Protecting effect of PrP codons M142 and K222 in goats orally challenged with bovine spongiform encephalopathy prions

Breeding towards genetic resistance to prion disease is effective in eliminating scrapie. In sheep, classical forms of scrapie have been eradicated almost completely in several countries by breeding programs using a prion protein (PrP) gene (PRNP) amino acid polymorphism. For goats, field and experimental studies have provided evidence for several amino acid polymorphisms that are associated with resistance to scrapie, but only limited data are available concerning the susceptibility of caprine PRNP genotypes to BSE. In this study, goat kids representing five PRNP genotypes based on three polymorphisms (M142, Q211 and K222 and the wild type I142, R211 and Q222) were orally challenged with bovine or goat BSE. Wild type goats were killed with clinical signs between 24-28 months post inoculation (mpi) to both challenges, and goats with genotype R/Q211 succumbed between 29-36 mpi. I/M142 goats developed clinical signs at 44-45 mpi and M/M142 goats remained healthy until euthanasia at 48 mpi. None of the Q/K222 goats showed definite clinical signs. Taken together the highest attack ratios were seen in wild type and R/Q211 goats, and the lowest in I/M142, M/M142 and Q/K222. In all genotype groups, one or more goats remained healthy within the incubation period in both challenges and without detectable PrP deposition in the tissues. Our data show that both the K222 and M142 polymorphisms lengthen the incubation period significantly compared to wild type animals, but only K222 was associated with a significant increase in resistance to BSE infection after oral exposure to both BSE sources.

Protective effect of the T112 PrP variant in sheep challenged with bovine spongiform encephalopathy

Sheep with an ARQ/ARQ PRNP genotype at codon positions 136/154/171 are highly susceptible to experimental infection with bovine spongiform encephalopathy (BSE). However, a number of sheep challenged orally or intracerebrally with BSE were clinically asymptomatic and found to survive or were diagnosed as BSE-negative when culled. Sequencing of the full PRNP gene open reading frame of BSE-susceptible and -resistant sheep indicated that, in the majority of Suffolk sheep, resistance was associated with an M112T PRNP variant (TARQ allele). A high proportion (47 of 49; 96%) of BSE-challenged wild-type (MARQ/MARQ) Suffolk sheep were BSE-infected, whereas none of the 20 sheep with at least one TARQ allele succumbed to BSE. Thirteen TARQ-carrying sheep challenged with BSE are still alive and some have survival periods equivalent to, or greater than, reported incubation periods of BSE in ARR/ARR and VRQ/VRQ sheep.

Scavenger, transducer, RNA chaperone? What ligands of the prion protein teach us about its function

Prion protein, a misfolded isoform of which is the essential component of the agent of prion diseases, still remains an enigmatic protein whose physiological functions are at best hypothetical. To gain a better insight into its putative role, many studies were undertaken to look for molecules that bind prion protein, and have notably identified divalent metal ions, several proteins, and nucleic acids. At first sight, the diversity of prion protein's ligands seems of little help to infer a plausible function. However, the intrinsically disordered property of its N-terminal tail and the potential of the protein to adopt a transmembrane topology, can both be taken into account to predict its different states during its cellular cycle and its possible functions, of which the most promising correspond to a general scavenger, a sensor or adaptor in a signaling cascade, and an RNA chaperone.

Fast, reversible interaction of prion protein with RNA aptamers containing specific sequence patterns

One of the unsolved problems in prion diseases relates to the physiological function of cellular prion protein (PrP), of which a misfolded isoform is the major component of the transmissible spongiform encephalopathies agent. Knowledge of the PrP-binding molecules may help in elucidating its role and understanding the pathological events underlying prion diseases. Because nucleic acids are known to bind PrP, we attempted to identify the preferred RNA sequences that bind to the ovine recombinant PrP. An in vitro selection approach (SELEX) was applied to a pool of 80-nucleotide(nt)-long RNAs containing a randomised 40-nt central region. The most frequently isolated aptamer, RM312, was also the best ligand (20 nM KD value), according to both surface plasmon resonance and filter binding assays. The fast rates of association and dissociation of RM312 with immobilized PrP, which are reminiscent of biologically relevant interactions, could point to a physiological function of PrP towards cellular nucleic acids. The minimal sequence that we found necessary for binding of RM312 to PrP presents a striking similarity with one previously described PrP aptamer of comparable affinity. In addition, we here identify the two lysine clusters contained in the N-terminal part of PrP as its main nucleic-acid binding sites.

Effect of two candidate genes on the Salmonella carrier state in fowl

Selection for increased resistance to Salmonella carrier-state (defined as the persistency of the bacteria 4 wk after inoculation) could reduce the risk for the consumer of food toxi-infections. The effects of two genomic regions on chromosomes 7 and 17 harboring two genes, NRAMP1 (SLC11A1) and TLR4, known to be involved in the level of chicken infection 3 d after inoculation by Salmonella were thus tested on a total of 331 hens orally inoculated at the peak of lay with 10(9) bacteria. The animals and their parents were genotyped for a total of 10 microsatellite markers mapped on chromosomes 7 and 17. Using maximum likelihood analysis and interval mapping, it was found that the SLC11A1 region was significantly involved in the control of the probability of spleen contamination 4 wk after inoculation. Single nucleotide polymorphisms (SNP) within the SLC11A1 and TLR4 gene were tested on those animals as well as on a second batch of 279 hens whose resistance was assessed in the same conditions. As the former was significantly associated with the risk of spleen contamination and the number of contaminated organs, SLC11A1 appears to be involved in the control of resistance to Salmonella carrier state. The involvement of the TLR4 gene was also highly suspected as a significant association between SNP within the gene, and the number of contaminated organs was detected.

