Taenia crassiceps: Immunity to metacestodes in BALB/c and BDF1 mice

The kinetics of primary and secondary infections with Taenia crassiceps larvae and the effects of immune serum on T. crassiceps larvae were studied in BALB/c and BDF1 mice. In both strains of mice a substantial degree of resistance to reinfection comparable to that previously reported in C3H mice can be induced by subcutaneous injection of three larvae 3 weeks prior to intraperitoneal challenge infection. Both early immune damage in the absence of adherent host cells and encapsulation by host cells are involved in rejection of larvae by BALB/c and BDF1 mice, but in both of these strains early immune damage is less pronounced and the cellular encapsulation response considerably more prominent than in the C3H mice studied previously. This difference is also reflected in the effect of immune serum on T. crassiceps metacestodes in vitro: immune serum from BALB/c and BDF1 mice is less effective than immune serum taken from C3H mice at comparable times after challenge infection in mediating damage to T. crassiceps larvae in vitro in the absence of host cells. These results suggest that genetically determined differences in immune capability can alter the state of equilibrium existing among different immune effector mechanisms without producing measurable effects upon overall host resistance to reinfection.     

Multiple helminth infection of the skin causes lymphocyte hypo-responsiveness mediated by Th2 conditioning of dermal myeloid cells

Infection of the mammalian host by schistosome larvae occurs via the skin, although nothing is known about the development of immune responses to multiple exposures of schistosome larvae, and/or their excretory/secretory (E/S) products. Here, we show that multiple (4x) exposures, prior to the onset of egg laying by adult worms, modulate the skin immune response and induce CD4(+) cell hypo-responsiveness in the draining lymph node, and even modulate the formation of hepatic egg-induced granulomas. Compared to mice exposed to a single infection (1x), dermal cells from multiply infected mice (4x), were less able to support lymph node cell proliferation. Analysis of dermal cells showed that the most abundant in 4x mice were eosinophils (F4/80(+)MHC-II(-)), but they did not impact the ability of antigen presenting cells (APC) to support lymphocyte proliferation to parasite antigen in vitro. However, two other cell populations from the dermal site of infection appear to have a critical role. The first comprises arginase-1(+), Ym-1(+) alternatively activated macrophage-like cells, and the second are functionally compromised MHC-II(hi) cells. Through the administration of exogenous IL-12 to multiply infected mice, we show that these suppressive myeloid cell phenotypes form as a consequence of events in the skin, most notably an enrichment of IL-4 and IL-13, likely resulting from an influx of RELMα-expressing eosinophils. We further illustrate that the development of these suppressive dermal cells is dependent upon IL-4Rα signalling. The development of immune hypo-responsiveness to schistosome larvae and their effect on the subsequent response to the immunopathogenic egg is important in appreciating how immune responses to helminth infections are modulated by repeated exposure to the infective early stages of development.     

Expansion of Foxp3+ regulatory T cells in mice infected with the filarial parasite Brugia malayi

Many helminths, including Brugia malayi, are able to establish long-lived infections in immunocompetent hosts. Growing evidence suggests that the immune system's failure to eliminate parasites is at least partially due to the effects of regulatory T cells (Tregs). To test whether parasites may directly stimulate host regulatory activity, we infected mice with two key stages of B. malayi. Both mosquito-borne infective larvae and mature adults i.p. introduced were found to preferentially expand the proportion of CD25(+)Foxp3(+) cells within the CD4(+) T cell population. The induction of Foxp3 was accompanied by raised CD25, CD103, and CTLA-4 expression, and was shown to be an active process, which accompanied the introduction of live, but not dead parasites. CTLA-4 expression was also markedly higher on Foxp3(-) cells, suggesting anergized effector populations. Peritoneal lavage CD4(+)CD25(+) cells from infected mice showed similar suppressive activity in vitro to normal splenic "natural" Tregs. Both B. malayi larvae and adults were also able to induce Foxp3 expression in adoptively transferred DO11.10 T cells, demonstrating that filarial infection can influence the development of T cells specific to a third party Ag. In addition, we showed that induction was intact in IL-4R-deficient animals, in the absence of a Th2 or alternatively activated macrophage response. We conclude that filarial infections significantly skew the balance of the host immune system toward Treg expansion and activation, in a manner dependent on live parasites but independent of a concomitant Th2 response.     

