Immunopotentiation of cattle vaccinated with a soluble Brucella abortus antigen with low LPS content: an analysis of cellular and humoral immune responses.

The adjuvant effects of dimethyl dioctadecyl ammonium bromide (DDA) alone or in combination with trehalose dimycolate (TDM) or muramyl dipeptide (MDP) on bovine humoral and cellular responses to a soluble protein extract of gamma irradiated Brucella abortus strain 19 (SPEBA) were investigated. Thirty-five beef steers were randomly allotted to nine groups. Three of these groups received SPEBA (2 mg protein per dose) subcutaneously in combination with adjuvants, one group received the reduced dose of B. abortus strain 19 (S19), and one group received SPEBA alone. Controls included groups receiving adjuvant preparations only or no vaccine. Immune responses to the various immunizations were assessed sequentially for 56 days using various in vitro and in vivo assays. The humoral response to B. abortus was measured using standard serologic tests, an enzyme-linked immunosorbent assay, and a quantitative fluorometric immunoassay. The cell-mediated immune (CMI) response was measured by antigen-specific lymphoproliferation (LP), interleukin 2 (IL 2) production, and soluble suppressor factor release. Skin testing at day 35 for delayed-type hypersensitivity (DTH) to SPEBA was also performed. Minimal humoral responses were induced with SPEBA alone. The highest and most sustained serum antibody responses to B. abortus antigens were elicited by the S19 vaccine. A combination of SPEBA with DDA + TDM induced higher antibody levels than SPEBA with DDA or SPEBA with DDA + MDP. Responses to DTH among the groups receiving SPEBA were most notable in the SPEBA with DDA + TDM groups. Increased IL 2 production was greatest in the S19 and SPEBA with DDA + TDM vaccinates. The results indicated that a combination of DDA + TDM best potentiated immune responses to a soluble B. abortus antigen preparation and may be useful as adjuvants for future vaccines.     

Transient enhancement of the serum antibody response to Brucella abortus strain 19 in cattle treated with levamisole

Two experiments were done on 57 steers. These cattle were allotted to 8 groups (4 groups/experiment) and vaccinated with 1 to 3 X 10(9) colony-forming units of Brucella abortus strain 19. Cattle in 3 of the 4 groups/experiment were given 6 mg of levamisole/kg, subcutaneously, either at the time of vaccination (day 0), 7 days later, or at both times. Serum antibody titers to B abortus were measured sequentially for 28 days in experiment 1 and for 56 days in experiment 2, using the card test, Rivanol test, complement-fixation test, fluorometric immunoassay, and an enzyme-linked immunosorbent assay. In general, the highest mean antibody titers, as determined by all serologic tests, occurred in steers treated with levamisole at 7 days after vaccination or in those treated at the time of vaccination and 7 days later. By the card test on day 56, there was a significantly (P less than 0.05) greater number of seropositive cattle among those given levamisole 7 days after seropositive cattle among those given strain 19 alone. Simultaneous administration of strain 19 and levamisole did not alter antibody responses to B abortus.     

The effects of adjuvants on immune responses in cattle injected with a Brucella abortus soluble antigen.

