Production and characterization of monoclonal antibodies specific for bovine gamma-interferon

Development of a monoclonal antibodies-based interferon-gamma enzyme-linked immunosorbent assay (ELISA) for rapid and accurate diagnosis of bovine tuberculosis.. [DOI: 10.21203/rs.3.rs-1918522/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Bovine tuberculosis is an infectious and chronic disease affecting cattle, caused by Mycobacterium bovis (M. bovis). The zoonotic nature of the disease has a serious worldwide impact on human health. Also, the significant economic costs caused by such disease in addition to the deficiency of precise estimate of the actual disease prevalence necessitate more efficient detection and control measures, particularly in developing countries. The main target of the present work was to develop a local, less expensive bovine tuberculosis interferon-gamma ELISA (Bo-IFN-γ ELISA) kit for the rapid and accurate diagnosis of bovine tuberculosis. In the current study, three murine hybridomas producing monoclonal antibodies (mAbs) against bovine interferon-gamma (Bo-IFN-γ) were developed and their monoclonal antibodies were characterized. The produced mAbs were of IgM isotype and its specificity was proved using the western blot technique. The prepared mAbs were used for the development of the bovine IFN- γ ELISA test that was evaluated for laboratory diagnosis of bovine tuberculosis. The sensitivity and specificity of the developed ELISA kit as compared with the standard tuberculin skin test was determined. This method is based on the measurement of IFN-γ released from sensitized bovine lymphocytes upon exposure to the mycobacterial antigens. Using checkerboard titration, the optimal coating concentration of anti- Bo-IFN-γ was 20µg/well. Blood samples from apparently healthy cattle proved negative in the tuberculin test were examined with the developed kit and the cut-off value (COV) was equal to 0.30 optical density (OD). In a preliminary study for evaluation of the sensitivity and specificity of the developed ELISA, 23 cattle were examined with both the Bo-IFN-γ ELISA and the standard tuberculin skin test. The developed Bo-IFN-γ ELISA showed high sensitivity (98%) and specificity (71.4%) in the diagnosis of bovine tuberculosis as compared to the standard tuberculin skin test.

A review of the leishmanin skin test: A neglected test for a neglected disease

The leishmanin skin test (LST) has been used for decades to detect exposure and immunity to the parasite Leishmania, the causative agent of the neglected tropical disease leishmaniasis. In the LST, Leishmania antigen (leishmanin) is intradermally injected into the forearm. In an individual who has been previously infected, a delayed-type hypersensitivity (DTH) reaction results in a measurable induration at the site of the injection, indicating that previous exposure to Leishmania has resulted in the development of cell-mediated immunity. LST positivity is associated with long-lasting protective immunity against reinfection, most notably as reported for visceral leishmaniasis (VL). Despite efforts over the past few decades, leishmanin antigen is no longer produced under good manufacturing practice (GMP) conditions anywhere in the world. Consequently, the use of the LST in epidemiological studies has declined in favor of serological and molecular tests. In this review, we provide a historical overview of the LST and justification for the reintroduction of leishmanin. A GMP-grade leishmanin can be used to detect immunity in vivo by the LST and can be investigated for use in an interferon-γ release assay (IGRA), which may serve as an in vitro version of the LST. The LST will be a valuable tool for surveillance and epidemiological studies in support of the VL elimination programs and as a surrogate marker of immunity in vaccine clinical trials.

Systemic infusions of anti-interleukin-1β neutralizing antibodies reduce short-term brain injury after cerebral ischemia in the ovine fetus

Perinatal hypoxic-ischemic reperfusion (I/R)-related brain injury is a leading cause of neurologic morbidity and life-long disability in children. Infants exposed to I/R brain injury develop long-term cognitive and behavioral deficits, placing a large burden on parents and society. Therapeutic strategies are currently not available for infants with I/R brain damage, except for hypothermia, which can only be used in full term infants with hypoxic-ischemic encephalopathy (HIE). Moreover, hypothermia is only partially protective. Pro-inflammatory cytokines are key contributors to the pathogenesis of perinatal I/R brain injury. Interleukin-1β (IL-1β) is a critical pro-inflammatory cytokine, which has been shown to predict the severity of HIE in infants. We have previously shown that systemic infusions of mouse anti-ovine IL-1β monoclonal antibody (mAb) into fetal sheep resulted in anti-IL-1β mAb penetration into brain, reduced I/R-related increases in IL-1β expression and blood-brain barrier (BBB) dysfunction in fetal brain. The purpose of the current study was to examine the effects of systemic infusions of anti-IL-1β mAb on short-term I/R-related parenchymal brain injury in the fetus by examining: 1) histopathological changes, 2) apoptosis and caspase-3 activity, 3) neuronal degeneration 4) reactive gliosis and 5) myelin basic protein (MBP) immunohistochemical staining. The study groups included non-ischemic controls, placebo-treated ischemic, and anti-IL-1β mAb treated ischemic fetal sheep at 127days of gestation. The systemic intravenous infusions of anti-IL-1β mAb were administered at fifteen minutes and four hours after in utero brain ischemia. The duration of each infusion was two hours. Parenchymal brain injury was evaluated by determining pathological injury scores, ApopTag® positive cells/mm², caspase-3 activity, Fluoro-Jade B positive cells/mm², glial fibrillary acidic protein (GFAP) and MBP staining in the brains of fetal sheep 24h after 30min of ischemia. Treatment with anti-IL-1β mAb reduced (P<0.05) the global pathological injury scores, number of apoptotic positive cells/mm², and caspase-3 activity after ischemia in fetal sheep. The regional pathological scores and Fluoro-Jade B positive cells/mm² did not differ between the placebo- and anti-IL-1β mAb treated ischemic fetal sheep. The percent of the cortical area stained for GFAP was lower (P<0.05) in the placebo ischemic treated than in the non-ischemic group, but did not differ between the placebo- and anti-IL-1β mAb treated ischemic groups. MBP immunohistochemical expression did not differ among the groups. In conclusion, infusions of anti-IL-1β mAb attenuate short-term I/R-related histopathological tissue injury, apoptosis, and reduce I/R-related increases in caspase-3 activity in ovine fetal brain. Therefore, systemic infusions of anti-IL-1β mAb attenuate short-term I/R-related parenchymal brain injury in the fetus.

