Identification of a family of four UDP-polypeptide N-acetylgalactosaminyl transferases in Cryptosporidium species

Although mucin-type O-glycans are critical for Cryptosporidium infection, the enzymes catalyzing their synthesis have not been studied. Here, we report four UDP N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyl transferases (ppGalNAc-Ts) from the genomes of C. parvum, C. hominis and C. muris. All are Type II membrane proteins which include a cytoplasmic tail, a transmembrane domain, a stem region, a glycosyltransferase family 2 domain and a C-terminal ricin B lectin domain. All are expressed during C. parvum infection in vitro, with Cp-ppGalNAc-T1 and -T4 expressed at 24 h and Cp-ppGalNAc-T2 and -T3 at 48 and 72 h post-infection, suggesting that their expression may be developmentally regulated. C. parvum sporozoite lysates display ppGalNAc-T enzymatic activity against non-glycosylated and pre-glycosylated peptides suggesting that they contain enzymes capable of glycosylating both types of substrates. The importance of mucin-type O-glycans in Cryptosporidium-host cell interactions raises the possibility that Cp-ppGalNAc-Ts may serve as targets for intervention in cryptosporidiosis.

Release of luminal exosomes contributes to TLR4-mediated epithelial antimicrobial defense

Exosomes are membranous nanovesicles released by most cell types from multi-vesicular endosomes. They are speculated to transfer molecules to neighboring or distant cells and modulate many physiological and pathological procedures. Exosomes released from the gastrointestinal epithelium to the basolateral side have been implicated in antigen presentation. Here, we report that luminal release of exosomes from the biliary and intestinal epithelium is increased following infection by the protozoan parasite Cryptosporidium parvum. Release of exosomes involves activation of TLR4/IKK2 signaling through promoting the SNAP23-associated vesicular exocytotic process. Downregulation of let-7 family miRNAs by activation of TLR4 signaling increases SNAP23 expression, coordinating exosome release in response to C. parvum infection. Intriguingly, exosomes carry antimicrobial peptides of epithelial cell origin, including cathelicidin-37 and beta-defensin 2. Activation of TLR4 signaling enhances exosomal shuttle of epithelial antimicrobial peptides. Exposure of C. parvum sporozoites to released exosomes decreases their viability and infectivity both in vitro and ex vivo. Direct binding to the C. parvum sporozoite surface is required for the anti-C. parvum activity of released exosomes. Biliary epithelial cells also increase exosomal release and display exosome-associated anti-C. parvum activity following LPS stimulation. Our data indicate that TLR4 signaling regulates luminal exosome release and shuttling of antimicrobial peptides from the gastrointestinal epithelium, revealing a new arm of mucosal immunity relevant to antimicrobial defense.

Exosomes are secreted membranous nanovesicles produced by a variety of cells. Exosomes shuttle various molecules to transfer them to neighboring or distant cells, and have been implicated as mediators in cell-cell communications to modulate physiological and pathological procedures. Here, we report that luminal release of exosomal vesicles is an important component of Toll-like receptor 4 (TLR4)-associated gastrointestinal epithelial defense against infection by Cryptosporidium parvum, an obligate intracellular protozoan that infects gastrointestinal epithelial cells. Activation of TLR4 signaling in host epithelial cells following C. parvum infection promotes luminal release of epithelial exosomes and exosomal shuttling of antimicrobial peptides from the epithelium. By direct binding to the C. parvum surface, exosomal vesicles reveal anti-C. parvum activity. Activation of TLR4 signaling in epithelial cells after LPS stimulation also increases exosomal release and exosome-associated anti-C. parvum activity. Therefore, we speculate that TLR4-mediated exosome release may be relevant to innate mucosal immunity in general, representing a new target for therapeutic intervention for infectious diseases at the mucosal surface.

