Angiostrongylus cantonensis: development following pulmonary arterial transfers into permissive and nonpermissive hosts

Stat3/IL-6 signaling mediates sustained pneumonia induced by Agiostrongylus cantonensis

Angiostrongylus cantonensis (AC) is well-documented that parasitizes the host brain and causes eosinophilic meningitis. The migration route of AC in permissive hosts is well demonstrated, while in nonpermissive hosts, it remains to be fully defined. In the present study, we exploited live imaging technology, morphological and pathological configuration analysis, and molecular biological technologies to explore the migration route of AC and the accompanying tissue damage in nonpermissive and permissive hosts. Our data indicated that, in nonpermissive host mouse, AC larvae migrated from intestinal wall to liver at 2 hours post-infection (hpi), from liver to lung at 4 hpi and then from lung to brain at 8 hpi. AC larval migration caused fatal lung injury (pneumonia) during acute and early infection phases, along with significant activation of Stat3/IL-6 signaling. In addition, AC induce sustained interstitial pneumonia in mouse and rat and pulmonary fibrosis only in rat during late infection phase. Moreover, during the early and late infection phases, Th2 cytokine expression and Stat3 and IL-6 signaling were persistently enhanced and myeloid macrophage cells were notably enriched in host lung, and administration of Stat3 and IL-6 inhibitors (C188-9 and LMT-28) attenuated AC infection-induced acute pneumonia in mice. Overall, we are the first to provide direct and systemic laboratory evidence of AC migration route in a nonpermissive host and report that infection with a high dose of AC larvae could result in acute and fatal pneumonia through Stat3/IL-6 signaling in mice. These findings may present a feasible to rational strategy to minimize the pathogenesis induced by AC.

Angiostrongylus cantonensis is a well-known nematode parasitizing the host brain and is the leading cause of eosinophilic meningitis worldwide. Our study reports the migration route of Angiostrongylus cantonensis larvae in non-permissive host mouse and discovers that the larvae could induce fatal pneumonia in mouse lung during acute and early infection phase characterized by activation of Stat3/IL-6 signaling. Moreover, administration of inhibitors targeting Stat3/IL-6 signaling could significantly attenuate the AC-induced pneumonia of non-permissive host mouse, providing an effective candidate target for intervention of this severe parasitic pneumonia. These findings expand our understanding of Angiostrongyliasis cantonensis and indicate that more attention to AC-induced pneumonia is required when treatment for Angiostrongyliasis cantonensis in the future.

Angiostrongylus cantonensis: scanning electron microscopic observations on the cuticle of moulting larvae

Angiostrongylus cantonensis is a parasitic nematode that needs to develop in different hosts in different larval stages. Freshwater snails, such as Pomacea canaliculata, are the intermediate host, and rats are the definitive host. Periodic shedding of the cuticle (moulting) is an important biological process for the survival and development of the parasite in the intermediate and definitive hosts. However, there are few studies on the cuticle alterations between different stages of this parasite. In this study, we observed the ultrastructural appearance and changes of the cuticle of the 2nd/3rd stage larvae (L2/L3) and the 3rd/4th stage larvae (L3/L4) using a scanning electron microscope. We also first divided L2/L3 into late L2 and early L3. The late L2 lacked alae, but possessed a pull-chain-like fissure. Irregular alignment of spherical particles on the cuticle were noted compared to the L3. Alae appeared in the early L3. The old cuticle turned into a thin film-like structure which adhered to the new cuticle, and spherical particles were seen regularly arranged on the surface of this structure. Regular rectangular cavities were found on the surface of L3/L4. The caudal structure of L3/L4 was much larger than that of L3, but caudal inflation, such as seen in L4, was not observed. These results are the first to reveal the ultrastructural changes of the cuticle of A. cantonensis before and after moulting of L2/L3 and L3/L4.

Angiogenesis and parasitic helminth-associated neovascularization

Successful metazoan parasitism, among many other factors, requires a supply of nutrients and the removal of waste products. There is a prerequisite for a parasite-defined vasculature. The angiogenic mechanism(s) involved presumably depend on the characteristics of the tissue- and vascular system-dwelling, parasitic helminths. Simplistically, 2 possibilities or a combination of both have been considered in this review. The multifactorial induction of parasitic helminth-associated neovascularization could arise through, either a host-, a parasite- or a host-/parasite-dependent, angiogenic switch. Most studies appear to support the first and third hypotheses, but evidence exists for the intrahepatic cestodeEchinococcus multilocularis, the free-living nematodeCaenorhabditis elegansand the intravascular trematodeSchistosoma mansonifor the second inference. In contrast, the nematode anti-coagulant protein NAPc2 from adultAncylostoma caninumis also an anti-angiogenic factor.