Five different adjuvants were examined for potentiation of humoral and cell-mediated immune (CMI) responses in cattle to a Brucella abortus soluble antigen (BASA). Two separate experiments were performed involving a total of 64 steers, divided among six groups (Experiment 1) and 9 groups (Experiment 2). The adjuvants used were: muramyl dipeptide, Freund's incomplete adjuvant, dimethyl-dioctadecyl ammonium bromide (DDA), Bordetella pertussis and Propionibacterium acnes. In each experiment, three groups received BASA (2 mg protein) subcutaneously with adjuvant, one group received a reduced dose of B. abortus Strain 19 (S19), one group served as unvaccinated controls, and another group received BASA alone. Primary responses were studied following a single immunization in comparison to the single inoculation with S19. For each experiment serum antibody responses and CMI responses were sequentially determined over a period of 56 days. Antibody responses to B. abortus were measured using the brucellosis card, rivanol precipitation-plate agglutination, complement fixation, and fluorometric immunoassay tests, and as well as with an enzyme-linked immunosorbent assay. The CMI response was measured using antigen-specific lymphoproliferation (LP) and skin testing for delayed-type hypersensitivity (DTH) to BASA (Experiment 2). Specific aspects of induced CMI responses investigated were macrophage activation (IL-1 production), helper T cell activation (IL-2 production), and release of soluble suppressor factor(s). In general, mean antibody responses were significantly higher (P less than 0.05) in immunized steers than in control steers and those receiving BASA alone. The LP responses to heat-killed B. abortus were generally higher in immunized groups than in the controls. The LP and DTH responses were greatest in the groups receiving S19 and BASA + DDA. Increased induction of IL-1 was largest in the group receiving BASA + DDA whereas IL-2 release was greatest in S19 vaccinated steers. Suppressor T cell responses were most obvious in the groups receiving S19, BASA + B. pertussis, and P. acnes. These studies demonstrated that DDA potentiates CMI responses to a soluble B. abortus antigen and may be useful as an adjuvant for future vaccines, particularly subunit vaccines.     

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.     

Immunomodulation in cattle immunized with Brucella abortus strain 19

Regulation of the bovine immune response to immunization with Brucella abortus Strain 19 (S19) was investigated through application of a modification of an assay to measure suppressor T lymphocyte activities in humans and through development and characterization of antigen-stimulated T lymphocyte lines in vitro. A total of nine of steers were alloted into two groups: control (n = 4) and S19-immunized (n = 5). Peripheral blood mononuclear cells (PBMC) from each animal were cultured in vitro with mitogens (concanavalin A (Con A) and pokeweed mitogen (PWM], B. abortus antigens (B. abortus soluble antigen (BASA) and whole heat-killed B. abortus cells (HKC)) and media alone periodically from days 4 through 49 of the experiment. Supernates from these cultures were assayed for immunomodulatory activity(s) by addition to indicator cultures stimulated with suboptimal concentrations of Con A. Supernates from PBMC of S19-immunized steers generated with B. abortus antigens significantly (P less than 0.05) suppressed indicator cell responses as compared to those from control steers on days 35 and 49 post-immunization. This suppressive activity from PBMC of immunized cattle with respect to that of control cattle could also be induced through mitogenic stimulation with Con A or PWM. On day 49 of the study, suppressive activity was spontaneously released from the PBMC of immunized cattle. T lymphocyte lines were initiated from two S19-immunized steers at 2 and 9 weeks post-immunization. These T cell lines were characterized with respect to proliferative responses to B. abortus antigens through in vitro assay and surface marker expression through indirect immunofluorescence with a limited panel of monoclonal antibodies. Results from the present study indicated that S19 immunization induces a subpopulation(s) of cells in the PBMC of cattle capable of regulating the in vitro response to B. abortus. This regulatory activity is detectable by in vitro assay as early as 7 weeks post-immunization. Furthermore, the regulatory cell(s) appear to involve BoCD8+ T, lymphocytes which are specific for B. abortus antigens.     

Cytokine responses in camels (Camelus bactrianus) vaccinated with Brucella abortus strain 19 vaccine

In the present study, we determined the levels of cytokines produced by camel (Camelus bactrianus) peripheral blood mononuclear cells (PBMCs) in response to live attenuated Brucella abortus (B. abortus) S19 vaccine. Seven camels were vaccinated with commercial B. abortus S19 vaccine, and their cytokine responses were determined using a real-time PCR assay. Cytokine responses to B. abortus S19 were examined at 6 hr, 48 hr and 1, 2 and 3 weeks post-vaccination. Serological tests were performed to further confirm these immune responses. The results revealed that IFN-gamma and IL-6 were upregulated during the first week post-vaccination. Low level expressions of IL-1alpha, IL-1beta, TNFalpha and IL-10 and no expression of IL-2 and IL-4 were observed compared with the control camels. The findings showed that B. abortus stimulates cell-mediated immunity by directly activating camel Th1 cells to secrete IFN-gamma. This quantification of cytokine expression in camels is essential for understanding of Camelidae disease development and protective immune responses. This is the first report of in vivo camel cytokine quantification after vaccination.     

