Association among filamentous actin content, CD11b expression, and membrane deformability in stimulated and unstimulated bovine neutrophils

Effect of the synthetic Toll-like receptor ligands LPS, Pam3CSK4, HKLM and FSL-1 in the function of bovine polymorphonuclear neutrophils

Toll-like receptors (TLR) are a family of pattern recognition receptors that sense microbial associated molecular patterns (MAMP) such as microbial membrane components and nucleic acids of bacterial origin. Polymorphonuclear neutrophils (PMN) are the first cell of the innate immune system to arrive at the site of infection or injury and elicit oxidative and non-oxidative microbicidal mechanisms. Observations in human and mouse suggest that TLR ligands can induce direct responses in PMN. So far, there is no information of the effect of synthetic TLR ligands on the response of bovine PMN. The objective of this study was to evaluate the functional response of bovine PMN incubated with four synthetic TLR ligands: ultrapure LPS (TLR4), Pam(3)CSK(4) (TLR2/1), HKLM (TLR2) and FSL-1 (TLR2/6). The results show that all the ligands increment cells size as identified by changes in the FSC-SSC as part of the flow cytometric analysis. Interestingly, only Pam(3)CSK(4) consistently induced a calcium influx, increased ROS production and secretion of gelatinase granules, whereas no response was seen using other ligands. Furthermore, exposure of bovine PMN to ultrapure LPS, Pam(3)CSK(4), HKLM or FSL-1 for 24 hours did not impact on apoptosis of these cells. Our data provide evidence for a selective response of bovine PMNs to TLR ligands.

D-lactic acid interferes with the effects of platelet activating factor on bovine neutrophils

D-lactic acidosis occurs in ruminants, such as cattle, with acute ruminal acidosis caused by ingestion of excessive amounts of highly fermentable carbohydrates. Affected animals show clinical signs similar to those of septic shock, as well as acute laminitis and liver abscesses. It has been proposed that the inflammatory response and susceptibility to infection could both be caused by the inhibition of phagocytic mechanisms. To determine the effects of d-lactic acid on bovine neutrophil functions, we pretreated cells with different concentrations of D-lactic acid and measured intracellular pH using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) and calcium flux using FLUO-3 AM-loaded neutrophils. Reactive oxygen species (ROS) production was measured using a luminol chemiluminescence assay, and MMP-9/gelatinase-B granule release was measured by zymography. CD11b and CD62L/l-selectin expression, changes in cell shape, superoxide anion production, phagocytosis of Escherichia coli-Texas red bioparticles, and apoptosis were all measured using flow cytometry. Our results demonstrated that D-lactic acid reduced ROS production, CD11b upregulation and MMP-9 release in bovine neutrophils treated with 100 nM platelet-activating factor (PAF). D-lactic acid induced MMP-9 release and, at higher concentrations, upregulated CD11b expression, decrease L-selectin expression, and induces late apoptosis. We concluded that D-lactic acid can interfere with neutrophil functions induced by PAF, leading to reduced innate immune responses during bacterial infections. Moreover, the increase of MMP-9 release and CD11b expression induced by 10mM D-lactic acid could promote an nonspecific neutrophil-dependent inflammatory reaction in cattle with acute ruminal acidosis.

Platelets and innate immunity

Although platelets are best known as primary mediators of hemostasis, this function intimately associates them with inflammatory processes, and it has been increasingly recognized that platelets play an active role in both innate and adaptive immunity. For example, platelet adhesive interactions with leukocytes and endothelial cells via P-selectin can lead to several pro-inflammatory events, including leukocyte rolling and activation, production of cytokine cascades, and recruitment of the leukocytes to sites of tissue damage. Superimposed on this, platelets express immunologically-related molecules such as CD40L and Toll-like receptors that have been shown to functionally modulate innate immunity. Furthermore, platelets themselves can interact with microorganisms, and several viruses have been shown to cross-react immunologically with platelet antigens. This review discusses the central role that platelets play in inflammation, linking them with varied pathological conditions, such as atherosclerosis, sepsis, and immune thrombocytopenic purpura, and suggests that platelets also act as primary mediators of our innate defences.

