Duration of strain 2308 infection and immunogenicity of Brucella abortus lipopolysaccharide in five strains of mice

A study was conducted to compare immunogenicity of a Brucella abortus lipopolysaccharide (LPS) and the duration of infection in 5 strains of mice. Mice of strains CBA/NJ, BALB/c, CD-1, C3H/HeN, and C3H/HeJ were allotted into 2 large groups (vaccinated with proteinase K-treated LPS or nonvaccinated) and 6 subgroups based on the intervals between challenge exposure to B abortus strain 2308 and the week the response data were obtained. Criteria used in comparing responses between the various strains of mice as well as between vaccinated and nonvaccinated mice were splenomegaly, colony-forming units (CFU) from spleens, and antibody titers. Responses were evaluated at 1, 2, 3, 5, 8, and 12 weeks after challenge exposure. Results indicated that all strains of mice became infected and maintained infection throughout the 12-week period, the percentages of mice infected were significantly (P less than 0.05) less in vaccinated mice for the first 5 weeks after challenge exposure, and there were no direct correlations between increased immunoglobulins (IgM and IgG titers) and reduction in CFU. Vaccinated mice of strains BALB/c, CD-1, C3H/HeN, and C3H/HeJ had increased titers when challenge exposed and also had significantly (P less than 0.05) smaller spleens and lower CFU. Vaccinated CBA/NJ mice did not have marked antibody titers. The overall results indicated that vaccination with LPS offers some initial protection against B abortus strain 2308 infection, but this protection disappears gradually and in various degrees in the 5 strains of mice studied.     

Reduced cerebral infection of Neospora caninum in BALB/c mice vaccinated with recombinant Brucella abortus RB51 strains expressing N. caninum SRS2 and GRA7 proteins

Neospora caninum, an obligate intracellular protozoan parasite, is the causative agent of bovine neosporosis, an important disease affecting the reproductive performance of cattle worldwide. Currently there is no effective vaccine available to prevent N. caninum infection in cattle. In this study, we examined the feasibility of developing a live, recombinant N. caninum vaccine using Brucella abortus vaccine strain RB51 as the expression and delivery vector. We generated two recombinant RB51 strains each expressing SRS2 (RB51/SRS2) or GRA7 (RB51/GRA7) antigens of N. caninum. BALB/c mice immunized by single intraperitoneal inoculation of the recombinant RB51 strains developed IgG antibodies specific to the respective N. caninum antigen. In vitro stimulation of splenocytes from the vaccinated mice with specific antigen resulted in the production of interferon-gamma, but not IL-5 or IL-10, suggesting the development of a Th1 type immune response. Upon challenge with N. caninum tachyzoites, mice vaccinated with strain RB51/SRS2, but not RB51/GRA7, showed significant resistance to cerebral infection when compared to the RB51 vaccinated mice, as determined by the tissue parasite load using a real-time quantitative TaqMan assay. Interestingly, mice vaccinated with either strain RB51 or RB51/GRA7 also contained significantly lower parasite burden in their brains compared to those inoculated with saline. Mice vaccinated with strain RB51/SRS2 or RB51/GRA7 were protected to the same extent as the strain RB51 vaccinated mice against challenge with B. abortus virulent strain 2308. These results suggest that a recombinant RB51 strain expressing an appropriate protective antigen(s), such as SRS2 of N. caninum, can confer protection against both neosporosis and brucellosis.     

The adjuvant effect of a single dose of interleukin-12 on murine immune responses to live or killed Brucella abortus strain RB51.

This study was designed to determine if a single 0.5 microg administration of recombinant murine interleukin-12 (IL-12) would influence immune responses of mice vaccinated with live or killed Brucella abortus strain RB51 (SRB51). Mice were vaccinated intraperitoneally with 5 x 10(8) cfu of live or gamma-irradiated SRB51 bacteria alone, or in combination with 0.5 microg of IL-12. Control mice received saline or 0.5 microg of IL-12. Serologic responses and spleen weights after vaccination were greater in mice vaccinated with live SRB51 when compared to mice receiving killed SRB51 or control treatments. Administration of a single dose of IL-12 as a vaccine adjuvant did not influence immune responses, clearance of live SRB51, or resistance against B. abortus strain 2308 (S2308) challenge. The results of this study suggest that a single administration of 0.5 microg of IL-12 at the time of vaccination does not have significant adjuvant effects on vaccine-induced immune responses against live or killed Brucella.     

