Antigenic differences within the Cryptosporidium hominis and Cryptosporidium parvum surface proteins P23 and GP900 defined by monoclonal antibody reactivity

A highly antigenic fragment within the zoonotic Cryptosporidium parvum Gp900 glycoprotein (Domain 3) is absent in human restricted Cryptosporidium species

We identified a fragment (Domain 3-D3) of the immunodominant sporozoite surface glycoprotein of the zoonotic parasite Cryptosporidium gp900, which is absent C. hominis and C. parvum anthroponosum. The fragment is highly antigenic and is able to effectively differentiate between zoonotic C. parvum and species/genotypes that infect preferentially humans. D3 detection provides a serological tool to determine whether the source of human cryptosporidiosis is of animal or human origin. We demonstrate this in experimentally challenged piglets, mice, rats, and alpaca. We speculate that the absence of this fragment from the C. hominis and C. parvum anthroponosum gp900 protein may play a key role in their host restriction.

Cryptosporidiuminfections: molecular advances

Cryptosporidiumhost cell interaction remains fairly obscure compared with other apicomplexans such asPlasmodiumorToxoplasma. The reason for this is probably the inability of this parasite to complete its life cyclein vitroand the lack of a system to genetically modifyCryptosporidium. However, there is a substantial set of data about the molecules involved in attachment and invasion and about the host cell pathways involved in actin arrangement that are altered by the parasite. Here we summarize the recent advances in research on host cell infection regarding the excystation process, attachment and invasion, survival in the cell, egress and the available data on omics.

A highly divergent 33 kDa Cryptosporidium parvum antigen

Previous studies comparing the genome sequences of Cryptosporidium parvum with Cryptosporidium hominis identified a number of highly divergent genes that might reflect positive selection for host specificity. In the present study, the C. parvum DNA sequence cgd8-5370, which encodes a protein whose amino acid sequence differs appreciably from its homologue in C. hominis , was cloned by PCR and expressed as a recombinant protein in Escherichia coli . Antisera raised against the recombinant cgd8-5370 antigen strongly recognized a unique 33 kDa protein in immunoblots from reducing and non-reducing SDS-PAGE of native C. parvum protein. However, anti-Cp33 sera did not recognize the native 33 kDa homologue in C. hominis . In an immunofluorescence assay (IFA), anti-Cp33 serum recognized an antigen in the anterior end of air-dried C. parvum sporozoites but failed to bind at any sites in C. hominis sporozoites, indicating its specificity for C. parvum . IFA staining of live C. parvum sporozoites with anti-Cp33 serum failed to bind to the parasite, indicating that the CP33 antigen is not on the sporozoite surface, which is consistent with topology predictions based on the encoded amino acid sequence. RT-PCR analysis of cgd8-5370 mRNA before or during C. parvum oocyst excystation revealed transcripts only in excysting sporozoites. Thus, Cp33 represents one of a small number of proteins shown to differentiate C. parvum from C. hominis sporozoites and oocysts.

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.

Production of anti-Cryptosporidium polyclonal antibodies and standardization of direct immunofluorescence for detecting oocysts in water

INTRODUCTION

The production of anti-Cryptosporidium polyclonal antibodies and its use in direct immunofluorescence assays to determine the presence of Cryptosporidium in water are described in the present work.

METHODS

Two rabbits were immunized with soluble and particulate antigens from purified Cryptosporidium oocysts. The sera produced were prepared for immunoglobulin G extraction, which were then purified and conjugated with fluorescein isothiocyanate (FITC). Slides containing known amounts of oocysts were prepared to determine the sensitivity of the technique. To test the specificity, slides containing Giardia duodenalis cysts were prepared.

RESULTS

The conjugate was successfully used in water samples experimentally contaminated with Cryptosporidium oocysts, and it was possible to detect up to five oocysts/spot, corresponding to contamination of 250 oocysts/mL.

CONCLUSIONS

The three immunizations performed in the rabbits were enough to produce antibodies against Cryptosporidium, the standard direct immunofluorescence assay permitted the detection of five oocysts in 20% of the samples, and no cross-reaction with Giardia duodenalis cysts occurred.

Infection with Cryptosporidium hominis provides incomplete protection of the host against Cryptosporidium parvum

Cryptosporidium hominis and Cryptosporidium parvum, which infect humans equally, are genetically/antigenically almost identical. It remains unclear, however, whether infection with C. hominis protects against C. parvum. Gnotobiotic piglets were used to investigate cross-protection. After ≥3 days of recovery from C. hominis infection, the piglets were completely protected against subsequent challenge with C. hominis but only partially against challenge with C. parvum, as compared with age-matched control animals challenged with either species. In conclusion, C. hominis-specific immunity was sufficient to completely protect against challenge with the same species but insufficient to provide the same level of protection against C. parvum.

Serum antibody responses to polymorphic Cryptosporidium mucin antigen in Bangladeshi children with cryptosporidiosis

Cryptosporidium is a significant cause of diarrheal disease in children in developing countries. The sporozoite antigen Muc4 is important for infection of host cells, and could be a candidate vaccine antigen. However, this antigen is polymorphic between Cryptosporidium hominis and C. parvum. We investigated antibody responses to C. hominis Muc4 and C. parvum Muc4 antigen in children in Bangladesh infected with C. hominis. Antibody responses were compared between children with cryptosporidial diarrhea (cases) and uninfected children with diarrhea (controls). There was a significant IgM response to Muc4 from both species in cases compared with controls, which increased over time, and was higher in children with persistent diarrhea. Despite sequence polymorphisms, antibody responses to C. hominis Muc4 and C. parvum Muc4 were significantly correlated. These results suggest that the human antibody response to Muc4 is cross-reactive between species, but in young children does not mature to an IgG response within the period observed in this study.