Trichinella pseudospiralis larvae express natural killer (NK) cell-associated asialo-GM1 antigen and stimulate pulmonary NK activity

Human hydatid cyst fluid-induced therapeutic anti-cancer immune responses via NK1.1+ cell activation in mice

Echinococcus granulosus is a cestode parasite which causes cystic echinococcosis disease. Previously we observed that vaccination with E. granulosus antigens from human hydatid cyst fluid (HCF) significantly inhibits colon cancer growth. In the present work, we evaluate the anti-tumor immune response induced by human HCF against LL/2 lung cancer in mice. HCF vaccination protected from tumor growth, both in prophylactic and therapeutic settings, and significantly increased mouse survival compared to control mice. Considering that tumor-associated carbohydrate antigens are expressed in E. granulosus, we oxidized terminal carbohydrates in HCF with sodium periodate. This treatment abrogates the anti-tumor activity induced by HCF vaccination. We found that HCF vaccination-induced IgG antibodies that recognize LL/2 tumor cells by flow cytometry. An antigen-specific immune response is induced with HCF vaccination in the tumor-draining lymph nodes and spleen characterized by the production of IL-5 and, in less extent, IFNɣ. In the tumor microenvironment, we found that NK1.1 positive cells from HCF-treated mice showed higher expression of CD69 than control mice ones, indicating a higher level of activation. When we depleted these cells by administrating the NK-specific antibody NK1.1, a significantly decreased survival was observed in HCF-induced mice, suggesting that NK1.1⁺ cells mediate the anti-tumor protection induced by HCF. These results suggest that HCF can evoke an integrated anti-tumor immune response involving both, the innate and adaptive components, and provide novel insights into the understanding of the intricate relationship between HCF vaccination and tumor growth.

Early peritoneal immune response during Echinococcus granulosus establishment displays a biphasic behavior

Background

Cystic echinococcosis is a worldwide distributed helminth zoonosis caused by the larval stage of Echinococcus granulosus. Human secondary cystic echinococcosis is caused by dissemination of protoscoleces after accidental rupture of fertile cysts and is due to protoscoleces ability to develop into new metacestodes. In the experimental model of secondary cystic echinococcosis mice react against protoscoleces producing inefficient immune responses, allowing parasites to develop into cysts. Although the chronic phase of infection has been analyzed in depth, early immune responses at the site of infection establishment, e.g., peritoneal cavity, have not been well studied. Because during early stages of infection parasites are thought to be more susceptible to immune attack, this work focused on the study of cellular and molecular events triggered early in the peritoneal cavity of infected mice.

Principal Findings

Data obtained showed disparate behaviors among subpopulations within the peritoneal lymphoid compartment. Regarding B cells, there is an active molecular process of plasma cell differentiation accompanied by significant local production of specific IgM and IgG2b antibodies. In addition, peritoneal NK cells showed a rapid increase with a significant percentage of activated cells. Peritoneal T cells showed a substantial increase, with predominance in CD4⁺ T lymphocytes. There was also a local increase in Treg cells. Finally, cytokine response showed local biphasic kinetics: an early predominant induction of Th1-type cytokines (IFN-γ, IL-2 and IL-15), followed by a shift toward a Th2-type profile (IL-4, IL-5, IL-6, IL-10 and IL-13).

Conclusions

Results reported here open new ways to investigate the involvement of immune effectors players in E. granulosus establishment, and also in the sequential promotion of Th1- toward Th2-type responses in experimental secondary cystic echinococcosis. These data would be relevant for designing rational therapies based on stimulation of effective responses and blockade of evasion mechanisms.

Cystic echinococcosis is a zoonotic disease caused by the larval stage of the cestode Echinococcus granulosus and shows a cosmopolitan distribution with a worldwide prevalence of roughly 6 million infected people. Human cystic echinococcosis can develop in two types of infection. Primary infection occurs by ingestion of oncospheres, while secondary infection is caused by dissemination of protoscoleces after accidental rupture of fertile cysts. Murine experimental secondary infection in Balb/c mice is the current model to study E. granulosus-host interaction. Secondary infection can be divided into two stages: an early stage in which protoscoleces develop into hydatid cysts (infection establishment) and a later stage in which already differentiated cysts grow and eventually become fertile cysts (chronic infection). During infection establishment parasites are more susceptible to immune attack, thus our study focused on the immunological phenomena triggered early in the peritoneal cavity of experimentally infected mice. Our results suggest that early and local Th2-type responses are permissive for infection establishment.