Histopathological appearances in primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S., Muir G. M. & Grove D. I. 1981. Histopathological appearances in primary and secondary infections with Strongyloides ratti in mice. International Journal for Parasitology11: 97–103. The histological appearances of the skin, lungs and small intestines of mice with primary and secondary infections with S. ratti are described. When the skins of mice with a primary infection were examined, larvae were seen scattered throughout the dermis. An inflammatory reaction of neutrophils and eosinophils was first noted around larvae 12 h after infection. By 48 h, mononuclear cells were prominent. The intensity of the inflammatory reaction gradually increased to a maximum on the fifth day and the larvae were destroyed. Very few larvae were seen in the lungs; those observed were located in the alveolar spaces and were not surrounded by an inflammatory infiltrate. Worms in the small intestines were found mostly in the crypts of Leiberkuhn, and were probably located within the epithelial layer; there was no significant villous atrophy or cellular infiltration. Marked differences were found in the tissues of mice with secondary infections. In the skin, oedema and neutrophils and eosinophils were seen around worms as early as 2 h after infection. By 24 h after infection, there was a mixed inflammatory infiltrate and worms were undergoing disintegration. Larvae in the lungs were surrounded by polymorphonuclear and mononuclear cells 48 h and 72 h after infection and the engulfed larvae were undergoing lysis. Only a few worms were seen in the intestines of mice with a secondary infection; the histological appearances were similar to that found in animals with primary infections. It is suggested that the rapid development of an oedematous reaction in the skins of immune mice may facilitate the entry of larvae into the bloodstream and that inflammatory cells destroy many larvae in the lungs of immune mice.     

Ultrastructural aspects of the host cellular immune response to Taenia crassiceps metacestodes.

When three Taenia crassiceps metacestodes were injected intraperitoneally into C3H mice primed by previous subcutaneous inoculation of metacestodes, larvae which were resistant to early immune damage by the humoral response were encapsulated by host cells and rejected. Initially, normal larvae were encapsulated primarily by eosinophils and macrophages. In the early stages of encapsulation, both cell types showed severe degenerative changes and disruption of cell membranes, but there was no evidence of tegumental damage to the encapsulated larvae. Later, mast cells appeared in the capsules surrounding the larvae. After mast cells became common, all of the cell types present were normal, and damage to the larval Tegument became apparent. Ultimately, interaction of eosinophils, mast cells, macrophages, and lymphocytes resulted in death of the encapsulated larvae. These results suggest that larvae may secrete substances toxic to host cells, and that mast cells are necessary for rejection of larvae.     

Susceptibility of different strains of mice to various levels of infection with the eggs of Taenia taeniaeformis

Susceptibility of different mouse strains to varying levels of Taenia taeniaeformis eggs has been studied. C3H are shown to be susceptible to any quantity of eggs. However C57 and NMRI are only susceptible to 1–2 eggs, while larvae from an infection of 30–50 eggs are precociously destroyed. Sometimes fertile larvae can also develop in resistant strains of mice infected with some hundred eggs. In C3H the challenge larvae are unable to survive even from an infection given 24–48 h post-first inoculum. The hypothesis is proposed that in resistant strains, infection with 30–50 eggs induces a more rapid immune response which becomes effective while the larva is still vulnerable; in massive infections, however, immune paralysis may occur. Although susceptible strains allow primary infections to develop, they show resistance to challenge infections because larvae are destroyed before they become insusceptible to host attack.     

