Effects of the lipopolysaccharide-protein complex and crude capsular antigens of Pasteurella multocida serotype A on antibody responses and delayed type hypersensitivity responses in the chicken.

The effects of the lipopolysaccharide-protein complex (LPS) and crude capsular antigen (CCA) prepared from Pasteurella multocida serotype A isolated from a duck in the Philippines, on antibody responses to sheep red blood cells (SRBC) and Brucella abortus (BA) and delayed type hypersensitivity (DTH) responses to bovine serum albumin (BSA) in the chickens were studied. Chickens injected subcutaneously with LPS and CCA at 1 and 2 weeks of age and immunized intravenously with the mixed antigens of SRBC and BA, at 3 and 4 weeks of age showed significantly increased antibody responses against both SRBC and BA, when evaluated at 7 days after each immunization. In addition, these chickens sensitized intramuscularly with the emulsion of BSA in complete Freund's adjuvant at 5 weeks of age, and then injected into the wattle with BSA at 7 weeks of age also showed significantly increased DTH responses against BSA, when evaluated at 24 and 48 hr after challenge. These results indicate that LPS and CCA of P. multocida serotype A have a property enhancing humoral and cell-mediated immune responses.     

Induction of mucosal immune responses following enteric immunization with antigen delivered in alginate microspheres

Oral immunization is the most effective way of inducing immune responses in the intestinal tract. Biodegradable microspheres have been used extensively for the delivery of antigens to the Peyer's patches (PPs) within the gut-associated lymphoid tissue (GALT). We evaluated various formulations of alginate microspheres for their capacity to induce mucosal immune responses in vivo. Multiple intestinal "loops" each containing a single PP, were surgically prepared in lambs. We have previously showed that PP in individual intestinal loops function as independent sites for the induction of immune responses. This animal model provides a system for directly comparing different antigen formulations within the same animal. Individual intestinal loops were injected with a model antigen, porcine serum albumin (PSA) encapsulated in three different formulations of alginate micropsheres. Three weeks after immunization, PSA-specific immune responses were assayed with antibody secreting cell (ASC) ELISPOT, lymphocyte proliferative responses (LPRs), IFN-gamma production and antibody secreted into intestinal loops. PSA encapsulated in alginate micropsheres or in saline induced humoral immune responses as indicated by the presence of numerous ASC. However, PSA-specific T-cell responses (LPR and IFN-gamma production) were not induced.     

The effect of immunity to core lipopolysaccharides (LPS) on the production of thromboxane and prostacyclin by equine peritoneal macrophages

An experiment was designed to determine whether a change in the ability of macrophages to respond to lipopolysaccharides (LPS) of gram-negative bacteria was involved in the development of cross-reactive immunity to endotoxemia. The endotoxin-induced production of thromboxane A2(TxA2) and prostacyclin (PGI2) by peritoneal macrophages from horses which were hyperimmunized against the common core region of LPS were compared to those in unimmunized horses. Bacterins used for induction of core LPS immunity were prepared from the J-5 mutant of Escherichia coli 0111:B4, and the R 595 mutant of Salmonella minnesota. Serum antibody titers to core LPS were determined by an indirect enzyme-linked immunosorbent assay. Immunized horses had a marked increase in titer to core LPS (p less than 0.05), while there was no change in titer in unimmunized control horses. The only significant difference in the in vitro LPS-induced production of TxA2 and PGI2 by peritoneal macrophages between immunized and control horses was a greater production of TxA2 by macrophages from immunized horses in response to 10 ng/ml LPS (p less than 0.05). Results of this experiment do not support the concept that cross-reactive immunity to LPS is attended by reduced production of TxA2 and PGI2 by equine peritoneal macrophages.     

