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F A Lewis

Publications and source records attributed to F A Lewis.

At least 91 records · Page 5Linked to original sources
PubMed1986

Large-scale laboratory maintenance of Schistosoma mansoni, with observations on three schistosome/snail host combinations.

This review discusses the large-scale laboratory maintenance of Schistosoma mansoni. Emphasized are features which increase efficiency in such facilities, and problems most frequently encountered. Profiles are given of the long-term, high-level production of 3 strains of S. mansoni. Two of the strains, NMRI and PR-1, were of Puerto Rican origin and the other, LE, was from Brazil. Three to 8 million cercariae of each strain were usually obtained per week. The most obvious differences between the 3 strains were cercarial output per snail and snail mortality rates. Maintenance problems encountered were usually related to water quality, temperature, genetics of the parasite or snail host, predators or contaminants, feeding, or crowding of snails. Examination of the production data from these 3 life cycles led to identification of features that could be of benefit for increasing the productivity and efficiency of other S. mansoni life cycles used in research activities.

Animals↗
PubMed1985

Effect of a cryopreserved live vaccine on resistance in mice with a pre-existing Schistosoma mansoni infection.

Experiments were conducted to determine the effect of anti-schistosomal vaccine exposure on the level of pre-existing resistance in mice with a bisexual Schistosoma mansoni infection. C57BL/6 mice with light S. mansoni infections of 8 weeks duration were injected with 10 Krad-irradiated, cryopreserved and thawed schistosomules. Four weeks later the mice were exposed to normal cercariae, and adult worms collected by perfusion 6 weeks post-challenge. In 4 experiments, the baseline levels of resistance in infected mice ranged from 19% to 50% reduction in challenge worm burden (mean of 36%). Although vaccine administration slightly raised the overall level of resistance in infected mice (mean of 49%), in only 1 experiment was the increase over that in infected mice statistically significant. The levels of resistance attributed to the patent infection and vaccine exposure were not additive. Vaccine exposure had no effect on recovery of the adult worms of the primary infection.

Animals↗
PubMed1985

Evidence against the existence of specific Schistosoma mansoni subpopulations which are resistant to irradiated vaccine-induced immunity.

When mice are immunized with irradiated Schistosoma mansoni cercariae a proportion of the subsequent cercarial challenge always escapes killing and matures to egg-laying adults. This report investigates the possibility that incomplete immunity in this system is governed by a genetically-determined insusceptibility of a particular schistosome subpopulation. To do this we tested whether more immunoresistant schistosomes would develop following successive passages of progeny of the resistant worms through immunized mice. Mice were immunized with 500 50 Krad-irradiated cercariae, and challenged with normal cercariae when immunity was at its peak. After five successive passages through snails and immune mice, progeny of those parasites which escaped immune killing were no more refractory to vaccine-induced resistance than the original stock maintained in nonimmune mice. Additionally, the "passaged" isolates did not differ from the original stock in their ability to induce protection following irradiation. Our results indicate that with this model of acquired resistance incomplete immunity is unlikely to be due to a subpopulation of the parasites possessing a genetically-determined insusceptibility to killing.

Animals↗
PubMed1984

The arrangement of ribosomal RNA genes in Schistosoma mansoni. Identification of polymorphic structural variants.

The two large ribsomal RNA subunits of Schistosoma mansoni are encoded within a 10 000-base sequence, which is tandemly repeated in the schistosome genome. Restriction endonuclease digestion with Bam HI cuts the rRNA gene into three fragments, which have been clones separately in pBR322 and used to constract a physical map of the gene. The sequence encoding the smaller rRNA subunit is about 2000 bases in length and is situated on the 5' sie of the sequence encoding the larger subunit, which is about 4000 bases. Approximately 4000 bases of the rRNA gene are spacer and do not code for mature rRNA. There are approximately 100 copies of the rRNA gene per haploid genome of which about 10% exhibit length heterogeneity, as judged by the hybridization of the rDNA plasmids to restriction endonuclease digests of genomic DNA. These structural variants appear to contain additional DNA sequences at more than one site within the gene and are polymorphic within the species S. mansoni.