Statistical power of QTL mapping methods applied to bacteria counts

Most QTL mapping methods assume that phenotypes follow a normal distribution, but many phenotypes of interest are not normally distributed, e.g. bacteria counts (or colony-forming units, CFU). Such data are extremely skewed to the right and can present a high amount of zero values, which are ties from a statistical point of view. Our objective is therefore to assess the efficiency of four QTL mapping methods applied to bacteria counts: (1) least-squares (LS) analysis, (2) maximum-likelihood (ML) analysis, (3) non-parametric (NP) mapping and (4) nested ANOVA (AN). A transformation based on quantiles is used to mimic observed distributions of bacteria counts. Single positions (1 marker, 1 QTL) as well as chromosome scans (11 markers, 1 QTL) are simulated. When compared with the analysis of a normally distributed phenotype, the analysis of raw bacteria counts leads to a strong decrease in power for parametric methods, but no decrease is observed for NP. However, when a mathematical transformation (MT) is applied to bacteria counts prior to analysis, parametric methods have the same power as NP. Furthermore, parametric methods, when coupled with MT, outperform NP when bacteria counts have a very high proportion of zeros (70.8%). Our results show that the loss of power is mainly explained by the asymmetry of the phenotypic distribution, for parametric methods, and by the existence of ties, for the non-parametric method. Therefore, mapping of QTL for bacterial diseases, as well as for other diseases assessed by a counting process, should focus on the occurrence of ties in phenotypes before choosing the appropriate QTL mapping method.

Establishment and characterisation of ovine blood monocyte-derived cell lines

Studies of the important functions in host defense assured by macrophages, both as functional elements and as potential targets for intracellular pathogens, are often inhibited by the lack of a source of large numbers of uniform, well-characterised cells. To address this lack for ovine studies, we have established cell lines from spontaneously-proliferating adherent mononuclear cells from sheep blood. Eight such lines which have been continuously cultured for over 400 passages have phagocytic activities and cytochemical characteristics indicating that they retain the nature of mononuclear phagocytes. They display typical functional membrane proteins such as CD14, Fc receptors and MHC class II. Such cells can facilitate in vitro studies of pathogen-monocyte interactions and can furnish copious amounts of cells for transfer experiments.

Cytokine gene expression in lymph node and spleen of sheep in response to Salmonella infection by two serotypes displaying different host specificity

In order to investigate the determinism of the host specificity and to better understand the host resistance mechanisms, infections of sheep were performed with either S. abortusovis, serotype specific for ovine species, or with S. dublin, serotype adapted to cattle and accidentally transmissible to human. Following a subcutaneous challenge, S. dublin disseminated more rapidly towards lymphoid tissues than S. abortusovis. However, S. abortusovis tended to persist in spleen more efficiently than S. dublin. Using a quantitative RT-PCR method, the expression level of ovine cytokines genes was measured in the draining lymph node and in the spleen, in the course of infection. Inflammatory cytokine response was characterised by an early and strong increase of IL-1beta and TNFalpha mRNA in both lymphoid organs following S. dublin infection, while S. abortusovis challenge only induced IL-1beta mRNA increase in the spleen at day 3 post-inoculation. Likewise, S. dublin infection provoked a marked increase of IL-12 mRNA and a slight up-regulation of IFNgamma gene transcription in the local lymphoid site, in contrast to S. abortusovis infection. Elsewhere, both serotypes induced a strong and early IL-10 mRNA production and had no effect on IL-4 gene expression. Finally, taken together, these data suggest that the intensity of inflammatory and anti-infectious cytokine responses, but not the type 2 cytokine response, is serotype-dependent. They also suggest that the host-specific serotype, by limiting the host cytokine-mediated defence, could favour its persistence within lymphoid organs.

Effect of the mouse Nramp1 genotype on the expression of IFN-gamma gene in early response to Salmonella infection

The early interferon-gamma (IFN-gamma) response after Salmonella infection was compared in resistant and susceptible congenic mice strains differing by the allele of Nramp1. IFN-gamma gene expression in vivo was studied by quantitative reverse transcription-PCR performed from the spleen of mice challenged by Salmonella either in multiplication or in resting phase. The spleen colonisation by Salmonella in vivo was investigated and was shown to be identical in a genetically defined host, whatever the initial phase of the bacteria. However, the bacterial load of the spleen was significantly reduced in Nramp1(r) (resistant) mice compared to Nramp1(s) (susceptible) mice. The background level of IFN-gamma mRNA was higher in the spleen of resistant mice than in the susceptible mice, before infection. Interestingly, the early upregulation of IFN-gamma gene transcription, which was observed after infection with Salmonella, was reproducibly delayed in susceptible mice compared to resistant mice. Finally, the kinetics of the host IFN-gamma response seems to be Nramp1 dependent. Resistant mice present the advantage of being more prompt to express this anti-infectious cytokine gene than susceptible mice in response to Salmonella infection.