Interleukin-8 expression by mammary gland endothelial and epithelial cells following experimental mastitis infection with E. coli

Epithelial and endothelial cells play a pivotal role in initiating and controlling the movement of leukocytes into tissues during inflammation through the production of cytokines and chemokines such as interleukin-8 (IL-8). In situ hybridization with an IL-8 riboprobe was used to determine IL-8 mRNA expression by mammary gland epithelial and endothelial cells in cows with experimental Escherichia coli mastitis. Epithelial cells of the gland, especially surrounding the alveoli, had increased IL-8 mRNA levels at all time points at which tissue samples were collected (8, 12, and 24h) after E. coli challenge. Levels of IL-8 expression in the epithelial cells decreased at 24h post-infection. IL-8 expression by mammary gland endothelial cells was low, but did increase slightly at 24h post-infection. Both epithelial and endothelial cells of the mammary gland can contribute to the production of IL-8 that is typically seen in coliform mastitis.

Determination of specific receptor sites for platelet activating factor in bovine neutrophils

OBJECTIVE

To identify and characterize a platelet activating factor (PAF) receptor in bovine neutrophils by use of radioligand binding, reverse transcription-polymerase chain reaction (RT-PCR) assay, and western blot analysis.

ANIMALS

4 healthy adult cows.

PROCEDURE

Bovine neutrophil membranes were isolated for association, dissociation, and saturation binding experiments with PAF labeled with hydrogen 3 (3H-PAF). The RT-PCR assay was performed with appropriate human primers, and western blot analysis was developed with a polyclonal antibody obtained from a peptide of bovine PAF receptor.

RESULTS

Analysis of kinetic binding data supported a single class of PAF receptor. Binding of 3H-PAF to membrane preparations was selectively displaced by PAF and a nonhydrolyzable analogue of guanine triphosphate (Gpp[NH]p) and by lyso-PAF (a biologically inactive analogue of PAF) to a lesser extent. Among other PAF receptor antagonists, 14-deoxyandrographolide and WEB 2086 were the most effective in inhibiting 3H-PAF binding sites in neutrophil membranes; 2 lignans, schisandrin-A and gamma-schisandrin were also effective, but 2 gingkolides (BN52020 and BN52021) only mildly inhibited 3H-PAF binding. Results of RT-PCR assay and western blot analysis of neutrophil crude membranes confirmed the presence of a PAF receptor.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that bovine neutrophils express only 1 type of PAF receptor, and it is likely that this receptor is involved in inflammatory responses. The most effective PAF antagonists were 14-deoxyandrographolide and WEB 2086; these PAF antagonists may be potentially useful in the treatment of inflammatory processes in cattle.

Evaluation of activated neutrophils in the blood of horses with colic

OBJECTIVE

To evaluate the activation status of neutrophils in blood samples obtained from horses with naturally occurring colic associated with strangulating obstruction, nonstrangulating obstruction, or inflammatory bowel disease.

ANIMALS

30 horses with naturally occurring colic and 30 healthy control horses.

PROCEDURE

Activation status of neutrophils was determined by assessing the number of neutrophils that could pass through filters with 5-microm pores, cell-surface CD11-CD18 expression, and alterations in size and granularity of neutrophils.

RESULTS

Horses with impaction or gas colic did not have evidence of activated neutrophils. Horses with inflammatory bowel disease consistently had evidence of activated neutrophils, including decreased leukocyte deformability, increased CD11-CD18 expression, increased neutrophil size, and decreased neutrophil granularity. Horses with strangulating colic had variable results. Of horses with strangulating colic, 7 of 14 had marked changes in filtration pressures, 5 of 14 had increased CD11-CD18 expression, 6 of 14 had changes in neutrophil size, and 5 of 14 had changes in neutrophil granularity. Among horses with strangulating colic, changes in deformability, size, and granularity of neutrophils correlated with an adverse outcome.

