Dynamics of experimentally induced Staphylococcus epidermidis mastitis in East Friesian milk ewes

The responses of five lactating East Friesian milk ewes to experimental mammary infection with Staphylococcus epidermidis and of five control ewes were examined over a period of 10 weeks. Infection caused an influx of neutrophils into milk, the numbers of which started to rise 4 h post infection and peaked 24 h after infection. The initial response was accompanied by mild fever and mild leucopaenia in blood (8 h after infection). No other signs of systemic infection were observed. Milk appeared normal at all times, although the milk yield of infected ewes tended to decline. Staphylococci were absent in milk from four ewes at 2 d and at 3 d after infection, but re-emerged intermittently in four of five ewes at subsequent samplings. Cytokines in milk were measured by ELISA. IL-8 was elevated in infected glands at 2 h and peaked at 8 h. In the four ewes intermittently shedding bacteria, IL-8 remained elevated until the final sampling at 10 weeks. IL-1beta was transiently elevated at 1 d and 2 d and showed a pronounced peak in one sheep. Milk samples from this ewe were bacteriologically negative, somatic cell count (SCC) was within the normal range and the concentrations of IL-1beta, as well as IL-8, were similiar to the control group (n=5) from 1 week after infection until the final sampling. Histological examination revealed leucocytic infiltrates in the four glands remaining infected at the end of the experiment, and a high level of CD5+ lymphocytes in three ewes. The results suggest that the relationship between the initial neutrophil influx and the proinflammatory cytokines may be responsible for determining the course of infection. Subclinical mastitis due to coagulase-negative staphylococci leads to minor changes in milk yield and milk constituents.

Cytokines in mammary lymph and milk during endotoxin-induced bovine mastitis

Cytokine kinetics were examined in milk and in afferent and efferent lymph of the supramammary lymph node after intramammary infusion of endotoxin from Escherichia coli. Cows were sampled 0, 2 and 4h after infusion (p.i.). Neutrophils appeared in afferent lymph 2h p.i., and in efferent lymph and milk 4h p.i. The milk contained high concentrations of interleukin-8 (IL-8) at 2 and 4h p.i. IL-8 was also found in lymph, but at lower concentrations. The tumor necrosis factor-alpha (TNF-alpha) concentration tended to increase in afferent lymph at 2h p.i., and increased in milk at 4h p.i. The level of IL-1beta increased at 4h p.i. in milk, but was not detected in lymph. Interferon-gamma was not detected in any sample, at any time. The results indicate a primary role for IL-8 in the recruitment of neutrophils into the gland, and suggest that IL-1beta and TNF-alpha are not necessary for IL-8 production and release in response to endotoxin.

Immunological responses of the lactating ovine udder following experimental challenge with Staphylococcus epidermidis

The responses of five lactating ewes to experimental mammary infection with Staphylococcus epidermidis were examined. Infection caused an intense but transient influx of neutrophils into milk, which peaked at 8 h and was accompanied by mild fever and mild leukopaenia in blood. No other signs of systemic infection were observed. Number of staphylococci in milk decreased logarithmically until 24 h, were absent from three ewes at 48 h and then increased in number or re-emerged in four of the five ewes at 72 or 144 h. At all times milk appeared grossly normal. Expression of the adhesion molecules CD11b and CD18 increased on neutrophils in milk at 24 h then tended to decline over subsequent days. The proportion of lymphocytes positive for CD4, CD8, WC1 and MHCII tended to decrease from 24 to 72 h then increased at 144 h. Cytokines in milk were measured by ELISA. IL-8 was elevated in infected glands at 2 h, peaked at 24 h and remained elevated until the final sampling at 144 h. IL-6 was transiently elevated at 4 and 8 h while IL-1beta remained elevated from 8 until 144 h. The results suggest that the intense early neutrophil infiltrate eliminated most but not all bacteria and a state of subclinical infection ensued. After 24 h , leukocyte numbers in milk declined while cytokines, especially IL-8 remained elevated, suggesting that sensitivity or responsiveness of gland to inflammatory signals decreased as infection progressed. This attenuation of the host defence response may have contributed to the failure of the gland to eliminate bacteria and may be an important feature of the development of chronic and subclinical mastitis.