Anti-IL-6 neutralizing antibody modulates blood-brain barrier function in the ovine fetus

Impaired blood-brain barrier function represents an important component of hypoxic-ischemic brain injury in the perinatal period. Proinflammatory cytokines could contribute to ischemia-related blood-brain barrier dysfunction. IL-6 increases vascular endothelial cell monolayer permeability in vitro. However, contributions of IL-6 to blood-brain barrier abnormalities have not been examined in the immature brain in vivo. We generated pharmacologic quantities of ovine-specific neutralizing anti-IL-6 mAbs and systemically infused mAbs into fetal sheep at 126 days of gestation after exposure to brain ischemia. Anti-IL-6 mAbs were measured by ELISA in fetal plasma, cerebral cortex, and cerebrospinal fluid, blood-brain barrier permeability was quantified using the blood-to-brain transfer constant in brain regions, and IL-6, tight junction proteins, and plasmalemma vesicle protein (PLVAP) were detected by Western immunoblot. Anti-IL-6 mAb infusions resulted in increases in mAb (P < 0.05) in plasma, brain parenchyma, and cerebrospinal fluid and decreases in brain IL-6 protein. Twenty-four hours after ischemia, anti-IL-6 mAb infusions attenuated ischemia-related increases in blood-brain barrier permeability and modulated tight junction and PLVAP protein expression in fetal brain. We conclude that inhibiting the effects of IL-6 protein with systemic infusions of neutralizing antibodies attenuates ischemia-related increases in blood-brain barrier permeability by inhibiting IL-6 and modulates tight junction proteins after ischemia.

Electrochemical impedance immunosensor for sub-picogram level detection of bovine interferon gamma based on cylinder-shaped TiO₂ nanorods

Bovine interferon gamma (BoIFN-γ) released by T cells plays very important roles in early diagnosis of Mycobacterium tuberculosis (MTB) infections and control of bovine tuberculosis. In this work, a label-free electrochemical impedance immunosensor is for the first time developed for highly sensitive determination of BoIFN-γ. Cylinder-shaped TiO2 nanorods are synthesized by a facile hydrothermal method, and show high surface area and good hydrophicility. The immunosensor is fabricated by the immobilization of BoIFN-γ monoclonal antibody on the TiO2 nanorods modified glassy carbon electrode. The prepared TiO2 and immunosensor are characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, contact angle measurement, cyclic voltammetry, and electrochemical impedance spectra. The BoIFN-γ concentration is measured through the relative increase of impedance values in corresponding specific binding of BoIFN-γ antigen and BoIFN-γ antibody. The relative increased impedance values are proportional to the logarithmic value of BoIFN-γ concentrations in a wide range of 0.0001 to 0.1 ng/mL with a low detection limit of 0.1 pg/mL. The developed BoIFN-γ immunosensor shows a 249-fold decrease in detection limit in comparison with current enzyme-linked immunosorbent assay. This study provides a new, simple, and highly sensitive approach for very potential application in early diagnosis of MTB infections and control of bovine tuberculosis.

Immunogenetic responses in calves to intranasal delivery of bovine respiratory syncytial virus (BRSV) epitopes encapsulated in poly (DL-lactide-co-glycolide) microparticles

Bovine respiratory syncytial virus (BRSV) is the principal aetiological agent of the bovine respiratory disease complex. A BRSV subunit vaccine candidate consisting of two synthetic peptides representing putative protective epitopes on BRSV surface glycoproteins in soluble form or encapsulated in poly(lactide-co-glycolide) (PLG) microparticles were prepared. Calves (10 weeks old) with diminishing levels of BRSV-specific maternal antibody were intranasally administered a single dose of the different peptide formulations. Peptide-specific local immune responses (nasal secretion IgA), but not systemic humoral (serum IgG) or cellular responses (serum IFN-γ), were generated by all forms of peptide. There was a significant reduction in occurrence of respiratory disease in the animals inoculated with all peptide formulations compared to animals given PBS alone. Furthermore no adverse effects were observed in any of the animals post vaccination. These results suggest that intranasal immunisation with the peptide subunit vaccine does induce an as yet unidentified protective immune response.

A multidisciplinary approach to diagnose naturally occurring bovine tuberculosis in Brazil

A herd infected naturally with tuberculosis was investigated by different diagnostic methods. Ninety days after a screening test that identified 21 cows as skin test positive, a Comparative Intradermal Tuberculin Test (CITT) was performed in those 21 cows and in 29 other randomly selected skin test negative cows. Milk samples and nasal swabs were collected prior to the CITT for bacteriological culture and PCR, while blood samples were collected for IFN release and antibody responses to MPB70 and MPB83, at three time points post tuberculin injection. Animals positive by CITT were slaughtered and disease confirmation undertaken. Based on the Kappa test, IFN was comparable to the standard tests (culture, PCR and CITT) at all three sampling points. Results from both antibody ELISAs were similar but were not comparable to the standard tests. T-test analysis of the CITT, IFN and ELISAs demonstrated that their performances were not correlated. There is increasing recognition that individually, available diagnostic tests do not detect all infected cattle. Therefore, a comprehensive strategy for the diagnosis of bovine TB should include test results for the detection of both cellular and humoral immune responses where there may be animals at different stages of infection.

In-vitro validation of cytokine neutralizing antibodies by testing with ovine mononuclear splenocytes

Cytokines have gained increasing attention as therapeutic targets in inflammation-related disorders and inflammatory conditions have been investigated in sheep. Monoclonal antibodies (mAbs) specific for the ovine pro-inflammatory cytokines interleukin (IL)-1β and IL-6 could be used to study the effects of blocking pro-inflammatory cytokines in sheep. Ovine-specific IL-1β and IL-6 proteins and mAbs specific for these molecules were produced and the ability of the mAbs to neutralize the proteins was tested in cultures of ovine splenic mononuclear cells. Expression of nuclear factor (NF)-κβ and signal transducer and activator of transcription (STAT)-3 was evaluated by western blotting and densitometric quantification. Treatment with purified IL-1β and IL-6 proteins increased NF-κβ (P < 0.001) and STAT-3 (P < 0.01) expression, respectively, in cell culture. Treatment with these proteins that were pre-incubated with IL-1β and IL-6 mAbs attenuated (P < 0.01) these effects. These results confirm the bioactivity of ovine IL-1β and IL-6 proteins and the neutralizing capacity of anti-ovine-IL-1β and -IL-6 mAbs in vitro. These mAbs could be used to investigate anti-inflammatory strategies for attenuation of the effects of these pro-inflammatory cytokines in sheep.