Quantification of ovine cytokine gene expression by a competitive RT-PCR method

A quantitative competitive RT-PCR method was developed in order to measure IL-1beta, IL-4, IL-12, IFNgamma, TNFalpha and G(3)PDH mRNA from samples of ovine tissue such as lymph node or spleen. The main advantage of the method relies on the use, for each target sequence, of an internal competitor construct similar to the relevant target, but 4-bp different in size. This competitive strategy is validated by the equivalence of the amplification process, observed separately between competitor DNA and target DNA species. Furthermore, the copy number of each cytokine cDNA is normalized to a fixed copy number of G(3)PDH cDNA. The cDNA level of this constitutive gene was effectively shown to remain constant whatever the tissue studied and independently of the experimental conditions used. The accurate and reproducible data obtained permit the application of this quantitative RT-PCR method to measure the sheep cytokine response to Salmonella infection. Early induction of IFNgamma mRNA was observed in the draining lymph node 1 day after infection. At the same time, a strong increase of IL-1beta mRNA was observed in local and systemic lymphoid organs, suggesting the initiation of the inflammatory response. Finally, the overall results demonstrate the efficiency of the method and its suitability for further studies of the immune response in the ovine species.

Regional characterization of a hamster-sheep somatic cell hybrid panel

The regional characterization of a previously obtained hamster-sheep hybrid panel is reported. Using data available from ruminant maps (sheep, cattle, and goat), we have selected a set of 300 markers and have analyzed them by PCR in this hybrid panel. Results obtained for 204 markers show the presence of all sheep chromosomes (including gonosomes) in entire or fragmented form. Analysis of syntenies has given 130 types of answer defining segments of variable sizes. This study has led to the regional characterization of this panel and provides comparative data on a set of bovine and caprine markers. With the level of characterization now achieved for this hybrid panel, the regional assignment of new genes or markers to sheep chromosomes can be rapidly obtained. Finally, this panel will help to collect new data for comparative mapping of domestic animals and to highlight the conservation of syntenic groups between closely related species, that is, sheep, cattle, and goat.

Host cytokine response and resistance to Salmonella infection

Knowledge of the host response, of the resistance process, and of the mediators committed against Salmonella infection is essential to progress towards better means of prophylaxis and eradication. In this context, the present contribution attempts to interconnect, with the pivotal role of the macrophage, the early resistance process under the control of the Nramp1 gene and the cytokine response for resolving infection. IL-12 produced by macrophages is an inducer of IFN-gamma production, which in turn activates the macrophage antibacterial activity and synergizes its effects with TNF-alpha. All three of these cytokines are powerful actors in the first line of anti-Salmonella defence. It can be pointed out that susceptible and resistant individuals do not seem to see the cytokine environment the same way, the former being unresponsive to IL-1 or GM-CSF treatment and deficient in IFN-gamma production. These discrepancies may rely on cell signalling events that could be defective in macrophages of the susceptible phenotype.

Genetic susceptibility and transmission factors in scrapie: detailed analysis of an epidemic in a closed flock of Romanov

Information from a scrapie epidemic in a closed INRA Romanov flock is presented. Performances, pedigree, histopathological diagnoses and PrP genotypes were recorded from the beginning of the outbreak (in 1993). Between 1st of April, 1993 and 1st of May, 1997, 1015 animals were exposed to scrapie, and 304 died from this disease. A major influence of the polymorphisms at codons 136, 154 and 171 is shown, A136H154Q171 allele carriers proving to be nearly as resistant as A136R154R171 carriers. A possible relationship between gastrointestinal parasitism and scrapie is discussed. There is evidence of maternal transmission, with a risk ratio for artificially fed lambs of 67 percent of the risk of lambs fed by their mother. Our results strongly suggest that resistant animals were not healthy carriers or at least were less infectious when comparing risk for lambs born to healthy dams either of resistant (risk = 0.431) or of susceptible (risk = 1.000) genotype.

cDNA cloning, structural organization, and expression of the sheep NRAMP1 gene

Mouse resistance to several intracellular pathogens including Mycobacteria, Leishmania, and Salmonella is under the control of the Chromosome (Chr) 1 Natural Resistance Associated Macrophage Protein I gene (Nramp1). This gene could have an economic and health importance for domestic animals and humans as well. Therefore, equivalents of the NRAMP1 gene have been cloned by several research groups in various animal species. To study in sheep the influence of the NRAMP1 gene on the susceptibility to intracellular pathogens induced diseases, we have cloned the sheep NRAMP1 cDNA by screening a splenic cDNA library. The genomic organization of the sheep NRAMP1 gene was then determined by sequencing the exon/intron boundaries. The transcription start points (tsp) from the NRAMP1 mRNA have been located with primer extension experiments. RT-PCR reactions have been used to determine the profile of mRNA expression of this gene.