Immune defense and eosinophilia in congenitally IgE-deficient SJA/9 mice infected with Angiostrongylus costaricensis

The roles of IgE in protective immunity and eosinophilia in Angiostrongylus costaricensis infection were examined by comparing IgE-deficient SJA/9 mice and IgE-producing SJL/J mice. In primary infection, mean total IgE levels increased to a maximum of 390 ng/ml, which was more than 10 times greater than the 29 ng/ml measured preinfection in SJL/J mice but less than the 10 ng/ml found in SJA/9 mice throughout the experiment. Immune defense as determined by recovery of adult worms and eosinophilia were similar in SJL/J and SJA/9 mice. Protective immunity was induced by infection with A. costaricensis followed by treatment with levamisole for 4-6 days postinfection. After the challenge infection, the numbers of adult worms and eosinophils in SJA/9 mice were not significantly different from those in SJL/J mice. Anti-A. costaricensis IgE antibody was not detected in either strain of mice during the experiment. These results indicate that A. costaricensis infection induced the production of IgE not specific for parasite antigens in IgE-producing mice. Potentiated nonspecific IgE played no significant role in immune defense and eosinophilia.

Characterization of monoclonal antibodies against eosinophil chemotactic factors from young adult worms of Angiostrongylus cantonensis

Two kinds of IgG1 monoclonal antibodies against eosinophil chemotactic factors (ECFs) derived from Angiostrongylus cantonensis young adult worms (YA) were established. Western blot analyses demonstrated that one monoclonal antibody recognized a 16.1 kD component of YA-whole worm extract, and the other an 85 kD component. These antibodies did not show any cross reactions against several helminth antigens, as assessed by ELISA. The chemotactic activity of YA-whole worm extract for guinea-pig-eosinophils was significantly inhibited by previous incubation of the extract with these monoclonal antibodies; the monoclonal antibody recognizing the 16.1 kD component inhibited 56-61% of the ECF activity whilst the antibody recognizing the 85 kD component inhibited 20-34% of the activity. The combination of both monoclonal antibodies showed a stronger inhibitory effect (71-81%) than either antibody alone. Similar magnitudes of inhibition were noted when the chemotactic activity for human eosinophils was measured using YA-whole worm extract preincubated with these monoclonal antibodies. Neither monoclonal antibodies inhibited the chemotactic activity of whole worm extracts of A. cantonensis first stage larvae, Metastrongylus apri adult worms, Spirometra erinacei plerocercoids and Fasciola sp. adult worms. These data suggest that the two monoclonal antibodies will be useful for the isolation and purification of ECF-YA as well as for elucidating the possible in vivo role of ECF-YA.

Differences in responses of rat- and guinea-pig-eosinophils to eosinophil chemotactic factors derived from Angiostrongylus cantonensis

Eosinophil chemotactic activity associated with whole worm extracts of the young adult worms (YA) and 1st stage larvae (L1) of Angiostrongylus cantonensis was assessed using guinea-pig- and rat-eosinophils. Both whole worm extracts were potently chemotactic to guinea-pig-eosinophils whereas only the whole worm extract of L1 was chemotactic to rat-eosinophils. Gel filtration chromatography of YA-whole worm extract yielded an eosinophil chemotactic factor (ECF-YA) with an estimated molecular weight of 16,900. ECF-YA was resistant to heating and pronase digestion but sensitive to periodate oxidation, suggesting that chemotactic activity was possibly associated with the sugar portion of the glycoprotein molecule. Guinea-pig- and rat-eosinophils were deactivated by previous incubation with homologous whole worm extracts but not with heterologous ones. When guinea-pig-eosinophils were treated with trypsin or pronase, their chemotaxis to ECF-YA was significantly inhibited, and pronase treatment was more effective. Both deactivated and trypsin-treated guinea-pig-eosinophils completely recovered their chemotaxis responses after in vitro culture for 12 and 24 h, respectively. When those eosinophils were cultured in vitro in the presence of puromycin or cycloheximide, however, their chemotaxis responses could not be recovered. These data clearly indicate that guinea-pig-eosinophils probably possess a kind of receptor (or 'recognition unit') capable of reacting to ECF-YA, and also that the receptor may be protein or glycoprotein molecules, and reproducible.