Development of an antibody to bovine IL-2 reveals multifunctional CD4 T(EM) cells in cattle naturally infected with bovine tuberculosis

Gaining a better understanding of the T cell mechanisms underlying natural immunity to bovine tuberculosis would help to identify immune correlates of disease progression and facilitate the rational design of improved vaccine and diagnostic strategies. CD4 T cells play an established central role in immunity to TB, and recent interest has focussed on the potential role of multifunctional CD4 T cells expressing IFN-γ, IL-2 and TNF-α. Until now, it has not been possible to assess the contribution of these multifunctional CD4 T cells in cattle due to the lack of reagents to detect bovine IL-2 (bIL-2). Using recombinant phage display technology, we have identified an antibody that recognises biologically active bIL-2. Using this antibody, we have developed a polychromatic flow cytometric staining panel that has allowed the investigation of multifunctional CD4 T-cells responses in cattle naturally infected with M. bovis. Assessment of the frequency of antigen specific CD4 T cell subsets reveals a dominant IFN-γ⁺IL-2⁺TNF-α⁺ and IFN-γ⁺ TNF-α⁺ response in naturally infected cattle. These multifunctional CD4 T cells express a CD44^hiCD45RO⁺CD62L^lo T-effector memory (T_EM) phenotype and display higher cytokine median fluorescence intensities than single cytokine producers, consistent with an enhanced ‘quality of response’ as reported for multifunctional cells in human and murine systems. Through our development of these novel immunological bovine tools, we provide the first description of multifunctional T_EM cells in cattle. Application of these tools will improve our understanding of protective immunity in bovine TB and allow more direct comparisons of the complex T cell mediated immune responses between murine models, human clinical studies and bovine TB models in the future.

Potential application of new diagnostic methods for controlling bovine tuberculosis in Brazil

Bovine tuberculosis, a chronic infection in cattle caused by Mycobacterium bovis, remains an economic and public health problem for several countries. Due to its economic impact on international trade, contagious nature, and implications for human health, global programs to eradicate the disease were implemented worldwide. Those programs are based on slaughtering PPD-reactive animals. Despite the National Programs in Brazil, complete eradication has not been achieved, and the disease remains, albeit at a lower prevalence. The central purpose of this review is to address diagnostic tests for tuberculosis. Considering the course of the infection in cattle, at least two tests, ideally complementary to one another, may be necessary for an adequate diagnosis: the first based on the cellular response, and the second capable of identifying anergic animals by detection of specific anti-M.bovis antibodies.

The use of a Gamma-Interferon assay to confirm a diagnosis of bovine tuberculosis in Brazil

Control of bovine tuberculosis (TB) is currently based on slaughter of cattle deemed positive on the basis of tuberculin testing; although the test has been broadly used for several years, there are some disadvantages such as the need for holding animals for 72 h. Besides it, test can lack both sensitivity and specificity depending on the interpretation and the site of the PPD inoculation. Therefore, the objective of the current study was to evaluate the use of the Gamma-Interferon (IFN) assay as a confirmatory test in Brazil. A Comparative Intradermal Tuberculin Test (CITT) was performed in 50 cows from a dairy herd known to be infected with TB. Blood samples for IFN testing were collected concurrent with the CITT, as well as seven and 21 days later. At 30 days after the CITT, all cattle deemed reactive to this test were slaughtered and samples were processed by both bacteriological culture and PCR. The sensitivity of IFN as a diagnostic tool was 91.4%, whereas specificity was 86.7%. When applied seven or 21 days after injection of PPD, sensitivity was 74.3 and 71.4%, respectively, whereas specificity was 86.7 and 80%. There was no significant difference between the reliability of the IFN assay and the other standards, on all three days of sampling. Therefore, we concluded that the IFN assay could be effectively used as a confirmatory test seven or 21 days after injection of PPD.

Veterinary applications of cytokines

In the recent past a large variety of cytokines have been cloned for most important veterinary species and more is planned with development of a coordinated approach to cytokine reagents production. Application of these cytokines in veterinary species can be found in the development of effective diagnostics, with the IFN-gamma-based detection of tuberculosis as a prime example. In addition, cytokines have been used to determine which immune responses are essential for immune protection with flow-on effects for the development of novel ways to induce these specific immune responses. The realisation that the murine immune system is quite different from the human, together with the increased availability of cytokine reagents for many large animals plus unique experimental approaches only available in these animals, has lead to an explosion in the use of veterinary species as models for human diseases.

Cooperative Expression of Monocyte Chemoattractant Protein 1 Within the Bovine Corpus Luteum: Evidence of Immune Cell-Endothelial Cell Interactions in a Coculture System1

Endothelial cells (EC) of the bovine corpus luteum (CL) are a known source of proinflammatory mediators, including monocyte chemoattractant protein 1 (CCL2) and endothelin 1 (EDN1). Here, a coculture system was devised to determine if immune cells and PGF 2alpha together affect CCL2 and EDN1 secretion by EC. Luteal EC were cultured either alone or together with peripheral blood mononuclear cells (PBMC), and treated without or with PGF 2alpha for 48 h (n = 6 experiments). Coculture of EC with PBMC increased CCL2 secretion an average of 5-fold higher compared with either cell type alone (P < 0.05). Basal secretion of EDN1 by EC was substantial (approximately 2 ng/ml), but was not affected by coculture with PBMC (P > 0.05). EC cocultured with concanavalin A-activated PBMC (ActPBMC) increased CCL2 secretion an average of 12-fold higher compared with controls (P < 0.05), but again, EDN1 secretion was unchanged (P > 0.05). Interestingly, PGF 2alpha did not alter either CCL2 or EDN1 secretion, regardless of culture conditions (P > 0.05). In a second series of experiments (n = 3 experiments), mixed luteal cells (MLC) were cultured alone or with PBMC as described above. Secretion of CCL2 and EDN1 was not affected by coculture or by PGF 2alpha (P > 0.05), but MLC produced less progesterone in the presence of ActPBMC (P < 0.05). Collectively, these results suggest that immune cells and EC can interact cooperatively to increase CCL2 secretion in the CL, but this interaction does not affect EDN1 secretion nor is it influenced by PGF 2alpha. Additionally, activated immune cells appear to produce a factor that impairs progesterone production by luteal steroidogenic cells.

Generation of monoclonal antibodies to porcine interleukin 6 (PIL-6) using the recombinant PIL-6 expressed in Escherichia coli

Porcine interleukin-6 (PIL-6) protein without signal peptide was expressed as a glutathione S-transferase (GST) fusion protein in Escherichia coli. The fusion protein was expressed in an insoluble fraction, however, it was solubilized by refolding procedure using urea. From the solubilized protein, the recombinant PIL-6 (rPIL-6) was purified by a batch method using glutathione sepharose 4B and PreScission protease cleavage. By the B3B1 hybridoma cell proliferation assay, biological activity of the purified rPIL-6 was confirmed. Three monoclonal antibodies (MAbs) named 2B-1, 5A-8 and 4C-3 were generated by using the rPIL-6 as an immunogen. Immunoglobulin isotypes of the MAbs were IgG2a (4C-3) and IgG2b (2B-1 and 5A-8). For the epitope analysis, additive enzyme-linked immunosorbent assay and immunoblot analysis using deletion mutants of PIL-6 were performed. These experiments revealed that the two MAbs (2B-1 and 5A-8) recognize an overlapped epitope and the other (4C-3) recognizes a distinct epitope, and all epitopes reside in the region of aa26-64 of PIL-6.