Variability in the resistance of four chicken lines to experimental intravenous infection with Salmonella enteritidis phage type 4

The capacity of four chicken lines (Y11, L2, B13, PA12) to control Salmonella enteritidis (SE) phage type 4 (PT4) systemic colonization was investigated. Thirteen-week-old chickens were intravenously inoculated with 10(6) SE colony-forming units, and the levels of SE colonization were determined at various time intervals after inoculation in liver, spleen, genital organs, and ceca. The course of SE infection showed a rapid contamination of liver, spleen, and genital organs, whereas the ceca were infected later. A significant (P < 0.001) effect of the chicken line on levels of SE was detected on day 3 postinoculation (PI) in liver and ceca, on day 10 PI in ceca, and on day 15 PI in spleen. Because an early control of systemic Salmonella infection by the Ity/Nramp1 gene has been demonstrated in mice, we aimed to study the early resistance of chickens to SE. As a consequence, we then focused our study on the between- and within-line variabilities of SE levels on day 3 PI. According to the SE levels in liver on day 3 PI, the chicken lines could be classified as susceptible (Y11 and L2) or resistant (PA12 and B13). This early variability was explored in resistant B13 and susceptible L2 lines. Differences between these two lines were confirmed in liver but not in ceca. A large within-line variability was observed in all organs of these two lines. The genetic origin of this variability will have to be determined as a prerequisite to an eventual selection.

Mouse susceptibility to infection by the Salmonella abortusovis vaccine strain Rv6 is controlled by the Ity/Nramp 1 gene and influences the antibody but not the complement responses

Early growth of Salmonella typhimurium in spleen and liver of mice is controlled by the mouse chromosome 1 locus Ity/Nramp 1. Genetic control of resistance to the attenuated vaccine strain Rv6 of Salmonella abortusovis was studied in mice infected by the intravenous route. Comparison of kinetics of bacterial colonization of spleen and liver in two congenic BALB/c-susceptible (Itys) and -resistant (Ityr) mouse lines showed that BALB/c mice (Itys) were significantly more susceptible to infection than C.D2 mice (Ityr) suggesting that infection by this vaccine strain is controlled by a gene which is close or identical to Ity/Nramp 1. Congenic mice also differed in their anti-Salmonella antibody response, measured by ELISA: susceptible mice had a significantly higher antibody level than resistant mice, whatever the immunoglobulin isotype (IgM, IgG1, IgG2a, IgG3, IgA, and total immunoglobulins). The two congenic BALB/c mouse lines had equal serum C3c levels in response to infection. However, we observed a highly significant difference according to the sex of mice, suggesting a role of sex hormones in the regulation of the level of some complement factors. These results, obtained with congenic mice, strongly suggest that the Ity/Nramp 1 locus controls susceptibility to infection by the S. abortusovis vaccine strain Rv6 and influences the antibody response.

Analysis of the immune response in sheep efferent lymph during Salmonella abortusovis infection

The efferent lymph duct of the ovine prescapular lymph node was cannulated, and Salmonella abortusovis (SAO), a specific pathogen for sheep inducing abortion and mortality of newborn lambs, was inoculated by the subcutaneous route in this lymph node drained area. While the prescapular lymph node draining the inoculation site represented an efficient barrier for the vaccinal SAO Rv6 strain spreading, SAO 15/5 virulent bacteria were steadily detected in efferent lymph of infected sheep. The inoculation of the virulent strain of SAO induced a greater increase of the cell output than did the attenuated vaccinal strain, but proportions of blast cells appearing in the efferent lymph were similar in both cases. Flow cytometry analysis showed that B and T cell outputs were both increased during SAO infections, but while T cell subset proportions slightly decreased, B cell percentages significantly rose, and, at the peak response, almost all of the lymphoblast cells were activated B cells. Typical antibody profiles characteristic of a primary immune response were observed, and antibody titres were greater in the efferent lymph of animals inoculated with the virulent strain of SAO. Many of the cytokine mRNAs we investigated were steadily detected by RT-PCR in efferent lymph cells of control sheep, but frequencies of detection of IL-2, IFN gamma, IL-1 beta and TNF alpha mRNAs were augmented in efferent lymph cells following inoculation of both SAO virulent or vaccinal strains. IL-10 and IL-8 mRNAs could only be detected after a SAO inoculation, while detection of IL-4 mRNAs was increased only in efferent lymph cells from SAO virulent strain-infected sheep. The efferent lymph cannulation technique thus appeared a very powerful way to study the in vivo development of the immune response to SAO, in its natural host, the sheep.