Protection of mice against Brucella abortus infection by inoculation with monoclonal antibodies recognizing Brucella O-antigen

Monoclonal antibodies recognizing the O-polysaccharide portion of Brucella abortus strain 2308 provided BALB/c mice with passive protection against challenge exposure with the homologous strain. Numbers of colony-forming organisms in the spleen were reduced by IgM and IgG monoclonal antibodies. Active immunization of mice, using B abortus 2308S lipopolysaccharide, resulted in production of IgM antibody at 14 days. Clearance of organisms in the actively immunized mice after challenge exposure at 14 days was nearly identical to that in passively immunized mice. Mice either passively or actively immunized were effectively protected from 0 to 28 days. Bacterial colonization of the spleen was observed to increase in both groups of mice at 56 days and indicated that humoral responses were effective in eliminating the organism in the early stages of infection, but other immune mechanisms were necessary for protection of mice in the later stage of infection with virulent strains of B abortus.     

Identification of a virulence factor for Brucella abortus infection in BALB/c mice

Immunogenic or pathogenic factors of recombinant proteins (rBCSP20, rBCSP-31, and rBCSP45 of Brucella abortus strain 19) for mice were compared with factors of a proteinase K-treated lipopolysaccharide extracted from B abortus strain 2308. Mice were vaccinated with 4 products, using different inoculation schedules and were challenge exposed with a virulent culture of B abortus strain 2308. Blood samples were collected 2 weeks after vaccination and at necropsy and sera were obtained. Spleens were cultured for B abortus at necropsy (3 to 4 weeks after challenge exposure). Mice given proteinase K-treated lipopolysaccharide alone or in conjunction with rBCSP20 or rBCSP45 proteins were protected, but mice given rBCSP31 on the same day as challenge exposure were not. Vaccination with recombinant proteins alone neither provide protection nor significantly (P greater than 0.05) increase the pathogenic effect of the challenge-exposure culture. Seemingly, rBCSP31 might be a virulence factor of B abortus.     

Enhanced efficacy of recombinant Brucella abortus RB51 vaccines against B. melitensis infection in mice

Brucella abortus strain RB51 is an attenuated rough strain, currently being used as the official live vaccine for bovine brucellosis in the USA and several other countries. In strain RB51, the wboA gene, encoding a glycosyltransferase required for the O-side chain synthesis, is disrupted by an IS711 element. Recently, we have demonstrated that strain RB51WboA, RB51 complemented with a functional wboA gene, remains rough but expresses low quantities of O-side chain in the cytoplasm. Mice vaccinated with strain RB51WboA develop greatly enhanced resistance against challenge with B. abortus virulent strain 2308. We have also demonstrated that overexpression of Cu/Zn superoxide dismutase (SOD) in strain RB51 (RB51SOD) significantly increases its vaccine efficacy against strain 2308 challenge. In this study, we constructed a new recombinant strain, RB51SOD/WboA, that over expresses SOD with simultaneous expression of O-side chain in the cytoplasm. We tested the vaccine potential of strains RB51SOD, RB51WboA, RB51SOD/WboA against challenge with virulent Brucella melitensis 16M and B. abortus 2308 in mice. In comparison with strain RB51, strain RB51SOD induced better protection against strain 2308, but not strain 16M, challenge. Similar to strain RB51WboA, vaccination with strain RB51SOD/WboA resulted in complete protection of the mice from infection with strain 2308. When challenged with strain 16M, mice vaccinated with either strain RB51WboA or strain RB51SOD/WboA were significantly better protected than those vaccinated with strain RB51 or RB51SOD. These results suggest that strains RB51WboA and RB51SOD/WboA are good vaccine candidates for inducing enhanced protection against B. melitensis infection.     

Effects of killed Brucella abortus strain 45/20 vaccine on reindeer later challenge exposed with Brucella suis type 4

Six seronegative pregnant reindeer (Rangifer tarandus L) were vaccinated with killed Brucella abortus strain 45/20 with added adjuvant. These were challenge exposed with B suis type 4 after 90 days; at the same time, 4 seronegative, nonvaccinated, pregnant reindeer (controls) were given the challenge inoculum. Humoral antibodies were detected in the vaccinated reindeer by postvaccination day 14. A marked increase in antibody levels also occurred after they were challenge exposed, but did not reach the levels observed in control reindeer which seroconverted within 8 days after they were given the challenge inoculum. One control reindeer aborted at 45 days after challenge exposure (at 165 days of a normal 225-day gestation period), and the fawn of another lived only a few days after delivery. Brucella suis type 4 was isolated from tissues of 3 of 4 control reindeer and of 2 of their fawns. All vaccinated reindeer gave birth to live fawns which were culture negative, although 1 fawn lived only a few days. Brucella suis type 4 was isolated from tissues of 1 vaccinated reindeer. Under the conditions of this experiment, killed B abortus 45/20 vaccine provided increased resistance to brucellosis.     