Angiostrongylus cantonensis: role of eosinophils in the neurotoxic syndrome (Gordon-like phenomenon)

The role of eosinophils in the pathophysiology of Angiostrongylus cantonensis infections was investigated in nonpermissive (guinea pig) and permissive (rat) hosts. Neurological symptoms similar to the Gordon phenomenon (ataxia, tremor, paralysis) together with a loss of Purkinje cells in the cerebellum were observed after intracraneal injection of human eosinophil extracts or after infection with A. cantonensis, only in guinea pigs and not in rats. Blood eosinophilia as well as eosinophil numbers present in the cerebellum and in the cerebrospinal fluid were higher in guinea pigs than in rats, at all times after infection with A. cantonensis. Increased levels of cytotoxicity toward L3 larvae in vitro were obtained in the presence of guinea pig eosinophils and IgE antibodies, rather than with the corresponding rat effector system. The detection of one eosinophil granule component, the eosinophil peroxidase, in the cerebrospinal fluid from infected guinea pigs but not from rats suggested that in nonpermissive hosts, neurological disorders, similar to the previously described Gordon phenomenon, might be due to eosinophil neurotoxins released after interaction of eosinophils with the parasites.

Total and specific IgE in serum and cerebrospinal fluid of rats and guinea pigs infected with Angiostrongylus cantonensis

The total and specific IgE response to Angiostrongylus cantonensis infection was evaluated according to host permissiveness. Total IgE levels measured by a double antibody radioimmunoassay (RIA) increased slowly in the permissive host (the rat), reaching a maximum between 4 and 8 weeks after infection. This maximum was earlier but significantly lower in the non-permissive host (the guinea pig). IgE antibodies specific for adult worms or L1 or L3 larvae of A. cantonensis were measured by a radioallergosorbent test (RAST). In the case of adult worms and L1 antigens, specific IgE antibody levels showed large variations in relation to the duration of infection in rats. In contrast to total IgE levels, the specific IgE response to L3 larvae was lower in rats than in guinea pigs in both the serum and cerebrospinal fluid (CSF). These results suggest variations in the total vs specific IgE response according to host permissiveness or non-permissiveness to A. cantonensis infection. These results are discussed in the context of the possible participation of IgE antibodies in immune defence.

T-cell-dependent eosinophilia in the cerebrospinal fluid of the mouse infected with Angiostrongylus cantonensis

Eosinophilia of the cerebrospinal fluid (CSF) in permissive (rats) and non-permissive (mice) hosts infected with Angiostrongylus cantonensis, and the possible mechanism of the eosinophilia were studied. In three strains of thymic mice (ICR, ddY and BALB/c), the infection provoked a marked CSF eosinophilia starting at around day 12, reaching a peak level at day 20 and maintaining significantly high levels until day 35. In contrast, in athymic nude mice of BALB/c strain the infection failed to evoke this eosinophilia, suggesting T-cell dependence of murine CSF eosinophilia. Humoral antibodies did not correlate with the induction of eosinophilia. A time-course study of worm recovery in the mouse brains indicated a gradual but consistent reduction in worm burden in accordance with the rapid rise in CSF eosinophil levels. Bone marrow eosinophilia occurred in mice at day 5, which preceded CSF eosinophilia. Jirds, a permissive but less susceptible host, developed a CSF eosinophilia with a peak level at day 17, but which declined rapidly following the peak. Permissive rat hosts developed significant peripheral and bone marrow eosinophilia at day 35 but their CSF eosinophilia was markedly less prominent than that of mice and jirds. These data clearly indicate that there are distinct differences in the mechanism of eosinophilia and eosinophilia-inducing factors between permissive and non-permissive hosts.

Angiostrongylus cantonensis: immunoblot analysis of the antigens recognized by rats

Following infection of rats with Angiostrongylus cantonensis, occurrence of anti-parasite antibody in the serum was determined with special reference to the antigens recognized by host IgG antibodies, using SDS-PAGE combined with an immunoblotting technique. Three saline extracts of digestive organ, reproductive organ and body wall, isolated from adult female A. cantonensis, were used as crude antigenic solutions. Then 7 to 49 days after infection, IgG antibodies directed predominantly against a single antigen, referred to as Ac-1 antigen, were detected. After 91 days or more, infected rats formed antibodies not only against the Ac-1 antigen, but also against a wide variety of other components with molecular weights in the range of 26,000-220,000 dalton. By using an antiserum against Ac-1 antigen as a probe, it was shown that the molecular weight and subunit structure, as well as the immunoelectrophoretic mobility, varied according to the organ from which the antigenic extract was prepared. The Ac-1 protein in the extract of the reproductive organ, one of the major sources of the Ac-1 antigen, showed the same electrophoretic mobility as alpha-globulin. It has a molecular weight in the range of 100,000-200,000 dalton under both non-reducing and reducing conditions. Immunohistochemical studies, using the same antiserum and sectioned adult female worms, found Ac-1 antigen in the cytoplasm of oocytes at different stages of development, and in the lateral cord.