Immunosuppressive effects of Marek's disease virus (MDV) and herpesvirus of turkeys (HVT) in broiler chickens and the protective effect of HVT vaccination against MDV challenge

Much of the impact of Marek's disease in broiler chickens is considered to be due to immunosuppression induced by Marek's disease virus (MDV). The present study evaluates the effects of an Australian isolate of pathogenic MDV (strain MPF 57) and a non-pathogenic vaccinal strain of herpesvirus of turkeys (HVT) (strain FC 126) on the immune system of commercial broiler chickens for 35 days following challenge at days 0 or 3 of age. It also investigates the extent of protection provided by HVT vaccine against MDV-induced immunosuppression. Immune system variables, including relative lymphoid organ weight, blood lymphocyte phenotype (CD45+/CD3+, putatively T, and CD45+/LC+, putatively B) and antibody production following vaccination against infectious bronchitis (IB) at hatch, were used to assess the immune status of chickens. Immunosuppression was also assessed by susceptibility to secondary challenge with pathogenic Escherichia coli on day 29 post-MDV challenge. MDV infection reduced the weight of the thymus and bursa of Fabricius, the numbers of circulating T lymphocytes and B lymphocytes, and IB antibody titre. The timing of these effects varied. MDV infection greatly increased susceptibility to E. coli infection. HVT alone caused mild depletion of T and B lymphocytes but no effect on immune organ weight or IB titre. Vaccination with HVT provided good protection against most of the immunosuppressive effects of MDV but not against MDV-induced growth impairment and reduced responsiveness to IB vaccination, suggesting that recent Australian strains of MDV may be evolving in virulence to overcome the protective effects of HVT.

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.

Use of lectin binding characteristics to identify gastrointestinal parasite eggs in faeces

Identification of the presence and abundance of species is important when choosing therapies and control strategies for internal parasitism of livestock. Here we examine lectin binding characteristics of eggs isolated from sheep faeces as a means for identifying the parasite genera contributing to infection. The intensity of lectin staining varied with incubation time, incubation volume, concentration of lectin and concentration of eggs. Formalin fixed eggs had greater autofluorescence but exhibited the same lectin staining pattern as fresh eggs. The stage of egg development did not influence staining. Eggs from Haemonchus contortus, H. placei, Trichostrongylus colubriformis, T. vitrinus, Ostertagia circumcincta, Nematodirus spathiger and the cestode Monezia expansa were incubated with a panel of fluoroscein isothiocyanate (FITC)-labelled lectins. Lectin binding exhibited a genus specific pattern. Haemonchus spp. stained strongly positive with peanut agglutinin (PNA), and were positive for concanavalin A (ConA), Ricinus communis agglutinin (RCA) and Maclura pomifera lectin (MPA). Trichostrongylus spp. were PNA-, ConA-, RCA- and strongly MPA+. O. circumcincta were weakly positive for PNA, MPA, ConA and negative for RCA. N. spathiger were weakly positive for the four lectins, and M. expansa were weakly positive for PNA, RCA and MPA and were strongly ConA+. The genus specificity of lectin staining was used to identify the presence of Trichostrongylus and Haemonchus eggs in faeces from sheep with mixed field infections, however correspondence between lectin staining and larval differentiation for identifying a low prevalence of Ostertagia in the field infection was poor. Refinements in methods for rapid egg isolation may improve egg differentiation on the basis of lectin staining, which could be undertaken by flow cytometry or microscopy.

