H.-F. Seow

Effects of purified bovine whey factors on cellular immune functions in ruminants

The immunomodulatory properties of bovine milk and whey have long been documented. The recent advance of whey protein fractionation technology has now allowed us to study the immunobiological properties of some highly purified components of whey, with a view to exploiting their possible industrial and biomedical applications. The effects of fractionated bovine whey proteins on cellular immune responses were therefore examined using a panel of in vitro assays. Both lactoferrin (LF) and lactoperoxidase (LP) were found to inhibit proliferation and interferon-gamma (IFN-gamma) production of ovine blood lymphocytes in response to mitogenic stimulation. However, their effects in a combined fraction or in whey protein concentrate (WPC) were either diminished or eliminated. LF and LP had no effect on lipopolysaccharide (LPS)-induced ovine blood lymphocyte proliferation, production of interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF alpha) by ovine bronchoalveolar lavage (BAL) macrophages, major histocompatibility complex (MHC) Class II antigen expression by ovine BAL macrophages and bovine natural killer (NK) cell activity. However, alpha-lactalbumin (alpha LA) exhibited an enhancing effect on IL-1 beta production. It is noteworthy that as bovine whey fractions become progressively more purified, their modulatory effects on the immune response also become more clear-cut. The effects of LF, LP and alpha LA may be eliminated by their combination in whey or by other minor components of whey. Further investigation of industrial applications for whey proteins of high purity is warranted.

Defence against the immune barrage: helminth survival strategies.

Parasites have generated a range of countermeasures against the host immune system which allows their survival long enough for reproduction to occur. Parasite subsistence is enhanced by evasion of the immune response utilizing mechanisms such as antigenic variation of exposed immunogenic proteins, shedding of surface proteins which are the target of an immune response, and protease production to neutralise specific anti‐parasite immune components. Recent advances in the fields of immunology and parasitology have highlighted a range of mechanisms by which the parasite actively modulates the immune response to allow survival. Parasite factors can directly suppress the function of certain subsets of immune cells as well as stimulating other cell populations which have suppressive activity. Strategies such as the skewing of the type 1‐type 2 cytokine profile to that of a less appropriate response, and the mimicry of host immune regulatory proteins are becoming more widely acknowledged as means by which helminths enhance their survival. An illustration of the extent by which parasites can exploit host immune components is emphasized by the use of host cytokines as parasite growth factors. This review will examine some of the strategies developed by helminths which enables them not only to survive in the host, but also to prosper.

Nucleic acid vaccination of sheep: Use in combination with a conventional adjuvanted vaccine against Taenia ovis

This report describes the use of a nucleic acid vaccine in a large outbred animal species both alone and in combination with a conventionally adjuvanted vaccine. The gene encoding a host‐protective antigen (45W) from the sheep parasite Taenia ovis was cloned into the expression vector pcDNA3 and the resultant plasmid termed pcDNA3‐45W. Eleven of 15 sheep injected either intramuscularly or intradermally with pcDNA3‐45W mounted a serum antibody response to 45W which for both routes of injection was predominantly IgG1. However, the level of antibody elicited by the nucleic acid vaccine was low and repeated vaccinations did not boost the response. Injection of pcDNA3‐45W into animals in which an immune response had previously been generated by vaccination with recombinant 45W using Quil A as adjuvant (rec45W vaccine), did not result in enhanced antibody levels. Initial vaccination with pcDNA3‐45W and subsequently with the rec45W vaccine resulted in antibody levels significantly higher (P < 0.05) than those obtained in sheep which had only received the rec45W vaccine. This enhanced antibody response was predominantly of the IgG1, subclass (IgG1: IgG2 5:1) in animals injected with the nucleic acid vaccine by the i.m. route. Surprisingly, a second rec45W vaccination of these animals led to little or no increase in IgG1 levels and a 10‐fold increase in IgG2 resulting in a predominance of 45W‐specific IgG2. (IgG1:IgG2, 0.25:1). These studies revealed that nucleic acid vaccination has efficacy, albeit limited, in the sheep and supports previous investigations which showed that antibody responses elicited by immunization are determined by both the route and mode of antigen delivery.

T cell cytokines and disease prevention

Until recently, work on cytokines has been dominated by the use of murine or human molecules. In the last 5 years we have seen a rapid expansion in the production of bovine, ovine and porcine cytokine reagents. cDNA clones, recombinant proteins and monoclonal antibody probes are not available for a wide variety of cytokines from veterinary species. One of the most interesting recent proposals in immunology has been the division of T helper cells into two classes. Th1 cells have been characterised by the production of gamma-interferon, interleukin (IL)-2, tumour necrosis factor-beta (lymphotoxin-alpha) and the ability to mediate delayed-type hypersensitivity responses, and Th2 cells by their production of IL-4, IL-5, IL-6 and IL-10 and the ability to stimulate production of mast cells, eosinophils and IgE. An important issue for us is to determine whether polarisation of T helper cells to Th1 or Th2 occurs in veterinary species. This paper will attempt to review the status of the Th1 and Th2 debate for sheep, cattle and pigs. It will also discuss the potential for the use of cytokines in modulating the type of immune response following vaccination. By incorporation of particular cytokines into vaccine formulations or the inhibition of production of specific cytokines it may be possible to redirect the nature of the immune response to a particular antigen.

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 10−1 mol oIL‐8, there was intense accumulation of neutrophils, and very mild accumulation of eosinophils, CD5, CD4 and T19 (a σδ5 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.