CONCLUSIONS AND CLINICAL RELEVANCE

Activated neutrophils were detected in all horses with inflammatory bowel disease and a few horses with strangulating colic. Correlation of activated neutrophils with horses that had strangulating colic that died or were euthanatized indicates that activated neutrophils are a negative prognostic indicator. Additional studies are needed to determine whether activated neutrophils contribute directly to the adverse outcome in horses with strangulating colic.

Application of flow cytometric techniques to veterinary clinical hematology

Flow cytometry has emerged as a major new technology in veterinary clinical laboratories. Flow cytometers in current use include stand-alone instruments and cytometers incorporated into hematology analyzers. Flow cytometers offer rapid and quantitative analysis of a variety of cell types based on cell size, molecular complexity, and antigenic composition. Therefore, flow cytometry complements and extends knowledge that can be obtained by light microscopy. Stand-alone instruments are very flexible, however, this flexibility opens the instrument to obtaining invalid or misleading results. The recent development of monoclonal antibodies specific for epitopes on blood cells of food and companion animals has greatly expanded the spectrum of tests with potential clinical application. Tests that appear to have the greatest potential for routine application include reticulocyte and reticulated platelet enumeration, detection of erythrocyte-bound immunoglobulin, immunophenotyping of leukemias and lymphomas, and bone marrow differential cell counting. This report will briefly review the technical aspects of flow cytometry and then focus on techniques with present or potential application to the veterinary clinical laboratory.

Complement activation in heart diseases. Role of oxidants

Increasing evidence demonstrated that atherosclerosis is an immunologically mediated disease. Myocardial ischemia/reperfusion injury is accompanied by an inflammatory response contributing to reversible and irreversible changes in tissue viability and organ function. Three major components are recognized as the major contributing factors in reperfusion injury. These are: (1) molecular oxygen; (2) cellular blood elements (especially the neutrophils); and (3) components of the activated complement system. The latter two often act in concert. Endothelial and leukocyte responses are involved in tissue injury, orchestrated primarily by the complement cascade. Anaphylatoxins and assembly of the membrane attack complex contribute directly and indirectly to further tissue damage. Tissue damage mediated by neutrophils can be initiated by complement fragments, notably C5a, which are potent stimulators of neutrophil superoxide production and adherence to coronary artery endothelium. The complement cascade, particularly the alternative pathway, is activated during myocardial ischemia/reperfusion. Complement fragments such as the anaphylatoxins C3a and C5a, are produced both locally and systematically, and the membrane attack complex is deposited on cell membranes and subsequent release of mediators such as histamine and platelet activating factor (PAF), thereby causing an increase in vascular permeability with concomitant manifestation of cellular edema. Complement increases the expression of CD18 on the neutrophils and increases P-selectin expression on the surface of the endothelium. Mitochondria may be a source of molecules that activate complements during ischemia/reperfusion injury to myocardium, providing therewith a stimulus for infiltration of polymorphonuclear leukocytes. Tissue salvage can be achieved by depletion of complement components, thus making evident a contributory role for the complement cascade in ischemia/reperfusion injury. The complexities of the complement cascade provide numerous sites as potential targets for therapeutic interventions designed to modulate the complement response to injury. The latter is exemplified by the ability of soluble form of complement receptor 1 (sCR1) to decrease infarct size in in vitro models of ischemia/reperfusion injury. The mechanism(s) that initiates complement activation is not clearly known, although loss of CD59 (protectin) from cells compromised by ischemia/reperfusion may contribute to direct damage of the coronary vascular bed by the terminal complement complex. Therapeutic approaches to ischemia/reperfusion injury in general, and especially those involving complements, are at the very beginning and their potential benefits have still to be adequately evaluated. It may be noted that complement activation has both positive and negative effects and, therefore, might be modulated rather than abruptly blunted.