tissues were assayed by a 22-multiplex bead immunoassay. CXCL10 (IP-10) and its receptor, CXCR3, in sections were studied by immunohistochemistry. In biopsies from AIDS patients with active cryptosporidiosis, four chemokines (CXCL10, CCL11 [eotaxin], CCL5 [RANTES], and CCL2 [monocyte chemoattractant protein 1]) and three cytokines (interleukin-1alpha [IL-1alpha], IL-10, and granulocyte colony-stimulating factor) were detected. The level of CXCL10 was significantly increased in AIDS patients with cryptosporidiosis compared to the level in AIDS patients without cryptosporidiosis or in normal volunteers (median in AIDS patients with cryptosporidiosis, 508 pg/mg protein, compared to 111 pg/mg and 72 pg/mg protein in AIDS patients without cryptosporidiosis and in normal volunteers, respectively [P < 0.05 and P < 0.005, respectively, as determined by a Mann-Whitney test]). The level of CXCL10 correlated with the parasite burden (as measured by the number of Cryptosporidium oocysts in the stools) and also with the IL-1alpha concentration (Pearson correlation values, 0.961 [P < 0.01] and 0.737 [P < 0.05]). As determined by immunohistochemistry, CXCL10 localized to epithelial cells at the site of infection. Following effective antiparasite and antiretroviral therapy, Cryptosporidium infections resolved, and the levels of CXCL10 decreased to normal levels. We hypothesized that CXCL10 plays an important role in the resolution of cryptosporidiosis by attracting immune effector cells to the site of infection. By contrast, in AIDS patients lacking effector cells, CXCL10 may contribute to the immunopathogenesis by recruiting inflammatory cells.

Heavy cryptosporidial infections in children in northeast Brazil: comparison of Cryptosporidium hominis and Cryptosporidium parvum

Cryptosporidium is an important cause of infectious diarrhoea worldwide, but little is known about the course of illness when infected with different species. Over a period of 5 years, Cryptosporidium was identified in the stools of 58 of 157 children prospectively followed from birth in an urban slum (favela) in northeast Brazil. Forty isolates were available for quantification and 42 for speciation (24 Cryptosporidium hominis and 18 C. parvum). Children with C. hominis shed significantly more oocysts/ml of stool (3.5 x 10(6) vs. 1.7 x 10(6)perml; P=0.001), and oocyst counts were higher among symptomatic children (P=0.002). Heavier C. parvum shedding was significantly associated with symptoms (P=0.004), and symptomatic C. parvum-infected children were significantly more likely than asymptomatic children to be lactoferrin-positive (P=0.004). Height-for-age (HAZ) Z-scores showed significant declines within 3 months of infection for children infected with either C. hominis (P=0.028) or C. parvum (P=0.001). However, in the 3-6 month period following infection, only C. hominis-infected children continued to demonstrate declining HAZ score and asymptomatic children showed even greater decline (P=0.01). Cryptosporidium hominis is more common than C. parvum in favela children and is associated with heavier infections and greater growth shortfalls, even in the absence of symptoms.

Transient neonatal Cryptosporidium parvum infection triggers long-term jejunal hypersensitivity to distension in immunocompetent rats

In 5-day-old immunocompetent Sprague-Dawley rats infected with either 10(2) or 10(5) Cryptosporidium parvum oocysts, transient infection resulted 120 days later in increased cardiovascular depressor response to jejunal distension and jejunal myeloperoxidase activity (P < 0.05). Nitazoxanide treatment normalized jejunal sensitivity (P < 0.001) but not myeloperoxidase levels (P > 0.05). Data warrant further evaluation of the role of early cryptosporidiosis in the development of chronic inflammatory gut conditions.

