Humoral immune response to Salmonella abortusovis in sheep: in vitro induction of an antibody synthesis from either sensitized or unprimed lymph node cells

Salmonella Abortusovis: An Epidemiologically Relevant Pathogen

The ovine pathogen Salmonella enterica serovar Abortusovis (SAO), a pathogen strictly adapted to ovine hosts, is endemic in several European and Asian countries, where it causes significant economic losses due to the high rates of abortion in infected flocks. In some countries (i.e. Switzerland and Croatia), re-emergence of infection by SAO occurred after decades during which the disease has not been reported. The introduction of (SAO) epidemic strains in new areas is difficult to control due to the asymptomatic behaviors in infected adult lambs, rams, and nonpregnant ewes. Culture-based diagnosis may provide false-negative results. Moreover, the retrospective identification of Salmonella infection in ewes is challenging as excretion of the causative agent is transient and the serum antibodies fall to low titres soon after the abortion. Therefore, regular monitoring of pathogen exposure, mainly through seroconversion assessment, is advisable to prevent disease introduction and spread in SAO-free areas, especially in case of animal export, and to reduce abortion risk.

The negative effect of repeated equine chorionic gonadotropin treatment on subsequent fertility in Alpine goats is due to a humoral immune response involving the major histocompatibility complex

In dairy goats, the use of eCG as a convenient hormone for the induction of ovulation is necessary for out-of-season breeding and artificial insemination. However, repeated eCG treatments are followed by decreased fertility in goats inseminated at a fixed time after treatment. In this report, we show the presence of anti-eCG antibodies in plasma of treated goats. A 500 IU eCG injection induces a humoral response, with variable concentrations of anti-eCG antibody being produced in individual goats. The analysis of successive anti-eCG immune responses over several years has demonstrated the existence of different populations of goats, defined as low, medium, and high responders. By the use of two caprine microsatellites located inside (OLADRB) and outside (BM1258) the major histocompatibility complex (MHC), a significant association (p < 0.05) between the anti-eCG antibody response and some MHC-DRB alleles was found. Goats with high antibody concentrations at the time of eCG injection (> 2.5 microg/ml) exhibited a much lower kidding rate than did other females (41.3% vs. 66.7%). Lower fertility of these goats, inseminated at a fixed time after eCG treatment, might be due to the observed delay in estrus occurrence and the preovulatory LH surge.

Salmonella abortusovis, strain Rv6, a new vaccinal vehicle for small ruminants

Salmonella abortusovis strain Rv6 (Sao Rv6) is a live attenuated vaccine used for a few years to protect ewes against abortive salmonellosis. As Salmonellae, particularly Salmonella aro mutants, have considerable potential as vehicles for the presentation of heterologous vaccine antigens, Sao Rv6 was tested in order to develop a vaccinal vehicle for small ruminants. Five vector plasmids were tested in Sao Rv6; these plasmids, which carry Maltose Binding Protein (MBP) expressed as protein, but differ in their promotors, had been previously tested in S. typhimurium strain SL3261, and were transferred into Sao Rv6. The five plasmids were stable in vitro, and the recombinant Sao Rv6 expressed MBP at various levels. Intraperitoneal infection of OF1 mice with the recombinant bacteria did not modify the characteristics of Sao Rv6; dissemination and infection levels were similar in all groups and all mice developed antibodies to Salmonella antigens as measured by ELISA. In contrast, only animals immunized with Sao Rv6 carrying the pNTE plasmid developed a serum antibody response to MBP. This plasmid was then tested in sheep; following subcutaneous immunization with Sao Rv6-pNTE, dissemination and infection levels were not modified in comparison with sheep immunized with Sao Rv6 lacking plasmid. Antibodies specific to MBP were detected in sera of sheep immunized with Sao Rv6-pNTE, purified MBP, and with S. typhimurium SL3261-pNTE as positive controls. These results demonstrate that Sao Rv6 can be used as a vehicle for heterologous antigens in sheep with pNTE as plasmid vector.

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.

Production and verification of an anti-ovine IgE monoclonal antibody

Recombinant mouse/sheep IgE was used in the production of an anti-IgE monoclonal using conventional hybridoma techniques. The specificity of hybridomas secreting anti sheep IgE monoclonal antibodies was verified using a number of assays including competitive ELISAs, ability to induce mediator release from mast cells, and IgE binding using western blotting. Immunohistochemical staining demonstrated the binding of putative anti-IgE monoclonals to the sheep mast cell surface. The isotype of the antibody was IgG1:K.

[Detection methods for Salmonella abortus ovis and examinations in sheep flocks in northern Baden-Württemberg]

Investigations into the incidence of Salmonella abortus ovis (S. abortus ovis) infections should not be neglected in diagnosis of ovine abortion cases. For detection of this pathogen agent, direct cultivation, as well as pre-enrichment combined with enrichment procedures in tetrathionate or Rappaport-Vassiliadis medium, should be performed with respect to the features of S. abortus ovis. The detection limit of S. abortus ovis using pre-enrichment and enrichment media could be determined using 6.5 x 10(3)-6.5 x 10(4) bacteria. For subsequent cultivation of S. abortus ovis Gassner, XLD or Rambach agar are suitable. In infected sheep showing no excretion of S. abortus ovis, the pathogen can be detected by serological studies using microagglutination or the ELISA test. The ELISA test proved to be more sensitive than the microagglutination test, detecting antibodies against S. abortus ovis in 17% of the 814 sheep tested. The microagglutination test revealed positive results in only 2% of the sheep tested.