Production of antibodies to recombinant antigens from Lucilia cuprina following cutaneous immunisation of sheep

Immunological control of cutaneous myiasis of sheep caused by Lucilia cuprina larvae has been an elusive goal. Antibody to antigens derived from the peritrophic membrane can stunt or kill larvae in a dose dependent fashion. Thus efficacy of vaccines employing these antigens may be limited by the amount of antibody in skin available for ingestion by larvae. The potential for elevating antibody concentrations in skin by intradermal immunisation with the recombinant peritrophic membrane antigens peritrophin-44, peritrophin-48 and peritrophin-95 was therefore examined. Using within-animal comparisons, specific antibody was significantly higher in skin transudates from locally immunised sites than from adjacent adjuvant control sites. It was concluded that cutaneous immunisation may assist immunological control of blowfly larvae.

Simulated solar UVB exposure inhibits transcutaneous immunization to cholera toxin via an irradiated skin site in cattle

Transcutaneous immunization (TCI) is a new needle-free vaccination technology with the potential to reduce the risk of needle-borne disease transmission and carcass damage within the livestock industries. The principal antigen-presenting cell involved in TCI is thought to be the epidermal Langerhans cell. Langerhans cell function is inhibited by cutaneous ultraviolet-B radiation (UVB) exposure. Such exposure may inhibit TCI through sun exposed skin sites due to the phenomenon of local low dose photoimmunosuppression. TCI of cattle to cholera toxin (CT) resulted in the generation of a serum anti-CT-specific IgG(2) response. However, exposure of cattle to a sub-inflammatory dose of simulated solar UVB (2.43 x 10(3)J/m(2)) significantly (P<0.05) inhibited TCI to CT via irradiated skin sites.

Expression of cell surface adhesion molecules by peripheral blood eosinophils during Trichostrongylus colubriformis infection in sheep

The effect of infection of sheep with the gastrointestinal nematode parasite Trichostrongylus colubriformis on expression of adhesion molecules CD11a, CD11b, CD11c, CD18, CD44, CD49d and CD62L by peripheral blood eosinophils was examined by flow cytometry. Initially, to establish the sensitivity of adhesion molecules to inflammatory signals, eosinophil-rich exudates were elicited in non-lactating mammary glands of immune sheep by infusion of 50 microg of soluble antigen extract from T. colubriformis third stage larvae. Eosinophils comprised 40.8% of mammary leucocytes and 4.5% of peripheral blood leucocytes. In comparison with blood, the percentage of eosinophils expressing CD18 increased and the percentage expressing CD62L decreased in exudates and the mean fluorescent intensity, an indicator of receptor number per cell, for CD11a and CD49d also decreased on exudate eosinophils. Peripheral blood eosinophils were examined over 8 weeks during trickle infection of immune sheep with infective or irradiated third stage larvae of T. colubriformis. During the last 3 weeks of infection, CD11a staining decreased in infected sheep and CD44 staining decreased in sheep receiving either infective or irradiated larvae. Other surface markers did not change. The results indicate that systemic changes in expression of adhesion molecules by eosinophils occur during T. colubriformis infection in sheep.

Effects of dietary protein types on immune responses and levels of infection with Eimeria vermiformis in mice

The present study reports the dietary effects of bovine alpha whey fraction, bovine casein and soy protein isolate on the immune responsiveness of C57BL/6J mice infected with Eimeria vermiformis. During the patent period, mice fed alpha whey fraction had significantly higher blood total white cell, CD4+ and CD8+ lymphocyte counts and higher Con A-stimulated IFN-gamma production by spleen cells than those fed other protein sources, but there was no significant difference in output of faecal oocysts. Casein-fed mice had significantly higher levels of Con A- stimulated IFN-gamma production and a lower output of faecal oocysts than soy-fed mice. The study demonstrated that dietary proteins have different impacts on immune responsiveness and level of parasitic infection in the gut; however, the mechanisms affecting level of infection are not clear. These effects appeared not to be solely related to nutritional properties of the diets. Further research into the underlying immune mechanisms and possible direct interactions between bioactive proteins and the parasite E. vermiformis should be fruitful.