Cryptosporidium parvum scavenges LDL-derived cholesterol and micellar cholesterol internalized into enterocytes

Cryptosporidium spp. are responsible for devastating diarrhoea in immunodeficient individuals. In the intestinal tract, the developmental stages of the parasite are confined to the apical surfaces of epithelial cells. Upon invasion, Cryptosporidium incorporates the microvillous membrane of the enterocyte to form the parasitophorous vacuole (PV) and sequesters itself from the host cytoplasm by rearranging the host cytoskeleton. Cryptosporidium parvum has minimal anabolic capabilities and relies on transporters and salvage pathways to meet its basic metabolic requirements. The cholesterol salvage pathway is crucial for the development of protozoan parasites. In this study, we have examined the sources of cholesterol from C. parvum infecting enterocytes. We illustrated that the intracellular stages of Cryptosporidium as well as the oocysts shed by the host, contain cholesterol. Incubation of infected enterocytes in lipoprotein-free medium impairs parasite development and results in substantial decrease in cholesterol content associated with the PV. Among lipoproteins, LDL constitutes an important source of cholesterol for Cryptosporidium. Dietary cholesterol incorporated into micelles is internalized into enterocytes by the NPC1L1 transporter. We showed that C. parvum also obtains cholesterol from micelles in enterocytes.Pharmacological blockade of NPC1L1 function by ezetimibe or moderate downregulation of NPC1L1 expression decreases parasite infectivity. These observations indicate that, despite its dual sequestration from the intestinal lumen and the host cytoplasm, C. parvum can, in fact, obtain cholesterol both from the gut's lumen and the host cell. This study highlights the evolutionary advantages for epicellular pathogens to access to nutrients from the outside and inside of the host cell.

Systemic antibody responses to the immunodominant p23 antigen and p23 polymorphisms in children with cryptosporidiosis in Bangladesh

Cryptosporidium is a major cause of diarrhea in children in developing countries. However, there is no vaccine available and little is known about immune responses to protective antigens. We investigated antibody responses to p23, a putative vaccine candidate, in children in Bangladesh with cryptosporidiosis and diarrhea (cases) and uninfected children with diarrhea (controls), and p23 gene polymorphisms in infecting species. Serum IgM, IgG, and IgA responses to p23 were significantly greater in cases than controls after three weeks of follow-up. Cases with acute diarrhea had significantly greater serum IgA and IgM responses than those with persistent diarrhea, which suggested an association with protection from prolonged disease. The p23 sequences were relatively conserved among infecting species and subtype families. Although most children were infected with Cryptosporidium hominis, there was a cross-reactive antibody response to C. parvum antigen. These results support further development of p23 as a vaccine candidate.

Analysis of human immune responses in quasi-experimental settings: tutorial in biostatistics

BACKGROUND

Human immunology is a growing field of research in which experimental, clinical, and analytical methods of many life science disciplines are utilized. Classic epidemiological study designs, including observational longitudinal birth cohort studies, offer strong potential for gaining new knowledge and insights into immune response to pathogens in humans. However, rigorous discussion of methodological issues related to designs and statistical analysis that are appropriate for longitudinal studies is lacking.

METHODS

In this communication we address key questions of quality and validity of traditional and recently developed statistical tools applied to measures of immune responses. For this purpose we use data on humoral immune response (IR) associated with the first cryptosporidial diarrhea in a birth cohort of children residing in an urban slum in south India. The main objective is to detect the difference and derive inferences for a change in IR measured at two time points, before (pre) and after (post) an event of interest. We illustrate the use and interpretation of analytical and data visualization techniques including generalized linear and additive models, data-driven smoothing, and combinations of box-, scatter-, and needle-plots.

RESULTS

We provide step-by-step instructions for conducting a thorough and relatively simple analytical investigation, describe the challenges and pitfalls, and offer practical solutions for comprehensive examination of data. We illustrate how the assumption of time irrelevance can be handled in a study with a pre-post design. We demonstrate how one can study the dynamics of IR in humans by considering the timing of response following an event of interest and seasonal fluctuation of exposure by proper alignment of time of measurements. This alignment of calendar time of measurements and a child's age at the event of interest allows us to explore interactions between IR, seasonal exposures and age at first infection.

CONCLUSIONS

The use of traditional statistical techniques to analyze immunological data derived from observational human studies can result in loss of important information. Detailed analysis using well-tailored techniques allows the depiction of new features of immune response to a pathogen in longitudinal studies in humans. The proposed staged approach has prominent implications for future study designs and analyses.

