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

Mammary Defences and Immunity against Mastitis in Sheep

The objectives of this review paper are to present udder defences, including teat of the udder, mammary epithelial cells, leucocytes, immunoglobulins, complement system and chemical antibacterial agents, to describe cooperation and interactions between them and to elaborate on potentials regarding their significance in mammary immunisation strategies. The teat of the udder provides initial protection to the mammary gland. The mammary epithelial cells synthesise antibacterial proteins and the leucocytes produce various inflammation mediators (cytokines or chemokines), phagocytose bacteria and recognise antigenic structures. In the mammary gland, four immunoglobulins (IgG1, IgG2, IgM and IgA) have important roles against bacterial pathogens. The complement system is a collection of proteins, participating in the inflammatory process through various pathways. Other components contributing to humoral mammary defence include lactoferrin, lysozyme and the lactoperoxidase/myeloperoxidase systems, as well as oligosaccharides, gangliosides, reactive oxygen species, acute phase proteins (e.g., haptoglobin and serum amyloid A), ribonucleases and a wide range of antimicrobial peptides. Management practices, genetic variations and nutrition can influence mammary defences and should be taken into account in the formulation of prevention strategies against ovine mastitis.

The Mammary Gland in Mucosal and Regional Immunity

The mammary gland (MG) lacks a mucosa but is part of the mucosal immune system because of its role in passive mucosal immunity. The MG is not an inductive site for mucosal immunity. Rather, synthesis of immunoglobulin (Ig)A by plasma cells stimulated at distal inductive sites dominate in the milk of rodents, humans, and swine whereas IgG1 derived from serum predominates in ruminants. Despite the considerable biodiversity in the role of the MG, IgG passively transfers the maternal systemic immunological experience whereas IgA transfers the mucosal immunological experience. Although passive antibodies are protective, they and other lacteal constituents can be immunoregulatory. Immune protection of the MG largely depends on the innate immune system; the monocytes–macrophages group together with intraepithelial lymphocytes is dominant in the healthy gland. An increase in somatic cells (neutrophils) and various interleukins signal infection (mastitis) and a local immune response in the MG. The major role of the MG to mucosal immunity is the passive immunity supplied to the suckling neonate.

The Immunology of Mammary Gland of Dairy Ruminants between Healthy and Inflammatory Conditions

The health of dairy animals, particularly the milk-producing mammary glands, is essential to the dairy industry because of the crucial hygienic and economic aspects of ensuring production of high quality milk. Due to its high prevalence, mastitis is considered the most important threat to dairy industry, due to its impacts on animal health and milk production and thus on economic benefits. The MG is protected by several defence mechanisms that prevent microbial penetration and surveillance. However, several factors can attenuate the host immune response (IR), and the possession of various virulence and resistance factors by different mastitis-causing microorganisms greatly limits immune defences and promotes establishment of intramammary infections (IMIs). A comprehensive understanding of MG immunity in both healthy and inflammatory conditions will be an important key to understand the nature of IMIs caused by specific pathogens and greatly contributes to the development of effective control methods and appropriate detection techniques. Consequently, this review aims to provide a detailed overview of antimicrobial defences in the MG under healthy and inflammatory conditions. In this sense, we will focus on pathogen-dependent variations in IRs mounted by the host during IMI and discuss the potential ramifications of these variations.

Changes Occurring in Immune Responsiveness of Single- and Twin-Bearing Comisana Ewes During the Transition Period

Changes induced by twin and single lambing in the immune response of 16 periparturient Comisana ewes were studied. Cell-mediated immune responses were evaluated by means of skin tests performed from 3 wk before and up to d 35 after parturition. At d 21 and 7 before lambing, the sheep received an intramuscular injection of the antigen keyhole limpet hemocyanin (KLH), to which the animals had not been previously exposed, to determine their humoral immune response. Starting 3 wk before lambing and up to d 35 postlambing, the ewes were sampled to determine the plasma concentrations of anti-KLH antibody (IgG), IL-6, and IL-1 beta. From parturition through d 35 postpartum, individual milk samples were collected for determination of anti-KLH IgG titers and IL-6 and IL-1beta concentrations by means of a capture ELISA. The number of lambs born affected IL-6 concentrations in ewe plasma; IL-6 secretion always was higher in ewes birthing twins than in single-lambing ewes. Apart from the number of lambs born, the concentrations of plasma IL-6 in ewes were higher at lambing than at d 21 antepartum and at d 35 postpartum. An interaction of number of lambs born x time of sampling was observed for plasma antibody titers to KLH. The IgG concentrations were significantly higher in single-bearing ewes than in twin-bearing ewes before parturition and were very similar across groups after parturition. A time effect was found for the cell-mediated immune response and for anti-KLH IgG concentrations in milk, such that at parturition, cellular responses were lowest, and the anti-KLH IgG concentration was highest. A significant correlation was found for IgG titers to KLH in plasma and milk. Results indicate that IL-6 concentrations in blood can be considered a reliable indicator of stress connected to lambing and that the mammary gland is a microenvironment unrelated to blood stream with respect to interleukins expression. In contrast, a relationship was found for the IgG secretions in milk and blood, which suggests that the assessment of humoral immune status may be combined with milking routine in dairy animals.