Induction of systemic immune responses in sheep by topical application of cholera toxin to skin

Cholera (and related) toxins (CT) when applied topically on unbroken skin induce systemic immune responses in mice, a procedure called transcutaneous immunization (TCI). The current study examined the capacity for TCI to induce systemic immune responses in sheep. Three groups (n=5 per group) were immunized at day 0 (priming) and day 28 (boosting) with 250 microg of CT in water by TCI, with 25 microg of CT in alum by intramuscular injection, or not immunized. Serum samples were taken at days 0, 28, 42, 56 and 70 after immunization for measurement of CT-specific IgG as well as CT-specific IgG1, IgG2, IgA and IgM antibodies by ELISA. After immunization, IgG, IgG1 and IgG2 antibody in immunized groups were significantly higher than in the control group, and boosting further increased these titres. IgG, IgG1 and IgG2 in the injection group were significantly higher than in the TCI group. There was a preponderance of IgG1 antibody, relative to IgG2, in both immunized groups. CT-specific IgA and IgM were detected in both immunized groups. Lymphocyte proliferation to CT was measured at day 90. A CT-specific lymphocyte proliferative response (stimulation index>2) was detected in all sheep from the injection group, in two sheep from the TCI group and in none of the controls. Results demonstrated that TCI induces primary and secondary antibody responses and specific proliferative responses to CT in sheep.

Effect on systemic antibody concentrations of topical application of choleratoxin to skin of sheep

OBJECTIVE

To examine the ability of a vaccine formulation combining choleratoxin with an experimental antigen to induce a systemic antibody response when applied topically on unbroken skin of sheep.

DESIGN

Seven treatment groups of five adult sheep received systemic or topical priming followed 4 weeks later by systemic or topical boosting with choleratoxin and/or bovine serum albumin. Topical vaccines were administered to clipped skin on the ventral abdomen for 2 h. Booster immunisations were repeated 8 weeks after initial boosting. Serum antibody titres to choleratoxin and bovine serum albumin were determined by ELISA.

RESULTS

An antibody response to choleratoxin was observed in serum, but no antibody response to bovine serum albumin was detected.

CONCLUSION

Transdermal delivery may be feasible for livestock vaccines, however, further work is necessary to develop formulations that induce protective immunity by this route.

The effect of dexamethasone on some immunological parameters in cattle

Immunosuppression as a consequence of acute and chronic stress can increase the susceptibility of cattle to a range of infectious diseases. In order to develop a panel of immune function assays for investigating the effects of potential stressors on immune competence in cattle, the effect of treatment with short- and long-acting preparations of the synthetic glucocorticoid dexamethasone was examined. Short-acting dexamethasone (dexamethasone sodium phosphate 0.08 mg/kg) followed 37 h later by long-acting dexamethasone (dexamethasone-21 isonicotinate 0.25 mg/kg) was injected intramuscularly and blood was collected to assess immune functions at intervals over the subsequent 11 days from 6 treated and 6 control Hereford steers. Dexamethasone induced leukocytosis (neutrophilia, eosinopenia, lymphopenia, monocytosis), an increased neutrophil:lymphocyte ratio, an elevated percentage of CD4+ lymphocytes, a decreased total CD8+ lymphocyte count, decreased total and percentage WC1+ lymphocytes, an elevated percentage of IL-2 receptor alpha (IL-2Ralpha)+ lymphocytes, and an elevated percentage of B lymphocytes. In vitro chemotaxis of peripheral blood neutrophils to human C5a and ovine IL-8 was increased by dexamethasone treatment. Lymphocyte proliferation in the presence of phytohaemagglutinin, and serum concentrations of IgM, but not IgA or IgG1, were suppressed by dexamethasone treatment, whereas mitogen-induced production of interferon-gamma (IFN-gamma), neutrophil expression of CD18, neutrophil myeloperoxidase activity and natural killer (NK) cell activity were not influenced by dexamethasone treatment. The results indicate the potential for haematology and immune function assays to reflect elevated activity of the hypothalamic-pituitary-adrenocortical axis in cattle. Immunological parameters may thus provide a useful adjunct to cortisol and behavioural observations for assessing the impact of stress on the welfare of cattle.