Monophosphoryl lipid A-induced immune enhancement of Brucella abortus salt-extractable protein and lipopolysaccharide vaccines in BALB/c mice.

A study was conducted to determine the effect of monophosphoryl lipid A (MPL) and trehalose dimycolate (TDM) as adjuvants on the protective responses in BALB/c mice vaccinated with Brucella abortus salt-extractable protein (BCSP) or proteinase-K-treated B abortus lipopolysaccharide (PKLPS). Mice were vaccinated with different doses of BCSP or PKLPS given alone or in combination with MPL or TDM. Mice were challenge-exposed 4 weeks later with virulent B abortus strain 2308. Two weeks after challenge exposure, the number of B abortus colony-forming units (CFU) per spleen, spleen weights, and spleen cell interleukin 1 production were measured. Serum IgG and IgM concentrations specific for vaccinal immunogens were measured before and after challenge exposure with B abortus. Spleen weights and mean B abortus CFU per vaccine group were significantly lower in BCSP- and PKLPS-vaccinated mice, compared with those of nonvaccinated control mice. Monophosphoryl lipid A enhanced the suppression of splenic infection when given with the BCSP vaccine, but not when given with the PKLPS vaccine. Trehalose dimycolate had no effect on mean CFU when given with BCSP, but incorporation of TDM resulted in a significant increase in mean CFU when given with PKLPS. Spleen weights in BCSP- or PKLPS-vaccinated mice were not different when these vaccines were combined with MPL or TDM. Because of the wide variation in the results, we could not conclude that vaccination with BCSP or PKLPS alone, or in combination with MPL altered spleen cell interleukin-1 production in B abortus-infected mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mice immune responses to Brucella abortus heat shock proteins. Use of baculovirus recombinant-expressing whole insect cells,purified Brucella abortus recombinant proteins,and a vaccinia virus recombinant as immunogens

Brucella abortus resists the microbicidal mechanisms of macrophages, and the expression of its heat shock proteins (HSPs) such as GroEL, GroES and HtrA may play a role in this resistance. Bacterial HSPs can be very immunogenic, inducing protective immunity in various types of bacterial infections. However, the significance of immune responses directed against B. abortus HSPs in the protection against brucellosis is currently unresolved. To elucidate the role of these proteins in protection against Brucella challenge, individual, divalent or trivalent baculovirus (BV) recombinants of B. abortus GroEL, GroES and/or HtrA were injected into BALB/c mice either as protein-expressing whole cells or as purified proteins. The preparations were given to mice in combination with Freund's or Ribi adjuvant, respectively. In addition, some mice were primed with a vaccinia virus-GroEL recombinant, followed by inoculation with purified GroEL-Ribi adjuvant combination. Antibodies were observed against B. abortus GroEL and HtrA, but not against GroES. Cellular immune response was demonstrated by observing significant IFN-gamma release by lymphocytes of mice immunized with the purified HtrA-Ribi adjuvant combination. However, none of the mice inoculated with individual, divalent or trivalent HSP-expressing cells combined with complete Freund's adjuvant or inoculated with purified B. abortus HSPs combined with Ribi adjuvant, were protected against challenge with B. abortus virulent strain 2308. Priming with vaccinia virus-GroEL recombinant and boosting with GroEL-Ribi combination did not induce protective immunity. Based on the results obtained, we suggest that although humoral and cell-mediated immune responses are induced, but protective immune response is not induced by B. abortus HSPs.     