Antibody responses to the immunodominant Cryptosporidium gp15 antigen and gp15 polymorphisms in a case-control study of cryptosporidiosis in children in Bangladesh

Although Cryptospridium hominis is the dominant Cryptosporidium species infecting humans, immune responses to cognate antigens in C. hominis-infected persons have not been reported. We investigated antibody responses to the immunodominant gp15 antigen from C. hominis and C. parvum, in C. hominis-infected Bangladeshi children less than five years of age with diarrhea (cases) and uninfected children with diarrhea (controls). We also investigated polymorphisms in the C. hominis gp15 sequence from cases. Serum IgG responses to gp15 from both species were significantly greater in cases than controls. In spite of polymorphisms in the gp15 sequence, there was a significant correlation between antibody levels to gp15 from both species, indicating cross-reactivity to conserved epitopes. Cases with acute diarrhea had a significantly greater serum IgA response to gp15 compared with those with persistent diarrhea, suggesting that this response may be associated with protection from prolonged disease. These findings support further investigation of gp15 as a vaccine candidate.

Cryptosporidiosis: environmental, therapeutic, and preventive challenges

Cryptosporidium spp. are responsible for endemic and epidemic disease worldwide. Clinical manifestations may include acute, persistent, or chronic diarrhea, biliary, and pulmonary disease. Disease severity ranges from asymptomatic or mild to severe, intractable diarrhea with wasting depending on immune status, nutrition, and age. Transmission is fecal-oral with both human and animal reservoirs. Disease is often self limited in healthy individuals, but therapy remains a challenge in the immune-compromised. Prevention currently depends on appropriate hygiene and proper water management and treatment.

Human CD8(+) T cells clear Cryptosporidium parvum from infected intestinal epithelial cells

Intracellular protozoans of the genus Cryptosporidium are a major cause of diarrheal illness worldwide, especially in immunocompromised individuals. CD4(+) T cells and interferon-gamma are key factors in the control of cryptosporidiosis in human and murine models. Previous studies led us to hypothesize that CD8(+) T cells contribute to clearance of intestinal epithelial Cryptosporidium infection in humans. We report here that antigen expanded sensitized CD8(+) T cells reduce the parasite load in infected intestinal epithelial cell cultures and lyse infected intestinal epithelial cells. These effects are most likely mediated by the release of cytotoxic granules. Elimination of parasites seems to require antigen presentation through both human leukocyte antigen (HLA)-A and HLA-B. These data suggest that cytotoxic CD8(+) T cells play a role in clearing Cryptosporidium from the intestine, a previously unrecognized feature of the human immune response against this parasite.

Recent diarrhea is associated with elevated salivary IgG responses to Cryptosporidium in residents of an eastern Massachusetts community

BACKGROUND

Serological data suggest that Cryptosporidium infections are common but underreported. The invasiveness of blood sampling limits the application of serology in epidemiological surveillance. We pilot-tested a non-invasive salivary anti-Cryptosporidium antibody assay in a community survey involving children and adults.

MATERIALS AND METHODS

Families with children were recruited in a Massachusetts community in July; symptoms data were collected at 3 monthly follow-up mail surveys. One saliva sample per person (n = 349) was collected via mail, with the last survey in October. Samples were analyzed for IgG and IgA responses to a recombinant C. hominis gp15 sporozoite protein using a time-resolved fluorometric immunoassay. Log-transformed assay results were regressed on age using penalized B-splines to account for the strong age-dependence of antibody reactions. Positive responses were defined as fluorescence values above the upper 99% prediction limit.

RESULTS

Forty-seven (13.5%) individuals had diarrhea without concurrent respiratory symptoms during the 3-month-long follow-up; eight of them had these symptoms during the month prior to saliva sampling. Two individuals had positive IgG responses: an adult who had diarrhea during the prior month and a child who had episodes of diarrhea during each survey month (Fisher's exact test for an association between diarrhea and IgG response: p = 0.0005 for symptoms during the prior month and p = 0.02 for symptoms during the entire follow-up period). The child also had a positive IgA response, along with two asymptomatic individuals (an association between diarrhea and IgA was not significant).

CONCLUSION

These results suggest that the salivary IgG specific to Cryptosporidium antigens warrants further evaluation as a potential indicator of recent infections.