Effect of intramammary infusion of beta-1,3-glucan or interleukin-2 on leukocyte subpopulations in mammary glands of sheep

OBJECTIVE

To investigate effects of intramammary infusion of beta-1,3-glucan or recombinant ovine interleukin-2 (rOvIL-2) on blood and mammary leukocyte subpopulations and their expression of various surface antigens in sheep.

ANIMALS

12 healthy multiparous, nonpregnant, nonlactating fine-wool Merino ewes.

PROCEDURE

Beta-1,3-glucan in pyrogen-free saline solution (PFSS; n = 6), rOvIL-2 in PFSS (3), or PFSS (3) was infused on days 0 and 7 in 1 udder half of each ewe. Jugular vein blood and mammary secretion samples were taken before infusion and on days 2, 7, and 21 after infusion. Total and differential leukocyte counts were obtained, and blood and mammary cells were labeled for flow cytometry.

RESULTS

Slight swelling of the mammary glands was observed on day 2 after rOvIL-2 but not after beta-1,3-glucan infusion. Both substances induced significant increase in mammary secretion leukocyte numbers, compared with controls. Beta-1,3-Glucan induced an influx of monocyte/macrophages, whereas neutrophils were the predominating cell population after rOvIL-2 infusion. Beta-1,3-glucan induced selection for CD4+, B-cell+, WC1+, and L-selectin+ lymphocytes on day 14 after infusion. By comparison, rOvIL-2 induced selection for B-cell+ and L-selectin+ lymphocytes on days 14 and 21 and depletion of CD8 and, to some degree, of IL-2R+ lymphocytes. Beta-1,3-Glucan induced an increase in the proportion of CD14+ leukocytes, indicating selective migration of monocyte/ macrophages to the nonlactating udder.

CONCLUSION

Beta-1,3-Glucan and rOvIL-2 can modulate nonspecific immunity in the udder of sheep but may exert their effects by differing mechanisms. Clinical Relevance-Stimulation of the nonspecific defense against udder infections may improve control of mastitis.

The effect of experimental infectious mastitis on leukocyte subpopulations and cytokine production in non-lactating ewes

The interactions between leukocytes and cytokines during the acute response to intramammary infections in the dry mammary gland of sheep were studied. Dry ewes were experimentally infected in one udder half with either Staphylococcus aureus or Escherichia coli, or infused with saline as control. Udder secretion samples, blood samples and udder tissue samples were collected before and 4, 8 and 24 h after infections/infusions. Total and differential leukocyte counts were calculated in both blood and mammary secretions, and flow cytometry was used to detect the presence of CD4+, CD8+, WC1+, IL-2R+, CD18+ or L-selectin + lymphocytes, CD18+ or L-selectin + neutrophils, and CD14+ leukocytes. Moreover, the concentrations of interleukin-1 beta (IL-1 beta), interleukin-8 (IL-8) and granulocyte-macrophage colony stimulating factor (GM-CSF) in udder secretions were measured using ELISA, and RT-PCR was used to detect the presence of corresponding cytokine mRNA in udder tissue biopsies. The results suggest an association between the concentrations of IL-1 beta, IL-8 and the intensity of neutrophil infiltration of the infected gland. Immunologically relevant changes in proportions of lymphocyte subpopulations might also occur in the acute phase of the inflammatory reaction of the udder. Greater cellular and cytokine responses to E. coli infection may have contributed to the milder clinical picture and more rapid resolution of infection than that seen for S. aureus. Enhancing the production of pro-inflammatory cytokines may improve defence against bacterial mastitis.

Variation in the immune status of two Australian pig breeds

OBJECTIVE

To investigate the variation in immune competence of two Australian pig breeds.

DESIGN

A panel of immune tests were used to assess breed and sire differences in weaner piglets of Large White and Duroc breeds.

PROCEDURE

All piglets were immunised against porcine leptospirosis. Blood samples were taken for studies on lymphocyte phenotypes, mitogenic responses of blood cells and serological analysis.