Recent developments and potentialities for reducing embryo mortality in ruminants: the role of IFN-tau and other cytokines in early pregnancy

This review considers the potential reduction of embryo mortality in vitro and in vivo in ruminants. Data on cytokines provided by different fields of reproductive immunology and biology were collated. Because of the crucial importance of the local interactions between the embryo and its dam, the expression of growth-factor and cytokine genes was analysed in the embryo proper, trophoblast, oviduct and endometrium by reverse transcriptase polymerase chain reaction in sheep and in cattle during the pre- and periimplantation periods. Many deleterious cytokines, such as tumour necrosis factor-alpha, interferon-gamma (IFN-gamma), interleukin-2 (IL-2), and beneficial cytokines, such as transforming growth factor-beta, leukaemia inhibiting factor, colony-stimulating factor-1 (CSF-1), granulocyte-macrophage CSF, IL-1, IL-3, IL-4, IL-6, IL-10 and IFN-tau appeared to be involved in embryo survival in ruminants and other species. Their administration is efficient in a murine experimental model (CBA/J x DBA/2) of embryonic and fetal mortality. For instance, recombinant ovine IFN-tau (roIFN-tau) injected at the moment of implantation drastically reduces embryonic mortality in this model. In ruminants, roIFN-tau and recombinant bovine IFN-tau are very efficient in maintaining progesterone luteal secretion in cyclic animals. The involvement of IFN-tau in the mechanisms of maternal pregnancy recognition are particularly detailed in relation to inhibition of 13,14 dihydro-15-keto-prostaglandin F2 alpha (PGFM) pulses and oxytocin uterine receptivity. A synthetic model of the anti-luteolytic effects of IFN-tau on the endometrial cell is proposed. Finally, the particular potential of serum pregnancy-specific proteins (PSPs: PSPB, PSP60, pregnancy-associated glycoprotein) for monitoring embryo survival, with examples given for cattle and sheep is underlined.

Flow cytometric analysis of the reactivity of workshop monoclonal antibodies on sheep lymph node cells, after infection with Salmonella abortusovis

Of the 302 monoclonal antibodies included in the Third Workshop on Ruminant Leukocyte Antigens, 167 have been tested for their reactivity on uninfected and Salmonella-infected sheep lymph node leukocytes using FACS analysis. Only 47 of them showed specificities which could be related to those of some control monoclonal antibodies, such as the anti-CD5, anti-Ig light chain and anti-MHC Class II monoclonal antibodies.

Immunohistochemical study on the reactivity of workshop monoclonal antibodies with sheep lymph nodes

Of the 302 monoclonal antibodies submitted to the Third Workshop on Ruminant Leukocyte Antigens, 167 have been tested for their reactivity on sheep lymph node sections, according to the APAAP immunohistochemical technique. Of the 57 monoclonal antibodies able to react on ovine tissue sections, only 37 induced a clear and well-contrasted staining. The more striking results are presented in this paper.

Line differences in resistance to Salmonella enteritidis PT4 infection

1. Four groups of hens, each of a different line, were inoculated at peak of lay, per os in the crop with 1 ml of a suspension containing 10(9) cfu/ml Salmonella enteritidis PT4 (SE). The kinetics of SE contamination in the environment, egg shell and yolk were studied during the first 28 d post inoculation. On the day of slaughter, intestines, caeca, spleen, liver, ovary, oviduct and content were investigated for SE contamination. 2. The commercial egg-type line L2 was found to be the most susceptible to SE. It laid many SE-positive yolks (13.8%) and internal and faecal organs were frequently infected. 3. Certain lines are found to exhibit a degree of resistance to SE; the cause of which is unknown and might be attributed to major genes.

Regional localization of the ovine NRAMP gene to chromosome 2q41-->q42 by in situ hybridization

The murine Ity/Lsh/Bcg locus belongs to a conserved region between mouse Chromosome 1 and human chromosome 2. This gene governs mouse resistance to several intracellular pathogens. We have localized the gene on sheep chromosome 2q41-->q42 by radioactive in situ hybridization using a 2.1-kb fragment of the ovine equivalent of this gene.

Role of H-2 and non-H-2-related genes in mouse susceptibility to Chlamydia psittaci

The genetic control of mouse susceptibility to Chlamydia psittaci was investigated after intravenous inoculation of 2 x 10(5) plaque-forming units (pfu). Splenic counts 6 days after inoculation gave the level of susceptibility. Results from inoculation of mice from H-2 congenic strains with three different genetic backgrounds (B10, BALB and C3H) suggested that both the non-H-2 genes and the genes of H-2 complex or those closely associated with it, were responsible for the observed differences in the innate capacity of various inbred lines of mice to control bacterial load in their infected organs following a challenge with C. psittaci.

Reactivity of workshop monoclonal antibodies with normal and pathological ovine lymph nodes

The monoclonal antibodies (82 mAbs) included in the Second Workshop that belonged to agreed named bovine CD and workshop clusters were tested for their reactivity and tissue distribution on (1) normal sheep lymph nodes and (2) pathological sheep lymph nodes. Pathological lymph nodes were induced following experimental infection with Corynebacterium pseudotuberculosis and were characterized by the presence of typical pyogranulomas. Amongst the 82 mAbs tested, 38 reacted with sheep lymph nodes. The results of these tests are presented and discussed.