Characterization of monoclonal antibodies to ovine tumor necrosis factor-α and development of a sensitive immunoassay

Monoclonal antibodies (mAbs) and a polyclonal rabbit antiserum were raised against recombinant ovine tumor necrosis factor-alpha (rovTNF alpha). Ten mAbs specific for rovTNF alpha were isolated and designated TNF1-10. All mAbs were of the IgG1 isotype and reacted with rovTNF alpha in Western blot analysis. Eight of the ten mAbs, TNF1, TNF3-7 and TNF9 and 10, completely blocked the activity of rovTNF alpha and macrophage derived native ovTNF alpha, as measured by their ability to inhibit TNF alpha-mediated lysis of WEHI-164 or L929 cells. In addition, TNF3, -7, -9 and -10 blocked the cytolytic activity of recombinant human TNF alpha (rhuTNF alpha). However, when tested for the ability to inhibit TNF alpha induced thymocyte proliferation, only mAbs TNF1, -3, -5, -7, -9 and -10 could completely block activity. Competitive binding analysis using unlabelled and horseradish peroxidase (HRPO) labelled mAbs indicated that the mAbs could be divided into five groups based on their reactivity with rovTNF alpha. The mAbs were used to develop a sensitive sandwich immunoassay for the detection of ovTNF alpha. All combinations of mAbs and the polyclonal antiserum were tested to determine which pair of antibodies gave the most sensitive assay. The combination of TNF5 as the capture antibody and the polyclonal antiserum gave the most sensitive result, detecting less than 0.24 ng rovTNF alpha ml-1. A similar sensitivity was obtained when TNF4 was used as the capture antibody and TNF10 HRPO labelled mAb as the second antibody. The immunoassay was more sensitive than the WEHI-164 bioassay which had a detection limit of 1 ng ml-1 for rovTNF alpha. This immunoassay also detected glycosylated ovTNF alpha in the supernatant of COS-7 cells which had been transfected with an ovTNF alpha cDNA.

Cyclosporin A abrogates the acquired immunity to cutaneous reinfection with the parapoxvirus orf virus.

The effect of cyclosporin A (CsA) on host immunity to cutaneous reinfection with the parapoxvirus orf virus was studied in 6‐month‐old lambs. In control reinfected animals, clinical lesions and viral replication (measured by the presence of vesicular/pustular lesions and viral antigen) in regenerating epidermal cells were at a maximum on day 4 with resolution by day 9. Lesion histology revealed recruitment of T cells, B cells and dermal dendritic cells (DDC) which increased and decreased in parallel with the clinical course of the reinfection. In animals treated with CsA (25 mg/kg/day) 1 day before and for 8 days after reinfection, more severe clinical lesions and viral replication typical of primary infections were recorded and had not resolved by 28 days following reinfection. During CsA treatment, the recruitment of T cells, B cells and DDC was inhibited. With cessation of CsA treatment there was dramatic recruitment of CD4 T cells followed by DDC then B cells to the lesion site but rapid onset of acquired immunity was not recorded. Reverse transcription–polymerase chain reaction (RT–PCR) analysis of cytokine mRNAs from lesion biopsies showed individual sheep variations. However, interleukin‐2 (IL‐2) and interferon‐γ (IFN‐γ) mRNAs were detected in the control reinfected animals on days 3 and/or 9 after reinfection but not on these days in animals undergoing treatment with CsA. In the untreated lambs there was an inexplicable lack of IL‐2 and IFN‐γ mRNAs on day 6 after reinfection. Tumour necrosis factor‐α (TNF‐α) and vascular endothelial growth factor (VEGF) mRNAs were unaffected by CsA treatment. The data suggest that CsA abrogates acquired immunity to orf virus reinfection by targetting T‐cell lymphokine production.

The use of recombinant ovine IL-1β and TNF-α as natural adjuvants and their physiological effects in vivo

In the present study we have investigated the use of recombinant ovine IL‐1β and TNF‐α both alone and in combination, as natural adjuvants in vaccination trials in sheep. Initial experiments were conducted to investigate the physiological effects of the cytokines in vivo and determine what dose could be administered without adverse pyrogenic effects. Even at the maximum dose tested (100 μg) the only significant physiological effect was a transient increase in body temperature of approximately 2°C in sheep injected with TNF‐α. Administration of either cytokine had profound effects on the levels of circulating leucocytes for up to 5 days postinjection. The incorporation of either IL‐1β or TNF‐α in aqueous or Al(OH)3 vaccine formulations enhanced antibody responses to a recombinant antigen from the cestode parasite Taenia ovis. The addition of IL‐1β to aqueous vaccine formulations increased antibody responses 15–20‐fold and in Al(OH)3 formulations by three to six fold. TNF‐α stimulated 1.5 to six‐fold and 2.5 to seven‐fold increases in antibody levels in aqueous and Al(OH)3‐based formulations, respectively, in a dose‐dependent manner. The addition of either cytokine to Quil A or IFA vaccines did not enhance the antibody levels elicited. When 10 μg of both IL‐1β and TNF‐α were incorporated in the aqueous or Al(OH)3 vaccine formulations, increases of 21‐fold and 25‐fold, respectively, were observed in antibody levels. The adjuvant activity of IL‐1β and TNF‐α in combination in the Al(OH)3‐based vaccine resulted in antibody levels commensurate with those obtained using Quil A or IFA.

Leukocyte and Cytokine Accumulation in the Ovine Teat and Udder during Endotoxin-Induced Inflammation

Persson Waller, K., Colditz, I.G., Flapper, P. and Seow, H.-F., 1997. Leukocyte and cytokine accumulation in the ovine teat and udder during endotoxin-induced inflammation. Veterinary Research Communications, 21 (2), 101-115The accumulation of leukocytes, ovine serum albumin and the cytokines interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α), interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-γ (IFN-γ) 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 µg 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-α, IL-8 and GM-CSF, but not for IL-1β and IFN-γ, during endotoxin-induced inflammation in the ovine udder. Release of TNF-α, 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-1β and IFN-γ were occasionally found in all three groups.

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.