RESULTS

Significantly larger blood leucocyte numbers were found in Large White piglets compared with Duroc piglets after vaccinations. No significant difference in concanavalin A induced blood cell proliferation was found between these two breeds before or after vaccinations. Some significant breed variation in blood lymphocyte phenotypes was found. While the age-related changes of lymphocyte phenotypes were similar for the two breeds, the Large White breed had significantly larger numbers of CD2+ and CD4+ cells than the Duroc breed after the two vaccinations. There were also significant sire effects on CD8+ cells within the Large White breed after the first vaccination. No significant breed difference was detectable in serum IgG concentrations but sire differences within each breed before the primary vaccination were found. The serum antibody response to vaccination against leptospirosis was generally small, and showed no variations due to either breed or sire. No gender effects were found during the entire study.

CONCLUSION

The study demonstrated significant differences in some important immune components of the pig breeds studied. This may in turn indicate the variation in their immune competence or disease resistance. However, further investigation into the heritability and correlation with specific immune responses is required.

Expression of surface antigens on blood and mammary leukocytes in lactating and dry ewes

Flow cytometry was used to study the expression of CD4, CD8, CD14, CD18, WC1, MHCII, B-cell and L-selectin on CD45+ leukocytes in ovine blood and mammary secretions from lactating and dry ewes. The proportion of CD4+ lymphocytes was significantly lower and the proportion of CD8+ lymphocytes significantly higher in mammary secretions than in blood. This suggests that a selective migration to or retention of CD8+ cells in favour of CD4+ cells occurs in the mammary gland. L-selectin staining intensity on lymphocytes and neutrophils was lower in mammary secretions than in blood. In contrast, CD18 staining intensity was higher on leukocytes in milk, but not in dry secretions, than on corresponding cells in blood. These changes in adhesion molecules are in accord with shedding of L-selectin and up-regulation of CD18 during transendothelial migration. Expression of leukocyte antigens differed with lactational status mainly in mammary secretions. In milk, the staining intensity of CD18+ lymphocytes and neutrophils was higher than in dry secretions and more milk neutrophils expressed L-selectin. In contrast, greater numbers of IL-2R+ and MHCII+ lymphocytes and CD14+ leukocytes were observed in dry secretions. An increased proportion of these subpopulations could lead to increased immunological responsiveness of the udder during the dry period.

Leukocyte and cytokine accumulation in the ovine teat and udder during endotoxin-induced inflammation

The accumulation of leukocytes, ovine serum albumin and the cytokines interleukin-1 beta(IL-1 beta), tumour necrosis factor-alpha(TNF-alpha), interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma(IFN-gamma) was studied during endotoxin-induced inflammation in lactating and dry ovine udders, and in the teat cisterns of dry ewes after surgical closure of the passage between the teat and udder cisterns. Samples were taken before infusion and hourly up to 10 h after infusion of 0.1, 1 or 10 micrograms of endotoxin, or infusion of pyrogen-free saline (PFS) as a control. Rectal temperatures were measured. A significant dose- and time-dependent accumulation of leukocytes, mainly neutrophils, was observed in the lactating udders and in the teat cisterns. In the dry udders, the leukocyte accumulation was significant for time but not for dose. Peak numbers of cells were reached at 3-4 h in the dry udders and in the teat cisterns, but not until 10 h after infusion in the lactating udders. The changes in the ovine serum albumin concentrations mostly paralleled changes in leukocyte numbers. A role was indicated for TNF-alpha, IL-8 and GM-CSF, but not for IL-1 beta and IFN-gamma, during endotoxin-induced inflammation in the ovine udder. Release of TNF-alpha, IL-8 and GM-CSF was most prominent in lactating udders, peaking at 2 or 3 h after infusion, but was also detected in dry udders and teat cisterns. Detectable levels of IL-1 beta and IFN-gamma were occasionally found in all three groups.