Some physiological responses associated with reduced wool growth during blowfly strike in Merino sheep

OBJECTIVE

To examine the effect on wool growth of physiological changes associated with experimental flystrike in superfine Merino wethers.

DESIGN

An animal house study comparing experimentally fly struck sheep with non-infected control groups that were pair fed or fed ad libitum.

PROCEDURE

Sheep in the blow fly larval challenge group were each artificially infected with 500 first instar larvae per day for 8 days. Infections were terminated with insecticide on day 10. For all sheep, live weight change, feed intake and body temperature were monitored and blood collected for analysis of haematology, cortisol, serum haptoglobin, serum amyloid A and the pro-inflammatory cytokines, TNFa, IL-1 b, IL-6 and IL-8. Wool growth and staple strength were examined 4 months after infection.

RESULTS

Experimental fly strike included moderate fever, depressed feed intake, and elevated cortisol, IL-6, serum amyloid A and haptoglobin. Staple strength was significantly decreased in struck sheep and did not differ between wool from sites adjacent to and remote from strike lesions.

CONCLUSIONS

The results suggest that depression in feed intake alone is not sufficient to account for the decline in staple strength seen during fly strike. Cortisol, IL-6 and metabolic consequences of the acute phase response are likely to be major contributors to the systemic effects of blowfly strike on wool.

Increased Levels of LPS-Binding Protein in Bovine Blood and Milk Following Bacterial Lipopolysaccharide Challenge

Several species of gram-negative bacteria, including Escherichia coli, Klebsiella pneumoniae, and various species of Enterobacter, are common mastitis pathogens. All of these bacteria are characterized by the presence of endotoxin or lipopolysaccharide (LPS) in their outer membrane. The bovine mammary gland is highly sensitive to LPS, and LPS has been implicated, in part, in the pathogenesis of gram-negative mastitis. Recognition of LPS is a key event in the innate immune response to gram-negative infection and is mediated by the accessory molecules CD14 and LPS-binding protein (LBP). The objective of the current study was to determine whether LBP levels increased in the blood and mammary gland following LPS challenge. The left and right quarters of five midlactating Holstein cows were challenged with either saline or LPS (100 microg), respectively, and milk and blood samples collected. Basal levels of plasma and milk LBP were 38 and 6 microg/ml, respectively. Plasma LBP levels increased as early as 8 h post-LPS challenge and reached maximal levels of 138 microg/ ml by 24 h. Analysis of whey samples derived from LPS-treated quarters revealed an increase in milk LBP by 12 h. Similar to plasma, maximal levels of milk LBP (34 microg/ml) were detected 24 h following the initial LPS challenge. Increments in milk LBP levels paralleled a rise in soluble CD14 (sCD14) levels and initial rises in the levels of these proteins were temporally coincident with maximal neutrophil recruitment to the inflamed gland. Because LBP and sCD14 are known to enhance LPS-induced host cell activation and to facilitate detoxification of LPS, these data are consistent with a role for these molecules in mediating mammary gland responses to LPS.

Intramammary infusion of beta1,3-glucan for prevention and treatment of Staphylococcus aureus mastitis

Udder health problems associated with Staphylococcus aureus infections in dairy cows are difficult to control and antibiotics have limited effects. Lately, more interest has been directed towards ways to stimulate the innate immune mechanisms of the animal for better prevention and treatment of mastitis. The objectives of this study were to investigate if intramammary infusion at drying off with the immune modulator beta1,3-glucan can make the udder more resistant to experimental intra mammary S. aureus infection at this time, and to study if intramammary infusion of beta1,3-glucan into lactating udder quarters with chronic subclinical S. aureus infection can stimulate the clearing of the infection. Another aim was to evaluate the effect of beta1,3-glucan on the expression of major histocompatibility complex (MHC class II) on mammary leucocytes, measured by flow cytometry, during these circumstances. The results indicated a slight, but not statistically significant, positive effect of beta1,3-glucan at drying off on the clinical and anti-bacterial response to S. aureus infection, but no therapeutic effect of beta1,3-glucan treatment of udder quarters with chronic subclinical S. aureus mastitis. However, the proportion of MHCII+ milk lymphocytes tended to increase after glucan infusion in those udder quarters indicating a stimulation of the antigen presenting ability. To further evaluate a possible preventive effect of beta1,3-glucan infusion at drying off more studies are needed involving a larger number of animals.