CD8+ T cells clear human intestinal Cryptosporidium infection through cytotoxic granule release (129.8)

INTRODUCTION: A key factor in the human adaptive immune response towards Cryptosporidium, associated with resistance to infection, is IFNg. Its function and the cells involved in clearing the parasite from the human intestinal epithelium are unknown. As CD4+ and CD8+ cells produce IFNg after re-stimulation with parasite antigens in vitro we hypothesized that CD8+ cells contribute to control of the infection. METHODS: We studied CD8+ cell cytotoxicity by 51Chromium (51Cr) release assay and fluorescent microscopy. Targets were 51Cr labeled CaCo2 cells. Effectors were CD8+ cells isolated from peripheral blood mononuclear cells of sensitized or naïve volunteers after 6 day culture with IL-2 + IL-15 +/- C. hominis glycoprotein 15 (gp15). RESULTS: Gp15 stimulated CD8+ cells from a sensitized donor matched at HLA-A and HLA-B killed infected cells, with killing increasing with effector numbers, in contrast to CD8+ cells from a naïve donor. In microscopy experiments the same primed CD8+ cells released cytolytic granules into infected cells. CD8+ cells from sensitized donors matched at HLA-A, but not at HLA-B did not kill infected targets as efficiently. HLA-A and HLA-B antibodies inhibited cytotoxicity. CONCLUSION: The data suggest that re-stimulated CD8+ cells from sensitized individuals kill infected cells through release of cytotoxic granules. HLA-B seems to be at least partially required for peptide recognition.

Seasonality of Cryptosporidium oocyst detection in surface waters of Meru, Kenya as determined by two isolation methods followed by PCR

Meru, Kenya has watersheds which are shared by wildlife, humans and domesticated animals. These surface waters can be contaminated by the waterborne pathogen Cryptosporidium. To quantify the seasonality and prevalence of Cryptosporidium in Meru regional surface waters, we used a calcium carbonate flocculation (CCF) and sucrose floatation method, and a filtration and immunomagnetic bead separation method, each of which used PCR for Cryptosporidium detection and genotyping. Monthly water samples were collected from January through June in 2003 and 2004, bracketing two April-May rainy seasons. We detected significant seasonality with 8 of 9 positive samples from May and June (p<0.0014), which followed peak rainy season precipitation and includes some of the subsequent dry season. Six of 9 positive samples revealed C. parvum, and 3 contained C. andersoni. None contained C. hominis. Our results indicate that Meru surface waters are Cryptosporidium-contaminated at the end of rainy seasons, consistent with the timing of human infections reported by others from East Africa and contrasting with the onset of rainy season peak incidence reported from West Africa.

Cryptosporidium p30, a galactose/N-acetylgalactosamine-specific lectin, mediates infection in vitro

Cryptosporidium sp. cause human and animal diarrheal disease worldwide. The molecular mechanisms underlying Cryptosporidium attachment to, and invasion of, host cells are poorly understood. Previously, we described a surface-associated Gal/GalNAc-specific lectin activity in sporozoites of Cryptosporidium parvum. Here we describe p30, a 30-kDa Gal/GalNAc-specific lectin isolated from C. parvum and Cryptosporidium hominis sporozoites by Gal-affinity chromatography. p30 is encoded by a single copy gene containing a 906-bp open reading frame, the deduced amino acid sequence of which predicts a 302-amino acid, 31.8-kDa protein with a 22-amino acid N-terminal signal sequence. The p30 gene is expressed at 24-72 h after infection of intestinal epithelial cells. Antisera to recombinant p30 expressed in Escherichia coli react with an approximately 30-kDa protein in C. parvum and C. hominis. p30 is localized to the apical region of sporozoites and is predominantly intracellular in both sporozoites and intracellular stages of the parasite. p30 associates with gp900 and gp40, Gal/GalNAc-containing mucin-like glycoproteins that are also implicated in mediating infection. Native and recombinant p30 bind to Caco-2A cells in a dose-dependent, saturable, and Gal-inhibitable manner. Recombinant p30 inhibits C. parvum attachment to and infection of Caco-2A cells, whereas antisera to the recombinant protein also inhibit infection. Taken together, these findings suggest that p30 mediates C. parvum infection in vitro and raise the possibility that this protein may serve as a target for intervention.