Accumulation of leucocytes and cytokines in the lactating ovine udder during mastitis due to Staphylococcus aureus and Escherichia coli

The accumulation of leucocytes in milk and in teat cistern tissues, and the presence of the cytokines interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma) in milk was studied during inflammation in the lactating ovine udder induced by Staphylococcus aureus and Escherichia coli. Milk and/or teat tissue samples were taken before and four, eight and 24 hours after inoculation. Both S aureus and E coli induced a significant accumulation of leucocytes in milk, S aureus from eight hours with a peak after 24 hours, and E coli from four hours, with a peak after eight hours. After the inoculation of S aureus the numbers of subepithelial neutrophils in the teat cistern tissues were increased after four hours and had increased further by eight hours. After the inoculation of E coli, tissue neutrophil numbers peaked at four hours and were still high at eight hours. Large numbers of S aureus were recovered from milk throughout the experiments whereas the recovery of E coli diminished over time. TNF-alpha, IL-8 and IL-1 beta were detected in milk during the inflammation, and low levels of GM-CSF and IFN-gamma were also observed occasionally. Of the cytokines measured, TNF-alpha and IL-8 reached the highest concentrations, accumulating in a similar pattern to the leucocytes for both infections. IL-1 beta was detected mainly during S aureus-induced inflammation, indicating differences in the inflammatory responses elicited by the organisms.

In vivo depletion of T-cells and cytokines during primary exposure of sheep to parasites

This study examined the role of CD8+ and WC1+ T-cells and of interferon (IFN)-gamma in the development of protective immunity against infection with the enteric nematode parasite Trichostrongylus colubriformis in sheep. Monoclonal antibodies (mAb) were administered during induction of the immune response to deplete or neutralise these components. Protection against the primary and challenge infections was assessed by faecal egg count and total worm count. Prolonged administration of mAb recognising IFN-gamma and CD8 resulted in significantly increased protection during the 6 week primary infection and following challenge. CD8+ cells were depleted from blood but not from intestinal mucosa. After injection of mAb (CC15) recognising the surface antigen WC1, WC1+ and Tcr gamma delta + cells were depleted from blood but not markedly from enteric mucosa, and protection against challenge, although variable, was increased by up to 88%. It appears that CD8+ and WC1+/gamma delta+ cells and IFN-gamma all retard the potential development of naturally acquired immunity against the parasite.

Cytokine-induced inflammation in the ovine teat and udder

The inflammatory response, as measured by the accumulation of leukocytes and ovine serum albumin, induced by interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), interleukin-beta (IL-8), and granulocyte-macrophage colony stimulating factor (GM-CSF) was studied in lactating ovine udders, and in test cisterns of dry ewes after surgical closure of the passage between the teat and udder cisterns. In the lactating udders, IL-1 beta and TNF-alpha, but not IL-8 and GM-CSF, induced significant accumulation of cells. In the teat cisterns, all four cytokines IL-1 beta, TNF-alpha, IL-8, and GM-CSF induced significant cell accumulation. IL-1 beta was the most potent cytokine. A slight increase in serum albumin, paralleling the changes in leukocyte numbers, was observed after infusion of IL-1 beta and, to some extent, TNF-alpha. The cell accumulation induced by IL-1 beta or TNF-alpha was dose and time dependent in lactating udders, and time-dependent in teat cisterns. The cell numbers were considerably higher in lactating udders than in teat cisterns after infusion with IL-1 beta. The first influx of cells was observed earlier, and the cell numbers peaked earlier in the teat cisterns than in the lactating udders. IL-8 and GM-CSF induced dose and time dependent cell accumulation in teat cisterns only. The differences between lactating udders and teat cisterns may be attributable to the differences in tissue area involved and the number of receptors available, or to dilution of cytokines in milk, or to presence of inhibitory factors. Differences between cytokines in their inflammatory effects may be explained by their modes of action. IL-1 beta and TNF-alpha have a wide range of cellular functions enabling them to induce a more prominent response than IL-8 and GM-CSF. Furthermore, receptors for IL-1 beta and TNF-alpha are present on a larger number of cell types. Finally, the results indicated that the teat cisterns, being the port of entry for udder infections, as well as the lactating udders are capable of a diversified inflammatory response which is important in the defence against udder infections.