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.

Chemokines in health and disease

Chemokines belong to a large family of structurally related proteins that play a pivotal role in immune system development and deployment. While a large number of chemokines (approximately 50) and their receptors (approximately 20) have been identified from humans or mice, only a few are known in domestic veterinary species. Recent data implicate CXCL8 (old name, IL-8), CXCL10 (old name, IP-10) (both CXC chemokines) and CCL2 (old name, MCP-1) (a CC chemokine) in veterinary infections, inflammatory diseases or reproduction. There is compelling evidence for neutrophil targeting chemokines such as CXCL8, in ovine bacterial mastitis, bovine pneumonic pasturellosis and equine chronic obstructive pulmonary disease (COPD). Monocyte and lymphocyte targeting chemokines appear to play a role in caprine arthritis encephalitis (CCL2) and canine endotoxemia (CXCL10). Interestingly CCL2 is considered a missing link between hormonal and cellular control of luteolysis. On the other hand, canine cardiovascular conditions are associated with overexpression of CCL2 and CXCL8. Furthermore, a number of veterinary viral pathogens encode chemokine/chemokine receptor like molecules or chemokine binding proteins that may help viruses to evade the immune system. Here, we provide an overview of the chemokine system and critically evaluate the current literature implicating chemokines in veterinary pathophysiology. Furthermore, we highlight promising areas for further research and discuss how and why chemokine antagonists are viewed as next generation anti-inflammatory drugs for the 21st century.

Subclinical mastitis as a risk factor for mother-infant HIV transmission

Subclinical mastitis, as diagnosed by an elevated sodium/potassium ratio in milk accompanied by an increased milk concentration of the inflammatory cytokine, interleukin-8 (IL8), was found to be common among breast feeding women in Bangladesh and Tanzania. Subclinical mastitis results in leakage of plasma constituents into milk, active recruitment of leukocytes into milk, and possible infant gut damage from inflammatory cytokines. Therefore, we wished to investigate whether subclinical mastitis was related to known risk factors for postnatal mother-to-child HIV transmission, that is, high milk viral load or increased infant gut permeability. HIV-infected South African women were recruited at the antenatal clinic of McCord's Hospital, Durban. Risks and benefits of different feeding strategies were explained to them and, if they chose to breast feed, they were encouraged to do so exclusively. Women and infants returned to the clinic at 1, 6 and 14 weeks postpartum for an interview about infant health and current feeding pattern, a lactulose/mannitol test of infant gut permeability, and milk sample collection from each breast separately for analysis of Na/K ratio, IL8 concentration and viral load in the cell-free aqueous phase. Only preliminary cross-sectional analyses from an incomplete database are available at this point. Moderately (0.6-1.0) or greatly (>1.0) raised Na/K ratio was common and was often unilateral, although as a group right and left breasts did not differ. Considering both breasts together, normal, moderately raised or greatly raised Na/K was found, respectively, in 51%, 28%, 21% of milk samples at 1 week (n=190); 69%, 20%, 11% at 6 weeks (n=167); and 72%, 16%, 12% at 14 weeks (n=122). IL8 concentration significantly correlated with both Na/K and viral load at all times. Na/K correlated with viral load at 1 and 14, but not 6 weeks. At 1 and 14 weeks, geometric mean viral loads in samples with Na/K > 1.0 were approximately 4 times those in samples with Na/K < 0.6. At 1 week but not later times, exclusive breast feeding was associated with lower milk viral load than was mixed feeding. Gut permeability was unrelated to milk Na/K ratio or IL8 concentration and was not significantly increased by inclusion of other foods than breast milk in the infant's diet. The results suggest that subclinical mastitis among HIV-infected women may increase the risk of vertical transmission through breast feeding by increasing milk viral load. The importance of various causes of subclinical mastitis, which likely differ at 1 week from at later times and may include local infection or sterile inflammation, systemic infection, micronutrient deficiencies, or poor lactation practices, needs to be further clarified so that appropriate interventions can be 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.