A preliminary study to evaluate the immune responses induced by immunization of dogs with inactivated Ehrlichia canis organisms

Ehrlichia canis is an intracellular pathogen that causes canine monocytic ehrlichiosis. Although the role of antibody responses cannot be discounted, control of this intracellular pathogen is expected to be by cell mediated immune responses. The immune responses in dogs immunized with inactivated E. canis organisms in combination with Quil A were evaluated. Immunization provoked strong humoral and cellular immune responses, which were demonstrable by Western blotting and lymphocyte proliferation assays. By Western blotting antibodies to several immunodominant E. canis proteins were detected in serum from immunized dogs and antibody titres increased after each immunization. The complement of immunogenic proteins recognized by the antisera were similar to those recognized in serum from infected dogs. Upon challenge with live E. canis, rapid anamnestic humoral responses were detected in the serum of immunized dogs and primary antibody responses were detected in the serum from control dogs. Following immunization, a lymphocyte proliferative response (cellular immunity) was detected in peripheral blood mononuclear cells (PBMNs) of immunized dogs upon stimulation with E. canis antigens. These responses were absent from non-immunized control dogs until after infection with live E. canis, when antigen specific-lymphocyte proliferation responses were also detected in the PBMNs of the control dogs. It can be thus concluded that immunization against canine monocytic ehrlichiosis may be feasible. However, the immunization regimen needs to be optimized and a detailed investigation needs to be done to determine if this regimen can prevent development of acute and chronic disease.     

Antibody responses of calves to Histophilus somni recombinant IbpA subunits

Histophilus somni causes bovine pneumonia and septicemia, but protective immune responses are not well understood and immunodiagnostic methods are not well defined. We previously showed that antibody to a new virulence factor, IbpA, neutralizes cytotoxicity and immunization with a recombinant IbpA domain protects calves against experimental H. somni pneumonia. To further define immune responses to IbpA, we determined isotypic serum antibody responses to three IbpA domains (IbpA3, an N-terminal coiled coil region; IbpA5, a central region of 200 bp repeats and IbpA DR2, a C-terminal cytotoxic domain). ELISA was used to quantitate IgG1 or IgG2 antibodies to each of the IbpA subunits as well as H. somni whole cells (WCs) or culture supernatant (SUP). Calves experimentally infected with H. somni and monitored for up to 10 weeks had the least "0 time" (background) antibody levels to IbpA5, as well as the earliest and highest responses of greatest duration to the IbpA5 subunit. Responses of these calves were high to WC or SUP antigens but with higher "0 time" (background) antibody levels. We concluded that IbpA5 may be a useful immunodiagnostic antigen. Calves immunized with H. somni WC vaccine had antibody responses to WC antigens, but not to IbpA subunits before challenge. After challenge with H. somni, vaccinated calves had slight anamnestic responses to IbpA3 and IbpA5, but not to IbpA DR2. Since IbpA DR2 is a protective antigen, the data suggest the IbpA DR2 would be a useful addition to H. somni vaccines.     

Effect of pasteurella multocida toxin on in vivo immune responses in piglets

Summary

Atrophic rhinitis is characterized by a lack of an immune response towards Pasteurella multocida toxin (Pm‐T). The effects of intranasal administration of Pm‐T on cellular and T‐cell dependent antibody responses of piglets against various other antigens were studied in a 3 by 2 factorial arrangement of treatments: three levels of challenge with Pm‐T (either once; on three consecutive days; or no Pm‐T challenge), and with or without simultaneous immunization with a ‘cocktail’ containing Keyhole limpet haemocyanin (KLH), ovalbumin (OA) and tetanus toxoid (TT). Challenge with Pm‐T affected but did not abolish the in vivo humoral immune response against OA, KLH, or TT. Pigs treated once with Pm‐T showed lower total antibody responses, caused by lower IgG responses to the antigens. We found no clear consistent effects of Pm‐T on cellular immune responses to the various T‐cell‐dependent antigens in vitro. The lack of immune responsiveness to Pm‐T in Pm‐T challenged pigs is discussed. The absence of detectable immune responses does not depend on a general suppression of the cellular immune system.     

Oral immunisation of pigs with fimbrial antigens of enterotoxigenic E. coli: an interesting model to study mucosal immune mechanisms

The intestinal mucosal immune system can discriminate actively between harmful pathogenic agents and harmless food antigens resulting in different immune responses namely IgA production and oral tolerance, respectively. Recently, a pig model has been developed for studying intestinal mucosal immune responses in which F4 fimbrial antigens of enterotoxigenic Escherichia coli (F4 ETEC) are used as oral antigens. A unique feature of this model is that soluble F4 antigens can be administered to pigs which have a receptor for this fimbriae (F4R(+)) on their small intestinal villous enterocytes and pigs which do not have this receptor (F4R(-)). Oral administration of F4 to the F4R(+) pigs results in an intestinal mucosal immune response that completely protects the pigs against a challenge infection. In F4R(-) pigs such an intestinal mucosal immune response does not occur. However, a priming of the systemic immune system can be seen similar to the priming in pigs fed with the same dose of a food antigen, suggesting that F4 in F4R(-) pigs behaves as a food antigen. The fact that different mucosal immune responses can be induced with soluble F4, makes it an interesting model to study mucosal immune mechanisms in the pig.     