Some relationships between age, immune responsiveness and resistance to parasites in ruminants

In the Australian livestock industries, susceptibility to infectious diseases is generally greater in young than in mature ruminants. The increased susceptibility is manifest as respiratory and intestinal infections (viral and bacterial) of calves, as well as fleece rot, flystrike and, especially, gastrointestinal parasitic infestations of young sheep. Lower resistance to infectious disease in young ruminants appears to be due largely to immunological hyporesponsiveness, and is not simply a consequence of their not having been exposed sufficiently to pathogens to develop active immunity. Young sheep have significantly lower proportions of CD4+ and CD8+ lymphocytes, but similar proportions of T19+ and B lymphocytes in blood, lymph and skin compared with mature sheep. Blood lymphocytes from young sheep produce less interferon-gamma in culture and young sheep invariably mount smaller antibody responses than do mature animals. Taken together, these findings begin to explain why young ruminants are more susceptible to infectious diseases in general, and to gastrointestinal parasites in particular, when compared to mature animals. Haematological markers of disease resistance, the prevalence of non-selected diseases and immune responses to vaccination were examined in the internal parasite-resistance flocks in Armidale NSW and the fleece rot/flystrike selection flocks at Trangie NSW. Any programme that seeks to improve resistance to parasitic or any other disease should have the capacity to make contemporary measurements of resistance to other diseases which are important in, or threaten, the production system.

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.

Cloning, sequencing, expression and inflammatory activity in skin of ovine interleukin-8

Ovine IL-8 (oIL-8) cDNA was obtained by probing a spleen cell cDNA library with human IL-8 (hIL-8) cDNA. The oIL-8 cDNA was 1434 base pairs long with a single open reading frame encoding a 101 amino acid precursor protein of relative molecular mass 11,268. The inferred amino acid sequence has 78, 82, 84 and 67% similarity with human, rabbit, porcine and guinea-pig IL-8, respectively. By analogy with the most prevalent form of hIL-8, a 72 amino acid form of oIL-8 was expressed as a fusion protein containing glutathione-S-transferase and purified by affinity chromatography on a glutathione-Sepharose column yielding 8 mg IL-8/L broth culture. The fusion protein lacked chemotactic activity for ovine neutrophils, whereas the 72 amino acid form of oIL-8 was equipotent with rhIL-8. At 6 and 24 h after intradermal injection of 10(-9) mol oIL-8, there was intense accumulation of neutrophils, and very mild accumulation of eosinophils, CD5, CD4 and T19 (a gamma delta TCR subset) cells but not CD8 cells. The availability of roIL-8 and its cDNA probes will permit the role of this important member of the IL-8 family of chemotactic cytokines to be determined in inflammatory diseases of sheep.

Age-dependent immune response in Merino sheep

The numerical and functional attributes of populations of lymphocytes were compared in the blood, lymph and skin of young and mature sheep. Young sheep, four to eight months old, had a lower proportion of CD4+ cells in blood, lymph and skin than mature sheep three to six years old. In contrast, B cells and T19+ cells were as prevalent or more prevalent in young sheep as in mature sheep. Blood lymphocytes from young sheep, cultured in vitro produced less interferon-gamma, both spontaneously and in the presence of concanavalin A than did lymphocytes from older sheep. The serum antibody responses of adult sheep to the T cell-independent antigen Brucella abortus lipopolysaccharide (LPS) were greater over a range of antigen doses, suggesting that an apparent excess of antigen could not overcome the relative immune deficiency of young sheep. The adjuvant Quil A corrected the depressed antibody response of young sheep to B abortus LPS, but dextran sulphate did not. The skin contact hypersensitivity of mature sheep to dinitrochlorobenzene was greater. However, the T cell phenotypes present in infiltrates of lymphocytes elicited by the intradermal injection of tetanus and diphtheria, but not tuberculin antigens, were comparable for the two age groups. The capacity of Quil A to raise the antibody responses of both young and mature sheep to a similar titre suggests that it may be possible to overcome the immunological hyporesponsiveness that may contribute to the disease susceptibility of young sheep.