Pulmonary strongyloidiasis associated CD3+ large granular lymphocytosis

We report a case of pulmonary strongyloidiasis in a patient with large granular lymphocytosis. He was on short-term high dose immunosuppressant therapy. A 77-year-old white male presented to the emergency room with fever and shortness of breath for 10 days. The patient had been diagnosed about 3 months prior to this presentation with “large granular lymphocytosis” (LGL) after a workup for pancytopenia. Methotrexate and prednisone had been started 1 month ago for the treatment of LGL. Five days prior to the current presentation, he had been started on moxifloxacin as an outpatient but got progressively worse and came to an emergency room. Bronchial washings (bronchoalveolar lavage) demonstrated numerous filariform larvae of Strongyloides stercoralis. The patient was treated with ivermectin and improved. Pulmonary strongyloidiasis should be considered in the differential if X-ray findings show a interstitial or alveolar pattern and if the patient has visited the endemic areas, even in the remote past.

Filarial parasites induce NK cell activation, type 1 and type 2 cytokine secretion, and subsequent apoptotic cell death

NK cells are an important source of early cytokine production in a variety of intracellular viral, bacterial, and protozoan infections; however, the role of NK cells in extracellular parasitic infections such as filarial infections is not well-defined. To investigate the role of NK cells in filarial infections, we have used an in vitro model system of culturing live infective-stage larvae (L3) or live microfilariae (Mf) of Brugia malayi, a causative agent of human lymphatic filariasis, with PBMC of normal individuals. We found that NK cells undergo early cell activation and produce IFN-gamma and TNF-alpha within 24 h after stimulation with both live L3 and Mf. Interestingly, NK cells also express IL-4 and IL-5 at this time point in response to live Mf but not L3. This is accompanied by significant alterations in NK cell expression of costimulatory molecules and natural cytotoxicity receptors. This activation is dependent on the presence of monocytes in the culture, IL-12, and direct contact with live parasites. The early activation event is subsequently followed by apoptosis of NK cells involving a caspase-dependent mechanism in response to live L3 but not live Mf. Thus, the NK cell-parasite interaction is complex, with filarial parasites inducing NK cell activation and cytokine secretion and finally NK cell apoptosis, which may provide an additional mechanism of down-regulating the host immune response.

The innate host defence against nematode parasites

Nematode parasites cause significant infections in both humans and animals. They are complex, multicellular organisms that present unique challenges for the host, in particular with respect to the recognition of their unusual surface structures by the innate defence system. The innate immune system is now recognized to be a critical component in the development of an adaptive effector response as well as a driver of vaccine-induced immunity. This paper will give an overview of current research on the innate barriers and immune mechanisms, cells, and receptors involved in the innate host response to nematode parasites. It will also review the 'nematode-associated molecular patterns' that may be specifically recognized by the host, in addition to other signals, such as nervous stimulation and tissue damage, that may alert the innate system to parasite invasion.

Amelioration of influenza-induced pathology in mice by coinfection with Trichinella spiralis

Illness due to respiratory virus infection is often induced by excessive infiltration of cells into pulmonary tissues, leading to airway occlusion. We show here that infection with Trichinella spiralis results in lower levels of tumor necrosis factor in bronchoalveolar lavage fluid and inhibits cellular recruitment into the airways of mice coinfected with influenza A virus. Infiltration of neutrophils and CD4+ and CD8+ lymphocytes was reduced, resulting in animals gaining weight more rapidly following the initial phase of infection. Influenza resulted in a generalized increase in vascular permeability in pulmonary tissues, and this was suppressed by parasite infection, although the effects were restricted to the early phase of trichinosis. Moreover, the number of cells producing interleukin-10 (IL-10), and the local levels of this cytokine, were reduced, suggesting that amelioration of pulmonary pathology by parasite infection occurs independently of IL-10 production.