Restriction fragment length polymorphism of DQB and DRB class II genes of the ovine major histocompatibility complex

The ovine major histocompatibility complex (MhcOvar) class II region was investigated by Southern blot hybridizations using ovine probes specific for the second exons of Ovar-DRB and Ovar-DQB genes. Multiple bands were revealed when genomic DNA was digested with each of five restriction enzymes (BamHI, EcoRI, HindIII, PvuII and TaqI), and successively hybridized with the two radiolabelled ovine probes. Restriction fragment length polymorphisms (RFLPs) were analysed in 89 sheep originating from six inbred families and the inheritance of the fragment patterns was determined. Forty-one fragments were recorded with the DQB probe; 32 were detected with the DRB probe. They constituted 9 DQB and 10 DRB allelic patterns. Twelve DQB-DRB haplotypes were resolved in this study.

Acquired immunity after primary caseous lymphadenitis in sheep

Caseous lymphadenitis (CLA) caused by Corynebacterium pseudotuberculosis is a worldwide disease of sheep and goats and is characterized by development of pyogranulomas in lymph nodes and lungs. Control of this disease by vaccination remains controversial, although toxoid vaccines are now commercially available in some countries. To determine the efficacy of acquired immunity to control CLA, the effect of primary infection on subsequent challenge exposure was investigated. Adult seronegative ewes were primarily inoculated with a streptomycin-sensitive strain of C pseudotuberculosis on the external part of the left ear and thereafter challenge-exposed by inoculation of the streptomycin-resistant strain 19R in the right ear. This protocol indicated that primary infection with at least 10(7) viable bacteria induced strong protection against subsequent challenge exposure; the ewes with primary infection did not develop lesions as a result of challenge exposure, whereas immune-naive ewes developed numerous pyogranulomas in the right car, in lymph nodes draining the inoculation site, and in the lungs. However, ewes with primary infection remained carriers of the disease as a result of primary inoculation. These results offer experimental support for development of more effective vaccination to control CLA in sheep and goats, and this model indicates that animals with primary infection can be used as positive controls for protection when testing a candidate vaccine against CLA.

Salmonella abortusovis infection in susceptible BALB/cby mice: importance of Lyt-2+ and L3T4+ T cells in acquired immunity and granuloma formation

The role of T cells in granulomatous responses and in acquired immunity against Salmonella abortusovis (SAO) infection was studied in a murine model. Mice were subcutaneously (s.c.) vaccinated with a live attenuated strain of SAO. One month after vaccination, the transfer of primed spleen cells (1 x 10(8) cells per mouse) to syngeneic recipient mice conferred a significant protection of 3 log10, measured by spleen colonization on day 6 after s.c. challenge. In vitro treatment of spleen cells, before the transfer, with anti-Lyt-2 monoclonal antibody (IgG2b isotype MAb) and complement significantly impaired the protective activity. Treatment with anti-L3T4 MAb also diminished transferred protection, but to a lesser degree. Depletion of both L3T4+ and Lyt-2+ T cells completely abrogated protection. MAb treatment of spleen cells in vitro did not seem to have any effect on antibody response in recipient mice. Six days after the challenge protected recipient mice showed organized granulomas in the liver containing Mac-1+ macrophages and L3T4+ T cells. In non-protected mice at 6 days post-challenge, large infiltrates of T lymphocytes and macrophages were observed, but as numerous lesions with necrosis of hepatocytes; no granuloma were seen. In our experimental conditions, Lyt-2+ and L3T4+ T cells appeared to play, alone and in synergy, a role in vaccine-induced immunity against SAO and hepatic granulomas may contribute to the control of the infection.

Intraperitoneal infection with Salmonella abortusovis is partially controlled by a gene closely linked with the Ity gene

The aim of the present study was to determine whether the Ity gene, which controls the resistance to S. typhimurium infection in mice, also governs the resistance to S. abortusovis, a serotype specific for goat and sheep. During either i.v. or i.p. infection, BALB/c mice (Itys) were not able to control the growth of S. abortusovis and eventually died from infection. In contrast CBA (Ityr) or (C.CB)F1 (Ityr/s) mice were able to control the growth of these bacteria. Using congenic C.D2 Ityr mice, we found that the gene controlling resistance to S. abortusovis was tightly linked to the Ity gene on chromosome 1. Furthermore, in the spleen and the liver of backcross BALB/c x (CBA x BALB/c) mice, the S. abortusovis resistance phenotype cosegregated with the two alleles of the Len-1 gene, a gene tightly linked to the Ity gene. By contrast, in these backcross mice, the level of infection of the peritoneal cavity, the site of inoculation, did not correlated with the Len-1 phenotype of the animal. These results provide evidence that after i.p. inoculation the control of S. abortusovis growth in the spleen and the liver is controlled by the Ity gene, but also suggest that additional gene(s) regulate the number of bacteria at the site of inoculation.

Stimulation of antimycobacterial activity in mouse peritoneal macrophages by priming with trehalose dimycolate (TDM)

We examined the potential of two bacterial immunomodulators, trehalose dimycolate (TDM) and lipopolysaccharide (LPS), to stimulate the capacity of mouse peritoneal macrophages to control the growth of the intracellular bacterium, Mycobacterium tuberculosis BCG. Macrophages were obtained from mice innately susceptible (Bcgs) or resistant (Bcgr) to BCG infection. In all mouse strains tested (Bcgr and Bcgs), with the exception of BALB/c (Bcgs), TDM was sufficient to elicit macrophages with strong antimycobacterial activity in vitro. In BALB/c mice, the induction of anti-BCG activity required two signals, TDM and LPS, given in sequence. Our data suggest that additional gene(s), besides the Bcg locus, control macrophage resistance to BCG.