Base Sequence↗
PubMed1984

Schistosoma mansoni: vaccination of mice with 10-krad-irradiated, cryopreserved schistosomules.

Protection against a Schistosoma mansoni cercarial challenge was evaluated in mice immunized with a vaccine composed of 10-krad-irradiated, cryopreserved schistosomules. The level of resistance induced in C57B1/6 or NMRI (CV) mice increased with the number of schistosomules injected. Up to 83% reduction in challenge worm burden was achieved when 5000 schistosomules were injected per mouse. Intramuscular injection of the vaccine was superior to subcutaneous. Multiple immunizations, up to 3 at 4-week intervals, did not increase the resistance induced by a single immunization. A high level of protection developed in as little as 2 weeks and was maintained through at least 12 weeks postimmunization. The vaccine irradiated with 10 krad from either a 60-cobalt or 137-cesium source induced equivalent levels of resistance, and no differences were found in the immunogenicity of vaccines comprised of organisms irradiated as cercariae or as 1- to 3-hr-old schistosomules. These findings are basic to the development of a cryopreserved, live vaccine against schistosomiasis of humans or domestic animals.

Animals↗
PubMed1984

Schistosoma mansoni egg granuloma size reduction in challenged baboons after vaccination with irradiated cryopreserved schistosomula.

Young male baboons born in captivity were immunized with an attenuated, cryopreserved schistosomular vaccine derived from gamma-irradiated (50 krad) cercariae of the Puerto Rican strain of Schistosoma mansoni. Protection against a heterologous Kenyan strain of S. mansoni, after percutaneous infection, was assessed. Partial protection (33-53% reduction in worm burden) was obtained in three of six vaccinated-challenged baboons, an unremarkable result. Of greater interest was the fact that all six unvaccinated-challenged control baboons, but only one of the six vaccinated-challenged baboons, had macroscopic egg granulomas on their liver surfaces. This difference in granuloma size was substantiated by measuring hepatic and colonic granulomas. The mean (+/- SEM) hepatic and colonic granuloma diameters for the six unvaccinated baboons were 406 +/- 38 micron and 313 +/- 27 micron, respectively, and for the five "typical" vaccinated-challenged baboons the mean diameters were 283 +/- 27 micron and 202 +/- 23 micron, respectively. Both hepatic and colonic granulomas were significantly smaller in the five typical vaccinated-challenged baboons. Not only did the exceptional vaccinated-challenged baboon have very large hepatic and colonic granulomas, but also it was the only one of its group whose mesenteric lymph node cells were not suppressed in their in vitro proliferative response to a schistosome antigen. These results strongly suggest that granuloma size reduction in the majority of the vaccinated baboons was the result of immunoregulation--i.e., the small postvaccination granulomas were "modulated." Despite their small size, hepatic granulomas in the typical vaccinated baboons were apparently as effective in sequestering egg toxins and preventing hepatocyte damage as the larger granulomas of the control baboons. Smaller, less obstructive granulomas are thought to be more beneficial to the host than large, vigorous granulomas, with respect to lessening chronic disease. The present results give encouragement that a vaccine to ameliorate disease in human schistosomiasis is possible. This effect should add to the attractiveness of partial protection against challenge infections conferred by attenuated larval vaccines, as reported by others, to yield a dually beneficial vaccine for human use.

Animals↗
PubMed1984

Cryopreservation of schistosomules of Schistosoma mansoni in quantity.

Large quantities of Schistosoma mansoni schistosomules were cryopreserved in 35% ethanediol, and attempts were made to improve their morphology and infectivity after thawing. Several variables affected the appearance of the thawed organisms. These included: 1) the particular in vitro method used to transform cercariae to schistosomules; 2) addition of serotonin to the thawing medium; 3) changing the thawing temperature; and 4) culturing schistosomules for extended post-thaw times before assessing their condition. Varying either the postemergence age of the cercariae before transformation or the concentration of organisms in the freezing suspension had no effect on their survival. Although damage to many of the thawed schistosomules became apparent only upon extended in vitro cultivation, the addition of fetal calf serum to the thawing medium usually retarded this deterioration. When injected into mice, approximately 5% of cryopreserved schistosomules matured to adult worms, representing 71% of the value for maturation of unfrozen schistosomules. These studies define conditions of importance for the successful preservation of very large quantities of schistosomules (up to 500,000 in 1 ml volume) in liquid nitrogen.