Immune response against protozoal and nematodal infection in mice with underlying Schistosoma mansoni infection

Schistosoma mansoni infection induces T helper (Th) 2-dominant immune response in mice not only to S. mansoni itself but also to other coexisting antigens. In the present study, we challenged S. mansoni-infected mice with the intestinal nematode, Strongyloides venezuelensis, and the intracellular protozoa, Leishmania major to see whether such Th2-dominant immune responses alter susceptibility of the host to other concomitant parasitic infections. The recovery of S. venezuelensis adult worms from the small intestine was significantly decreased by S. mansoni infection, and the protection to S. venezuelensis appeared to act on migrating larvae. Antibodies elicited by S. mansoni infection showed cross-binding to third-stage larvae antigen of S. venezuelensis. On the other hand, S. mansoni infection did not affect the outcome of L. major infection in both susceptible BALB/c and resistant C57BL/6 mice. Popliteal lymph node cells of BALB/c mice expressed mRNA for interleukin (IL)-10 rather than IL-4, regardless of S. mansoni infection, and those of C57BL/6 mice expressed IFN-gamma mRNA upon L. major antigen stimulation, even in S. mansoni-infected mice. Our findings suggest that Th2-dominant immune response induced by S. mansoni protects mice from intestinal helminthic infections, whereas they do not always modulate protozoal infections.     

Dissociation of the protective immune response in the mouse to Strongyloides ratti

The generation of protective immunity by various stages in the life-cycle of Strongyloides ratti and the phases against which resistance is directed has been examined in murine strongyloidiasis. Mice were exposed to natural, complete infections, were treated with thiabendazole (which largely resembles the natural infection), were treated with cambendazole (which restricts infection to the larval stage), or infected directly by oral transfer of adult worms. Mice that were infected with infective larvae alone did not become resistant to infective larvae or the complete infection but were resistant to adult worms implanted directly into the gut. Mice exposed to adult worms alone were resistant to natural infections and adults worms implanted directly but were not resistant to infective larvae. On the other hand, mice that had received prior natural infections showed evidence of resistance to infective larvae, adult worms, and natural, complete infections. It is concluded that there is immunological cross-reactivity between infective larvae and adult worms but that under certain circumstances the infective larvae are able to evade the host's protective immune response.     

Impairment of primary expulsion of Trichuris muris in mice concurrently infected with Nematospiroides dubius

Primary immune expulsion of Trichuris muris was markedly delayed by concurrent infection with Nematospiroides dubius. Maximum delay of expulsion was dependent on size and timing of N. dubius infection relative to T. muris infection. In NIH mice infection with 400 N. dubius larvae immediately before or after T. muris infection was found to be most effective in suppressing expulsion. Infection on day 8 of T. muris infection, when mice are sensitized to T. muris, also impaired expulsion. From this evidence it is suggested that the larvae of N. dubius are immunosuppressive and that the efferent role of the immune response to T. muris is inhibited. The results are discussed in terms of non-specific immunosuppression and their relevance to the tropical disease situation is emphasized.     

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite. International journal for Parasitology4: 183–191. Migration of the pre-intestinal larval stages of N. brasiliensis was studied in rats undergoing either primary or challenge infections. In rats undergoing a primary infection, more than 67 percent of larvae successfully migrated from the skin to the oesophagus by 70 h after infection, and subsequently over 90 per cent of these larvae became established in the small intestine as sexually mature adults. In immune rats undergoing a second infection, 46 per cent of larvae completed migration to the oesophagus by 70 h and of these, only 1·6 per cent became established in the intestine to produce eggs. These inhibitory effects on the pre-intestinal and intestinal larval stages were even more pronounced in immune rats undergoing a third or fourth infection and in addition, there was a prolonged sojourn and substantial retention of larvae in their lungs. There was no evidence that the immune response had an adverse effect on oesophageal fourth stags larvae as these organisms (obtained from immune donors) were able to establish and develop to maturity when transferred per os to normal animals.Syngeneic transfer of immune mesenteric lymph node cells to normal recipients, caused expulsion of parasites from the intestine but failed to effect migration of pre-intestinal larval stages. The implications of these findings are discussed in the context of current knowledge of the mechanisms of immunity to helminths.     