Experimental Corynebacterium pseudotuberculosis infection in lambs: kinetics of bacterial dissemination and inflammation

Infection and pyogranulomas induced by Corynebacterium pseudotuberculosis were experimentally reproduced in lambs. In two separate experiments, bacterial multiplication and dissemination were studied in 30 male lambs inoculated subcutaneously into the right ear with 1.1 or 1.5 X 10(8) viable C. pseudotuberculosis strain 19R. Infected lambs were necropsied at various times until the 28th day following inoculation. After a transient hyperthermia and a strong local inflammatory reaction, an abscess developed in the right ear from postinoculation day (PID) 6; it enlarged until PID 14 and stabilized thereafter and was associated with adenopathy of lymph nodes draining the head. Three acute phase indicators of inflammation were followed in 14 out of 30 lambs; plasma levels of copper and haptoglobin increased rapidly following inoculation whereas zinc levels decreased. The peaks were reached from PID 1 to 5, and thereafter the values came back slowly to the baseline. Antibodies against C. pseudotuberculosis exotoxin increased from PID 5 and reached a plateau on PID 21. Bacterial dissemination, assessed by the number of infected organs per lamb, was maximal on PID 16 and then stabilized until the end of the experiment. Lungs were infected in seven out of 18 lambs necropsied on PID 28. These results demonstrate a significant relationship between the clinical score of superficial lymph nodes or inoculation site and the infection level of these organs, and an early localization of pyogranulomatous lesions in regional lymph nodes. The subsequent development of the disease was related to the enlargement of these lesions and, in some animals, to a bacterial dissemination from primary sites of infection in the right prescapular lymph node and in the lung.

Experimental ovine salmonellosis (Salmonella abortusovis): pathogenesis and vaccination

Salmonella enterica subsp. enterica ser. Abortusovis, a sheep-adapted serotype, causes a contagious disease. Abortion is the major symptom and the main source of contamination. Research on this ovine disease may aid farmers, but may also contribute to comparative biological knowledge. Innate resistance partly controlled by the Ity locus, increased resistance to reinfection and humoral and T-cell-mediated immunity were observations gained with a murine model. In ewes, abortion regularly occurs following subcutaneous challenge carried out from the third month of gestation onwards. This ovine model was used to evaluate prevention methods for Salmonella Abortusovis infection. One subcutaneous injection of a live attenuated lyophilized vaccine containing a selected streptomycin-independent reverse mutant was shown to protect ewes against abortion and excretion of Salmonella Abortusovis. This vaccine could be administered simultaneously with other commercial live vaccines such as Brucella melitensis Rev. 1 vaccine. In sheep, application of the vaccine to the conjunctiva (an easy, individual and hygienic route of mucosal vaccination) was followed by lymph node bacterial colonization and a serological response without local or general clinical reactions. The early events of natural infection remain to be explored, as do the mechanisms underlying the host specificity of Salmonella Abortusovis.

Classical and alternative pathway haemolytic activities of ovine complement: variations with age and sex

The classical (CH50) and alternative (ACH50) pathway haemolytic activities of sheep complement were measured with microtechniques. Storage of blood at room temperature (instead of 4 degrees C) before centrifugation and usage of sera stored at -70 degrees C were compatible with complement titration. The effects of age and sex were tested in 303 sera obtained from animals aged between 2 weeks and 3.5 years old. ACH50 titres were low during the first 1.5 months of life then increased to reach the level found in adults at the age of 3 months. Conversely, CH50 titres were very high in suckling lambs, decreased up until the age of 3 months and then increased to reach the adult level at 1 year old. In lambs, the haemolytic complement activity was significantly higher in females than in males.

Mouse models for evaluation of virulence of Chlamydia psittaci isolated from ruminants

Intestinal strains of Chlamydia psittaci isolated from faeces of clinically healthy sheep or goats were differentiated from pathogenic strains isolated from animals affected with chlamydial diseases by their virulence in mice. The invasiveness of strains after footpad inoculation was estimated in non-pregnant mice by recording the colonisation and the enlargement of the spleen on days 6 and 9 after inoculation. The abortifacient effect was judged by measuring the colonisation of placenta and fetuses of pregnant mice inoculated intravenously on day 11 +/- 1 of pregnancy. While 25 of 27 pathogenic strains were invasive and able to colonise placenta and fetuses, eight of 10 intestinal strains were not. The model permits graded differentiation between virulent and non-virulent strains and suggests that in propitious circumstances intestinal chlamydia could reach and colonise the placenta and disturb the pregnancy.

