D Gold

Publications of D Gold

• The antiparasitic actions of plant jasmonates.

  Authors: D Gold, I Pankova-Kholmyansky, O Fingrut, E Flescher

  The Journal of parasitology. 01/2004; 89(6):1242-4.

  Jasmonates are a group of small lipids produced in plants, which function as plant stress hormones. We have previously shown that jasmonates can exert significant cytotoxic effects upon human cancerJasmonates are a group of small lipids produced in plants, which function as plant stress hormones. We have previously shown that jasmonates can exert significant cytotoxic effects upon human cancer cells. The purpose of the present study was to determine the effects of jasmonates on parasites. To that end, we chose 2 major human blood parasites, Plasmodium falciparum, a unicellular parasite, and Schistosoma mansoni, a multicellular helminth parasite, and studied the effects of jasmonates on these parasites in vitro. We found that jasmonates are cytotoxic toward both parasites, with P. falciparum being the more susceptible. Jasmonates did not cause any damage to control human erythrocytes at the maximum concentration used in the experiments. This is the first study demonstrating the antiparasitic potential of plant-derived jasmonates.

• Ceramide mediates growth inhibition of the Plasmodium falciparum parasite.

  Authors: I Pankova-Kholmyansky, A Dagan, D Gold, Z Zaslavsky, E Skutelsky, S Gatt, E Flescher

  Cellular and molecular life sciences : CMLS. 04/2003; 60(3):577-87.

  In mammalian cells, ceramide mediates death by chemotherapeutic drugs. We analysed, for the first time, the role of ceramide in inhibiting growth of the malaria-causing parasite PlasmodiumIn mammalian cells, ceramide mediates death by chemotherapeutic drugs. We analysed, for the first time, the role of ceramide in inhibiting growth of the malaria-causing parasite Plasmodium falciparum. Added exogenously, ceramide significantly decreased the number of parasites, and this effect was abolished by sphingosine-1-phosphate, a biological antagonist of ceramide action. Ceramide can induce death of cancer cells by decreasing glutathione levels, and in our work it induced dose- and time-dependent depletion of glutathione in P. falciparum parasites. N-acetylcysteine, a precursor of glutathione, abrogated the cytotoxic effect of ceramide. Thus, ceramide can mediate growth inhibition of P. falciparum parasites by decreasing glutathione levels. The antimalarial drugs artemisinin and mefloquine induced the death of P. falciparum parasites by sphingomyelinase-generated ceramide and by decreasing parasite glutathione levels. Altogether, ceramide was identified as a signalling molecule capable of inducing growth inhibition of P. falciparum malarial parasites.

• Surface and subsurface irrigation with effluents of different qualities and presence of Cryptosporidium oocysts in soil and on crops.

  Authors: R Armon, D Gold, M Brodsky, G Oron

  Water science and technology : a journal of the International Association on Water Pollution Research. 02/2002; 46(3):115-22.

  A large variety of human pathogens are excreted in wastewater including bacteria, viruses, protozoan cysts and helminth eggs. In raw sewage, human pathogens reach high numbers, thereafter decreasingA large variety of human pathogens are excreted in wastewater including bacteria, viruses, protozoan cysts and helminth eggs. In raw sewage, human pathogens reach high numbers, thereafter decreasing successively at each treatment step. However, the final effluents still contain a large fraction of these pathogens that may pose a serious public health. Among the various crops irrigated with effluents, vegetables are the most vulnerable to contamination. Vegetables, usually eaten raw (uncooked) or with rich dressings (causing regrowth of some pathogenic bacteria) pose the main threat to humans. The importance of microbiological and parasitological criteria for reused water has been repeatedly emphasized. Some microbiological recommendations based on epidemiological data have been established for untreated wastewater, there is still a need to define the criteria for effluent quality required for unrestricted crop irrigation. This paper presents a field study comparison of two irrigation methods: surface and subsurface of field crops (mainly vineyard) and follow-up of Cryptosporidium oocysts in soil at different depths (0 to 90 cm). Oocysts were isolated at all depths without a clear pattern of distribution (0 to 640 oocysts/g). In addition different vegetables irrigated with different effluent qualities were tested for the presence of Cryptosporidium oocysts and Giardia cysts. The highest prevalence of oocysts was found on zucchini that has a sticky and hairy outer surface (80 to 10,000 oocysts/0.5 kg).

• The utilization of sodium taurocholate in excystation of Cryptosporidium parvum and infection of tissue culture.