Identification of monoclonal antibodies that cross-react with cytokines from different animal species

Eleven monoclonal antibodies specific for ovine, bovine and human cytokines were investigated by flow cytometry for cross-reactivities with cytokines produced by peripheral blood mononuclear cells (PBMCs) from sheep, cattle, goat, swine, horse, dog, mink, rabbit and human. Four antibodies specific for IL-4, IL-8, IFN-gamma and TNF-alpha cross-reacted with cytokines from a majority of the species investigated. These antibodies can be applied to flow cytometric studies of cytokine production by PBMCs from several veterinary species. Another five antibodies specific for IL-2, IL-6, GM-CSF and IFN-gamma (two antibodies) cross-reacted weakly and with a variable number of animal species. These antibodies could in certain situations be useful in flow cytometry. In a number of cases the immunological cross-reactivities were confirmed by Western blot analyses. Overall, the results of this study will remedy some of the lack of species-specific anti-cytokine antibodies in veterinary research.

Development of detection methods for ruminant interleukin (IL)-12

Recombinant bovine IL-12 (rbo IL-12) was transiently expressed in COS-7 cells and shown to upregulate the synthesis of IFNgamma by bovine cells stimulated with a suboptimal concentration of mitogen in vitro. Mice were immunised with a plasmid encoding rbo IL-12 and boosted with rbo IL-12 and a number of monoclonal antibodies (mAb) were generated that reacted with rbo IL-12 in an ELISA. Some of these mAb neutralised the ability of rbo IL-12 to induce IFNgamma synthesis by bovine cells. A pair of mAb was identified that together could be used to detect both recombinant and natural bovine IL-12 by ELISA and a luminometric detection method was applied to the ELISA making it more sensitive. Using this method native bovine IL-12 was detected in supernatants of dendritic cells (DC) cultured in vitro with a synthetic lipopeptide known to stimulate secretion of IL-12 by human DC. The ELISA was also able to detect recombinant ovine IL-12 and, less effectively, recombinant human IL-12. In contrast, bovine IL-12 was not detected by a commercial human IL-12 ELISA kit. Intracytoplasmic IL-12 was detected in bovine DC using the antibodies described herein. The ability to detect ruminant IL-12 by three methods: ELISA, bioassay with neutralising mAb and cytoplasmic staining, will permit studies of the role of this important cytokine in the immunology and pathogenesis of animal diseases.

Australia's campaign to eradicate bovine tuberculosis: the battle for freedom and beyond

In 1970, voluntary State-based TB control programs in Australia were replaced by a coordinated national campaign to eliminate both brucellosis and tuberculosis from the cattle population. The campaign was funded and managed under tripartite agreement by State/Territory and Commonwealth governments and Industry. The tuberculosis component of the campaign relied on test and slaughter with surveillance for the disease in abattoirs and trace-back to property of origin an essential component. Because of the moderate sensitivity of the skin test ( approximately 70%), testing was repeated at prescribed intervals over a number of years. In the more hostile environment of northern Australia, novel strategies were developed to maximize musters and remove 'at risk' animals. Australia is fortunate it did not have a feral host for M. bovis (apart from buffalo, which were included in the campaign) to complicate eradication. A national granuloma submission program was implemented in 1992 to increase the intensity of abattoir monitoring. Selective or total depopulation was used in some herds to achieve the requirements of the national Standard Definitions and Rules of the Campaign and achieve the status of 'TB Free Area' in December 1997. Monitoring for tuberculosis has continued under the 5-year Tuberculosis Freedom Assurance Program and measures to further reduce the risk of new cases have been implemented.

BOVIGAM: an in vitro cellular diagnostic test for bovine tuberculosis

BOVIGAM which is based on the detection of gamma interferon (IFN- gamma) is a rapid, laboratory assay of a cell mediated immune response that may be used for the detection of tuberculosis (TB) infection in animals. Whole blood is first incubated overnight with bovine PPD, avian PPD or negative control antigens, and IFN- gamma in the supernatant plasma is then measured by EIA. TB infection is indicated by a predominant IFN- gamma response to bovine PPD. Since 1988, BOVIGAM has been extensively trialed on more than 200 000 cattle in Australia, Brazil, Ireland, Northern Ireland, Italy, New Zealand, Romania, Spain and the USA. Sensitivity has varied between 81.8% and 100% for culture-confirmed bovine TB and specificity between 94% and 100%. The IFN- gamma assay detects M. bovis infection earlier than the skin test and in New Zealand is applied to detect skin-test negative cattle with TB, where after slaughter a significant number of IFN- gamma reactors have TB. BOVIGAM is also approved in New Zealand for serial testing skin test positive cattle when non-specificity is suspected. Cattle are tested 7-30 days after a positive caudal fold test. The boosting effect of the skin test on T-cell activity allows blood to be cultured with PPD up to 30 h after collection without effecting accuracy. The BOVIGAM results are not affected by poor nutritional condition and are only mildly and briefly affected by dexamethasone treatment and parturition. IFN- gamma responses of cattle vaccinated with BCG are dose-dependent and short-lived. The BOVIGAM kit is now used routinely in many countries for the detection of M. bovis infected cattle, buffalo and goats.

Characterisation of monoclonal antibodies to ovine interleukin-6 and the development of a sensitive capture ELISA

A purified recombinant ovine (rOv) interleukin-6 (IL-6) was used to generate specific murine monoclonal antibodies (mAbs) and a polyclonal rabbit antisera to this cytokine. From the 31 initial hybridoma cell lines generated, three stable clones were established which secreted mAbs to rOvIL-6, as judged by a direct enzyme-linked immunosorbent assay (ELISA) and Western blotting. Their specificity was further confirmed by demonstrating that none of the mAbs recognised any of the six other irrelevant recombinant ovine cytokines tested by direct ELISA. All three mAbs displayed cross-reactivity with human and African green monkey IL-6 as demonstrated by direct ELISA and Western blotting. In contrast, the polyclonal antibodies only cross-reacted with bovine IL-6 and not with either of the human or monkey homologues. By combining a mAb with the polyclonal antisera a sensitive, IL-6-specific, capture ELISA was developed that had a sensitivity of 150 pg/ml. This detection system was unequivocally validated by demonstrating that native OvIL-6 could be detected in efferent lymph draining from a stimulated popliteal lymph node. In addition, one of the mAbs was shown to allow the detection of OvIL-6 by intracellular cytokine staining and flow cytometry.