Mouse mast cell tryptase mMCP-6 is a critical link between adaptive and innate immunity in the chronic phase of Trichinella spiralis infection

Although the innate immune function of mast cells in the acute phase of parasitic and bacterial infections is well established, their participation in chronic immune responses to indolent infection remains incompletely understood. In parasitic infection with Trichinella spiralis, the immune response incorporates both lymphocyte and mast cell-dependent effector functions for pathogen eradication. Among the mechanistic insights still unresolved in the reaction to T. spiralis are the means by which mast cells respond to parasites and the mast cell effector functions that contribute to the immunologic response to this pathogen. We hypothesized that mast cell elaboration of tryptase may comprise an important effector component in this response. Indeed, we find that mice deficient in the tryptase mouse mast cell protease-6 (mMCP-6) display a significant difference in their response to T. spiralis larvae in chronically infected skeletal muscle tissue. Mechanistically, this is associated with a profound inability to recruit eosinophils to larvae in mMCP-6-deficient mice. Analysis of IgE-deficient mice demonstrates an identical defect in eosinophil recruitment. These findings establish that mast cell secretion of the tryptase mMCP-6, a function directed by the activity of the adaptive immune system, contributes to eosinophil recruitment to the site of larval infection, thereby comprising an integral link in the chronic immune response to parasitic infection.     

Nippostrongylus brasiliensis infections in mice: the immunological basis of worm expulsion.

Nippostrongylus brasiliensis infections in mice were terminated more rapidly than in rats and immunologically induced damage occurred earlier. Like rats, mice expelled damaged worms more rapidly than normal worms. Recipients of cells from the spleen or mesenteric node of immune mice expelled their worms by day 8 of the infection. Recipients of cells alone or antiserum alone did not expel their worms by day 5 but mice given both cells and antiserum expelled their worms by this stage of the infection. Damaged worms were expelled more rapidly than normal worms from mice given immune cells, This work indicated that antibodies and cells collaborate to expel N. brasiliensis from mice as has been shown to occur in rats.     

Alterations in the longevity and fecundity of adult Trichinella pseudospiralis related to method of isolation of infective larvae

The infectivity of Trichinella pseudospiralis infective larvae was reduced significantly following exposure to low pH or a combination of 1% pepsin at low pH compared to that for larvae isolated in phosphate-buffered saline (PBS) at pH 7.0. Reduction of host gastric pH by administration to mice of sodium bicarbonate solution in PBS was accompanied by an increase in the infectivity of larvae isolated in 1% pepsin/HCl (P/HCl) compared to that for worms inoculated into hosts given PBS alone. Fewer adult worms developing from larvae isolated in P/HCl became established in the host small bowel than was seen with larvae isolated in PBS; moreover, the fecundity in vitro of adult worms developing from P/HCl-isolated larvae was reduced below that for adults developing from larvae isolated from host muscle in PBS. More adult worms were recovered following infection of immune hosts with PBS-isolated larvae than were recovered from immune mice challenged with larvae isolated in P/HCl. Similar findings were observed in mice immunized by infection with Trichinella spiralis and challenged with T. pseudospiralis larvae isolated in either P/HCl or PBS. Immunization of mice with T. pseudospiralis larvae isolated by either method and challenged with larvae of T. spiralis resulted in recovery of similar percentages of the challenge inoculum.     

Extracellular traps are associated with human and mouse neutrophil and macrophage mediated killing of larval Strongyloides stercoralis

Neutrophils are multifaceted cells that are often the immune system's first line of defense. Human and murine cells release extracellular DNA traps (ETs) in response to several pathogens and diseases. Neutrophil extracellular trap (NET) formation is crucial to trapping and killing extracellular pathogens. Aside from neutrophils, macrophages and eosinophils also release ETs. We hypothesized that ETs serve as a mechanism of ensnaring the large and highly motile helminth parasite Strongyloides stercoralis thereby providing a static target for the immune response. We demonstrated that S. stercoralis larvae trigger the release of ETs by human neutrophils and macrophages. Analysis of NETs revealed that NETs trapped but did not kill larvae. Induction of NETs was essential for larval killing by human but not murine neutrophils and macrophages in vitro. In mice, extracellular traps were induced following infection with S. stercoralis larvae and were present in the microenvironment of worms being killed in vivo. These findings demonstrate that NETs ensnare the parasite facilitating larval killing by cells of the immune system.     