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.     

Immune responses against excreted/secreted antigens of Toxoplasma gondii tachyzoites in the murine model

In the present study, excretory secretory antigens (ESA) of Toxoplasma gondii were evaluated in immunization of 8-10 week inbred female Balb/c mice. Tachyzoites of the parasite were cultured in cell-free incubation medium (RPMI-1640), and then supernatant of the medium was loaded on an ion-exchange chromatography column. Two fractions (ESA-F(1) and ESA-F(2)) were collected from the column. For immunization of the mice, 50 were allocated into 5 groups of 10. The first, second, third, and fourth groups were immunized, twice with total-ESA, ESA-F(1), ESA-F(2) or toxoplasma lysate antigen (TLA), respectively. The fifth group was selected as a negative control group (non-immunized). The virulent RH strain of Toxoplasma gondii was used to challenge. Delayed-type hypersensitivity responses (DTHs) were measured by intra-footpad injection measuring induration at timed intervals. Lymphocyte transformation tests (LTTs) were done on lymph node cells using [3H] thymidine incorporation as an indication of reactivity. Peritoneal macrophages from sensitized mice were stimulated and nitric oxide was measured by Griess method. The ESA-F(1) and ESA-F(2) fractions were separated on poly acrylamide gel electrophoresis (PAGE) and SDS-PAGE. ESA-F(1) had 4 bands on PAGE and 14 bands on SDS-PAGE. ESA-F(2) had one band on PAGE and two bands on SDS-PGE. Sensitized mice showed DTH and lymphocyte transformation responses to total-ESA, ESA-F(1), and ESA-F(2) and peritoneal macrophages produce nitric oxide following stimulation. In challenge experiments, all non-immunized mice died within 10 days, whereas immunized mice survived for longer time periods (P<0.05). The highest survival rate was observed in mice that immunized with ESA-F(2). We suggest that these antigens especially ESA-F(2) should be of value for the development of new strategies for immunization against toxoplasmosis.     

Comparison of the Antibody Response in Adult Cattle Against Different Epitopes of Brucella abortus Lipopolysaccharide

The comparison of serological responses in a sample of adult, vaccinated and field‐infected bovines with Brucella abortus is reported. Indirect enzyme immunoassay (EIA) titration curves and Western blotting tests for smooth‐type lipopolysaccharide (S‐LPS), rough‐type LPS (R‐LPS) and lipid A were performed. In the initial screening of sera, an overall prevalence of 20.5 % was found, which corresponds to a country with a high incidence of brucellosis. End‐point EIA titres against LPS antigens from vaccinated and field‐infected cows were not significantly different. However, the absorbance values in the titration curves were significantly higher for S‐LPS as compared with the other antigens. A high correlation coefficient (r=0.933) was obtained when the titres to R‐LPS versus lipid A were compared. Western blotting reactions of vaccinated and field‐infected animals were indistinguishable. S‐LPS, R‐LPS and lipid A epitopes were recognized in a heterogeneous manner. In general, the number of bovines that reacted against LPS was higher in the field‐infected group, with a stronger binding to S‐LPS. Based on our observations, the vaccinated and field‐infected bovines are capable of producing similar antibody responses to the Brucella main outer surface antigen, LPS. It should be emphasized that the humoral response of cattle to Brucella LPS contains significant amounts of antibodies to other antigenic moieties of this important surface molecule, which may contribute to the immunity to brucellosis.     