Field evaluation of the single intradermal cervical tuberculin test and the interferon-gamma assay for detection and eradication of bovine tuberculosis in Spain

A field comparison of the interferon-gamma (IFN-gamma) assay and the single intradermal cervical tuberculin (SICT) test for the diagnosis of bovine tuberculosis was conducted. A total of 1136 cattle belonging to 85 herds placed in 'Castilla y León' (northwestern Spain) were chosen, and 21 of these herds were subjected to the diagnostic assays two or three times at intervals of at least 4 months. All the animals positive to any of the tests were slaughtered and tuberculosis was confirmed by culture isolation method (CIM) and further identification by means of PCR. Only 10.6% of cattle reacted with the bovine PPD in the SICT test, a percentage that increased to 12.8% in the IFN-gamma assay. The sensitivity of the IFN-gamma assay compared to CIM was shown to be higher (84.9%) than that of the SICT test (80.2%), but the combination of both tests offered the highest sensitivity (92.9%). The number of false positive reactors (those animals in which CIM was negative) was considerably higher for the IFN-gamma assay than for the SICT test and, conversely, the number of false negative animals (M. bovis isolation but negative immunological result) was higher for the skin test than for the interferon assay. In the herds tested twice, tuberculosis was eradicated after the second cycle of testing in 50%, and in 75% after the third cycle in herds tested three times. The combination of these two techniques instead of separately seems, therefore, to be useful in eradication programmes against bovine tuberculosis.

Production and characterisation of monoclonal antibodies specific for bovine interleukin-4

Genetic immunisation is a simple method for producing polyclonal antibodies in mice. By this method, we produced antibodies against bovine interleukin-4 (BoIL-4). After a final injection with a recombinant BoIL-4 protein, nine stable hybridoma cell lines were established which secreted monoclonal antibodies (MAbs) against this cytokine. Specific binding of each of the MAbs to recombinant BoIL-4 produced by Escherichia coli, baculovirus, and Trypanosoma brucei was demonstrated in an indirect ELISA and/or in Western blotting. These MAbs recognise the same antigenic region localised in the first 47 amino acids of the mature protein. None of them was able to neutralise the biological activity of the BoIL-4 under the conditions tested but one allowed the detection of BoIL-4 by flow cytometry.

Cellular immune responses in cattle experimentally infected with Neospora caninum

Neospora caninum has recently been identified as an important cause of infectious abortion in cattle. The parasite is closely related to Toxoplasma gondii, but the two species are antigenically distinct. To examine cell proliferative responses and the induction of IFN-gamma in experimentally infected cattle, four 2-4 months old calves were subcutaneously inoculated with N. caninum tachyzoites. Peripheral blood mononuclear cells were collected regularly and stimulated in vitro with a crude lysate of N. caninum or T. gondii tachyzoites. Significant proliferative responses to N. caninum antigen were recorded in all calves from days 4-6 postinoculation. This response was accompanied by production of high levels of IFN-gamma. Although the calves remained seronegative to T. gondii, while seroconverting to N. caninum, stimulation with T. gondii lysate resulted in cell proliferation of a similar magnitude as that obtained using the N. caninum lysate. However, the T. gondii lysate appeared less effective than the N. caninum lysate to stimulate IFN-gamma production. Cells taken from uninfected control animals did not show any significant proliferation to either N. caninum or T. gondii antigen and no IFN-gamma was produced. These results suggest that the two parasites may possess cross-reacting T-cell epitopes, but that the T cells specific for N. caninum may have a different functional capacity. This highlights the need to investigate the antigen specificity and cytokine profile of T cells from infected animals to help understand their role in immunity to N. caninum.

Early immunopathological events in experimental ovine paratuberculosis

An experimental oral infection of neonatal (< 2 weeks old) lambs with a cervine isolate of Mycobacterium avium subspecies paratuberculosis (M.a. paratuberculosis), the causal agent of ruminant paratuberculosis (Johne's disease) was used to investigate bacteriological, histopathological and immunological changes during the early (up to 8 weeks) post-infection phase. In vitro culture for mycobacteria was positive in one faecal and three mesenteric lymph node (MLN) samples from the eight infected lambs. All mycobacterial isolates from MLN were identified as M.a. paratuberculosis by polymerase chain reaction (PCR). Small-to-medium sized focal granulomata were observed in jejunal (JPP) and ileal Peyer's patches (IPP) from four of the eight infected lambs. Compared with controls, JPP from all infected lambs had significantly (p < 0.05) higher proportions of CD8+ and CD2+ lymphocytes, and there were significantly (p < 0.05) fewer cells expressing B lymphocyte-associated markers in IPP and MLN. The T/B cell ratio was significantly (p < 0.05) increased in both JPP and MLN from infected lambs. The expression of a range of genes for cytokines was examined using specific reverse transcriptase PCR (RT-PCR) amplification of messenger RNA (mRNA) template isolated from MLN, JPP and IPP from both groups of animals. Densitometric analyses indicated that, in infected animals, MLN expressed significantly (p < 0.05) more mRNA for TNF-alpha: JPP had significantly increased (p < 0.05) mRNA for GM-CSF and significantly decreased (p < 0.05) mRNA for IL-4 and IFN-gamma. Infected lambs had significantly (p < 0.05) decreased titres of both circulating IgG and gut mycobacteria-associated IgG antibody. Infection was not associated with any consistent changes in lymphocyte reactivity to specific mycobacterial antigens, IFN-gamma release into supernatants from in vitro intestinal lymphocyte cultures or gut IgA antibody levels.

Evaluation of the gamma-interferon assay for eradication of tuberculosis in a goat herd

OBJECTIVE

To evaluate the usefulness of the gamma-interferon assay in the diagnosis of caprine tuberculosis in comparison with a single intradermal tuberculin test, and to obtain a group of animals free from this infection in a herd with a high prevalence.

DESIGN

An immunological study involving four serial comparative gamma-interferon and single intradermal tuberculin tests.

ANIMALS

A herd of 87 goats of Guadarrama breed.

PROCEDURE

Serial testing and segregation of animals.

RESULTS

We found that the number of infections detected by the gamma-interferon test was considerably greater than the number detected by the single intradermal tuberculin test. A group of 10 animals was negative to both tests in two consecutive rounds and three kids were negative in the last round of testing.