Anti-chlamydial immunity in ewes conferred by vaccination with a combination of three live chlamydia, brucella and salmonella vaccines

Live attenuated vaccines against Chlamydia psittaci var ovis, Brucella melitensis and Salmonella abortus ovis have previously been shown to be compatible in mice by subcutaneous administration. Immunity against challenge with virulent chlamydia was, however, slightly decreased in associations including the B melitensis Rev 1 vaccine. The chlamydia strain 1B vaccine was administered to four- to five-month-old female lambs, either alone or in combination with the B melitensis Rev1 and the S abortus ovis Rv6 vaccines. Clinical, serological and bacteriological observations demonstrated the compatibility of the three vaccines. Control, singly and triply vaccinated ewes were challenged with a virulent strain of chlamydia during their second pregnancy, 15 months after vaccination. Five of the 12 control ewes lambed normally and 10 of them were infected, as shown by the excretion of the challenge chlamydia in genital secretions. Sixteen of the 17 ewes in the triple vaccine group lambed normally and none was infected. All 12 in the single vaccine group lambed normally and three of the 12 were infected. In spite of this unusually poor protection by the single vaccine, antichlamydial immunity was clearly not decreased by the association with the two other vaccines.

Corynebacterium pseudotuberculosis infection in adult ewes by inoculation in the external ear

Caseous lymphadenitis, caused by Corynebacterium pseudotuberculosis, was studied in ewes to devise a reliable method of induced infection that would help to understand mechanisms by which abscesses develop in lymph nodes or internal organs, especially the lungs. Fifteen adult ewes, from a flock where the occurrence of caseous lymphadenitis was unknown, were inoculated SC in the auricle with various doses of a virulent strain of C pseudotuberculosis. Ewes inoculated with at least 10(8) viable corynebacteria develop a strong local reaction that was apparent 4 hours after challenge exposure and lasted 7 to 14 days. Of these ewes, all developed at least 1 abscess and 3 developed multiple abscesses in lymph nodes draining the inoculated auricle and in the lungs. All infected ewes developed a strong antibody response against C pseudotuberculosis exotoxin, which persisted for 3 months. Of 9 ewes infected with 1.2 X 10(8) corynebacteria, 3 developed lesions because of field strains of C pseudotuberculosis and had an increased capacity to limit the dissemination of challenge-inoculum bacteria by developing only one abscess in the draining lymph node (parotid or prescapular lymph node). Seemingly, inoculation in the external ear was a suitable method for obtaining a reproducible infection and indicated that a primary infection might protect against reinfection by limiting dissemination of C pseudotuberculosis.

Simultaneous vaccination by three living attenuated strains of Brucella, Salmonella and Chlamydia in mice

Associations of vaccines for simultaneous administration were successfully developed long ago, in particular in human medicine, although there have been very few attempts to associate living bacterial vaccines. Unfortunately, living vaccines can interact with one another resulting in either a virulent infection or an exclusion of one by the other. Having developed two new low virulence vaccinal strains of Chlamydia psittaci var. ovis and Salmonella abortus ovis for use in veterinary medicine, we studied associations of both and with the Brucella melitensis Rev1 vaccine in mice. There was no interaction between the Chlamydia and the Salmonella vaccines and between the Salmonella and the Brucella vaccines from the point of view of immunogenicity. In contrast, anti-Chlamydia immunity was decreased by about 15-19% when the Chlamydia vaccine was associated with the Brucella vaccine in double or triple association. Surprisingly, the Chlamydia vaccinal strain infection was slightly extended when administered in association. The simultaneous vaccination we tested could be of great interest in veterinary medicine, but special attention must be devoted to anti-Chlamydia immunity and would have to be studied in a ewe model.

Immunogenicity of a low-virulence vaccinal strain against Salmonella abortus-ovis infection in mice

Strain Rv6, a streptomycin-independent reverse mutant of Salmonella abortus-ovis, multiplied and disseminated in vivo to a lesser extent than the virulent parental strain 15/5, as determined by subcutaneous inoculation of two outbred strains of mice with different susceptibilities to salmonella infection. This lower virulence of strain Rv6 was not modified by 10 passages in susceptible mice. Vaccination with strain Rv6 induced a dose-dependent capacity of mice to control subsequent infection with the virulent parental strain. Induced resistance began as early as 3 days after vaccination and lasted at least 11 months. Its efficiency was controlled by different routes and doses of challenge. Strain Rv6 induced a greater protection than that conferred by heat-killed bacteria or by tested commercial killed vaccines.

Vaccinal properties of Salmonella abortus ovis mutants for streptomycin: screening with a murine model

Streptomycin-dependent and streptomycin-independent reverse mutants of Salmonella abortus ovis were selected on medium with and without added streptomycin. Their in vivo properties were tested with a murine model. Reduced capacities of dissemination and multiplication of all mutant strains were evidenced by means of subcutaneous, intraperitoneal, and intravenous inoculations of two outbred strains of mice with different susceptibilities to experimental S. abortus ovis infection. A factorial immunization experiment demonstrated the effects of vaccinal strains and doses. It showed large differences among the mutants. First-time infection with the fully virulent parent strain excepted, the best protection was given by independent reverse mutants which had kept residual capacity of in vivo dissemination and multiplication. This screening partly determined the selection of strain Rv6 as a potential live vaccine.