Levamisole potentiation of antigen specific lymphocyte blastogenic response in Brucella abortus exposed but nonresponsive cattle

Incubation of Brucella abortus (field strain) infected and strain 19 vaccinated bovine peripheral blood lymphocytes with B. abortus antigen and levamisole caused a consistently significant increase in [3H] thymidine uptake when compared to cultures without levamisole. Levamisole did not potentiate B. abortus-induced blastogenic response of lymphocytes from non-exposed cattle. A dose response study showed that 10 micrograms/culture induced maximum potentiation of B. abortus-induced lymphocyte stimulation. Using the 10 micrograms/well concentration of levamisole, further studies were conducted to determine the net potentiation of the blastogenic responses in lymphocytes from B. abortus (field strain) infected cattle. B. abortus strain 19 vaccinated but nonresponsive and non-exposed cattle. Levamisole significantly potentiated the B. abortus-induced lymphocyte blastogenesis in lymphocytes from unresponsive cattle.     

Immune response of cattle to Haemophilus somnus lipid A-protein conjugate vaccine and efficacy in a mouse abortion model.

Immunogenicity of the lipid A component of Haemophilus somnus lipooligosaccharide in cattle and mice was examined after purification, detoxification, and covalent conjugation to a protein carrier. After 2 inoculations, a substantial antibody response was induced in most cattle to lipid A and the protein carrier. To determine whether antibodies to lipid A would be protective, 5 x 10(7) colony-forming units of H somnus strain 649 were administered IV to endotoxin-responsive (C3H/HeN) mice. In one study, 8 of 13 C3H/HeN mice aborted when inoculated. In contrast, abortion did not result when mice were inoculated with the same dose of an isolate of H somnus normally found in the prepuce or with the rough mutant Escherichia coli J5. In addition, endotoxin-nonresponsive (C3H/HeJ) mice were significantly (P = 0.03) more resistant to abortion by strain 649 than were C3H/HeN mice, but inoculated C3H/HeN mice were only slightly more resistant to H somnus abortion, compared with control mice. Although a large antibody response to lipid A was detected, there was no significant difference in the immunized group between mice that aborted and mice that delivered normally. Thus, lipooligosaccharide and other properties of virulent H somnus strains may contribute to abortion in mice.     

Chemical and protective properties of Brucella lipopolysaccharide obtained by butanol extraction

Lipopolysaccharide (LPS) fractions were obtained from smooth cultures of Brucella abortus strains 2308 and S-19 by butanol extraction procedures. The LPS from the initial butanol extraction contained 10 to 15% protein and was reduced to less than 1% protein by treatment with proteinase K. The LPS fractions were identified and characterized on the basis of the chemical analysis, sodium dodecyl sulfate gel electrophoresis, cesium chloride gradients, electron microscopy, and gel immunodiffusion. Results indicated that the butanol procedure is a reliable method in the extraction of LPS from Brucella abortus cells. Proteinase K-treated LPS containing less than 1% protein from strain 2308 was used to vaccinate BALB/cByJ mice. Immune and protective criteria for vaccinated and nonvaccinated mice were increased immunoglobulin (IgG and IgM) titers in sera of prechallenge-exposed mice, reduced colony-forming units/spleen, and splenomegaly in post-challenge-exposed mice. Results indicated that proteinase K-treated LPS was immunogenic as well as protective for mice.     

Specific lymphocyte stimulation in cattle naturally infected with strains of Brucella abortus and cattle vaccinated with Brucella abortus strain 19.

Cell-mediated immune responses in cattle naturally infected with strains of Brucella abortus and in cattle vaccinated with B abortus strain 19 during calfhood were studied by an in vitro lymphocyte-stimulation procedure. Lymphocytes were prepared from peripheral bovine blood by the Ficoll-diatrizoate technique, suspended in RPMI-1640 medium (1.5 X 10(6) lymphocytes/ml), cultured with B abortus-soluble antigen or phytohemagglutinin, and incubated for 6 days. Sixteen hours prior to termination of incubation, cultures were labeled with 1 muCi of [3H]thymidine (3HdT) and, after harvesting, assayed for 3HdT incorporation into DNA by liquid scintillation spectrometry. Lymphocytes from cattle with bacteriologically confirmed isolation of B abortus underwent a significantly higher lymphocyte stimulation with B abortus-soluble antigen than did cattle vaccinated with B abortus strain 19 during calfhood (P less than 0.005). Standard seroagglutination tests were conducted simultaneously with lymphocyte-stimulation tests, but there was no apparent correlation between levels of humoral antibodies and the cell-mediated immune responses as measured by in vitro specific lymphocyte stimulation.     