Inhibitory activities of epidermal growth factor receptor tyrosine kinase-targeted dihydroxyisoflavone and trihydroxydeoxybenzoin derivatives on Sarcocystis neurona, Neospora caninum, and Cryptosporidium parvum development

Several gene sequences of parasitic protozoa belonging to protein kinase gene families and epidermal growth factor (EGF)-like peptides, which act via binding to receptor tyrosine kinases of the EGF receptor (EGFR) family, appear to mediate host-protozoan interactions. As a clue to EGFR protein tyrosine kinase (PTK) mediation and a novel approach for identifying anticoccidial agents, activities against Sarcocystis neurona, Neospora caninum, and Cryptosporidium parvum grown in BM and HCT-8 cell cultures of 52 EGFR PTK inhibitor isoflavone analogs (dihydroxyisoflavone and trihydroxydeoxybenzoine derivatives) were investigated. Their cytotoxicities against host cells were either absent, mild, or moderate by a nitroblue tetrazolium test. At concentrations ranging from 5 to 10 microg/ml, 20 and 5 analogs, including RM-6427 and RM-6428, exhibited an in vitro inhibitory effect of > or = 95% against at least one parasite or against all three, respectively. In immunosuppressed Cryptosporidium parvum-infected Mongolian gerbils orally treated with either 200 or 400 mg of agent RM-6427/kg of body weight/day for 8 days, fecal microscopic oocyst shedding was abolished in 6/10 animals (P of <0.001 versus untreated controls) and mean shedding was reduced by 90.5% (P of <0.0001) and 92.0% (P of <0.0001), respectively, higher levels of inhibition than after nitazoxanide (200 mg/kg/day for 8 days) or paromomycin (100 mg/kg/day for 8 days) treatment (55.0%, P of <0.001, and 17.5%, P of >0.05, respectively). After RM-6427 therapy (200 mg/kg/day for 8 days), the reduction in the ratio of animals with intracellular parasites was nearly significant in ileum (P = 0.067) and more marked in the biliary tract (P < 0.0013) than after nitazoxanide or paromomycin treatment (0.05 < P < 0.004). RM-6428 treatment at a regimen of 400 mg/kg/day for 12 days inhibited oocyst shedding, measured using flow cytometry from day 4 (P < 0.05) to day 12 (P < 0.02) of therapy, when 2/15 animals had no shedding (P < 0.0001) and 11/15 were free of gut and/or biliary tract parasites (P < 0.01). No mucosal alteration was microscopically observed for treated or untreated infected gerbils. To our knowledge, this report is the first to suggest that the isoflavone class of agents has the potential for anticoccidial therapy.

Selective upregulation of immune regulatory and effector cytokine synthesis by intestinal intraepithelial lymphocytes following CD43 costimulation

The involvement of the CD43 molecule in the activation of mouse small intestinal intraepithelial lymphocytes (IELs) has been studied using a panel of twenty-two regulatory and effector immune response analytes. In the absence of stimulation in vitro, IELs produced low levels of CCL5 only. Upon CD3 stimulation, the activity of seven of twenty-two analytes was elevated relative to unstimulated cultures, including several proinflammatory cytokines and chemokines. Notably, CD3 stimulation in the presence of CD43 costimulation resulted in elevated levels of five analytes (interleukin-2, interferon-gamma, CCL5, granulocyte colony-stimulating factor, and granulocyte-monocyte colony-stimulating factor) above that produced by CD3 stimulation alone. That CD43 costimulation was responsible for elevated cytokine/chemokine activity was confirmed at the transcriptional level by real-time PCR for IFN-gamma and CCL5, and by ELISA for IFN-gamma. These findings open the way to a better understanding of the process by which T cells are activated in the intestinal epithelium.

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.

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.

Cryptosporidium parvum regulation of human epithelial cell gene expression

Cryptosporidium parvum is an obligate intracellular protozoan capable of causing life-threatening diarrhoeal disease in immunocompromised individuals. Efforts to develop novel therapeutic strategies have been hampered by the lack of understanding of the pathogenesis of infection. To better understand the host response to C. parvum infection, gene expression profiles of infected human ileocecal adenocarcinoma cells were analysed by using Affymetrix oligonucleotide microarrays containing probe sets for 12,600 human genes. Statistical analysis of expression data from three independent experiments identified 223 genes whose expression was reproducibly regulated by C. parvum infection at 24 h post-inoculation (125 up-regulated and 98 down-regulated), 13 of which were validated by quantitative reverse transcriptase polymerase chain reaction analysis. This analysis revealed the consistent up-regulation of host heat-shock genes and genes for pro-inflammatory chemokines IL-8, RANTES, and SCYB5. Multiple genes for host actin and tubulin genes were up-regulated whereas genes for actin binding proteins were down-regulated, confirming previous observations of host cytoskeleton rearrangement in response to C. parvum infection. In addition, host genes associated with cell proliferation and apoptosis were differentially regulated, reflecting the complexity of host-parasite interaction. Together, this study demonstrated that C. parvum infection results in significant changes in host biochemical pathways and provides new insights into specific biological processes of infectious disease caused by an intracellular protozoan parasite.