CONCLUSIONS

Gamma-interferon assay is appropriate for diagnosis and eradication of tuberculosis in goats. This test is able to detect early Mycobacterium bovis infection. Avian reactors with simultaneous increased reaction to bovine PPD in the gamma-interferon assay (designated as avian reactors) should be considered test positive for M bovis. By serial testing with the gamma-interferon and the single intradermal tuberculin tests, and a policy of segregation of kids at birth, it is possible to achieve a group of animals test negative for tuberculosis from a herd of goats with high immunoreactivity to this infection.

Analysis of ovine IL-1 beta production in vivo and in vitro by enzyme immunoassay and immunohistochemistry

A monoclonal antibody (mAb) specific for ovine IL-1 beta was produced and, in conjunction with a polyclonal rabbit antiserum, used to develop a sensitive enzyme immunoassay (EIA) for ovine interleukin 1 beta (IL-1 beta). The mAb neutralised the activity of recombinant ovine IL-1 beta (rOvIL-1 beta) and native OvIL-1 in an ovine thymocyte proliferation assay. However, it did not neutralise the biological activity of rOvIL-1 beta in the murine NOB1/CTLL assay. The mAb did not react with rOvIL-1 alpha, IL-2, IL-4, IL-8, tumor necrosis factor-alpha, gamma-interferon or recombinant human IL-1 beta in indirect EIA. Immunohistological staining of activated alveolar macrophages and frozen lymph node sections sections demonstrated that the mAb detected IL-1 beta secreted by ovine macrophages (CD11c-positive). The EIA was highly sensitive, detecting less than 50 pg ml-1 of rOvIL-1 beta and low levels of native IL-1 beta in supernatants from lipopolysaccharide-stimulated macrophages. The EIA did not detect heat-inactivated IL-1 beta.

Effect of dexamethasone treatment of tuberculous cattle on results of the gamma-interferon test for Mycobacterium bovis

The purpose of this project was to determine the effect of dexamethasone (DEX) treatment of tuberculous cows on antigen-stimulated gamma-interferon (gamma-IFN) production in a commercial Mycobacterium bovis gamma-interferon test (gamma-IFN test) developed for diagnosis of bovine tuberculosis. In the gamma-IFN test an enzyme-linked immunosorbent assay is used to detect bovine gamma-IFN in the plasma from whole blood samples cultured with M. bovis and Mycobacterium avium tuberculin purified protein derivatives (PPDs). DEX is a synthetic glucocorticoid commonly used as a potent anti-inflammatory agent, and experimentally as a model of stress-induced immunosuppression in cattle. DEX treatment has previously been associated with decreased lymphocyte response to mitogens in cattle, which led to the current hypothesis that DEX treatment would suppress stimulated gamma-IFN production resulting in false negative results in the gamma-IFN test. In replicate studies using naturally infected dairy cows, blood was drawn daily for at least 2 days prior to DEX treatment, during 3 days of DEX treatment, and for at least 9 days post-DEX. Results of the gamma-IFN test were evaluated by optical density (OD), and by three OD calculation methods: two different methods suggested by the manufacturer, and a method adapted from the evaluation of a bovine gamma-IFN test used in Australia. Prior to DEX treatment all cows had positive gamma-IFN tests by each calculation method. As early as 24 h after the first DEX injection a decline in PPD-stimulated gamma-IFN production was reflected in OD data for all cows. Calculated gamma-IFN test results were negative after DEX treatment for all but one cow, which was known to produce relatively large amounts of gamma-IFN as measured by this test. The degree of gamma-IFN suppression, and the number of days that gamma-IFN test results were negative after DEX treatment (1-8 days), varied by cow and by data calculation method. Treatment with DEX is associated with suppressed PPD-stimulated gamma-IFN production, which may be reflected as false negative results in the gamma-IFN test depending on the data calculation method applied. The results have implications for the management conditions and medical treatment schedule under which samples for the gamma-IFN test are collected.

Growth of Lucilia cuprina larvae following treatment of sheep divergently selected for fleece rot and fly strike with monoclonal antibodies to T lymphocyte subsets and interferon gamma

Intensive lymphocytic infiltration of the underlying dermis occurs during cutaneous myiasis caused by larvae of the blow fly, Lucilia cuprina. To determine the effect of this infiltrate on larval growth, monoclonal antibodies (mAb) to CD4, CD8 or WC1 lymphocyte subset determinants were injected intravenously before and during experimental infection of sheep with larvae. The effect of intravenous injection of mAb to ovine interferon (IFN) gamma was also examined. The experiments were performed in 18-month-old maiden ewes with genetic resistance or susceptibility to the disease complex, bacterial dermatitis/cutaneous myiasis. mAbs induced profound depletion of CD8+ and WC1+ subpopulations from blood and skin at sites of larval growth. mAb to CD4+ gave only a moderate reduction in lymphocytes from blood or skin. mAb treatments did not modify larval growth or survival at 20 or 50 h after infection. Larval growth rates did not differ between resistant and susceptible genotypes. No evidence was found for a role of T lymphocyte subpopulations or the cytokine IFN, in modifying larval growth during the first 50 h of infection. It seems unlikely that T lymphocyte-dependent immunological effector mechanisms contribute to the lower prevalence of fly strike seen in the resistant genotype in the field.

Kinetics of interferon gamma production in vivo during infection with the S48 vaccine strain of Toxoplasma gondii

The kinetics of interferon gamma (IFN gamma) production in vivo was examined in sheep during a primary and secondary infection with the sheep vaccine strain (S48) of Toxoplasma gondii. Efferent lymph plasma from a node draining the site of inoculation was tested for anti-viral activity which could be neutralized with monoclonal antibodies against IFN gamma. Within 2 to 5 days of primary infection IFN gamma was detected in each of five sheep and persisted for 6 to 9 days. Accelerated production of IFN gamma occurred after secondary infection, the cytokine being detected in the first 24 h, and persisting in lymph for a further 4-5 days. From day 6 onwards after primary infection, efferent lymph cells produced IFN gamma when stimulated in vitro with a crude T. gondii antigen. These results show that IFN gamma is induced in sheep after infection with the S48 strain of T. gondii.