Seropositive human subjects produce interferon gamma after stimulation with recombinant Cryptosporidium hominis gp15

Cryptosporidiosis is an important cause of diarrhea worldwide. In normal hosts, infection is self-limited and associated with seroconversion and partial immunity to reinfection. Immunity is associated with interferon gamma (IFNgamma) production. Cryptosporidium surface proteins gp15 and gp40 are among the immunodominant proteins in terms of antibody responses. We asked the question of whether these antigens also stimulate production of IFNgamma in patients who have serologic evidence of prior infection. Whole blood from seropositive donors was stimulated with recombinant gp15 and gp 40 from Cryptosporidium hominis and Cryptosporidium parvum or His-tag controls. C. hominis gp15 stimulated increased production of IFNgamma. By contrast, there was no significant increase after stimulation with C. parvum gp15 or either gp40 preparation. IFNgamma production in response to C. hominis gp15 was noted in both CD4(+) and CD8(+) cells. This highlights the potential for C. hominis gp15 as a vaccine candidate for human cryptosporidiosis.

Cryptosporidium parvum glycoprotein gp40 localizes to the sporozoite surface by association with gp15

Cryptosporidium spp. are waterborne apicomplexan parasites responsible for outbreaks of diarrheal disease worldwide. Antigens involved in zoite invasion into host cells have been the focus of many investigations as these may prove to be good vaccine candidates. gp40/15 is a zoite antigen synthesized as a precursor protein and proteolytically cleaved into the mature glycoproteins, gp40 and gp15. gp15 is anchored in the sporozoite membrane by a glycosylphosphatidyl inositol moiety, while gp40 is predicted to be soluble. However, gp40 bears epitopes that recognize a host cell receptor. If this interaction is important for zoite invasion, then gp40 must have some mechanism of associating with the parasite membrane. In these studies we demonstrate that gp40 and gp15 co-localize to the surface membrane of sporozoites and merozoites, and co-immunoprecipitate, suggesting that these antigens associate after proteolytic cleavage to generate a protein complex capable of linking zoite and host cell surfaces.

Proteolytic processing of the Cryptosporidium glycoprotein gp40/15 by human furin and by a parasite-derived furin-like protease activity

The apicomplexan parasite Cryptosporidium causes diarrheal disease worldwide. Proteolytic processing of proteins plays a significant role in host cell invasion by apicomplexan parasites. In previous studies, we described gp40/15, a Cryptosporidium sp. glycoprotein that is proteolytically cleaved to yield two surface glycopeptides (gp40 and gp15), which are implicated in mediating infection of host cells. In the present study, we showed that biosynthetically labeled gp40/15 is processed in Cryptosporidium parvum-infected HCT-8 cells. We identified a putative furin cleavage site RSRR downward arrow in the deduced amino acid sequence of gp40/15 from C. parvum and from all Cryptosporidium hominis subtypes except subtype 1e. Both human furin and a protease activity present in a C. parvum lysate cleaved recombinant C. parvum gp40/15 protein into 2 peptides, identified as gp40 and gp15 by size and by immunoreactivity with specific antibodies. C. hominis gp40/15 subtype 1e, in which the RSRR sequence is replaced by ISKR, has an alternative furin cleavage site (KSISKR downward arrow) and was also cleaved by both furin and the C. parvum lysate. Site-directed mutagenesis of the C. parvum RSRR sequence to ASRR resulted in inhibition of cleavage by furin and the C. parvum lysate. Cleavage of recombinant gp40/15 and a synthetic furin substrate by the C. parvum lysate was inhibited by serine protease inhibitors, by the specific furin inhibitor decanoyl-Arg-Val-Lys-Arg-chloromethylketone (Dec-RVKR-cmk), and by calcium chelators, suggesting that the parasite expresses a Ca2+ dependent, furin-like protease activity. The furin inhibitor Dec-RVKR-cmk decreased C. parvum infection of HCT-8 cells, suggesting that a furin-like protease activity may be involved in mediating host-parasite interactions.

Quantification of in vitro and in vivo Cryptosporidium parvum infection by using real-time PCR

Established methods for quantifying experimental Cryptosporidium infection are highly variable and subjective. We describe a new technique using quantitative real-time PCR (qPCR) that can be used to measure in vitro and in vivo laboratory infections with Cryptosporidium. We show for the first time that qPCR permits absolute quantification of the parasite while simultaneously controlling for the amount of host tissue and correlates significantly with established methods of quantification in in vitro and in vivo laboratory models of infection.