Infection of human and bovine epithelial cells with Cryptosporidium andersoni induces apoptosis and disrupts tight junctional ZO-1: effects of epidermal growth factor

The effects of Cryptosporidium andersoni on human or bovine epithelia are poorly defined. Epidermal growth factor inhibits colonisation of the gastrointestinal epithelium with bacteria and the enteric protozoan parasite Giardia lamblia. This study characterised whether C. andersoni infects human or bovine epithelial cells in vitro, assessed its impact on apoptosis and tight junctional Zonula-Occludens-1, and determined whether these effects may be altered by epidermal growth factor. Monolayers of human colonic CaCo(2) cells, SCBN (non-malignant small intestinal epithelial cells), and Madin Darby bovine kidney epithelial cell lines (MDBK and NBL-1) were grown to confluency in Dulbecco's Modified Eagle Medium. Monolayers were assigned to one of three experimental groups-(1) control: exposed to culture medium alone; (2) untreated: exposed to 10(3) live C. andersoni oocysts or (3) epidermal growth factor-treated: apically pre-treated with recombinant human epidermal growth factor and then exposed to Cryptosporidium. Oocyst viability, infection with Cryptosporidium, apoptosis, and integrity of tight junctional Zonula-Occludens-1 were assessed. In addition, live Cryptosporidium oocysts were incubated with epidermal growth factor to assess whether epidermal growth factor had cryptosporicidial activity. Cryptosporidium andersoni oocysts infected all human and bovine monolayers, increased nuclear fragmentation, and disrupted Zonula-Occludens-1. Apical epidermal growth factor significantly reduced infection with C. andersoni in all cell lines and inhibited the Cryptosporidium-induced apoptosis and disruption of Zonula-Occludens-1. Epidermal growth factor did not affect oocyst viability.

Interleukin-4 and transforming growth factor beta have opposing regulatory effects on gamma interferon-mediated inhibition of Cryptosporidium parvum reproduction

It was shown previously that enterocytes activated by gamma interferon (IFN-gamma) are efficient effector cells in the killing of Cryptosporidium parvum. How this function is regulated is not clearly understood, but transforming growth factor beta (TGF-beta) and the Th2 regulatory cytokines may play a role. Using an in vitro cell culture system, we investigated how the key regulatory cytokines interleukin-4 (IL-4), IL-10, IL-13, and TGF-beta might modulate the effect of IFN-gamma in inducing resistance to infection in enterocyte cell lines. The results showed that TGF-beta can abolish the inhibitory effect on C. parvum development and that neither IL-13 nor IL-10 influenced the action of IFN-gamma. In contrast, IL-4 cooperated with low concentrations of IFN-gamma (1 and 10 U/ml) to enhance parasite killing. One mechanism that appeared to be involved in the combined activity of IFN-gamma and IL-4 was intracellular Fe(2+) deprivation, but induction of nitric oxide production was not involved. In one cell line, the extents and durations of phosphorylation of STAT1, a transcription factor involved in IFN-gamma signaling, were similar when cells were stimulated with IFN-gamma alone and with IFN-gamma and IL-4 gamma, suggesting that the cooperative effect of the cytokines was not related to STAT1 activation. The effects of the presence of TGF-beta and IL-4 on IFN-gamma function did not appear to involve any alteration in the level of expression of IFN-gamma receptors.

Adhesion of lactic acid bacteria to caco-2 cells and their effect on cytokine secretion

Cytokines secreted by human enterocytes play a critical role in mucosal and systemic immunity. Intestinal microorganisms can influence this secretion. In the present study, 30 strains of lactic acid bacteria were characterized for their adhesion to Caco-2 cells and their potential to stimulate proinflammatory cytokine secretion by this cell line. The bacteria adhered in a strain-dependent manner to Caco-2 cells. Contact with lactobacilli did not result in the production of IL-6 or IL-8. A slight IL-6 and IL-8 production by a Caco-2 cell was detected after exposure to 8 of the tested Bifidobacterium strains. No correlation was found between adhesion and cytokine induction among the bacteria tested. This indicates that lactic acid bacteria, even those with strong adhesive properties, are not very likely to trigger an inflammatory response in human enterocytes.