  Authors: D Gold, B Stein, S Tzipori

  The Journal of parasitology. 11/2001; 87(5):997-1000.

  The present work deals with optimization of excystation of Cryptosporidium parvum oocysts and the infection process of tissue culture cells by the parasite. It was shown that presence of the bileThe present work deals with optimization of excystation of Cryptosporidium parvum oocysts and the infection process of tissue culture cells by the parasite. It was shown that presence of the bile salt sodium taurocholate in the incubation medium expedited excystation of the tested GCH1 isolate and enhanced it, as compared with bleaching of the oocysts. This bile salt had no effect on the viability of tissue culture cell lines MDBK and HCT-8 at the tested concentration of 0.375% for up to 2 hr of coincubation. Infection studies conducted on tissue culture cells showed higher infection rates in the presence of sodium taurocholate than with bleached oocysts in the absence of this bile salt. It may be concluded that, at least as regards the GCH1 strain of C. parvum, the whole infection process can be performed in the presence of sodium taurocholate, and does not require separation and cleaning of the excysted sporozoites before their application to tissue culture cells.

• Influence of mechanical tail-detachment techniques of schistosome cercariae on the production, viability, and infectivity of resultant schistosomula: a comparative study.

  Authors: D Gold, E Flescher

  Parasitology research. 08/2000; 86(7):570-2.

  Two decaudation methods used by Schistosoma mansoni cercariae for the production of schistosomula by in vitro transformation were comparatively tested. Both low-pressure syringe passage and vortexTwo decaudation methods used by Schistosoma mansoni cercariae for the production of schistosomula by in vitro transformation were comparatively tested. Both low-pressure syringe passage and vortex mixing of the cercariae produced schistosomula of similar percentages of viability, and the levels of worm recovery following subcutaneous injection in mice were also comparable, though low. By all criteria tested, including simplicity and time requirement, the two methods are equally efficient and are well applicable for mass production of schistosomula.

• A walk in the woods with Tunga penetrans.

  Authors: T Zehavi, I Shwartz, D Gold, J Lengy

  The Israel Medical Association journal : IMAJ. 01/2000; 1(4):279.

• Evaluation of a portable differential continuous flow centrifuge for concentration of Cryptosporidium oocysts and Giardia cysts from water.

  Authors: U Zuckerman, R Armon, S Tzipori, D Gold

  Journal of applied microbiology. 07/1999; 86(6):955-61.

  A portable device was developed and assembled from a stationary differential continuous flow centrifuge usually employed for blood cell separation, for the purpose of concentrating CryptosporidiumA portable device was developed and assembled from a stationary differential continuous flow centrifuge usually employed for blood cell separation, for the purpose of concentrating Cryptosporidium and Giardia from large volumes of water. Following compaction onto the wall of the disposable plastic centrifuge bowl and aspiration of residual water, the oocysts and cysts were dislodged by injection of a 20 ml solution containing 0.01% Tween-80 and 1% SDS and vigorous shaking. Following aspiration, the oocysts were pelleted, reacted with specific FITC-conjugated monoclonal antibodies, and enumerated via fluorescence microscopy. The entire procedure required about 2 h. Initially, 55% and 87% of Cryptosporidium oocysts and Giardia cysts, respectively, were recovered from 45 litres of tap water, and 27% and 57%, respectively, from river water. Adjustments in centrifuge speed and flow rates improved recovery to about 90% for Cryptosporidium oocysts and hence, this method compared favourably with the recently developed calcium carbonate flocculation method. It was superior in time requirement and volume flexibility, and showed a distinct advantage over the standard cartridge filtration method in all respects. The continuous flow centrifugation equipment is compact, mobile, flexible, and yields reproducibly high recovery rates. The ease of handling, speed of performance and minimal requirements for post-concentration equipment, reagents and labour make the system highly cost-effective. It appears to offer an improved method, well suited for use by water utilities for monitoring the burden of water-borne protozoan pathogens.

• Assessment of the viability of Schistosoma mansoni schistosomula by comparative uptake of various vital dyes.

  Authors: D Gold

  Parasitology research. 02/1997; 83(2):163-9.