Brucella abortus-specific immunoglobulin in isotypes in serum and vaginal mucus from cattle vaccinated with strain 19 and challenge exposed with virulent strain 2308

The immunoglobulins (IgG1, IgG2, IgM, and IgA) of the Brucella-specific antibody response of 69 crossbred beef heifers were studied after Brucella abortus strain 19 vaccination and strain 2308 challenge exposure. The immunoglobulin isotype responses in serum and vaginal mucus were measured by use of fluorescent immunoassay. Serum antibody responses were detected also by 3 standard serologic tests (complement fixation [CF], Rivanol precipitation, and the CARD test] and 2 primary bindings assays that detect IgG antibodies. One month after vaccination, mean antibody titers for all immunoglobulin isotypes were higher for vaccinated cattle (n = 46) than for nonvaccinated controls (n = 23). After vaccination, IgA antibody responses in vaccinated cattle were only 2-fold higher than those for controls, whereas IgG1, IgG2, and IgM antibody responses were 3- to 90-fold greater than those for controls. Measurement of IgA antibody responses classified 21 of 39 vaccinates as seropositive after vaccination, whereas the other isotypes classified 28 or 34 cattle as seropositive. Three months after challenge exposure, the mean antibody responses for each isotype were higher in cattle that aborted or were culture positive than in cattle that did not abort and were culture negative. Although IgG1, IgG2, and IgM antibody titers were each of benefit in identifying B abortus-infected cattle, it did not appear that the magnitude of the antibody responses provided sufficient discrimination between S19-vaccinated cattle and S2308 challenge-exposed cattle. Serum IgA antibody responses were 10-fold higher after challenge exposure than after vaccination and may be a response to mucosal infection with the virulent organism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dose of Brucella abortus strain 19 in yearling heifers on the relative risk of developing brucellosis from challenge exposure with strain 2308

Yearling heifers were given SC injections of 10(8) (n = 40), 10(9) (n = 44), or 10(10) (n = 44) colony-forming units of Brucella abortus strain 19 (S19). The proportion of heifers with positive serologic test results at 1 month following vaccination increased as the dose of S19 increased. These proportions decreased with time, and all heifers had negative card, rivanol, and complement fixation test results within 4 months. Positive ELISA results persisted beyond 4 months in all three S19 dose groups; however, all heifers were ELISA-negative within 9 months after vaccination. Comparable lymphocyte transformation activity was stimulated by S19 dose of 10(9) or 10(10) and approximately half of the heifers in both groups had a positive stimulation index at 9 months. Immunity of the pregnant heifers was challenged 9 months after vaccination with 10(7) B abortus strain 2308 as follows: diluent controls (n = 69); 10(8) B abortus S19 (n = 40); 10(9) B abortus S19 (n = 39); and 10(10) B abortus S19 (n = 39). Tissue specimens from heifers were obtained at parturition and necropsy for culturing of B abortus. The proportion of heifers that developed brucellosis, ie, had positive culture results, increased as gestation days at challenge exposure increased. The effect of gestational age was controlled in the analysis using logistic regression. The relative risk of brucellosis was reduced to 0.38, 0.15, and 0.06 for B abortus S19 doses of 10(8), 10(9), and 10(10), respectively, compared with diluent controls at 1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of an enzyme-linked immunosorbent assay using monoclonal antibodies and a complement fixation test for cattle vaccinated and infected with Brucella abortus