Immune responses of infected and vaccinated Hereford cattle to antigens of the cattle tick, Boophilus microplus

Responses of infested and vaccinated Hereford cattle to Boophilus microplus antigens were measured by enzyme-linked immunosorbent assay (ELISA), lymphocyte blastogenesis assay (LBA) and intradermal skin tests. Responses against soluble salivary gland extracts (SGS), salivary gland membrane (SGM), soluble gut extracts (GS), gut membrane (GM), soluble larval extracts (LS) and larval membrane (LM) antigens were tested. In one experiment, cattle infested with up to 160,000 ticks had positive cellular responses to SGS and significant antibodies against LM, GM, SGM, and SGS. Cellular responses to Concanavalin A were not depressed following infestation. Cattle vaccinated with GM, using Quil A as adjuvant, had positive cellular responses to gut and salivary gland antigens and significant antibody responses to all antigens tested. The antibody levels of vaccinated cattle were significantly higher than the antibody levels of infested cattle (P less than 0.05). In a second experiment, immune responses of cattle infested with 40,000 ticks were studied during 38 days. Cellular responses in LBA to several tick antigens were transiently elevated and significant levels of antibody were measured against LM, GM, SGM and SGS, from day 25 (P less than 0.05). Infested cattle had positive skin reactions following intradermal injection of larval and adult tick antigens (P less than 0.05).     

Effect of maternal cells transferred with colostrum on cellular responses to pathogen antigens in neonatal calves

OBJECTIVE: To assess the effect of maternal cells or cellular components on neonatal immune responses to intracellular pathogens in calves. ANIMALS: 15 Holstein calves. PROCEDURES: Calves were fed whole colostrum, frozen colostrum, or cell-free colostrum within 4 hours after birth. Leukocytes were obtained from calves before feeding colostrum and 1, 2, 7, 14, 21, and 28 days after ingestion. Proliferative responses against bovine viral diarrhea virus (BVDV) and mycobacterial purified protein derivatives were evaluated. Dams received a vaccine containing inactivated BVDV, but were not vaccinated against mycobacterial antigens. RESULTS: All calves had essentially no IgG in circulation at birth, but comparable and substantial concentrations by day 1. Calves that received whole colostrum had enhanced responses to BVDV antigen 1 and 2 days after ingestion of colostrum. In contrast, calves that received frozen colostrum or cell-free colostrum did not respond to BVDV. No differences were identified among the 3 groups in response to mycobacterial antigens. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that transfer of live maternal cells from colostrum to neonatal calves enhanced responses to antigens against which the dams had previously responded (BVDV), but not to antigens to which the dams were na?ve (mycobacterial purified protein derivatives). Results suggested that cell-mediated immune transfer to neonates can be enhanced by maternal vaccination.     

Enhancement of protective immune responses by oral vaccination with Saccharomyces cerevisiae expressing recombinant Actinobacillus pleuropneumoniae ApxIA or ApxIIA in mice

We previously induced protective immune response by oral immunization with yeast expressing the ApxIIA antigen. The ApxI antigen is also an important factor in the protection against Actinobacillus pleuropneumoniae serotype 5 infection; therefore, the protective immunity in mice following oral immunization with Saccharomyces cerevisiae expressing either ApxIA (group C) or ApxIIA (group D) alone or both (group E) was compared with that in two control groups (group A and B). The immunogenicity of the rApxIA antigen derived from the yeast was confirmed by a high survival rate and an ApxIA-specific IgG antibody response (p < 0.01). The highest systemic (IgG) and local (IgA) humoral immune responses to ApxIA and ApxIIA were detected in group E after the third immunization (p < 0.05). The levels of IL-1β and IL-6 after challenge with an A. pleuropneumoniae field isolate did not change significantly in the vaccinated groups. The level of TNF-α increased in a time-dependent manner in group E but was not significantly different after the challenge. After the challenge, the mice in group E had a significantly lower infectious burden and a higher level of protection than the mice in the other groups (p < 0.05). The survival rate in each group was closely correlated to the immune response and histopathological observations in the lung following the challenge. These results suggested that immunity to the ApxIA antigen is required for optimal protection.     

Orientation of bovine CTL responses towards PIM, an antibody-inducing surface molecule of Theileria parva, by DNA subunit immunization

East Coast fever, an acute lymphoproliferative disease of cattle, is caused by the apicomplexan parasite Theileria parva. Protective immunity is mediated by CD8(+) cytotoxic T lymphocytes directed against schizont-infected cells. The polymorphic immunodominant molecule, although an antibody-inducing surface molecule of the schizont, has been hypothesized to play a role in protective immunity. In order to evaluate the immunogenicity of PIM for inducing CTL, cattle were immunized with PIM in isolation from other T. parva antigens, forcing the presentation of PIM-derived epitopes on the MHC class I molecules. Although parasite-specific cytotoxicity was induced in both vaccinated animals, their immune response was clearly different. One animal generated MHC-restricted parasite-specific CTL against PIM while the other calf exhibited a strong PIM-specific proliferative response but non-MHC-restricted parasite-specific cytotoxicity. Only calf 1 survived a lethal sporozoite challenge. This DNA immunization technique with an antigen in isolation of CTL-immunodominant antigens might open possibilities for directing CTL responses against predefined antigens, such as strain cross-reacting CTL antigens.     