  Of various vital dyes used to assess schistosomula viability, toluidine blue enabled differential counting of the schistosomula on microscope slides but not in culture wells, whereas methylene blueOf various vital dyes used to assess schistosomula viability, toluidine blue enabled differential counting of the schistosomula on microscope slides but not in culture wells, whereas methylene blue could be added directly to the schistosomula suspension in culture wells of microtiter plates. Toluidine blue uptake by dead parasites was very fast. It mostly also partially stained damaged but not dead organisms. Its main disadvantage was rapid, nonspecific staining of live schistosomula, requiring prompt counting of a preparation and additional reliance on motility for assessment of viability. Methylene blue staining of dead worms was slower, but it did not stain the live worms until about 1 h after dye application, enabling its addition to a series of preparations for consecutive counting. It did not always stain flattened, dead schistosomula or it stained them an uncontrasting pale blue. This dye remarkably induced movement in seemingly inert and probably damaged worms, thus enabling determination of viability even following poor staining or a lack of staining.

• Anti- schistosomular activity of human monocytes/macrophages in response to interleukin-3 and granulocyte-macrophage colonystimulating factor stimulation.

  Authors: D Gold, L Nissimov, J Lengy, Y Keisari

  Mediators of inflammation. 02/1994; 3(5):329-33.

  Human monocytes, co-incubated for 7 days in culture with GM-CSF or IL-3 but not with IFN-gamma, exerted a variable schistosotnulicidal effect on Schistosoma mansoni parasites when grown in 96-wellHuman monocytes, co-incubated for 7 days in culture with GM-CSF or IL-3 but not with IFN-gamma, exerted a variable schistosotnulicidal effect on Schistosoma mansoni parasites when grown in 96-well round-bottomed plates but not in flat-bottomed plates. Addition of LPS or IFN-gamma or both, for the last 48 h did not enhance the cidal effect. Addition of LPS but not IFN-gamma to the pre-incubated cells with GM-CSF or IL-3 markedly stimulated TNF-alpha production by the cells but not their cidal activity. The variable cidal effects obtained with the monocytes/macrophages from different donors suggest that these effects may be genetically predetermined and are possibly linked to blood group markers or to MHC class I or II antigens.

• IL-1, TNF-alpha and IL-2 production by peritoneal and spleen cells from Schistosoma mansoni infected mice and its potentiation by preimmunization with schistosomal antigens and immunostimulants.

  Authors: Y Keisari, M Seger, J Lengy, H Pauli, E Nathan, D Gold

  Immunobiology. 09/1993; 188(4-5):446-59.

  In the present study we tested the effect of immunization with schistosome derived antigens such as frozen-thawed schistosomula in combination with either BCG, liposomes or liposomal muramylIn the present study we tested the effect of immunization with schistosome derived antigens such as frozen-thawed schistosomula in combination with either BCG, liposomes or liposomal muramyl tripeptide-phosphatidyl ethanolamine (MTP-PE), on the resistance of mice to infection, and on the function of their macrophages and lymphocytes. Immunization with either F-T schistosomula + BCG or F-T schistosomula + MTP-PE and subsequent infection, resulted in a 2-3-fold increase in adherent peritoneal macrophage-mediated schistosomulicidal activity (SCA). Peritoneal and spleen macrophages from immunostimulant treated and/or immunized animals showed a significant increase in LPS triggered TNF-alpha production, as compared to non-treated controls. The highest increase in TNF-alpha production was achieved after immunization with either F-T schistosomula + BCG or F-T schistosomula + MTP-PE. LPS triggered IL-1 production was elevated in spleen and peritoneal macrophages from F-T schistosomula + BCG treated mice, and also in spleen macrophages treated with F-T schistosomula + MTP-PE. Only immunization with F-T schistosomula + BCG increased ConA-induced spleen lymphocyte proliferation and IL-2 production. Immunization of mice with F-T schistosomula + BCG also induced protection against parasite infection, while F-T schistosomula + MTP-PE failed to do so. Potentiation of antischistosomal resistance seems to require both macrophage and lymphocyte activation which was achieved only when BCG served as an immunostimulant.

• The schistosomulicidal activity and the production of IL-1 and TNF-alpha by peritoneal macrophages from infected mice and their potentiation by muramyl tripeptide-phosphatidyl ethanolamine (MTP-PE) treatment.

  Authors: M Seger, D Gold, J Lengy, H Pauli, Y Keisari

  Parasite immunology. 07/1993; 15(6):339-47.

