The intensity and duration of primary Heligmosomoides polygyrusinfection in TO mice modify acquired immunity to secondary challenge

The effect of dose and duration of immunizing infections of Heligmosomoides polygyrus on protection against homologous challenge was studied in female TO mice. Primary infections were terminated at various levels with pyrantel embonate (adult infections) or ivermectin (larval infections) and mice were then challenged with 500 infective larvae (L3). The level of protection to secondary challenge positively correlated with the intensity of the primary immunizing infection but truncation of larval infection produced significantly better protection than termination of the adult nematode infection. The duration of the primary larval infection (1-6 days) positively correlated with the level of protection to secondary challenge, antibody responses and the proportion of circulating eosinophils. Histological changes in the gastrointestinal tract, peripheral leucocytic changes and antibody responses of the mice to H. polygyrus adult somatic antigens indicate both a cellular and humoral basis of host immunity to secondary challenge. Although the TO mice are slow responders in that they harbour chronic infections, immunization by intramucosal killing of the larval stage produced strong protection against secondary challenge infection. The presence of dead immunogenic larval stages within the intestinal wall may well be an important factor, since it exposes the host to stage specific antigens at an appropriate location. The implications of the findings for the control of gastrointestinal nematode infections are also discussed.     

Immunological differences in Eimeria maxima: effect of a mixed immunizing inoculum on heterologous challenge.

The immunological differences known to exist between laboratory strains of Eimeria maxima was confirmed. Protection against challenge with different strains or field isolates of the species could be achieved by including small numbers (25 oocysts) of each in the immunizing inoculum. Similar protection was obtained when 4 distinct populations which were allowed to interbreed were used in the immunizing inoculum. This hybrid mixture of E. maxima was used to immunize chickens against challenge with 7 new isolates of E. maxima from poultry houses in different parts of England. The results show that although immunological differences exist within E. maxima good protection against many strains of this species may be achieved by initial infection with the hybrid mixture of E. maxima.     

Active and passive immunization of mice against larval Dirofilaria immitis

The objective of this study was to determine if Dirofilaria immitis larvae would survive in diffusion chambers implanted in dogs and mice and secondly to determine if mice could be immunized against infection with D. immitis. Dirofilaria immitis third-stage larvae (L3) survived and grew in diffusion chambers implanted in dogs and mice for at least 3 wk. BALB/c mice, which were repeatedly infected with live L3, showed resistance to challenge infections. Dead L3, with or without adjuvants elicited no protective immunity. A correlation was found between the degree of immune protection seen in mice and antibody levels to soluble larval antigen but not to antibody levels to surface antigens. A monoclonal antibody was prepared that reacted with the surface of D. immitis and Onchocerca lienalis L3, but not to the surfaces of other stages and species of various filarial worms. When this antibody was administered to mice prior to challenge no significant reduction in larval survival was observed.     

Histopathological and parasitological evidence of immunization of mice against challenge with 17 wild isolates of Trypanosoma cruzi

The possibility of preventing chronic infection by a battery of 17 wild isolates of Trypanosoma cruzi was studied in Swiss mice preimmunized with culture forms of an attenuated strain (TCC). Mice were challenged intradermally with low numbers of wild trypomastigotes obtained from naturally infected insect vectors captured within a 57,000 km² subtropical area in northern Argentina and which had not undergone any laboratory propagation. A significant degree of protection was observed in all cases, according to one or more parameters. Immunization reduced the level of parasitemia (P < 0.05) in infections caused by 4 out of 13 isolates, as evaluated by microscope counts performed on fresh blood mounts and in 10 out of 15 isolates as evaluated by xenodiagnosis. A lesser degree of histopathology (P < 0.05) was detected in the heart (7 out of 17 isolates), urinary bladder (10 out of 17 isolates) and skeletal muscle (10 out of 17 isolates). None of these parameters reflected infection or pathology in TCC-immunized, non-challenged mice. While antigenic variation frustrates vaccination against African trypanosomes, the effective protection shown here against 17 T. cruzi primary isolates indicates lack of antigenic variation and thus the possibility of effective vaccination in Chagas' disease.     