Role of breast-feeding in managing malnutrition and infectious disease

Breast-feeding policy tends to be an emotive issue. International agencies recommend exclusive breast-feeding for 4-6 months followed by continued partial breast-feeding into the second year of life in order to promote infant and child health and minimize the damage caused by the malnutrition-infection cycle. To what extent are these recommendations supported by the experimental evidence? Are they a simplification for emotional reasons or public health purposes? Breast-feeding is believed to benefit infants because breast milk contains the ideal mix of nutrients for infants, because it contains factors which promote development of the infant's gut and immune system and which prevent pathogen invasion, and because exclusive breast-feeding prevents intake of pathogens in food or water. However, some apparently contradictory evidence exists. First, in environments which are not highly contaminated breast-fed infants tend to growth falter relative to those fed formula. Second, in such environments partial breast-feeding is not associated with significantly increased gut damage relative to exclusive breast-feeding, suggesting that active promotion of gut development by breast-feeding is more important than simple avoidance of pathogens from other foods. Third, many immune factors in breast milk are probably present primarily to protect the mother, not the infant. Finally, breast milk itself may contain bacteria or viruses. This problem has come to the fore with the human immunodeficiency virus epidemic, since it is clear breast-feeding is an important mode of mother-to-child transmission. The present review will examine these challenges to the basis of the international infant feeding recommendations and will suggest that the science does actually support the policy.

The role of nitric oxide and prostaglandin signaling pathways in spinal nociceptive processing in chronic inflammation

Both nitric oxide (NO) and prostaglandins (PG) and their associated enzymes nitric oxide synthases (NOS) and cyclooxygenases (COX) (specifically COX-2) have been implicated in the development of hyperalgesia. This study examined the effects of naturally occurring chronic inflammation, chronic mastitis, on spinal nociceptive processing in sheep and focused on potential alterations in spinal PG and NO signaling pathways. Mechanical withdrawal thresholds were significantly lower in animals suffering from chronic inflammation (n=6) compared to control animals (n=6). Hyperalgesia was restricted to the side contralateral to the inflammation (decrease from ipsilateral side: hindlimb 33.2+/-5%, forelimb 19.4+/-5%). Neuronal NOS-immunoreactivity was significantly reduced bilaterally in lumbar and cervical spinal cord throughout laminae I-III (decrease 18.4+/-5% and 16.9+/-4%, respectively) and in lamina X (decrease 29.1+/-6% and 17.1+/-4%, respectively) in mastitic animals relative to control animals. No difference was detected in eNOS or iNOS-immunoreactivity or in NADPH-diaphorase staining, a marker of dynamically active NOS. RT-PCR failed to detect any change in levels of nNOS, eNOS, iNOS, COX-1 or COX-2 mRNAs. However, a marked increase in the PGE receptor, EP(3) (but not EP(2)) mRNA was detected in ipsilateral spinal cord tissue from animals with chronic inflammation. This increase in EP(3) receptor expression indicates that spinal PGs are important in the spinal response to chronic peripheral inflammation. Contralateral mechanical hyperalgesia may not be directly linked to changes in spinal EP(3) receptor mRNA expression, however, the bilateral changes in nNOS suggest that this pathway may contribute to the adaptive behavioural response observed.

Milk cytokines and subclinical breast inflammation in Tanzanian women: effects of dietary red palm oil or sunflower oil supplementation

Previously, we have found that subclinical breast inflammation, as indicated by raised breastmilk concentrations of sodium and the inflammatory cytokine, interleukin-8 (IL-8), was highly prevalent in Bangladesh and associated with poor infant growth. In order to investigate further the prevalence of subclinical breast inflammation and to assess the impact of dietary intervention, we studied rural Tanzanian women taking part in a study of dietary sunflower or red palm oil supplementation during late pregnancy and lactation. We measured breastmilk concentrations of IL-8, the anti-inflammatory cytokine, transforming growth factor-beta2 (TGF-beta) and the ratio of sodium to potassium. We also estimated systemic inflammation by plasma concentrations of the acute phase proteins, alpha1-acid glycoprotein and C-reactive protein. There were highly significant intercorrelations among milk Na/K ratio and concentrations of IL-8 and TGF-beta, the last only after treatment with bile salts which also improved TGF-beta recovery in the enzyme-linked immunosorbent assay (ELISA). Plasma acute phase protein concentrations tended to correlate with milk Na/K ratio and IL-8, suggesting that subclinical breast inflammation was related to systemic inflammation. Dietary supplementation with vitamin E-rich sunflower oil but not provitamin A-containing red palm oil decreased milk Na/K, IL-8 and TGF-beta at 3 months postpartum; however, the effect was significant only for Na/K ratio. The results suggest that milk Na/K ratio, IL-8, and TGF-beta all measure the same phenomenon of subclinical breast inflammation but that Na/K ratio, having the lowest assay variability, is the most useful. Subclinical breast inflammation may result in part from systemic inflammation and may be improved by increased dietary intake of vitamin E-rich sunflower oil.