Expansion of NK cells with reduction of their inhibitory Ly-49A, Ly-49C, and Ly-49G2 receptor-expressing subsets in a murine helminth infection: contribution to parasite control

Natural killer cell-associated direct cytotoxicity and cytokine production are crucial mechanisms for early innate host resistance against viruses, bacteria, or protozoa. The engagement of inhibitory NK cell receptors can influence host responses to viruses. However, these receptors have not been investigated to date in parasitic infections, and little is known about the role of NK cells in the defense against helminths. Therefore, we have correlated the frequencies of cells expressing the pan-NK marker DX5 and subsets bearing inhibitory Ly-49 receptors with worm survival and cytokine production during infection with Litomosoides sigmodontis in BALB/c mice (H2(d)), the only fully permissive model of filariasis. A marked influx of DX5(+)/CD3(-) NK cells and DX5(+)/CD3(+) T cells into the pleural cavity, where the parasites were located, was observed. The frequency of pleural NK cells expressing the H2(d)-reactive inhibitory receptors Ly-49A, Ly-49C, or Ly-49G2 declined most strongly compared with spleen and blood. In the peripheral blood, longitudinal analysis revealed an early and stable reduction of Ly-49C(+) and Ly-49G2(+) NK cells, a subsequent significant increase of the entire NK cell and DX5(+)/CD3(+) T cell populations, and a reduction in the Ly-49A(+) subset. The in vivo depletion of NK cells strongly enhanced the worm load and influenced IL-4 and IL-5 plasma levels. These data demonstrate a new role for NK cells in the host defense against filariae and, for the first time, alterations of Ly-49 receptor-expressing NK cell subsets in a parasitic infection.

Natural killer-cell lymphocytosis and strongyloides infection

We report a case of strongyloides infection in a 72-year-old man presenting with acute angio-oedema and urticaria. He was also found to have natural killer cell (NK) large granular lymphocytosis (LGL). We discuss the possible relationship between the strongyloides infection and the NK-LGL lymphocytosis.

Effects of maternal alcohol consumption on milk and blood lymphocytes and IgG antibody levels from Trichinella spiralis-infected rats

Immunity to the intestinal parasite Trichinella spiralis can be transferred from the mother to the neonate during lactation. Previous studies in our laboratory showed that the passage of immunity to pups from ethanol-treated dams was depressed. This study examined the effect of ethanol consumption during pregnancy and lactation on the T. spiralis-associated immune components in milk and blood. Groups of female rats were fed either ethanol-containing or isocaloric liquid diets for 30 days before T. spiralis infection, mated and maintained on corresponding diets through pregnancy and lactation. Two-color flow cytometric analysis was performed for lymphocyte populations, enzyme-linked immunoabsorbent assay for specific IgG, and radial immunodiffusion assay for total IgG. The percentage of total T cells and their subsets, T helper cells and T cytotoxic/suppressor cells in milk and those in blood were similar between pair-fed and ethanol-treated animals. However, the percentage of natural killer cells in milk from ethanol animals was significantly reduced compared with the pair-fed group (33% vs. 54%). The percentage of activated or memory type T helper cell subset (OX2-W3/25+) was significantly increased in the blood of the ethanol-treated group. Pair-fed animals showed higher T. spiralis-specific IgG antibody levels in both in milk and blood compared with ethanol-treated animals. In ethanol-treated animals, specific IgG levels and total IgG concentration in milk were significantly lower than those in blood, whereas in pair-fed animals, only total IgG concentration in milk was lower than that in blood. This study indicates that ethanol consumption during pregnancy and lactation alters the maternal immune system.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of variation in host strain and parasite isolate on inflammatory and antibody responses to Trichinella spiralis in mice

Variation in the immunogenicity of 3 isolates of Trichinella spiralis was assessed by the parameters of adult worm recovery, mast cell, eosinophil and antibody responses in mice of defined response phenotype. The levels of the protective, inflammatory and immune responses induced by infection differed between the isolates. Isolates showed considerable variation in the capacity to elicit mast cell and eosinophil responses. All induced increases in parasite-specific antibody, levels of total (IgGAM) antibody and of IgM and IgG isotypes rose steadily after infection, but there were significant differences in levels of response. The IgGAM response was correlated with the number of worms present, i.e. the greatest response was seen in low responder (C57BL/10) mice infected with the longest-surviving isolates. All isolates elicited specific IgG1 and IgG2a antibodies after infection, although, again, there were isolate-specific differences in the levels and kinetics of response. Levels of these isotypes were always higher, although not significantly so, in high-responder NIH mice. Low-responder mice showed higher IgE serum levels than high-responder mice after infection, one isolate giving much higher IgE values than the other two.