Isolates of Candida albicans that differ in virulence for mice elicit strain-specific antibody-mediated protective responses

Three distinct isolates of Candida albicans were used to establish systemic and oral infections in inbred mice that are genetically resistant or susceptible to tissue damage. Patterns of infection differed significantly between both yeasts and mouse strains. Systemic infection conferred significant protection against re-challenge with the homologous, but not the heterologous yeast; however, the protective effect was more evident in the tissue-susceptible CBA/CaH mice than in the resistant BALB/c strain. In contrast, oral infection induced protection against both homologous and heterologous oral challenge, although this was significant only in the CBA/CaH mice. CBA/CaH mice produced antibodies of both IgG1 and IgG2a subclasses, whereas BALB/c mice produced predominantly IgG1. Western blotting demonstrated considerable differences between epitopes recognised by serum antibodies from mice of both strains after immunisation with each of the three yeasts. Thus, different strains of yeast show considerable specificity in antibody responses elicited by either systemic or oral infection.     

Molecular and phenotypic characterisation of Bacillus thuringiensis isolated during epizootics in Cydia pomonella L

Twelve Bacillus thuringiensis strains were isolated from intestinal tracts of Cydia pomonella larvae during epizootics in different laboratory insect culture lines. Phenotypic and genetic similarity of these isolates, together with two cultured from Leucoma salicis larvae and 14 reference B. thuringiensis strains were determined. The epizootic bacteria did not form a single group based on numerical analysis of biochemical properties. Simple RAPD method with only one primer does not allow estimating the genetic similarity of B. thuringiensis strains. We propose a novel strategy based on combining several DNA patterns obtained by RAPD technique with different primers for B. thuringiensis typing. Majority of infections in the C. pomonella culture lines were caused by bacteria with different genotypes. However, two isolates cultured from infected insects at different time (one strain was isolated in 1990 and the other in 1992) had identical DNA fingerprint that suggested a possibility of these bacteria to survive in the laboratory and to cause infections in different years. The results of SDS-PAGE of whole-cell proteins revealed a possibility to apply protein profile analysis in epidemiological investigations of infections caused by B. thuringiensis. Strains with identical DNA patterns had very similar whole-cell protein profiles.     

Efficacy of UV-irradiated larval vaccine of Ancylostoma ceylanicum (Looss, 1911) in golden hamsters (Mesocricetus auratus)

A vaccination trial in golden hamsters with UV-irradiated infective larvae of Ancylostoma ceylanicum was attempted. One oral vaccination of hamsters with 100 infective larvae irradiated by means of UV-tube (390 nm) at different time intervals induced the development of resistance. As the time exposure of irradiation was increased, there was a corresponding decrease in the subsequent worm establishment. A high level of protection afforded by larvae irradiated for 15 min UV-exposure was recorded giving 99.0% and 95.0% worm reduction against the challenge doses of 100 and 1000 normal larvae respectively. There was no marked difference in worm establishment in hamsters vaccinated either orally or subcutaneously, followed by oral challenge. In the vaccinated hamsters, the manifestations of resistance at 15 min UV-exposure were shown by marked reduction in worm establishment and highly reduced epg in pellets with significantly higher blood haemoglobin levels compared with those given normal larvae as vaccine and challenge controls.     

Characterization of the major immunogen in the excretory-secretory products of exsheathed third-stage larvae of Trichostrongylus colubriformis

The excretory-secretory products of exsheathed third-stage larvae of Trichostrongylus colubriformis conferred some protection to guinea pigs against homologous challenge. A glycoprotein with an apparent molecular mass of approximately 94 kDa was the dominant immunogen in post-exsheathment products. Immunoblots revealed IgG antibodies to this glycoprotein in sera from multiply-infected guinea pigs and some sheep, and in sera of guinea pigs after three truncated infections which had been restricted by anthelmintic treatments to development of the third parasitic stage. IgA antibodies to this protein were also found in intestinal lymph of a naturally infected sheep. Fluorescent antibody studies indicated that this 94 kDa component was associated with cells in the central body cavity of third-stage larvae, but was absent from fourth-stage larvae or adult worms. Fractionation and protection assays in guinea pigs revealed that while the native and aggregated 94 kDa protein conferred some host protection, it was not the only protective component of the excretory-secretory products of exsheathed third-stage larvae of T. colubriformis.     