Cell-mediated immune responses differentiate infections with Brucella suis from Yersinia enterocolitica serotype O:9 in pigs

Due to almost identical lipopolysaccharide (LPS) O-antigens, infections with Yersinia enterocolitica serotype O:9 (YeO:9) cause false positive serological reactions (FPSR) in tests for Brucella and thus cause problems in National Brucella surveillance programs. As LPS are strong inducers of antibody responses it was hypothesized that cell-mediated immune responses to non-LPS antigens of the two bacteria can be used to separate immune responses to these two biologically very different infections. Following subclinical experimental infections with Brucella suis biovar 2, high interferon-gamma (IFN-gamma) assay responses with a commercial Brucella melitensis antigen preparation (Brucellergene OCB) preceded the development of antibodies. High IFN-gamma responses in the seven B. suis inoculated pigs with serological evidence of infection were consistent throughout a 20-week post-inoculation observation period. In contrast, IFN-gamma responses in two B. suis inoculated pigs without bacteriological or serological evidence of infection were below a cut-point of 25pg/ml at all samplings. IFN-gamma responses in repeated samplings from 5 uninfected control pigs and 18 pigs experimentally infected with YeO:9 were all negative, except for solitary false positives in 3.7% of the samples from both the experimentally YeO:9 infected pigs and control pigs. Skin tests using the same commercial Brucella antigen confirmed the ability of cell-mediated immune responses to differentiate between the two infections. In addition, a field evaluation of the diagnostic use of cell-mediated immune responses by IFN-gamma assay and skin test to resolve serological suspicions of Brucella was conducted in an YeO:9 infected pig herd. Following a screening of 200 pigs 39 pigs were identified with false positive serological Brucellosis reactions. While 36 of the 39 FPSR pigs were also FPSR in a second test, none of the pigs were test positive in whole blood IFN-gamma assay or Brucellergene OCB skin test. In conclusion, use of IFN-gamma assay and skin test as measurements of cell-mediated immune responses to non-LPS Brucella antigens were specific and sensitive in discriminating subclinical experimental infections with B. suis from both natural and experimental infections with YeO:9.     

Immune response in mice and cattle after immunization with a Boophilus microplus DNA vaccine containing bm86 gene

Plasmid pBMC2 encoding antigen Bm86 from a Colombian strain of cattle tick Boophilus microplus, was used for DNA-mediated immunization of BALB/c mice, employing doses of 10 and 50microg, delivered by intradermic and intramuscular routes. Anti-Bm86 antibody levels were significantly higher compared to control mice treated with PBS. In the evaluation of immunoglobulin isotypes, significant levels of IgG2a and IgG2b were observed in mice immunized with 50microg of pBMC2. Measurement of interleukine (IL) levels (IL-4, IL-5, IL-12(p40)) and interferon-gamma (IFN-gamma) in the sera of mice immunized with pBMC2 indicated high levels of IL-4 and IL-5, although there were also significant levels of IFN-gamma. Mice immunized with pBMC2 showed antigen-specific stimulation of splenocytes according to the incorporation of bromodeoxyuridine and IFN-gamma secretion. In all trials, mice injected intramuscularly with 50microg of pBMC2 presented the highest immune response. Moreover, cattle immunized with this DNA vaccine showed antibody production significantly different to the negative control. In conclusion, these results suggest the potential of DNA immunization with pBMC2 to induce humoral and cellular immune responses against B. microplus.     