Comparison between immune responses and resistance induced in BALB/c mice vaccinated with RB51 and Rev. 1 vaccines and challenged with Brucella melitensis bv. 3

BALB/c mice were immunized with live rough Brucella abortus RB51 or smooth Brucella melitensis Rev. 1 vaccines and challenged with a B. melitensis field strain. Protection was assessed by a variety of serological tests and recovery of vaccinal and challenge strains by culture. Mice vaccinated with RB51 gave negative results in the conventional serological tests prior to challenge, namely; standard tube agglutination test (SAT), Rose Bengal plate test (RBPT), buffered acidified plate antigen test (BAPAT), and mercaptoethanol test (MET). Sero-conversion took place to a whole-cell bacterial buffered RB51 antigen after vaccination and persisted for 7 weeks post-vaccination. Mice challenged with B. melitensis were assessed for bacterial load and immune response for 12 weeks after challenge. Protection units were showed that Rev. 1 vaccine was superior to RB51 vaccine in protection of mice against B. melitensis. However, RB51 vaccine has the advantage that it would not elicit antibodies to standard serological tests based on the LPS O antigen. RB51 vaccine could therefore be used for control of B. melitensis infection and avoid confusion in the use of standard sero-diagnostic tests.     

铜绿假单胞菌对TLR4缺失鼠的致病性研究

本研究旨在了解TLR4信号转导在铜绿假单胞菌感染所致急性肺损伤的发病机理中的作用.通过使用Tlr4基因突变致正常TLR4信号转导缺失的C3H/HeJ小鼠,评估TLR4信号转导在调节铜绿假单胞菌引起的急性肺损伤中的作用.选用6～8周龄、雄性、TLR4缺陷型(C3H/HeJ)和SPF级野生型(C3H/HeN)的小鼠各21只...     

The anamnestic response to Brucella abortus-infected and vaccinated cattle

Fifty-four cattle were sensitised to Brucella antigens either by vaccination with Brucella abortus strain 19 (S19) or B. abortus 45/20 (S45/20) and 24 of these were challenged 12 weeks after mating with virulent B. abortus strain 544 (S544). A further 12 cattle which were not vaccinated were exposed to S544. After 40 weeks, all these cattle (66), together with 5 cattle which were not sensitised by vaccination or challenge were subsequently inoculated with one dose of S45/20 and the anamnestic response was measured by the complement fixation test. Ten to 15 weeks later the cattle were slaughtered and tissues cultured. Of the 52 (2 died) vaccinated cattle, 35 gave a positive anamnestic response and 20 of these were not challenged. Of the 17 unvaccinated cattle, one gave a positive response and this animal had been exposed to S544 prior to the inoculation with S45/20. The results indicated that the method had a level of sensitivity of 75% and specificity of 100% in serologically negative cattle that had been exposed previously to Brucella antigens. An evaluation of the method for detecting serologically negative, but infected cattle was not possible as the number of cattle suitable for examination in this study was too low.     

Unresponsiveness of vaccinated BALB/c mice to a second inoculation of lipopolysaccharide from Brucella abortus strain 2308

A study was conducted to determine whether the protection induced in mice by a primary inoculation of lipopolysaccharide from Brucella abortus would be enhanced by a second inoculation given at different time intervals. Protection was challenged by exposure of the mice to a virulent culture of B. abortus strain 2308. Reduced mean viable count and/or splenic weights were the criteria of protection. There was no significant difference (P greater than 0.05) in the protective responses among mice given a single inoculation. Vaccinated mice were significantly (P less than 0.05) better protected than were nonvaccinated mice. Mice given vaccinal inoculations simultaneous with challenge exposure were less protected (P less than 0.001) than were mice vaccinated prior to challenge, but were better protected (P less than 0.010) than were nonvaccinated mice.     

Brucella abortus INTA2, a novel strain 19 (Delta)bp26::luc (Delta)bmp18 double mutant lacking drug resistance markers

