Potential of recombinant inorganic pyrophosphatase antigen as a new vaccine candidate against Baylisascaris schroederi in mice

Abstract

The intestinal nematode Baylisascaris schroederi is an important cause of death for wild and captive giant pandas. Inorganic pyrophosphatases (PPases) are critical for development and molting in nematode parasites and represent potential targets for vaccination. Here, a new PPase homologue, Bsc-PYP-1, from B. schroederi was identified and characterized, and its potential as a vaccine candidate was evaluated in a mouse challenge model. Sequence alignment of PPases from nematode parasites and other organisms show that Bsc-PYP-1 is a nematode-specific member of the family I soluble PPases. Immunohistochemistry revealed strong localization of native Bsc-PYP-1 to the body wall, gut epithelium, ovary and uterus of adult female worms. Additionally, Bsc-PYP-1 homologues were found in roundworms infecting humans (Ascaris lumbricoides), swine (Ascaris suum) and dogs (Toxocara canis). In two vaccine trials, recombinant Bsc-PYP-1 (rBsc-PYP-1) formulated with Freund complete adjuvant induced significantly high antigen-specific immunoglobulin (Ig)G but no IgE or IgM responses. Analysis of IgG-subclass profiles revealed a greater increase of IgG1 than IgG2a. Splenocytes from rBsc-PYP-1/FCA-immunized mice secreted low levels of T helper (Th)1-type cytokines, interferon-γ and interleukin (IL)-2, while producing significantly high levels of IL-10 and significantly elevated levels of IL-4 (Th2 cytokines) after stimulation with rBsc-PYP-1 in vitro. Finally, vaccinated mice had 69.02–71.15% reductions (in 2 experiments) in larval recovery 7 days post-challenge (dpc) and 80% survival at 80 dpc. These results suggest that Th2-mediated immunity elicited by rBsc-PYP-1 provides protection against B. schroederi, and the findings should contribute to further development of Bsc-PYP-1 as a candidate vaccine against baylisascariasis.

Update on Baylisascariasis, a Highly Pathogenic Zoonotic Infection

“…Inorganic pyrophosphatases (PPases) are pivotal in the development of the larval stages of several nematodes, and one homologue of PPases (Bsc-PYP-1) from B. schroederi has been identified. Its antigenicity has been demonstrated, and it may be considered a vaccine candidate against baylisascariasis (144). Considering the demonstrated homology and potential cross-antigenicity of PPases from other ascarid species, it is possible that this or other PPases will be identified as candidates for the development of vaccines against B. procyonis (144).…”

Cloning and characterization of a novel sigma-like glutathione S-transferase from the giant panda parasitic nematode, Baylisascaris schroederi

“…As with other ascaridoids, adult B. schroederi usually inhabit the intestines of the giant panda, while the larvae may disseminate into various body tissues. In pandas, damage to bodily tissues includes extensive inflammation and scarring of the intestinal wall and parenchyma of the liver and lung (also known as visceral larval migran, VLM; caused by larvae), as well as intestinal obstruction, inflammation, and even death (caused by adults) [ 5 - 8 ]. Currently, diagnosis and identification of B. schroederi infection in pandas relies on morphological examination of fecal eggs, which requires extensive expertise and is difficult, laborious, and prone to error (as the density of eggs in bamboos-enriched feces is low and subject to possible environmental cross-contaminating with the eggs of other parasites, including morphologically similar Baylisascaris spp.…”

Parasites of the Giant Panda: A Risk Factor in the Conservation of a Species

“…More recently, aside from these immunogens, more attention has focused on targets that play essential roles in the survival of the parasite. For example, Xie et al (2013) identified PYP-1, a new homologue of inorganic pyrophosphatases (PPases) (Kajander et al, 2013), which likely plays critical roles in nematode development and moulting (Islam et al, 2003;Ko et al, 2007) and is distributed widely in the body wall, gut epithelium, ovary and uterus of adult female Baylisascaris. Two separate vaccination experiments in mice (BALB/c) showed that recombinant PYP-1 induced 69%-71% reductions in the number of liver-stage and lung-stage larvae 7 days following challenge infection (Xie et al, 2013).…”

“…For example, Xie et al (2013) identified PYP-1, a new homologue of inorganic pyrophosphatases (PPases) (Kajander et al, 2013), which likely plays critical roles in nematode development and moulting (Islam et al, 2003;Ko et al, 2007) and is distributed widely in the body wall, gut epithelium, ovary and uterus of adult female Baylisascaris. Two separate vaccination experiments in mice (BALB/c) showed that recombinant PYP-1 induced 69%-71% reductions in the number of liver-stage and lung-stage larvae 7 days following challenge infection (Xie et al, 2013). An investigation of the IgG subclasses in the sera of immunised mice showed that the level of IgG1 was significantly higher than IgG2a, with increased levels of IL-4 and IL-10, indicating a type 2 protective immune response (Xie et al, 2013).…”

“…Two separate vaccination experiments in mice (BALB/c) showed that recombinant PYP-1 induced 69%-71% reductions in the number of liver-stage and lung-stage larvae 7 days following challenge infection (Xie et al, 2013). An investigation of the IgG subclasses in the sera of immunised mice showed that the level of IgG1 was significantly higher than IgG2a, with increased levels of IL-4 and IL-10, indicating a type 2 protective immune response (Xie et al, 2013).…”