  Production of TNF-alpha and IL-1 by adherent peritoneal exudate macrophages (APEM) was monitored for 20 weeks in Schistosoma mansoni infected mice in comparison to their schistosomulicidal activity.Production of TNF-alpha and IL-1 by adherent peritoneal exudate macrophages (APEM) was monitored for 20 weeks in Schistosoma mansoni infected mice in comparison to their schistosomulicidal activity. LPS-triggered IL-1 and TNF-alpha production by APEM peaked 10 weeks post infection (p.i.) and declined thereafter. The schistosomulicidal activity of APEM also peaked after 10 weeks but remained elevated thereafter. Infected mice were also treated with the immunostimulator liposomal muramyl tripeptide-phosphatidyl ethanolamine (MTP-PE) 6 or 10 weeks p.i., and their APEM were tested 4 weeks later. APEM from such treated animals showed elevated IL-1 and TNF-alpha production when treatment commenced 6 weeks p.i., while their schistosomulicidal activity increased when treatment commenced either 6 or 10 weeks p.i. The L-arginine inhibitor, NG monomethyl arginine, markedly inhibited the schistosomulicidal activity but not the IL-1 and TNF-alpha production of APEM. Our results show that monokine production increases during the acute phase of infection and declines during its chronic phase, while macrophage schistosomulicidal activity remains constant throughout. Furthermore, TNF-alpha or IL-1 may play a minor role in APEM mediated killing of schistosomula.

• A first instance of human philophthalmosis in Israel.

  Authors: Y Lang, Y Weiss, H Garzozi, D Gold, J Lengy

  Journal of helminthology. 07/1993; 67(2):107-11.

  Conjunctivitis due to the trematode Philophthalmus in a 13-year-old Israeli girl is described. A single worm, probably a mature Philophthalmus palpebrarum, was detected on the palpebral conjunctivaConjunctivitis due to the trematode Philophthalmus in a 13-year-old Israeli girl is described. A single worm, probably a mature Philophthalmus palpebrarum, was detected on the palpebral conjunctiva of the upper eyelid of the right eye. Removal of the worm resulted in rapid abatement of the ocular symptoms. This is the first documentation of human philophthalmosis in Israel.

• Trichomonas vaginalis: strain differences in adhesion to plastic and virulence in vitro and in vivo.

  Authors: D Gold

  Parasitology research. 02/1993; 79(4):309-15.

  Trichomonas vaginalis isolated from clinical cases were grown axenically in TYI-S-33 medium. Various strains of this flagellate showed different adhesion characteristics in medium containing bovineTrichomonas vaginalis isolated from clinical cases were grown axenically in TYI-S-33 medium. Various strains of this flagellate showed different adhesion characteristics in medium containing bovine serum or Cohn fractions thereof. These were not inversely related to the time in axenic culture. The adsorption of serum components to the parasites was assessed in relationship to adhesion but in many cases was probably not adhesion-related. All strains tested for virulence in vitro were almost equally cytotoxic for HeLa tissue cultures. However, in infectivity trials, one of these strains exhibited the highest adhesion capability and proved to be the most virulent for mice, and another (cloned) strain with the poorest adhesion capability failed to cause infection. Other strains exhibited lessened virulence following their extended axenic cultivation. It therefore appears that the in vivo pathogenic potential of the parasites growing in axenic culture is inherently strain-dependent. The findings suggest that although adhesion in whole serum-containing medium is sufficient to differentiate between various Trichomonas isolates, it is insufficiently sensitive to correlate adhesion with virulence. It apparently is important to identify the adhesion-mediating factor(s) in serum or in its Cohn fractions IV-1 and IV-4 and to use it (them) to elucidate the possible correlation between the parasite's capacity to adhere and its pathogenicity.

• Philophthalmus species, probably P. palpebrarum, in Israel: description of the eye fluke from experimental infection.

  Authors: D Gold, Y Lang, J Lengy

  Parasitology research. 02/1993; 79(5):372-7.

  Following a recent incident of human philophthalmosis in Israel, the intramolluscan larval trematode fauna in snails randomly collected from the suspected water source was checked. Of the snailsFollowing a recent incident of human philophthalmosis in Israel, the intramolluscan larval trematode fauna in snails randomly collected from the suspected water source was checked. Of the snails examined, only Melanopsis praemorsa shed cercariae, including a Philophthalmus cercaria. To identify the philophthalmid species involved, chicks were experimentally infected with metacercariae of the trematode, subsequently yielding mature trematodes resembling those of P. palpebrarum. The majority of trematodes obtained, whether from one-worm infections or from multiple-worm infections resulting in a single trematode in one of the eyes, were relatively small and showed only immature eggs in their uteri. This finding suggests that the existing descriptions of two species of Philophthalmus purportedly harbouring eggs with non-oculate miracidia, namely P. palpebrarum and P. nyrocae, are actually based on immature specimens from one-worm infections that precluded cross-fertilisation. If this be true, then all species of the genus Philophthalmus produce eggs that, when mature, contain oculate miracidia. The species encountered in Israel is thus most likely P. palpebrarum.