Effect of transcutaneous immunization with co-administered antigen and cholera toxin on systemic and mucosal antibody responses in sheep

Direct application of antigens to skin together with an adjuvant, a procedure called transcutaneous immunization (TCI), can induce systemic immune responses in mice, humans, cats and dogs. In previous studies we found that cholera toxin (CT) applied topically on unbroken skin induces systemic antibody and lymphocyte proliferative responses in sheep. The current study examined whether concurrent administration of CT and tetanus toxoid (TT) delivered transcutaneously could induce specific antibody responses to both antigens in sheep. Antibodies to both TT and CT were induced by TCI although antibody titres in serum to TT were higher in sheep receiving TT plus alum by intramuscular injection (n=5) than TT plus CT by TCI (n=5). The ratio of IgG1/IgG2 antibody to TT in serum was near unity, and the route of immunization, TCI versus injection, did not influence this ratio. In contrast, the ratio of IgG1/IgG2 antibody differed significantly between the two antigens, TT and CT, delivered by TCI, with a higher proportion of IgG1 antibody in serum to CT than TT. Antibody to TT was detected in lung washes from TCI and injection groups, with IgG1 predominating over IgG2 in both groups. IgA antibodies to CT and TT were detected in sera of CT and TT-immunized groups respectively but in lung washes IgA antibody to TT was detected only in the injection group. Results show that TCI induced systemic antibody responses to CT and the co-administered antigen TT, whereas no evidence was obtained for mucosal IgA responses following TCI.     

Evaluation of the opsonic capacity of core lipopolysaccharide antiserum of equine origin against smooth Escherichia coli 0111:B4, using macrophage chemiluminescence

A study was performed to determine whether equine antiserum to core lipopolysaccharide (LPS) would enhance phagocytosis of smooth gram-negative (GN) organisms by equine macrophages. Five healthy adult horses (group A) were immunized with a bacterin prepared from the J-5 mutant of Escherichia coli 0111:B4 and Salmonella minnesota R595 to produce antibodies to core LPS. Five horses (group B) served as nonimmunized controls and were given physiologic saline solution instead of the rough mutant bacterin. Serum antibody titers to core LPS and to smooth E coli 0111:B4 were determined by indirect ELISA. Four serum pools were prepared: pool 1 = sera from horses in group B prior to immunization; pool 2 = sera from horses in group A prior to immunization (preimmune serum); pool 3 = sera from horses in group B, 7 days after the last saline injection; pool 4 = sera from horses in group A, 7 days after the last immunization (core LPS antiserum). The serum pools, either unheated or heated 30 minutes at 56 C, in 3 dilutions (1/50, 1/100, 1/500) were used to opsonize smooth E coli 0111:B4 in an assay of equine peritoneal macrophage chemiluminescence (CL). Peritoneal fluid was collected from clinically normal horses and the macrophages were purified by adherence to borosilicate glass scintillation vials. Each serum type and dilution was added to triplicate vials containing 10(7) colony-forming units of E coli 0111:B4. Luminol-dependent CL was measured with a liquid scintillation counter in the out-of-coincidence mode. Each serum dilution was tested in duplicate vials without bacteria to asses serum-induced nonspecific CL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immune responses in piglets infected with highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) infection compromises the host's innate and adaptive immunity. The aim of this study was to investigate the immune responses of piglets infected with highly pathogenic (HP) PRRSV (HuN4 strain) with or without the immunization with CH-1R attenuated PRRSV vaccine. The response was evaluated for the clinical signs, pathological changes and virus load in immune organs, antibody responses and levels of serum IFN-γ, IL-4 and IL-10. The result showed that in comparison with the piglets received the immunization, the piglets infected with HP-PRRSV alone had the thymus atrophy, decreased serum levels of IL-4 and increased serum levels of IL-10 and INF-γ. These results suggest that elevated IL-10 levels at the early stage of the infection may enhance virus survival and delay the induction of protective immunity, while increased levels of IL-4 induce the effective immune responses and increase the animals' health status.     

Adjuvants in veterinary vaccines: modes of action and adverse effects

Vaccine adjuvants are chemicals, microbial components, or mammalian proteins that enhance the immune response to vaccine antigens. Interest in reducing vaccine-related adverse effects and inducing specific types of immunity has led to the development of numerous new adjuvants. Adjuvants in development or in experimental and commercial vaccines include aluminum salts (alum), oil emulsions, saponins, immune-stimulating complexes (ISCOMs), liposomes, microparticles, nonionic block copolymers, derivatized polysaccharides, cytokines, and a wide variety of bacterial derivatives. The mechanisms of action of these diverse compounds vary, as does their induction of cell-mediated and antibody responses. Factors influencing the selection of an adjuvant include animal species, specific pathogen, vaccine antigen, route of immunization, and type of immunity needed.