A competitive enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody conjugated to horseradish peroxidase MA(A) and a complement fixation test (CFT) were applied to sera collected over a two-year period from 60 cattle challenged with Brucella abortus strain 544. Forty-eight of the cattle were previously vaccinated with B. abortus strain 19 (S19) or B. abortus strain 45/20 (45/20). After challenge 33 of the cattle remained uninfected and nine of the 27 infected cattle showed aberrant reactions by the CFT. The performance of the MA(A) ELISA was as follows: after vaccination, the MA(A) ELISA, like the CFT, was unable to differentiate infected cattle from those recently vaccinated with S19. After challenge the MA(A) ELISA gave results comparable with the CFT for those cattle with aberrant reactions. For the non-infected cattle there was a similar number of weeks after challenge when both tests were negative. It is suggested that the main advantage of the MA(A) ELISA when compared with the CFT lies in its relatively simple test procedure.     

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.     

An enzyme-linked immunosorbent assay for detection of Brucella abortus in cattle using monoclonal antibodies

One group of 24 cattle was vaccinated with the usual calfhood dose of B. abortus strain 19 and a further 27 cattle were similarly vaccinated but as adults. Twenty-four cattle (12 from each group) and a control group of 12 cattle were subsequently challenged with B. abortus strain 544. Two monoclonal antibodies (MA (A) and MA (B) ) conjugated to horseradish peroxidase were used independently in a competitive enzyme-linked immunosorbent assay (ELISA) to test the serums. After vaccination with B. abortus strain 19, the performance of the monoclonal antibodies was in general agreement with the CFT as fewer calfhood vaccinates were positive 12 weeks after vaccination to the ELISA with MA (A) and MA (B) than adult vaccinates. After challenge, MA (A) and MA (B) ELISA tests detected the infected cattle earlier than the CFT, but more positive reactions occurred in the cattle that proved uninfected at slaughter.     

An evaluation of the anamnestic test for brucellosis in cattle of the northern pastoral area

SUMMARY An investigation of the anamnestic test for brucellosis using Brucella abortus 45/20 vaccine was carried out in 3 groups of weaner cattle on 2 farms in western Queensland. Each group originally consisted of about 500 cattle. They were bled before and at 6 or 10 weeks after vaccination and again in the following year. The serums were tested by the complement fixation (CFT), Rose Bengal (RBT) and indirect haemolysis tests (IHLT). Most of the cattle reacting to one or more of the tests were killed and selected tissues were subjected to bacteriological examination for B. abortus. B. abortus was isolated from 19 of 30 (63%) pre-vaccinal reactors, 23 (24%) of 96 cattle reacting at 6 or 10 weeks after vaccination (the anamnestic test) and 1 (2%) of 50 cattle reacting one year after vaccination. The reactor found to be infected the year after vaccination had high serological titres in each of the 3 serological tests: RBT of 3, CFT of 128 and IHLT of 256. A subsequent test showed the group to be brucellosis-free. The CFT was the most efficient test. In the pre-vaccination tests 17 of 19 infected animals were positive in the CFT compared with 11 positive in the IHLT and 17 in the RBT. In post vaccination tests 22 of 23 infected animals were positive in the CFT compared with 18 in the IHLT and 19 in the RBT. At the pre-vaccinal and anamnestic tests (6 or 10 weeks after vaccination) 19 of 57 (33%) cattle with CF titre of 4 or 8 yielded B. abortus on culture compared with none of 26 cattle with similar titres in the year after vaccination. The interpretation of CF titres in cattle following 45/20 vaccination needs to be re-examined.     