• Human urogenital myiasis due to Eristalis larva: an unusual cause of ureteric obstruction.

  Authors: Z Korzets, J Bernheim, J Lengy, D Gold

  Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association. 02/1993; 8(9):874-6.

• Adhesion of Trichomonas vaginalis to plastic surfaces: requirement for energy and serum constituents.

  Authors: D Gold, I Ofek

  Parasitology. 09/1992; 105 ( Pt 1):55-62.

  The ability of Trichomonas vaginalis to adhere to plastic surfaces in the presence of various agents and under different growth conditions was examined in wells of microtitre plates containingThe ability of Trichomonas vaginalis to adhere to plastic surfaces in the presence of various agents and under different growth conditions was examined in wells of microtitre plates containing unsupplemented TYI medium or the same, with various supplements. Following incubation, the wells were thoroughly washed and adhesion was determined by microscopic counting of the adherent organisms. There was no detectable adhesion in the absence of both serum and carbohydrate. Optimal adhesion (about 10-20% of the total number of parasites) was obtained throughout the growth curve in culture media supplemented with either serum or serum Cohn fractions IV-I (rich in alpha-globulin) or IV-4 (rich in alpha + beta-globulin) and 25 mM glucose, maltose or fructose, but not in plates pre-coated with the Cohn fractions. Cohn fraction II + III (rich in beta + gamma-globulin) moderately enhanced adhesion while Cohn fractions II (rich in gamma-globulin) or V (albumin), fibronectin, Tamm-Horsfall glycoproteins and polylysine were without effect. Non-metabolizable sugars (methyl derivatives of glucose, mannose or fucose) did not support growth, but, surprisingly, enhanced adhesion. At 4 degrees C, the trichomonads were not able to adhere and pre-adherent organisms detached from the plastic surface. Optimal adhesion was obtained at a pH range of 6.5-7.5 but was already detectable at pH 5.5. Cytochalasin E markedly suppressed adhesion.(ABSTRACT TRUNCATED AT 250 WORDS)

• On the interaction between macrophages and developmental stages of Schistosoma mansoni: effect of muramyl tripeptide phosphatidyl ethanolamine (MTP-PE) treatment on mice survival and the generation of schistosomulicidal macrophages.

  Authors: M Seger, D Gold, J Lengy, H Pauli, Y Keisari

  Parasite immunology. 08/1992; 14(4):355-69.

  Schistosomiasis is a chronic disease afflicting hundreds of millions of people throughout the world against which there is as yet no effective vaccine. In the present study we tested the effect ofSchistosomiasis is a chronic disease afflicting hundreds of millions of people throughout the world against which there is as yet no effective vaccine. In the present study we tested the effect of the immunomodulator muramyl tripeptide phosphatidyl ethanolamine (MTP-PE) on the survival of Schistosoma mansoni-infected mice and on the induction in them of schistosomulicidal macrophages. Mice exposed to 80 cercariae each and then treated with MTP-PE showed prolonged survival following either single or repeat infection. The treatment with MTP-PE, when initiated 70 days post the schistosome infection, diminished significantly the mortality of infected mice over an observed period of 110 days. In terms of treatment efficacy there was no evident difference between the intravenous and intraperitoneal mode of administration of the drug. MTP-PE treatment significantly reduced granuloma size and markedly diminished liver damaged as judged by the lower levels of alkaline phosphatase in the serum. Such treatment exerted no significant effect on the spleen or liver weight in infected mice nor on the worm burden resulting from either a single or double infection. In infected and non-treated mice, schistosomulicidal macrophages appeared after 8-10 weeks of infection. In infected mice treated with MTP-PE there was an accelerated appearance of such macrophages and these exhibited a greater cidal effect on the schistosomula. These immunostimulatory and life-prolonging effects of MTP-PE on S. mansoni-infected mice might indicate an effect of this reagent on cells involved in the granulomatous process.

• On the possible schistosomulicidal effect of macrophage-derived lysozyme.

