Function of neutrophils and chemoattractant properties of fetal placental tissue during the last month of pregnancy in cows.

Neutrophils were isolated from the blood of pregnant cows on days 255, 265, and 275 of pregnancy, and on the day of parturition (n = 5/group), and in addition, simultaneously from 4 ovariectomized healthy cows (control animals). Neutrophils were subjected to neutrophil function assays (chemotaxis against zymosan-activated serum, random migration, ingestion of 125I-iododeoxyuridine [IdUR]-labeled Staphylococcus aureus, iodination of proteins, cytochrome C reduction, antibody-independent and antibody-dependent cell-mediated cytotoxicity). Results were expressed as percentage of control animals. Fetal placental tissue (cotyledon), uterine wall tissue, and skeletal muscle were obtained from the principal animals on the aforementioned days via laparotomy, and tissue suspensions were prepared. Chemotaxis of neutrophils was tested against tissue supernatants. Compared with day 255, there was an increase in ingestion of 125I-IdUR-S aureus at parturition, whereas iodination of proteins and cytochrome C reduction were reduced on the day of calving. The other neutrophil functions tested did not change over time of gestation. Fetal placental and uterine wall tissue attracted neutrophils with uterine wall tissue having a tendency to be more potent than cotyledonary tissue. Skeletal muscle tissue did not attract neutrophils. There was no change in chemotaxis response of neutrophils evoked by intrauterine and uterine tissues over time of gestation. It was concluded that at parturition, neutrophil function is impaired with respect to their bactericidal effects, which may render the animal more susceptible to bacterial infections, and that the chemoattractant properties of fetal placental and uterine wall tissues are tissue-specific, at least when compared with skeletal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of arachidonic acid metabolites and steroids on function of bovine polymorphonuclear neutrophils.

Polymorphonuclear neutrophils (PMN) from 4 ovariectomized healthy cows were incubated with 0 (control), 10(-8), 10(-7), and 10(-6) M arachidonic acid metabolites of the cyclo- and lipoxygenase pathways for 30 minutes, and with steroids for 2 hours. Immediately after incubation, PMN were subjected to the following function assays: chemotaxis against zymosan-activated serum, chemotaxis against arachidonic acid metabolite or steroid at the doses given (only control PMN were tested), random migration, ingestion of 125I-iododeoxyuridine-labeled Staphylococcus aureus (125I-IdUR-S aureus), iodination of proteins, cytochrome C reduction, antibody-independent and -dependent cell-mediated cytotoxicity (AICC and ADCC). Prostaglandin F2 alpha was chemoattractant and stimulated ingestion of 125I-IdUR-S aureus. Prostaglandin E2 stimulated cytochrome C reduction, whereas prostacyclin inhibited iodination of proteins. Thromboxane B2 stimulated ADCC. Leukotriene B4 was chemoattractant for bovine PMN and stimulated random migration and AICC. 5-Hydroxyeicosatetraenoic acid was also chemoattractant, but inhibited ingestion of 125I-IdUR-S aureus. 15-Hydroxyeicosatetraenoic acid was chemoattractant and decreased ADCC. Lipoxin A4 stimulated random migration, whereas lipoxin B4 inhibited chemotaxis against zymosan-activated serum, but was chemoattractant and stimulated cytochrome C reduction. 12-Hydroxyhepadecatrienoic acid and 12-hydroxyeicosatetraenoic acid did not influence any of the PMN functions tested. Of the steroids tested, cortisol increased ADCC, and progesterone stimulated cytochrome C reduction, but decreased ADCC. 17 beta-Estradiol and estrone were chemoattractant and stimulated cytochrome C reduction. In addition, estrone also stimulated random migration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Defective function of leukocytes from cattle persistently infected with bovine viral diarrhea virus, and the influence of recombinant cytokines.

Cattle persistently infected with bovine viral diarrhea (BVD) virus have decreased neutrophil and lymphocyte functions. We reevaluated these functions and further characterized the inhibition of persistent BVD virus infection in neutrophils, using sensitive kinetic assays. In addition, the influence of in vitro incubation of neutrophils with recombinant bovine interferon gamma (rBoIFN gamma) and in vitro incubation of lymphocytes with recombinant bovine interleukin-2 was evaluated. Significant (P less than 0.05) decrease in random migration under agarose, Staphylococcus aureus ingestion, cytochrome-C reduction, iodination, antibody-independent cell-mediated cytotoxicity, oxidant production, and cytoplasmic calcium flux were observed in neutrophils from cattle persistently infected with BVD virus, compared with noninfected control cattle. Incubation of neutrophils from noninfected controls with rBoIFN gamma significantly (P less than 0.05) decreased random migration under agarose, cytochrome-C reduction, and cytoplasmic calcium flux. Neutrophils from cattle persistently infected with BVD virus also had decreased random migration under agarose after incubation with rBoIFN gamma; in addition, antibody-independent cell-mediated cytotoxicity, elastase release, and cytoplasmic calcium flux were significantly enhanced. The rBoIFN gamma induced significantly (P less than 0.05) different effects on chemotaxis, cytochrome-C reduction, iodination, and cytoplasmic calcium flux of neutrophils from infected and control cattle. The rBoIFN gamma was more effective at improving the function of neutrophils from cattle persistently infected with BVD virus, compared with neutrophils from controls. Lymphocytes from infected cattle had decreased blastogenesis in response to phytohemagglutinin, concanavalin A, and pokeweed mitogen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of bovine neutrophils by recombinant bovine tumor necrosis factor-alpha