Antibody isotype response in adult cattle vaccinated with Brucella abortus S19

In a chronological study of sera collected from eight adult cattle vaccinated with 3 X 10(-10) cfu of Brucella abortus S19, antibody of each of the four major isotypes was measured by indirect enzyme immunoassay (ELISA) and by direct and modified complement fixation tests (CFT). Six of the cattle gave antibody responses to the vaccine strain that commenced between days 5 and 8 for all the isotypes in the ELISA, peaked by 1 to 4 months and then declined to low levels by 10 months. Direct CFT and modified CFT titers were measurable by 7 or 8 days post-vaccination, and peaked by 1 month; direct CFT titers disappeared by 5 months while the modified CFT titers lingered for 10 months. Two animals gave cyclical direct CFT and modified CFT antibody responses, a cyclical IgG1 response, a low IgG2 and an elevated IgA response. The amplitude of the cycles was uniform over three cycles while the wavelength increased with time. A year post-vaccination, B. abortus S19 was isolated twice from milk from one of the animals (no attempt was made to culture B. abortus from the other). Sera from B. abortus naturally infected cattle were analysed for comparison.     

Variations in immunoglobulin isotype produced during the antibody response to Brucella abortus and Staphylococcus aureus vaccines in sheep

Experiments in sheep were carried out to examine factors modifying the immunoglobulin (Ig) isotype of the antibody response to Brucella abortus. Live B abortus (S19) stimulated higher titres of agglutinating antibody and IgG1 and IgG2 antibody than did killed B abortus. Live B abortus stimulated a more protracted synthesis of IgG2 antibody during the primary and secondary responses than did the killed S19 vaccine. In a second experiment, the capacity of live and killed Staphylococcus aureus to modify the antibody response to killed B abortus was examined. Both live and killed S aureus enhanced production of anti-brucella antibodies; this response was attributed to the adjuvant properties of S aureus. Killed S aureus enhanced production of anti-brucella antibody to a greater extent than live S aureus. Live S aureus did not preferentially enhance production of IgG2 anti-brucella antibody. The results suggested that the enhanced production of IgG2 antibody induced by live vaccines does not depend solely on a pyogenic lesion at the vaccination site.     

Biotypes of Brucella abortus and their value in epidemiologic studies of infected cattle herds.

Four Texas cattle herds containing cows infected with either Brucella abortus biotype 1, 2, or 4 were studied to determine the probability of transmission of Brucella between adjacent cattle herds, the most probable means by which Brucella was introduced into the herds, and the relative frequency of strain 19 isolation from vaccinated cattle. A total of 1,935 cattle in the four herds were tested for brucellosis; 339 reactors were identified, and isolations of B abortus were made from 143. The biotype of B abortus was used to determine that purchased cattle or reentry of bred heifers into the herds was probably responsible for introducing B abortus and that the biotype was not readily transmitted to adjacent herds. Three (9%) of 32 B abortus isolations from adult-vaccinated cattle were strain 19. The data supported the hypothesis that biotypes can be useful in determining the source of B abortus for cattle and in differentiating field and vaccine strain infections in adult-vaccinated cattle.     

VACCINATION OF PREGNANT COWS WITH LOW DOSES OF BRUCELLA ABORTUS STRAIN 19 VACCINE

Two groups, each of 9 Jersey cows, were vaccinated subcutaneously with reduced doses of Brucella abortus strain 19 vaccine (measured by the number of bacteria in the vaccine dose) early in their second pregnancy. Ten weeks later they were challenged, along with a similar group of non-vaccinated cows, by conjunctival instillation of a virulent strain of B. abortus biotype 1. Cows in Group 1 received 1/20th and those in Group 2 received 1/400th the recommended dose of strain 19. Marked reduction in the serological response to vaccination was seen only in Group 2. Four cows in Group 1 excreted strain 19 after parturition, one of them aborted and another calved prematurely with heavy infection of the placenta and foetus with strain 19 in both cases. Resistance to challenge was similar in both vaccinated groups, and higher than previously demonstrated after conventional calfhood vaccination with strain 19. It is concluded that pregnant cows can be effectively vaccinated by the subcutaneous administration of a dose of strain 19 vaccine containing approximately 3 x 10(8) organisms without undue interference with subsequent serological tests or inconvenience resulting from persistence of strain 19 infection.     

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.     

Effects of stage of gestation and breed on bovine responses to vaccination with Brucella abortus strain 19.