Animals↗
PubMed1984

Schistosoma mansoni: radiation dose and morphologic integrity of schistosomules as factors for an effective cryopreserved live vaccine.

The effectiveness of a cryopreserved, irradiated schistosomule vaccine against an homologous Schistosoma mansoni cercarial challenge was tested in C57B1/6 mice. Highly significant levels of protection developed consistently when mice were immunized with the vaccine irradiated at 10-20 Krad, i.e., doses below that considered optimal for irradiated cercariae (50 Krad). Cryopreserved schistosomules irradiated at 10 or 20 Krad induced greater levels of protection than did schistosomules irradiated at 2, 5, 30, or 50 Krad. Protective immunity developed as early as 3 weeks post-immunization. When immunizing inocula were injected at various times post-thaw, or when schistosomule subpopulations of normal-appearing, damaged or dead organisms were injected, those populations which had appeared to sustain the least degree of damage were those most capable of stimulating protective immunity. These findings highlight the hazards of extrapolating conditions considered standard for an irradiated cercarial vaccine to one in which cryopreservation, for storage of the schistosomules, is an added stress.

Animals↗
PubMed1983

Pathology of a live attenuated anti-schistosome vaccine in mice.

Tissue responses of mice to intramuscular injection of 50 kR 60Co-attenuated schistosomula of Schistosoma mansoni were studied. Controls included injection of unattenuated schistosomula, medium alone, antigen-coated beads, and alum-adsorbed tetanus/diphtheria toxoids. Primary reactions to tissue-confined deposits of injected schistosomula, whether attenuated or not, were relatively intense and prolonged. Parasite attrition proceeded steadily, with most destroyed by the 7th day; however, a few intact organisms persisted up to 4 weeks. Cryopreservation did not alter the course of parasite attrition nor host reaction. Irradiated larvae were not found in lymph nodes, lungs, or liver. Neutrophils dominated the early reactions and were gradually replaced by mononuclear phagocytes, lymphoid cells, and eosinophils. Fibroblast proliferation and muscle regeneration began by day 3; reaction size and intensity peaked by day 7. From weeks 1-4, inflammatory infiltrates and regenerative proliferation underwent gradual involution, and injection sites were healed with no scarring by the end of 4-5 weeks. Mice primed by infection or by prior injection showed an accelerated course of inflammation, enhanced tissue eosinophilia, and more rapid healing. An unwanted, but prominent, feature of schistosomular vaccine reactions in mice was tracking of the inflammatory infiltrate along connective tissue septal and nerve sheaths, the latter raising the question of the pain potential of the vaccine. To conclude, in mice, attenuated schistosomular vaccines cause relatively marked local inflammatory responses but no systemic lesions at all, and their injection sites heal without permanent damage.

Animals↗
PubMed1982

Regional and splenic lymphocyte proliferative responses of mice exposed to normal or irradiated Schistosoma mansoni cercariae.

Developing larvae of Schistosoma mansoni migrate through various tissues en route to the liver and mesenteric veins of their definitive host. Regional (lymph node) and systemic (spleen) blastogenic responses to cercarial, adult and egg antigens were measured in CBA/J mice at various times after exposure to normal or irradiated S. mansoni cercariae. Among the separate lymph node groups studied were those draining the tail, thoracic region, intestines, head and neck, and the pelvis. Blastogenic responses were assayed by a micromethod requiring 10(5) cells in 20 microliter volumes per culture. Up to 5 weeks post-cercarial exposure the pattern of responses in lymphoid tissues of infected mice coincided with the migratory route of the parasites. Following oviposition, cellular reactivity was pronounced in all lymph node groups. The reactivity of mice exposed to irradiated cercariae followed a pattern suggestive of a sustained antigenic stimulus only in the nodes draining the tail and lungs. Splenic (systemic) reactivity was roughly comparable between the two exposure groups. These data show the independence and vast differences in the host regional responses following normal or irradiated cercarial exposure.