Detection of specific T cell reactivity in sheep infected with Mycobacterium avium subspecies silvaticum and paratuberculosis using two defined mycobacterial antigens

A 30 kDa antigen (P30) from Mycobacterium avium ssp. paratuberculosis (M. a. paratuberculosis) and a 40 kDa (P40) antigen from Mycobacterium avium ssp. silvaticum (M. a. silvaticum) were employed in two different assays to measure the cell-mediated immune reactivity of ovine peripheral blood lymphocytes. In lymphocyte stimulation assays, proliferative responses to the P30 were observed only with lymphocytes from sheep inoculated with live M. a. paratuberculosis or M. a. silvaticum. Although this antigen was not subspecies-specific it differentiated between animals given live organisms and those inoculated with an inactive lysate. The P40 protein from M. a. silvaticum showed subspecies specificity by eliciting in vitro responses only with lymphocytes derived from sheep inoculated with live M. a. silvaticum. Similar results were obtained using an interferon-gamma release assay which proved to be a more rapid and sensitive system.

The survival and growth of ovine afferent lymph dendritic cells in culture depends on tumour necrosis factor-alpha and is enhanced by granulocyte-macrophage colony-stimulating factor but inhibited by interferon-gamma

An in vitro culture system is described which allows an analysis of the signals responsible for the survival, growth and functional maturation of afferent lymph dendritic cells (ALDC), a subpopulation of migrating dermal dendritic cells involved in antigen carriage and presentation to T-cells. Purified ALDC survived and grew for up to 30 days in lymph node conditioned medium and survived 14 days in recombinant ovine (rov) TNF-alpha whereas none were detected after 24 h in rov GM-CSF, rov IFN-gamma or rh M-CSF. However, when rov GM-CSF was added to cultures along with rov TNF-alpha, increased numbers of ALDC compared with input numbers (growth) were recorded on Days 14 and 21. In contrast, when 50-200 units ml-1 of rov IFN-gamma were added to cultures of ALDC along with TNF-alpha or rov TNF-alpha plus rov GM-CSF, cell survival and growth was inhibited. Antibody blocking studies confirmed the cytokine specificity of these effects. ALDC cultured in rov TNF-alpha or rov TNF-alpha plus rov GM-CSF retained MHC Class-II and ov CD-1 antigen expression and accessory function for autologous ov CD-4 T-cell proliferation, although at reduced levels compared with freshly isolated cells. Neither fresh nor cultured ALDC expressed coagulation factor XIIIa.

In vitro studies with lymphocytes from sheep orally inoculated with an aromatic-dependent mutant of Salmonella typhimurium

It was previously shown that a live aroA-strain of Salmonella typhimurium of ovine origin was a safe and effective vaccine against salmonellosis in sheep. The protective effect was observed in the apparent absence of a detectable, systemic T cell response. In the present study, populations of B and T cells from the peripheral blood of sheep vaccinated with S25/1aroA were separated and their responsiveness in vitro to Salmonella was examined. The purified T cells proliferated very weakly in response to Salmonella in the absence of interferon-gamma and interleukin 2/4 production. However, whole peripheral blood mononuclear cells and purified B cells proliferated strongly in response to Salmonella, and Salmonella-specific IgM antibodies could be detected in cell supernatants. Furthermore, Salmonella-specific IgM-producing cells were detected at low frequency by enzyme linked immunospot techniques. These observations extend the earlier findings that oral vaccination with S25/1aroA primes predominantly antigen-specific B cells in the absence of strong Salmonella-specific T cell responses.

Recombinant ovine interferon gamma inhibits the multiplication of Chlamydia psittaci in ovine cells

The local production of interferon-gamma (IFN-gamma) in sheep in response to Chlamydia psittaci was measured by cannulation of the efferent lymph duct draining the site of challenge inoculation. Peak production of IFN-gamma (256 U/ml) was detected 24 h after challenge. Based on these physiological data, functional studies were carried out in vitro to determine the effect of recombinant ovine (rOv) IFN-gamma on the multiplication of C. psittaci in ovine fibroblasts. IFN-gamma inhibited the multiplication of C. psittaci in ovine cells over a range of concentrations (250 U/ml to 2.5 U/ml) in a dose-dependent manner. The inhibition of chlamydial multiplication was most pronounced when cells were treated with rOvIFN-gamma for 24 h before infection. The addition of exogenous L-tryptophan (500 micrograms/ml) to cultures within 48th of infection abrogated the anti-chlamydial effect of rOvIFN-gamma thus suggesting that tryptophan deprivation is an anti-chlamydial mechanism induced by rOvIFN-gamma in these ovine cells.

In vitro immunodiagnostic assays for bovine tuberculosis

The immune response to mycobacterial infections in cattle is predominantly cellular in nature and current diagnostic tests for M. bovis are based on the measurement of T cell responses. The low sensitivity of serological assays for tuberculosis is therefore not surprising and serological tests will at best be used to complement rather than replace cellular assays. The recently developed bovine interferon gamma (IFN-gamma) assay is a rapid (24 hour) and simple whole blood in vitro assay, which in Australian field trials was found to be significantly more sensitive than the intradermal tuberculin test for the diagnosis of bovine tuberculosis. The problem of false-positive reactions, due to the cross-reactive nature of the antigen preparations used, can largely be overcome by using a comparative assay in which an animal's IFN-gamma response to bovine PPD and avian PPD are compared. Although reasonably M. bovis specific proteins have been identified and characterised, their use in either serological or cellular diagnostic assays is likely to be restricted due to the genetic diversity of the bovine immune response to M. bovis infection.

Expression of ovine gamma interferon in Escherichia coli and Corynebacterium glutamicum

Bacteria of two species, Escherichia coli and Corynebacterium glutamicum, were used as hosts to express recombinant ovine gamma interferon as a fusion protein with glutathione S-transferase. The recombinant gamma interferon produced by both bacteria was biologically active in vitro and was recognized by anti-gamma interferon monoclonal antibodies. E. coli produced large amounts of soluble recombinant protein which could be purified by a simple affinity chromatography method. Only a small fraction of the recombinant protein made by C. glutamicum was recovered by this method. Expression of recombinant protein in C. glutamicum was unstable but could be controlled by increased regulation of the tac promoter. Both hosts expressed ovine gamma interferon at high levels, with the recombinant protein making up a significant proportion of the cellular protein content.

The inhibitory effect of ovine recombinant interferon-gamma on intracellular replication of Toxoplasma gondii

A model for the in vitro infection of ovine cells with Toxoplasma gondii tachyzoites has been developed and used to investigate the effect of treatment with ovine recombinant interferon-gamma (ov.rIFN gamma) on parasite replication. Treatment of both alveolar macrophages and fibroblast cells either 24 h pre-infection or 2 h post-infection with ov.rIFN gamma inhibited replication of T. gondii and was quantified by suppression of 3H uracil uptake by the parasite. Replication of T. gondii in the fibroblast cells was significantly inhibited by treatment with 200-300 U/ml ov.rIFN gamma, whereas concentrations as low as 1 U/ml suppressed parasite replication in the alveolar macrophages.