Nematospiroides dubius: susceptibility to infection and the development of resistance in hypothymic (nude) BALB/c mice.

BALB/c-nu/nu mice and their intact nu/+ littermates are equally susceptible to infection with third-stage larvae of Nematospiroides dubius. Unlike their heterozygous littermates, however, the nu/nu mice are unable to form ganulomata in the intestinal wall and become only partially resistant to rechallenge. Following two or more infections, nu/nu mice maintain a high burden of adult intestinal worms, whereas worms are lost from immune nu/+ mice. Studies in T cell-injected nu/nu mice suggest that a full complement of T cells is needed to develop maximum resistance against the infective third-stage larvae and to expel adult worms. Measurement of serum immunoglobulin levels indicate that infected nu/+ mice have very high levels of IgG1 whereas the levels of IgG2a are reduced. In infected T cell-injected nu/nu mice, IgG1 levels increase with the number of T cells injected, whereas IgG2a levels are variable but always higher than in infected nu/+ mice.     

CCR3 is required for tissue eosinophilia and larval cytotoxicity after infection with Trichinella spiralis

The CCR3 binds at least seven different CC chemokines and is expressed on eosinophils, mast cells (MC), and a subset of Th cells (Th2) that generate cytokines implicated in mucosal immune responses. Using mice with a targeted disruption of CCR3 (CCR3(-/-)) and their +/+ littermates, we investigated the role of CCR3 in the amplification of tissue eosinophilia and MC hyperplasia in the mouse after infection with Trichinella spiralis. In CCR3(-/-) mice, eosinophils are not recruited to the jejunal mucosa after infection and are not present in the skeletal muscle adjacent to encysting larvae. In addition, the number of cysts in the skeletal muscle is increased and the frequency of encysted larvae exhibiting necrosis is reduced. The CCR3(-/-) mice exhibit the expected MC hyperplasia in the jejunum and caecum and reject the adult worms from the small intestine at a normal rate. This study is consistent with distinct functions for MC (adult worm expulsion) and eosinophils (toxicity to larvae) in immunity to a helminth, T. spiralis, and defines the essential requirement for CCR3 in eosinophil, but not MC recruitment to tissues.     

Concerted Activity of IgG1 Antibodies and IL-4/IL-25-Dependent Effector Cells Trap Helminth Larvae in the Tissues following Vaccination with Defined Secreted Antigens,Providing Sterile Immunity to Challenge Infection

Over 25% of the world''s population are infected with helminth parasites, the majority of which colonise the gastrointestinal tract. However, no vaccine is yet available for human use, and mechanisms of protective immunity remain unclear. In the mouse model of Heligmosomoides polygyrus infection, vaccination with excretory-secretory (HES) antigens from adult parasites elicits sterilising immunity. Notably, three purified HES antigens (VAL-1, -2 and -3) are sufficient for effective vaccination. Protection is fully dependent upon specific IgG1 antibodies, but passive transfer confers only partial immunity to infection, indicating that cellular components are also required. Moreover, immune mice show greater cellular infiltration associated with trapping of larvae in the gut wall prior to their maturation. Intra-vital imaging of infected intestinal tissue revealed a four-fold increase in extravasation by LysM⁺GFP⁺ myeloid cells in vaccinated mice, and the massing of these cells around immature larvae. Mice deficient in FcRγ chain or C3 complement component remain fully immune, suggesting that in the presence of antibodies that directly neutralise parasite molecules, the myeloid compartment may attack larvae more quickly and effectively. Immunity to challenge infection was compromised in IL-4Rα- and IL-25-deficient mice, despite levels of specific antibody comparable to immune wild-type controls, while deficiencies in basophils, eosinophils or mast cells or CCR2-dependent inflammatory monocytes did not diminish immunity. Finally, we identify a suite of previously uncharacterised heat-labile vaccine antigens with homologs in human and veterinary parasites that together promote full immunity. Taken together, these data indicate that vaccine-induced immunity to intestinal helminths involves IgG1 antibodies directed against secreted proteins acting in concert with IL-25-dependent Type 2 myeloid effector populations.     