Eighty-eight cattle were injected SC with 2.5 x 10(8) viable cells of Brucella abortus strain 19. All but 1 heifer became seropositive on the basis of the results of 7 brucellosis tests, and the proportion positive decreased with time. The proportion of cattle that were seropositive during a 20- to 67-week period after vaccination was as follows, in decreasing order: hemolysis-in-gel, 59%; buffered-acid plate antigen, 39%; ELISA, 16%; card, 10%; rivanol, 8%; cold complement-fixation, 7%; and automated complement-fixation, 5%. Using the serologic classification in Uniform Methods and Rules for brucellosis eradication, 7 cattle tested brucellosis-positive (2 suspects and 5 reactors). None of the 27 nonpregnant heifers tested positive. Of 18 heifers that were 84 to 135 days in gestation when vaccinated, 6 (33%) tested positive for brucellosis, compared with 0 of 13 and 1 (3%) of 30 heifers that were 11 to 78 and 145 to 253 days in gestation at vaccination, respectively (X2 = 12.07; 2 df; P less than 0.01). Neither breed (Angus, Hereford, Jersey, and Brahman) nor calf survival was related to brucellosis-positive results. Postpartum milk samples from 61 heifers and 24 tissues from 2 reactor cattle were culture-negative for B abortus.     

Immunomodulation with killed Propionibacterium acnes in guinea pigs simultaneously vaccinated with Brucella abortus strain 19

Immunomodulation with killed Propionibacterium acnes was attempted in guinea pigs simultaneously vaccinated with Brucella abortus strain 19. Two groups, each comprised of 9 guinea pigs, were injected by different routes (s.c. and or i.v.) with 1.4 mg of P. acnes and 5 X 10(8) CFU of B. abortus, S-19, while 3 other groups each received either P. acnes, B. abortus S-19, or saline (s.c.). The antibody titers to B. abortus measured at 6, 10 and 14 weeks after vaccination indicated no significant (P less than 0.01) response in the 2 groups immunopotentiated with P. acnes concurrent with B. abortus S-19 vaccination. The delayed hypersensitivity response to 3 Brucella antigens conducted 8 weeks after immunization did not show a significant difference between the B. abortus S-19 vaccinated group compared with the 2 groups immunopotentiated and vaccinated. However, the proliferative response of lymphocytes to the B. abortus soluble antigen diluted 1:100 indicated significantly enhanced blastogenesis in the (s.c.) immunopotentiated and immunized guinea pigs compared with the B. abortus S-19 vaccinated group. A slightly enhanced response was also observed in the group immunopotentiated (i.v.) and vaccinated (s.c.). The guinea pigs were challenged with B. abortus strain 2308 and necropsied 4 weeks later. The mean splenic CFU of the Brucella in the group immunopotentiated (i.v.) and vaccinated (s.c.) was significantly decreased when compared with the guinea pigs vaccinated with B. abortus S-19 alone. These findings indicated that P. acnes administered simultaneously with B. abortus S-19 vaccine was able to augment the immune response in guinea pigs. Immunomodulation as evidenced by enhanced clearance of B. abortus from the spleens of immunopotentiated animals was presumably brought about by activated macrophages or a T-cell mediated cytolytic mechanism or both.     

Temporal cell-mediated immune responses of cattle following experimental and natural exposure to living Brucella abortus.

A study on cell-mediated immune responses in cattle with different exposure experiences to Brucella abortus was conducted by an in vitro lymphocyte stimulation assay. The purpose of this study was to determine how soon the cell-mediated immune responses would be detected following experimental exposure to B. abortus and to study the cell-mediated immune trend following experimental and natural exposure of cattle to B. abortus. The first positive cell-mediated immune responses occurred one to two weeks after experimental inoculation with living B. abortus strain 2308. The cell-mediated immune responses in these animals appeared at least one week before the appearance of of B. abortus serum agglutinating antibodies. Animals which were naturally infected with B. abortus biotypes 1 and 2 demonstrated positive cell-mediated immune responses throughout the study.