Eosinophil responses of permissive and nonpermissive hosts to the young adult worms of Angiostrongylus cantonensis

Blood and bone marrow eosinophilia was assessed in nonpermissive (guinea pigs) and permissive (rats) hosts following the pulmonary arterial transfers of live or dead young adult worms of Angiostrongylus cantonensis. Guinea pigs showed a marked eosinophilic response to live worms but only a slight response to dead worms. Neither IgE nor haemagglutinating antibodies correlated with the induction of this eosinophilia. In contrast, the rat responded to neither form of the young adult worm. When the guinea pig and the rat were injected with whole worm extract (WWE) of the young adult worms either by an osmotic mini-pump connected to the jugular vein or by intermittent intravenous injections, the former animal showed blood eosinophilia but the latter failed to do so. Guinea pigs also developed blood eosinophilia after continuous exposure to the excretory and secretory products of the young adult worms, administered by the mini-pump. Eosinophil responses to WWE could be induced both in athymic CD-1 (ICR) nude mice and in its heterozygous litter mates, suggesting that T cell-independent mechanism(s) could be involved in the induction of blood eosinophilia in the nonpermissive, mouse host. These data clearly indicate that the eosinophilia-inducing factor(s) and the mechanism of eosinophilia are different in permissive and nonpermissive hosts.

Ultrastructural evidence for eosinophil-mediated destruction of Angiostrongylus cantonensis transferred into the pulmonary artery of non-permissive hosts

Ultrastructural and cytochemical analyses were carried out on cellular reactions to the young adult worms of Angiostrongylus cantonensis surgically transferred into the pulmonary arteries of permissive (rat) and non-permissive (rabbit and guinea-pig) hosts. In permissive hosts, no appreciable cellular reactions could be found around worms throughout the course of the observations. By contrast, the infiltration of neutrophils along with eosinophils was observed around worms in non-permissive hosts even at early stages (days 2 to 4). At day 7 and later, the prominent degranulation (solubilization of the whole granule or the matrix alone with preserved crystalloid, tubulovesicular structure formation, and vacuole formation containing lysosomal contents, etc.) of eosinophils, and subsequent release of the lysosomal contents on to the worm surface were noted. Discharge of large amounts of peroxidase on to the worm surface was also demonstrated. The worms were thus damaged and their cuticular fragments were frequently found removed. In addition to this, degenerative changes, such as lipid-droplet and vacuole formations, were detectable in the hypodermis, somatic musculature and intestine of the parasites transferred into the non-permissive hosts, as early as day 4 after transfer. These data suggest that eosinophils would serve as a potential effector cell for killing of pulmonary arterial A. cantonensis in non-permissive hosts.

Antibody responses in rats infected with Angiostrongylus cantonensis and the passive transfer of protective immunity with immune serum

Little haemagglutinating antibody was detected in the serum of rats with primary Angiostrongylus cantonensis infections until the juvenile worms left the brain and lodged in the lungs about 35 days after infection. Antibody titres reached a peak 50 days after infection and were maintained for at least a further 95 days. Increasing the infective dose of A. cantonensis larvae increased the peak antibody titres attained by the infected rats. Re-infection temporarily reduced the serum antibody titre, but later it increased and showed an anamnestic response. Reaginic antibody production was transient during primary infections; re-infection failed to stimulate further reaginic antibody production. Antiserum from immune donor rats protected recipients against A. cantonensis. The transferred immune serum suppressed anti-A. cantonensis antibody production in recipient rats.

The course of Angiostrongylus cantonensis infection in athymic nude and neonatally thymectomized mice

BALB/c athymic nude and thymus-reconstituted nude mice and neonatally thymectomized BALB/c mice were infected with stage 3 larvae of Angiostrongylus cantonensis and the worm burdens of the mice were determined at various times after infection. When the nude and thymectomized mice were exposed to the parasite, some worms were found to migrate from the brain to lungs but died there without reaching maturity. This pulmonary arterial migration of the worms in the nude did not occur following thymic reconstitution. These data suggest that the inability of murine intracranial worms to migrate to the lungs is at least in part due to thymus-dependent mechanisms, and also that the failure of worm maturation in mouse lungs might be due to thymus-independent immune mechanisms and/or nonimmunological mechanisms.