Identification of Cpgp40/15 Type Ib as the predominant allele in isolates of Cryptosporidium spp. from a waterborne outbreak of gastroenteritis in South Burgundy, France

Cryptosporidium sp. isolates from a waterborne outbreak of diarrhea in France were analyzed by PCR-restriction fragment length polymorphism analysis and sequencing of the Cpgp40/15 locus. Ninety-one percent of the isolates were Cryptosporidium hominis type Ib. The results of this study and those of studies of other outbreaks suggest that the type Ib allele is the predominant allele associated with waterborne cryptosporidiosis.

Multilocus genotyping of Cryptosporidium sp. isolates from human immunodeficiency virus-infected individuals in South India

This study characterized cryptosporidial infections in 48 human immunodeficiency virus-infected individuals in India by multilocus genotyping. Cryptosporidium hominis, C. parvum, C. felis, C. muris, and C. meleagridis were identified. Cpgp40/15 PCR-restriction fragment length polymorphism identified six subgenotypes. Cryptosporidial diarrhea was associated with decreased CD4 counts, below 200 (P = 0.009), but not high viral loads.

MyD88-dependent pathways mediate resistance to Cryptosporidium parvum infection in mice

Cryptosporidium spp. cause diarrheal disease worldwide. Innate immune responses mediating resistance to this parasite are not completely understood. To determine whether MyD88-dependent pathways play a role in resistance to Cryptosporidium parvum, we compared the course of infection in MyD88(-/-) mice to that in their wild-type (WT) littermate controls. Three- to 4-week-old mice were infected with C. parvum, and infection was monitored by quantifying fecal oocyst shedding. Twelve days postinfection, the histology of the intestines was examined to quantify intestinal parasite burden and to determine if there were any pathological changes. Fecal oocyst shedding and intestinal parasite burden were significantly greater in MyD88(-/-) mice than in littermate controls. Nonetheless, both WT and MyD88(-/-) mice cleared the infection within 3 weeks. These results indicate that MyD88-dependent pathways are involved in mediating initial resistance to C. parvum. Since gamma interferon (IFN-gamma) is known to mediate resistance to C. parvum, we also studied infection in MyD88(-/-) mice and WT controls in which this cytokine was temporarily neutralized. Fecal oocyst shedding, as well as intestinal parasite burden, intestinal inflammation, and mortality, was significantly greater in MyD88(-/-) mice in which IFN-gamma was neutralized than in IFN-gamma-neutralized WT mice or in MyD88(-/-) mice in which this cytokine was active. These results suggest that MyD88 and IFN-gamma had an additive effect in conferring protection from C. parvum infection. While this study confirms the importance of IFN-gamma in conferring resistance to infection with C. parvum, it suggests that MyD88-mediated pathways also play a role in innate immunity to this parasite.

Apical organelle discharge by Cryptosporidium parvum is temperature, cytoskeleton, and intracellular calcium dependent and required for host cell invasion

The apical organelles in apicomplexan parasites are characteristic secretory vesicles containing complex mixtures of molecules. While apical organelle discharge has been demonstrated to be involved in the cellular invasion of some apicomplexan parasites, including Toxoplasma gondii and Plasmodium spp., the mechanisms of apical organelle discharge by Cryptosporidium parvum sporozoites and its role in host cell invasion are unclear. Here we show that the discharge of C. parvum apical organelles occurs in a temperature-dependent fashion. The inhibition of parasite actin and tubulin polymerization by cytochalasin D and colchicines, respectively, inhibited parasite apical organelle discharge. Chelation of the parasite's intracellular calcium also inhibited apical organelle discharge, and this process was partially reversed by raising the intracellular calcium concentration by use of the ionophore A23187. The inhibition of parasite cytoskeleton polymerization by cytochalasin D and colchicine and the depletion of intracellular calcium also decreased the gliding motility of C. parvum sporozoites. Importantly, the inhibition of apical organelle discharge by C. parvum sporozoites blocked parasite invasion of, but not attachment to, host cells (i.e., cultured human cholangiocytes). Moreover, the translocation of a parasite protein, CP2, to the host cell membrane at the region of the host cell-parasite interface was detected; an antibody to CP2 decreased the C. parvum invasion of cholangiocytes. These data demonstrate that the discharge of C. parvum sporozoite apical organelle contents occurs and that it is temperature, intracellular calcium, and cytoskeleton dependent and required for host cell invasion, confirming that apical organelles play a central role in C. parvum entry into host cells.