Brucella abortus INTA2, a novel mutant strain, was constructed by inactivation of two B. abortus S19 genes: bp26 and bmp18, with the objective of obtaining a mutant strain that could be compatible with a diagnostic test and have less residual virulence than strain 19. The double mutant was constructed by replacing a large section of the bp26 coding region with the luciferase (luc) coding gene, resulting in mutant strain B. abortus M1luc, followed by partial deletion of bmp18 coding sequence. Both genes were inactivated by allelic replacement assisted by sacB counter-selection. Luciferase expression was evaluated and confirmed that it is a valid marker in the construction of mutant strains. When B. abortus INTA2 was inoculated in BALB/c mice, significantly fewer colony forming units (CFUs) were recovered from mice spleens during initial phase of infection. No splenomegaly was observed in strain INTA2-immunized mice at any time suggesting that strain INTA2 has lost some residual virulence of the parental strain. Nevertheless, similar protection levels against virulent challenge were observed in mice immunized with strains INTA2 or S19. Although strain INTA2 would still induce O-side antibodies, it does not express BP26. This would allow differentiation of INTA2-vaccinated animals from animals infected with field strains by measuring anti-BP26 antibodies, either by an agglutination test or ELISA using BP26 as antigen. Altogether these results indicate that B. abortus INTA2 might be a promising vaccine strain against brucellosis.     

Immunogenicity of Brucella-extracted and recombinant protein vaccines in CD-1 and BALB/c mice

A study was conducted to determine whether subcomponent proteins (previously identified as BCSP20, BCSP31, and BCSP45, and the corresponding recombinant proteins rBCSP20, rBCSP31, and rBCSP45) that were recovered from the cell surface of Brucella abortus strain 19 were immunogenic and protective for mice when compared with Brucella cell surface protein (BCSP) and with a proteinase K-treated lipopolysaccharide (PKLPS) extracted from B abortus strain 2308. Protection was evaluated after challenge exposure with a virulent culture of B abortus strain 2308, using CD-1 or BALB/c mice or both inoculated with vaccines of various combinations and concentrations, with and without PKLPS or BCSP. Protection was assessed by enumeration of splenic colony-forming units, reduced mean splenic weight relative to controls, and the relative serologic responses (immune response) in an ELISA. The general results indicate that BCSP, PKLPS, BCSP20, and BCSP31 are immunogenic or protective or both. Protectiveness was not observed for each of the recombinant proteins; however, results from the combined recombinant protein vaccine study suggest the immunogenicity of the recombinant proteins. The apparent immune-inducing properties of BCSP20 and BCSP31 are thought to be attributable to the presence of an immunogenic and protective BCSP fraction (possibly lipopolysaccharide) still associated. Serologic results support our conclusion that each of the recombinant protein vaccines did not induce a protective response comparable to that of BCSP or PKLPS, even when the subcomponents were combined. Although the results suggest that the subcomponents of BCSP apparently induced partial protection, they are thought to be only a part of the antigens contained in BCSP that influence the serologic response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Brucella abortus-specific immunoglobulin isotypes in serum and vaginal mucus from heifers vaccinated with Brucella abortus salt-extractable proteins and challenge exposed with virulent Brucella organisms

Serum and vaginal Brucella-specific immunoglobulin isotypes (IgG1, IgG2, IgM, and IgA), obtained from 62 crossbred beef heifers vaccinated with Brucella abortus salt-extractable proteins and subsequently challenge exposed with B abortus S2308, were studied. Brucella-specific IgG antibodies and Brucella-specific immunoglobulin isotypes were quantitated by a fluorometric immunoassay. Serum and vaginal immunoglobulin responses were evaluated as a method of distinguishing infected from noninfected heifers. Rivanol precipitation, complement-fixation, buffered-antigen brucellosis tests and an ELISA were performed on sera. For immunoglobulin isotypes, vaccinated heifers had mean antibody responses higher than baseline mean antibody responses for at least 31 weeks after vaccination. After challenge exposure, significant differences (P greater than 0.05) were not detected between mean antibody responses of vaccinated and nonvaccinated heifers. Vaginal Brucella-specific antibody responses did not correlate with protection from disease. Vaginal Brucella-specific IgM was detected only at the time of abortion. Vaginal IgA appeared specific for identification of virulent B abortus infection. All serotests appeared adequate in distinguishing baseline titers from titers of heifers that had aborted and were considered bacteriologic culture-positive. Results of serotests neither consistently distinguished vaccinates from challenge-exposed cattle nor distinguished heifers that were challenge exposed, had aborted, and were considered bacteriologic culture-positive adequately from heifers that were challenge-exposed, had not aborted, and were considered bacteriologic culture-negative. Brucella-specific IgA appeared to be the most effective in distinguishing vaccinated heifers from challenge- exposed heifers and heifers that were challenge exposed and had aborted, from heifers that were challenge exposed and had not aborted. Brucella-specific serum IgA was detected up to 13 weeks after abortion.