Acquired immunity in rats against Angiostrongylus cantonensis infection

Acquired immunity against Angiostrongylus cantonensis was induced by immunizing rats with somatic antigens from fifth-stage larvae and adult worms and live third-stage larvae. Rats immunized twice had significantly fewer worms than rats immunized three times. Fewer worms were recovered from rats immunized with 200 live third-stage larvae than from any other groups. Rats immunized with somatic antigens had higher enzyme-linked immunosorbent assay (ELISA) antibody levels than rats immunized with live larvae. Rats immunized with live third-stage larvae of Angiostrongylus cantonensis were more strongly protected against challenge infections (62-92%) than rats immunized with antigens extracted from fifth-stage larvae (0-30%) and adult worms (11-24%).     

Vaccination against the nematode Trichostrongylus colubriformis. I. Vaccination of guinea-pigs with worm homogenates and soluble products released during in vitro maintenance

Vaccination of guineapigs with homogenates of fourth larval stage and adult Trichostrongylus colubriformis and soluble products released by fourth stage larvae during in vitro maintenance, induced a high level of protection against challenge infection with the parasite.     

Herpes Simplex Virus Inhibits Apoptosis through the Action of Two Genes, Us5 and Us3

Apoptosis of virus-infected cells occurs either as a direct response to viral infection or upon recognition of infection by the host immune response. Apoptosis reduces production of new virus from these cells, and therefore viruses have evolved inhibitory mechanisms. We previously showed that laboratory strains of herpes simplex virus type 1 (HSV-1) protect infected cells from apoptosis induced by cytotoxic T lymphocytes or ethanol. We have now evaluated the ability of HSV-1 and HSV-2 laboratory and clinical isolates to inhibit apoptosis induced by anti-Fas antibody or UV irradiation and explored the genetic basis for this inhibition. HSV-1 isolates inhibited apoptosis induced by UV or anti-Fas antibody. In contrast, HSV-2 clinical isolates failed to inhibit apoptosis induced by either stimulus, although the HSV-2 laboratory strain 333 had a partial inhibitory effect on UV-induced apoptosis. Inhibition of apoptosis by HSV was accompanied by marked reduction of caspase-3 and caspase-8 activity. Deletion of the HSV-1 Us3 gene markedly reduced inhibition of UV-induced apoptosis and partially abrogated inhibition of Fas-mediated apoptosis. Conversely, deletion of the HSV-1 Us5 gene markedly reduced protection from Fas-mediated apoptosis and partially abrogated protection from UV. The Us11 and Us12 genes were not necessary for protection from apoptosis induced by either stimulus. The differences between HSV-1 and HSV-2 in the ability to inhibit apoptosis may be factors in the immunobiology of HSV infections.     

Protection against systemic infections with various Candida species elicited by vaccination with Candida albicans ribosomes

This study investigated whether subcutaneous vaccination of mice with ribosomes from Candida albicans strain CBS 562 would also provide protection against infections by other isolates of Candida. Experiments with a total of 628 mice demonstrated that vaccination induced significant protection against heterologous C. albicans (serotypes A and B) and C. tropicalis isolates in terms of their 30 day survival rates. In all instances, however, protection was lower than that obtained against the homologous strain. In addition, a significant decrease in fungal colonization of the kidneys was found in immunized animals as compared to the non immunized controls. Cell-mediated immune responses against cytoplasmic extracts of the various fungi, as detected in vivo by the foot pad swelling test and in vitro by the lymphocyte transformation assay, were induced by the C. albicans ribosomal vaccination. The results show it is possible to induce cross protection to various Candida species by immunization with C. albicans ribosomes.     

Trichinella spiralis: mediation of the intestinal component of protective immunity in the rat by multiple, phase-specific, antiparasitic responses.

Rats infected orally with Trichinella spiralis developed an immunity that was induced by and expressed against separate phases of the parasite's enteral life cycle. Infectious muscle larvae generated an immune response (rapid expulsion) that was directed against the very early intestinal infection and resulted in the expulsion of worms within 24 hr. This response eliminated more than 95% of worms in an oral challenge inoculum. Developing larvae (preadults) also induced an immune response that was expressed against adult worms. The effect on adults was dependent upon continuous exposure of worms to the immune environment throughout their enteral larval development. Immunity induced by preadult T. spiralis was not expressed against adult worms transferred from nonimmune rats. While adult worms were resistant to the immunity engendered by preadults they induced an efficient immunity that was autospecific. Both “preadult” and “adult” immunities were expressed in depression of worm fecundity as well as in the expulsion of adults from the gut. However, the two reactions differed in respect to their kinetics and their efficiency against various worm burdens. Preadult immunity was directed mainly against fecundity whereas adult immunity favored worm expulsion. All responses (rapid expulsion, preadult and adult immunity, and antifecundity) acted synergistically to produce sterile immunity against challenge infections of up to 5000 muscle larvae. These findings indicate that the host protective response to T. spiralis is a complex, multifactorial process that operates sequentially and synergistically to protect the host against reinfection.     