Generation of cytotoxic T lymphocytes during coxsackievirus tb-3 infection. II. Characterization of effector cells and demonstration cytotoxicity against viral-infected myofibers1.

This report describes studies characterizing the virus-specific cytotoxic effector cells which are present in the spleens of mice 7 days after infection with Coxsackievirus B-3. An in vitro 51Cr assay employing eyngeneic virus-infected neonatal fibroblasts was used to measure cytotoxic activity. Treatment of immune cells with (anti-thy-1.2) and complement abolished dtheir cytotoxic activity, but no reduction occurred when B cells were removed by incubation with anti-Ig and complement or macrophages eliminated by adherence depletion. The findings therefore imply that the cytotoxic reaction was mediated by sensitized T cells and that B cells and macrophages did not play an important role. Reciprocal assays performed with BALB/c and CBA/J cells showed that Coxsackievirus-immune spleen cells lysed infected syngeneic targets but not allogeneic targets, providing further evidence that cytotoxicity was mediated by effector T cells. In addition and in vitro assay system employing neonatal myocardial cells was developed and used to demonstrate that Coxsackievirus-infected myofibers were susceptible to destruction by immune spleen cells. The evidence suggests that mice infected with Coxsackie B viruses are able to mount a cell-mediated immune response with production of cytotoxic T cells which have the capacity to damage tissues infected with these agents.     

IL-10 regulates movement of intestinally derived CD4+ T cells to the liver

Diseases that affect the intestine may have hepatic manifestations, but the mechanisms involved in establishing hepatic disease secondarily remain poorly understood. We previously reported that IL-10 knockout (KO) mice developed severe necrotizing hepatitis following oral infection with Trichinella spiralis. In this study, we used this model of intestinal inflammation to further examine the role of IL-10 in regulating hepatic injury. Hepatic damage was induced by migrating newborn larvae. By delivering the parasite directly into the portal vein, we demonstrated that an ongoing intestinal immune response was necessary for the development of hepatitis. Intestinally derived CD4+ cells increased in the livers of IL-10 KO mice, and Ab-mediated blockade of MAdCAM-1 inhibited the accumulation of CD4+alpha(4)beta(7)+ cells in the liver. Moreover, adoptive transfer of intestinally primed CD4+ T cells from IL-10 KO mice caused hepatitis in infected immunodeficient animals. Conversely, transfer of wild-type donor cells reduced the severity of hepatic inflammation in IL-10 KO recipients, demonstrating regulatory activity. Our results revealed that IL-10 prevented migration of intestinal T cells to the liver and inhibited the development of hepatitis.     

The tissue reactions of mice to infection with Heligmosmoides polygyrus

The intestines of normal and resistant LAF1 mice were subjected to histologic study to determine the timing and mechanisms of resistance to reinfection by Heligmosmoides polygyrus. During reinfection third-stage larvae are less able to penetrate the intestinal wall. Larvae which are able to encyst develop at a slower rate and provoke an increase in nonspecific inflammation around their cysts. After emergence from intestinal cysts, preadults are rapidly lost, but at no time were injured or destroyed larvae or adults noted. Exsheathed larvae were injected via tail vein into control, sensitized and resistant BALB/c mice. The inflammatory response around entrapped larvae in the lung was measured at 1, 2, 4, and 8 days. A heightened inflammatory response, consisting primarily of polymorphonuclear cells with some round cells which peaked in size on day 2, was observed in both sensitized and resistant mice. A similar heightened inflammatory response was also observed in both AKR (non-resistant) BALB/c (resistant) mice vaccinated subcutaneously with exsheathed larvae.