Cryptosporidiosis among Bangladeshi children with diarrhea: a prospective, matched, case-control study of clinical features, epidemiology and systemic antibody responses

We conducted a prospective case-control study to investigate the epidemiology, clinical features, and systemic antibody responses of cryptosporidiosis in Bangladeshi children. Forty-six children presenting to the International Center for Diarrheal Disease Research, Bangladesh in Dhaka, Bangladesh with diarrhea and Cryptosporidium spp. oocysts in the stool were enrolled as cases. Forty-six age-matched children with diarrhea, but without cryptosporidial infection, were enrolled as controls. Thirty cases and 23 controls returned for follow-up three weeks after discharge. Infection with Cryptosporidium spp. occurred most commonly in those less than two years of age, was accompanied by watery diarrhea and vomiting, and was more likely to be associated with persistent diarrhea. Other than duration of diarrhea, there were no significant differences in clinical or epidemiologic features between cases and controls. Cryptosporidium-specific serum IgM levels were significantly higher in cases compared with controls at presentation. In addition, there was a significant increase in serum Cryptosporidium-specific serum IgG levels over the three-week follow-up period in cases compared with controls. Within the case group, there was no difference between children with acute and persistent diarrhea in the change in IgG levels over the follow-up period. However, there was a significant difference between children with acute and persistent diarrhea in changes in both IgA and IgM levels, with persistent diarrhea being associated with a decrease in levels of both antibodies.

Expression of Cpgp40/15 in Toxoplasma gondii: a surrogate system for the study of Cryptosporidium glycoprotein antigens

Cryptosporidium parvum is a waterborne enteric coccidian that causes diarrheal disease in a wide range of hosts. Development of successful therapies is hampered by the inability to culture the parasite and the lack of a transfection system for genetic manipulation. The glycoprotein products of the Cpgp40/15 gene, gp40 and gp15, are involved in C. parvum sporozoite attachment to and invasion of host cells and, as such, may be good targets for anticryptosporidial therapies. However, the function of these antigens appears to be dependent on the presence of multiple O-linked alpha-N-acetylgalactosamine (alpha-GalNAc) determinants. A eukaryotic expression system that would produce proteins bearing glycosylation patterns similar to those found on the native C. parvum glycoproteins would greatly facilitate the molecular and functional characterization of these antigens. As a unique approach to this problem, the Cpgp40/15 gene was transiently expressed in Toxoplasma gondii, and the expressed recombinant glycoproteins were characterized. Antisera to gp40 and gp15 reacted with the surface membranes of tachyzoites expressing the Cpgp40/15 construct, and this reactivity colocalized with that of antiserum to the T. gondii surface protein SAG1. Surface membrane localization was dependent on the presence of the glycophosphatidylinositol anchor attachment site present in the gp15 coding sequence. The presence of terminal O-linked alpha-GalNAc determinants on the T. gondii recombinant gp40 was confirmed by reactivity with Helix pomatia lectin and the monoclonal antibody 4E9, which recognizes alpha-GalNAc residues, and digestion with alpha-N-acetylgalactosaminidase. In addition to appropriate localization and glycosylation, T. gondii apparently processes the gp40/15 precursor into the gp40 and gp15 component glycopolypeptides, albeit inefficiently. These results suggest that a surrogate system using T. gondii for the study of Cryptosporidium biology may be useful.

Cryptosporidium species: new insights and old challenges

Cryptosporidium species are protozoan parasites that cause mainly enteric illnesses in humans and other animals. The mode of transmission is most commonly waterborne, but other sources of infection, including foodborne and person-to-person spread, have been documented. The environmental form of the parasite is resistant to most water purification methods, including chlorination. Cryptosporidium infection usually causes a self-limited diarrheal illness but can be life-threatening in immunocompromised individuals. There is no effective therapy for cryptosporidiosis.