The role of immunologically specific and non-specific components of resistance in cross-protection to intestinal nematodes

Vaccination of 6–8-month-old Merino sheep with irradiated Trichostrongylus colubriformis larvae gave a high level of protection (81 %) against single-species challenge with normal infective larvae of the same species. The level of protection (34%) was substantially reduced against challenge with a closely related species (T. vitrinus) and no significant protection occurred against single-species challenge with a generically unrelated nematode (Nematodirus spathiger). These results suggest that antigen(s) which stimulate protective immunity are shared by the related Trichostrongylus species but not by N. spathiger. By contrast with the results obtained for single-species challenge, vaccination with irradiated T. colubriformis produced 98–100% protection against all 3 species in animals challenged simultaneously with infective larvae of the 3 species. Comparison of the levels of protection recorded following the 2 types of challenge indicate that although a specific antigenic trigger is required to provoke an appropriate response, the results obtained, particularly in the case of N. spathiger, suggest that the terminal effector mechanism is not immunologically specific. The implications of these conclusions are discussed in relation to theories of the mechanism of resistance to gastrointestinal nematodes and the potential efficacy of vaccination in the field.     

Observations on the self-cure reaction and other forms of immunological responsiveness against Haemonchus contortus in sheep

Self-cure reactions and immunological responses preventing establishment of Haemonchus contortus in sheep may operate as separate entities. In one experiment, self-cure occurred when challenge infection with 5000 larvae was superimposed on an infection with 5000 larvae given to worm-free sheep 6 weeks previously. Resident worms were rejected and establishment of infection by incoming larvae was impeded. The latter effect was not observed in sheep treated similarly but with resident parasites removed by treatment with oxfendazole before challenge. In another experiment, younger worm-free sheep primed by three infections with 2000 larvae at intervals of 2 weeks or a single infection with 6000 larvae were challenged with 10,000 larvae 6 weeks after the first priming infection. Self-cure was not incited but establishment of infection was impeded in sheep primed with three divided doses of larvae whether or not priming infections had been removed by oxfendazole. Infection regimes used for priming did not influence numbers of arrested fourth-stage larvae derived from challenge infection. However, more arrested larvae were present when challenge was superimposed on extant infections, indicating that resident worms or a factor activated by their presence induced developmental arrest. In a third experiment, large burdens with H. contortus were established in sheep immunosuppressed with the corticosteroid, dexamethasone, at the time of infection. Self-cure was not triggered by a challenge infection given 32 days later either in these sheep, or in sheep with a smaller worm burden derived from infection given without immunosuppression. Faecal egg counts, however, indicated that development of the challenge infection was prevented in both groups of sheep.

Investigation of self-cure is restricted by lack of a predictable system for reproducing the phenomenon. Self-cure was induced by a single infection with 5000 larvae in mature sheep but not with 6000 larvae in immature sheep. Three infections with 3000 larvae given at intervals of 2 weeks to mature sheep did not prime for self-cure. Procedures aimed at heightening immediate hypersensitivity, i.e. treatment with pertussis vaccine or concurrent infections with Ostertagia circumcincta, did not promote self-cure reactivity in the latter situation.     

Efficacy of Bacillus thuringiensis against Lesser Grain Borer, Rhyzopertha dominica (Coleoptera: Bostrichidae)

Toxins from 36 isolates, representative of all available subspecies of Bacillus thuringiensis, were tested against larvae and adults of the lesser grain borer, Rhyzopertha dominica. beta -Exotoxin was effective against both larvae and adults. Spore-crystal complexes of subspecies darmstadiensis isolates from Germany were effective against larvae. Isolates of subspecies darmstadiensis from the US and Japan were not effective. The degree of control achieved by even the best isolate was not economically satisfactory.     