Susceptibility to Cryptosporidium parvum infections in cytokine- and chemokine-receptor knockout mice

To determine the role of cytokines and a chemokine receptor in the susceptibility to, and outcome of, infection, 4 different knockout mice (IL-4, IL-10, IL-12, and CCR5) were infected with Cryptosporidium parvum and monitored for infection intensity by collection of fecal pellets from individual mice. Because adult immunocompetent mice are refractory to infection, wild-type mice on the same background as the knockout mice (C57BL/6) were used as a negative control. No infection was detected over a 4-wk time period in IL-4, IL-10, and CCR5 knockout mice inoculated with 106 oocysts. IL-12 knockout mice inoculated with as little as 100 oocysts shed up to 10,000 oocysts/100 microl of feces on the peak infection day (day 8) and were able to fully recover by 2 wk after infection. IL-12 is an important inducer of IFN-gamma, which probably accounted for susceptibility to infection. Previous studies using IFN-gamma knockout mice have shown strain-related differences in infection intensity and outcome, with increased parasite loads and decreased survival among IFN-gamma knockout mice on a C57BL/6 background compared with those on a BALB/c background. Similar results were observed in IL-12 knockout mice on a BALB/c background, which exhibited little or no infection, despite higher levels of inoculation (10(6) oocysts/mouse).

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.

Vaccinology for control of apicomplexan parasites: a simplified language of immune programming and its use in vaccine design

Most mammalian immune systems and parasites have co-evolved over the millennia, interacting within a common environment and communicating through a common language. This language is comprised of copious dialects in which a variety of host innate and acquired immune pathways actively interact with a multitude of parasite-specific survival strategies. Nonetheless, a simplified language is likely present since the same basic molecular and cellular mechanisms are associated with resistance or susceptibility to parasite infection. Protective immunity against protozoa within the phylum Apicomplexa (e.g. Cryptosporidia, Eimeria, Neospora, Plasmodia and Toxoplasma) is generally CD4+ T cell-dependent and elicited along the IL-12/IFN-gamma/iNOS effector axis. This simplified language can be decoded in part by significant advances in understanding naïve T cell activation, differentiation and generation of immunologic memory. Vaccine adjuvants and new immunisation strategies for generation of more potent immunity can also be viewed through this common language lens. The aim of this paper is to summarise recently published fundamental immunology studies, their relevance through examples in specific coccidian-host immune dialects, and how this simplified language can be used for the more rationale design of parasite vaccine control strategies.

Lamina propria CD4+ T lymphocytes synergize with murine intestinal epithelial cells to enhance proinflammatory response against an intracellular pathogen

Acute and lethal ileitis can be elicited in certain strains of inbred mice after oral infection with the intracellular protozoan parasite Toxoplasma gondii. The development of this inflammatory process is dependent upon the induction of a robust Th1 response, including overproduction of IFN-gamma, TNF-alpha, and NO, as has been reported in other experimental models of human inflammatory bowel disease. In this study we have investigated the role of CD4(+) T cells from the lamina propria (LP) in the early inflammatory events after T. gondii infection using isolated and primary cultured intestinal cells from infected mice and immortalized mouse mIC(cl2) intestinal epithelial cells. Primed LP CD4(+) T cells isolated from parasite-infected mice produce substantial quantities of both IFN-gamma and TNF-alpha. IFN-gamma- and TNF-alpha-producing LP CD4(+) T cells synergize with infected mIC(cl2) and enhance the production of several inflammatory chemokines including macrophage-inflammatory protein-2, monocyte chemoattractant protein-1, monocyte chemoattractant protein-3, macrophage-inflammatory protein-1alphabeta, and IFN-gamma-inducible protein-10. Furthermore, primed LP CD4(+) T cells cocultured with infected mIC(cl2) inhibited replication of the parasite in the intestinal epithelial cells. Thus, LP CD4(+) T cells can interact with parasite-infected intestinal epithelial cells and alter the expression of several proinflammatory products that have been associated with the development of intestinal inflammation. The interaction between these two components of the gut mucosal compartment (CD4(+) T cells and enterocytes) may play a role in the immunopathogenesis of this pathogen-driven experimental inflammatory bowel disease model.