Synthesis of tumour necrosis factor-alpha and interferons by mononuclear cells from Theileria annulata-infected cattle

Bovine macrophage-derived tumour necrosis factor-alpha/cachectin (TNF-alpha) was synthesized when peripheral blood mononuclear cells (PBMC) and purified adherent PBMC from naive and Theileria annulata-infected cattle were incubated in vitro with concanavalin A (Con-A) or bovine recombinant interferon gamma (Bo rIFN-gamma). TNF-alpha production was also induced when adherent PBMC were cultured with T. annulata macroschizont-infected cells. In contrast, non-adherent PBMC from sublethally infected cattle produced interferon (IFN) when incubated with Hu rIL-2, Con-A, phytohaemagglutinin (PHA) or T. annulata macroschizont-infected cells growing as cell lines in vitro. Whilst PBMC from lethally infected cattle spontaneously produced IFN-gamma during advanced stages of infection, the sera of such animals contained type 1 IFN (alpha/beta). IFN was also produced by T. annulata macroschizont-infected cell lines maintained in vitro. This work suggests that cytokines serve as crucial links between proliferating Theileira-infected cells and the characteristic clinical symptoms of tropical theileriosis.

Current research on ovine cytokines

Cytokines are key mediators of the immune system, dictating the quality of the host response to infection. The importance of such immune mediators to the development of immune and inflammatory responses has emerged from work in mouse and man, however it has now become necessary to produce the equivalent (and novel) cytokines in ruminants. Over the past three years recombinant DNA techniques have allowed the cloning of numerous ovine cytokines. These include interleukins -1, -2 and -3 (IL-1, -2 and -3), interferon-gamma (IFN-gamma), ovine trophoblast protein (oTP-1), tumour necrosis factor-alpha (TNF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The predicted amino-acid sequences of these ovine proteins show varying degrees of similarity with the equivalent human proteins thus explaining why some of the cytokines are not biologically cross-reactive between species. Recombinant ovine proteins have been produced for IFN-gamma, oTP-1, IL-1, IL-3 and GM-CSF. Their biological activities are very similar to those of their human counterparts. Although it is too early to tell whether the recombinant ovine proteins will be of use in the treatment or prophylaxis of infectious disease, work in cattle and pigs has indicated the potential usefulness of cytokines in this role.

Removal of false-positive reactions from plasma in an enzyme immunoassay for bovine interferon-gamma

A monoclonal antibody-based sandwich enzyme immunoassay (EIA) for bovine interferon-gamma (IFN-gamma) has been developed and can be used in conjunction with a whole blood culture system to diagnose tuberculosis in cattle. During its development, normal bovine plasma samples were tested to establish background levels of circulatory IFN-gamma. Of 191 samples tested, 81 (42.4%) were positive (OD > 0.1) when tested undiluted in intact monoclonal antibody (IgG1)-coated wells compared to only 8 (4.2%) in F(ab')2-coated wells, which suggested non-specific interference in the EIA rather than circulatory IFN-gamma. Reactivity of all remaining samples was removed by diluting plasmas 1/2 with 1% casein-PBS-0.05% Tween 20 supplemented with an optimum amount (5%) of normal mouse serum (NMS). Serum pools derived from BALB/c, DBA/2, C3H/HeJ, CBA/CaH and Swiss, but not C57BL/6J, mice were found to inhibit equally the reactions of five strong false-positive bovine plasma samples but had no effect on the titre of IFN-gamma in the sample. Sera from other species tested were less effective. This suggests that the interfering factors possess a high degree of specificity, since the immunoglobulin heavy chain of IgG1 produced by all these five strains of mice are allotypically identical and different to IgG1 produced by C57BL/6J mice. The use of F(ab')2 antibody fragments to coat plate wells and sample diluent containing 5% NMS has resulted in an EIA for bovine IFN-gamma that is virtually free from false-positive reactions, has a high degree of reproducibility and a sample detection limit equivalent to approximately 80 pg/ml recombinant bovine IFN-gamma.

Kinetics of ovine interferon-gamma production: detection of mRNA and characterisation of biological activity

The kinetics of interferon-gamma (IFN-gamma) production were studied in sheep mesenteric lymph node (MLN) cells at the molecular level using an ovine IFN-gamma cDNA probe and by bioassay which was verified by blocking antiviral activity with a monoclonal antibody (Mab) against recombinant bovine IFN-gamma IFN-gamma mRNA appeared in MLN cells within 4 h of stimulation with phorbol ester and Concanavalin A and was not detectable by 72 h after stimulation. Biologically active IFN-gamma appeared in the culture supernatants 8 h after stimulation and was still present 96 h later when de novo synthesis had terminated. Acid dialysis and Mab neutralisation demonstrated conclusively that native ovine IFN-gamma is a pH 2 labile cytokine.

Characterisation of ovine alveolar macrophages: regulation of surface antigen expression and cytokine production

Regulation of ovine alveolar macrophage function by recombinant interferon gamma (rIFN gamma) and lipopolysaccharide (LPS) was investigated. Ten units per millilitre of rIFN gamma increased surface expression of MHC class I and class II (DR alpha, DP alpha, and DQ alpha) molecules but not other surface antigens examined. The upregulation of MHC class II expression was specifically blocked by rIFN gamma specific monoclonal antibodies and determination of a dose/response curve established that the minimum concentration of rIFN gamma required for increased class II expression was 0.1 U ml-1 and for increased class I expression, 1 U ml-1. Northern blot analysis indicated that rIFN gamma mediated increases in surface MHC class I and class II expression were due to increased levels of specific mRNA. Using Northern blot analysis and homologous human cDNA probes we failed to detect mRNA encoding the cytokines IL-1 alpha, IL-1 beta, and TNF alpha in RNA extracted from freshly isolated macrophages or macrophages cultured in medium alone. Exposure of macrophages to LPS increased production of all three cytokines although kinetics of upregulation varied. TNF alpha mRNA was induced to maximal levels within 1 h, declining thereafter. IL-1 alpha mRNA was detected at 1 h post stimulation with a maximal level at 5 h, but none at 24 h. In contrast, IL-1 beta mRNA was not detected until 5 h after stimulation with a low level remaining at 24 h. Dose response analysis indicated that LPS concentrations of 100 pg ml-1 induced detectable levels of TNF alpha mRNA while levels as low as 10 pg ml-1 induced secretion of bioactive IL-1. Analysis of the kinetics of secretion of bioactive IL-1 from LPS stimulated macrophages indicated that levels peaked at 24 h post stimulation.