Competition and reproduction in mixed infections of pathogenic and non-pathogenic Bacillus spp

Diamondback moth, Plutella xylostella, larvae were infected with a primary pathogen, Bacillus thuringiensis kurstaki (Btk) in single strain and mixed infections. Mixed infections comprised Btk and a non-pathogenic isolate, either Bacillus thuringiensis tenebrionis (Btt) or Bacillus cereus (Bc). All strains reproduced in larval cadavers, but there was evidence of competition between different isolates within hosts. Non-pathogenic isolates (Btt, Bc) had growth rates that were faster than Btk in vivo, whereas Btk outcompeted Btt in vitro. Passage through insects increased the in vitro competitive ability of Btk against Btt.     

Trichinella spiralis: immunization of pigs with newborn larval antigens

The potential of crude Trichinella spiralis newborn larval antigens for pig immunization was investigated. A preparation of whole newborn larvae killed by freezing and thawing, and combined with Freund's complete adjuvant, induced a high level of protection against challenge (78%), compared to a 40% resistance level in pigs immunized with excretory secretory antigens of muscle larvae. Sera from pigs immunized with newborn larvae contained antibodies which bound to the surface of the newborn larvae, as determined by immunofluorescence. In a second trial, the freeze thawed newborn larvae preparation was compared with a soluble and insoluble fraction prepared by sonication of whole newborn larvae. Pigs receiving whole newborn larvae or the insoluble fraction developed strong immunity to challenge (88.2 and 85.5%, respectively); the soluble fraction was ineffective. Immunization with all preparations induced antibody to newborn larval antigens, but not to adult or muscle larvae excretory secretory antigens. Polyacrylamide gel electrophoresis of the soluble and insoluble fractions indicated that sonication was ineffective in solubilizing the larger molecular weight components. These results demonstrate that newborn larval antigens are highly protective in pigs, but that their further development as a vaccine will require more efficient procedures for antigen solubilization and large-scale production.     

Suppression of multiclade R5 and X4 human immunodeficiency virus type-1 infections by a coreceptor-based anti-HIV strategy

A cyclic chimeric dodecapeptide (cCD) mimicking the conformation-specific domains of CCR5 and CXCR4 was prepared in which Gly-Asp links the amino and carboxyl termini of two combined pentapeptides (S169-G173 of CCR5; E179-R183 of CXCR4) derived from human immunodeficiency virus type-1 (HIV-1) coreceptors. The immunization of Balb/c mice with cCD conjugated with a multiple-antigen peptide (cCD-MAP) induced seven cCD-specific monoclonal antibodies (mAbs, CPMAb-I to -VII) that reacted with native CCR5 and CXCR4. Among the tested mAbs, CPMAb-I and -II potently inhibited the infection of both the R5 and X4 laboratory strains. CPMAb-III and -VI were effective against only R5 laboratory strains, and also against some X4 and R5 primary isolates. CPMAb-IV and -V had potent antiviral activities against the R5 and X4 primary isolates. In particular, CPMAb-VII was protective against not only R5 and X4 laboratory strains, but also most of the R5 and X4 primary isolates. Moreover, cCD-MAP immunization also induced antibodies that were effective against R5 and X4 multiclade HIV-1 isolates in vitro in two of three cynomolgus monkeys. Taken together, the results suggest that cCD-MAP is a candidate multiclade immunogen that can be used to block multiclade R5 and X4 HIV-1 infections.     

Outer membranes of a lipopolysaccharide-protein complex (LPS-17 kDa protein) as chemical tularemia vaccines

Abstract Immunisation with outer membranes of Francisella tularensis induced an efficient protection in guinea pigs against challenge with the virulent strains 503 or 144/713 (type B biovar holarctica ), both clinical isolates, and prevented the development of typical signs of infection in hamadryads (baboons), challenged with the virulent strain Schu (type A, biovar tularensis ) of F. tularensis . Immunisation with a lipopolysaccharide protein complex isolated from the outer membranes afforded protection in CBA mice against challenge with strain 503. Another LPS-protein complex obtained by the simple mixture of LPS preparations from strain 503 and a 17-kDa membrane protein from the avirulent R-variant of the vaccine strain 15 also demonstrated protective properties against experimental tularemia in mice.