The effects of maternal ethanol consumption on lactational transfer of immunity to Trichinella spiralis in rats

Transient immunity to the intestinal parasite Trichinella spiralis can be transferred from the mother to the neonate during lactation. The goal of this study was to determine whether maternal ingestion of ethanol during pregnancy and lactation inhibited expression of anti- T. spiralis immunity in nursing pups. Groups of female rats were infected with 1000 T. spiralis L1 larva, mated, and fed either ethanol-containing or isocaloric liquid diets and maintained on diets through pregnancy and lactation or were fed the liquid diets for 30 days before T. spiralis infection, mated, and maintained on diets through pregnancy and lactation. Pups were challenged orally with 200 T. spiralis larva at 14 days postdelivery (preweaning period) or 21 days postdelivery (postweaning period) and were sacrificed either 3 or 8 days after respective challenge. Intestinal worm counts and serum titers of anti-T. spiralis IgG antibodies were determined for each pup. No difference in the number of intestinal worms between pups of ethanol-treated and pair-fed dams that received ethanol diet after T. spiralis infection was observed in the preweaning period. This was also true of pups from the dams sacrificed at 3 days after challenge in the postweaning period. However, similar pups sacrificed at 8 days after challenge showed significantly higher worm counts (decreased immunity) relative to their pair-fed controls. Pups of dams that received ethanol containing diet 30 days prior to T. spiralis-infection showed significantly higher numbers of intestinal worms relative to pair-fed pups at both the preweaning and postweaning periods.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of ethanol consumption on the expression of immunity to Trichinella spiralis in rats

The effects of ethanol ingestion on immune responses of female rats against Trichinella spiralis (T. spiralis) infections were investigated. Female rats were pair-fed either ethanol-containing or isocaloric control liquid diets for 68 days, during which time they underwent one pregnancy cycle. For some studies, animals were fed ethanol diets for 68 days beginning prior to pregnancy and continuing through lactation and involution. They were infected on Day 7 of involution with 1000 L1 larvae of T. spiralis and tested for a primary rejection response 10 days later. To test for a secondary immune response, rats were infected with T. spiralis, placed on ethanol-containing liquid diet 15 days later, and after 68 days on diets, challenged with 1000 T. spiralis larvae and killed 3 days later. For primary immunized studies, ethanol-treated animals demonstrated significantly lower levels of anti-T. spiralis serum antibodies in ELISA, reduced rates of H3 thymidine incorporation by lymph node cells stimulated with T. spiralis antigen and significantly higher numbers of intestinal worm burdens (decreased immunity) compared with pair-fed controls. For animals sensitized to T. spiralis prior to pregnancy and given a secondary challenge during involution, no differences were found between ethanol and pair-fed animals in their ability to reject their worm burdens or in anti-T. spiralis serum antibody levels; however, ethanol-treated animals showed reduced rates of thymidine incorporation by lymph node cells when stimulated with T. spiralis antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological and immunological characteristics of Trichinella pseudospiralis

In 1972 three new species were proposed for the genus Trichinella, which for 137 years had contained a single species, Trichinella spiralis (Owen,1835). One of these proposed species, Trichinella pseudospiralis, was markedly different from the others in that it was smaller in size, the muscle-stage larvae were not surrounded by a capsule, and it was capable of parasitizing birds. Owing to a lack of information on the normal host range, geographic distribution, biochemistry, immunology and normal variation in biological characteristics of these organisms, several authors supported the more conservative position of designating them sibling species, subspecies or races of Trichinella. The summary statement following the session on Parasite Genetics and Speciation at the 7th International Conference on Trichinellosis recommended that pseudospiralis be accepted as a new species of Trichinella. In this article George Stewart reviews the available information on the biological and immunological characteristics of T. pseudospiralis.