  Authors: E Flescher, Y Keisari, J Lengy, D Gold

  Parasitology. 09/1991; 103 Pt 1:61-4.

  Lysozyme secretion from macrophages of Schistosoma mansoni-infected mice was time dependent, rising significantly from the 8th week post-infection, the macrophages thereafter exhibiting very highLysozyme secretion from macrophages of Schistosoma mansoni-infected mice was time dependent, rising significantly from the 8th week post-infection, the macrophages thereafter exhibiting very high levels (greater than 90%) of schistosomulicidal activity. Despite the ability of lysozyme to kill schistosomula in vitro, the concentrations required for such killing were several hundred-fold to several thousand-fold higher than those detected in the supernatants from infected-mice macrophages cultured with or without schistosomula. An in vitro lysozyme inhibitor, N,N,N-triacetyl chitobiose, did not abrogate the cytotoxic ability of macrophages from schistosome-infected mice, but an inhibitor of arginine-dependent cytotoxicity, NG-monomethyl arginine, markedly inhibited schistosomulicidal activity. Evidently, concentrations of ambient lysozyme from macrophage cultures are too low to affect schistosomula in culture, while the main schistosomulicidal pathway in vitro seems to be arginine dependent.

• The effect of immunosuppressive and immunostimulatory treatment on experimental amoebiasis.

  Authors: D Gold, Y Keisari

  Annals of tropical medicine and parasitology. 01/1991; 84(6):573-80.

  Immunosuppressive treatments consisting of ionizing irradiation or drugs were employed in inbred and outbred mice and in golden hamsters. Following treatment, mice were challenged intracaecally orImmunosuppressive treatments consisting of ionizing irradiation or drugs were employed in inbred and outbred mice and in golden hamsters. Following treatment, mice were challenged intracaecally or intrahepatically with virulent, axenically-grown Entamoeba histolytica. Hamsters were challenged by intraperitoneal injection of the amoebae. Many of the experimental animals died of the combined effects of treatment and challenge. Mice remained essentially refractory to infection with E. histolytica regardless of the immunosuppressive means employed. Liver infection rates in treated and control hamsters were largely similar to one another, i.e. immunosuppressive treatment had no effect on resistance to infection. Our inability to alter the susceptibility of mice and hamsters to amoebic infection by suppressing components of the immune system does not enable us to draw any clearcut conclusions as to the effect of immunosuppression on human amoebiasis. Of the various immunostimulatory materials employed in hamsters, including polysaccharides, BCG and muramyl peptides, only glucan displayed protective capacity against infection with E. histolytica, making it an effective protective agent in an extracellular parasitic infection in addition to its published effectiveness in intracellular protozoal infections. Peritoneal cells extracted from hamsters injected intraperitoneally with E. histolytica seemed capable of reducing the infectivity of virulent amoebae after coincubation in vitro, as shown by reduced infection rates in challenged hamsters. Apparently polymorphonuclear cells, which constituted the vast majority of the extracted cells 24 hours after the stimulatory injection, can, under certain conditions, diminish the infectivity of E. histolytica.

• Delayed-type hypersensitivity to Entamoeba histolytica in mice and hamsters: a comparison.

  Authors: D Gold

  Parasitology research. 02/1989; 75(5):335-42.

  Delayed-type hypersensitivity (DTH) to live or fixed Entamoeba histolytica was induced and compared in mice and hamsters. Peak reactions were obtained 24 h post-challenge. In mice, challenge withDelayed-type hypersensitivity (DTH) to live or fixed Entamoeba histolytica was induced and compared in mice and hamsters. Peak reactions were obtained 24 h post-challenge. In mice, challenge with 10(5) amoebae produced maximal, specific footpad swelling; in hamsters, 5 x 10(4) were required. Elicitation of DTH in mice was strongest 1 week after induction and remained comparatively high for 8 weeks. In hamsters, elicitability declined after 1-2 weeks. Cyclophosphamide increased footpad reactions in mice and hamsters when given 1 day prior to induction but not prior to challenge. Reactions were usually somewhat (but not significantly) stronger in mice than in hamsters, which was also evident from adoptive transfer experiments. Thus, differences in cell-mediated immunity as expressed by DTH in mice and hamsters do not explain the differential susceptibility of these animals to infection with this parasite. In hamsters, multiple footpad injections of live or fixed amoebae lowered the percentage of subsequent liver infections after i.p. injection of virulent amoebae.