Animals↗
PubMed1981

Strain differences in lymphocyte responses and in vitro suppressor cell induction between Schistosoma mansoni-infected C57BL/6 and CBA mice.

Splenic lymphocyte blastogenic responses to mitogens and antigens were compared in Schistosoma mansoni-infected C57BL/6 and CBA mice. At 1 and 2 weeks of infection, elevated responses to phytohemagglutinin (PHA) were noted in C57BL/6, but not in CBA cultures. During the same period, elevated responses to lipopolysaccharide were observed in cultures from CBA, but not from C57BL/6 mice. Responses to both mitogens were depressed in both strains later in infection. The magnitude of antigen-specific responses was greater in CBA than in C57BL/6 cultures. A cercarial extract (CE) induced significant suppressor cell activity in normal C57BL/6 cell cultures as assessed by inhibition of syngeneic cell responsiveness to PHA. CE did not induce suppressive activity in CBA cultures. CE-induced suppression was unaffected by adherent cell removal, but was sensitive to anti-Thy 1.2 plus complement treatment. CE also directly inhibited PHA-stimulated C57BL/6 cell cultures, but enhanced cultures of CBA mice. The significance of these findings is discussed in relation to the relative strain differences seen in antigen-specific lymphocyte proliferation and the levels of protection induced after immunization with irradiated cercariae.

Animals↗
PubMed1980

Studies on the degradation of HeLa non-histone proteins.

The hydrolysis of HeLa non-histone nuclear proteins over 24 h has been monitored in dilute alkali at 4, 15 and 25 degrees C using the standard ninhydrin estimation, dansylation and various electrophoresis techniques. Under conditions (up to 0.2 N NaOH, 4 degrees C) that do not release a significant quantity of ninhydrin-positive material or new N-terminal end group considerable breakdown was observed by two-dimensional electrophoresis analysis. The number of stained spots decreased from approx. 140 to 25--30. No internal protease activity could be found. Labelling studies (14C-labelled amino acids) showed that much of the hydrolysed material was extracted from the gel during normal staining and destaining procedures. Peptides could be extracted from alkali-hydrolysed non-histone protein with acid/ethanol and could be further separated by thin-layer chromatography on silica gel G. Short-term labelling of HeLa cells (14C-labelled amino acids for up to 60 min) revealed that these peptides probably have a high rate of turnover. [14C]Glucosamine studies also indicated the presence of considerable carbohydrate material in the low molecular weight products of this alkaline hydrolysis. Various standard proteins and histones were unaffected by hydrolysis in up to 0.2 N NaOH (4 degrees C, 24 h) as judged by gel electrophoresis. Seven different phosphate-splitting enzymes and an esterase had no effect on the non-histone protein electrophoresis patterns but a preparation of phospholipase C which had no protease activity towards eight standard proteins did produce considerable breakdown in HeLa non-histone proteins similar to that produced by 0.2 N NaOH at 4 degrees C.

Acids↗
PubMed1980

Natural killer cells (NK) and antibody-dependent cell-mediated cytotoxicity (ADCC) components of Schistosoma mansoni infection.

Schistosoma mansoni cercariae were used to infect CBA-J mice, a strain characterized by possessing a high level of NK cells. 4 days after infection with cercariae, the natural cytotoxic capacity of these mice, as measured by NK and ADCC, reached a peak level of enhancement significantly greater than that of uninfected controls. Infection by this parasite appears to activate natural cell-mediated immune defense systems. Further observation of the pattern of response of NK and ADCC effector cells to infection by cercariae may reveal important information regarding the inherent immunity to the schistosome infection.

Animals↗
PubMed1980

Cercaria-induced histamine release: a factor in the pathogenesis of schistosome dermatitis?

Cercariae, but not schistosomules, of Schistosoma mansoni are capable of activating the release of histamine from rat peritoneal mast cells in vitro. This activation occurs in the absence of serum and does not require adherence to mast cells. The amount of histamine released is proportional to the number of cercariae present. This mast-cell triggering factor from cercariae remains to be characterized biochemically, but may well play a causal role in the "swimmer's itch" associated with primary schistosome exposure.

Animals↗