The in vitro effect of bovine recombinant tumor necrosis factor-alpha (rbTNF-alpha) on bovine neutrophil function and the possibility that rbTNF-alpha and recombinant bovine interferon-gamma (rbIFN-gamma) act synergistically were investigated. Treatment of neutrophils with rbTNF-alpha (0.05 micrograms/ml; approximately 50 U/ml) at 37 degrees C for 2.5 h resulted in enhancement of antibody independent neutrophil-mediated cytotoxicity (AINC) and inhibition of random migration and chemotaxis. The same treatment resulted in a slight decrease in iodination and cytochrome C reduction, but did not affect Staphylococcus aureus ingestion, or antibody dependent cell-mediated cytotoxicity. Kinetic and inhibitor studies indicated that the action of rbTNF-alpha was rapid and was independent of protein and RNA synthesis by neutrophils. Evaluation of the synergistic activities of rbTNF-alpha and rbIFN-gamma indicated that treatment of neutrophils with these two cytokines simultaneously resulted in additive enhancement of AINC and inhibition of random migration and chemotaxis. There was no additive effect of the two cytokines on inhibition of iodination or cytochrome C reduction.     

Evaluation of neutrophil function in female goats

Polymorphonuclear neutrophils (PMN) were isolated from the blood of healthy adult female goats on each of 3 consecutive days. The PMN isolated were evaluated, using random migration, chemotaxis, Staphylococcus aureus ingestion, cytochrome C reduction, iodination, and antibody-dependent cell-mediated cytotoxicity assays. Over the 3 days, mean values for each of the assays ranged as follows: area of random migration, 11.3 to 19.9 mm2; chemotactic index, 6.4 to 11; chemotactic difference, 2.8 to 4.2 mm; S aureus ingestion, 18.3% to 26.1% ingested; cytochrome C reduction, 2.7 to 3.2 nmoles of O2- produced/well; iodination, 19.4 to 25.1 nmoles of NaI/10(7) PMN/h; and antibody-dependent cell-mediated cytotoxicity 59% to 90% 51Cr released. Significant (P less than 0.05) day-to-day variations were found for all assays. Parallel increases and decreases for all test results on a per day basis indicated a common denominator influencing cell functional status rather than variability inherent in the assays themselves. Alterations induced in the cells during the cell isolation procedure were considered a probable cause.     

Association of increased estradiol and progesterone blood values with altered bovine polymorphonuclear leukocyte function

Polymorphonuclear leukocyte (PMN) function and serum concentrations of estradiol, progesterone, and cortisol (hydrocortisone) were monitored concurrently in clinically normal cows during the estrous cycle. Five parameters were used to evaluate PMN function: (i) random migration under agarose, (ii) ingestion of 125I-labeled Staphylococcus aureus, (iii) nitroblue tetrazolium (NBT) reduction, (iv) iodination, and (v) antibody-dependent cell-mediated cytotoxicity. Increased serum estradiol concentrations were associated with enhanced random migration, but had no apparent effect on NBT reduction, iodination, or ingestion of S aureus by bovine PMN. Increased serum estradiol was also associated with increased serum cortisol. Increased serum progesterone values were associated with a depression of NBT reduction and iodination by PMN, but with enhanced random migration and antibody-dependent cell-mediated cytotoxicity. These results indicate that physiologic changes in steroid hormone values during the normal estrous cycle of the cow are associated with alterations in PMN function.     

The effects of danofloxacin and tilmicosin on neutrophil function and lung consolidation in beef heifer calves with induced Pasteurella (Mannheimia) haemolytica pneumonia

Pneumonia caused by Pasteurella (Mannheimia) haemolytica was induced in weaned beef heifer calves, approximately 6 months of age. Calves were treated at 20 h after challenge with therapeutic doses of danofloxacin or tilmicosin. Peripheral blood neutrophils were collected at 3, 24 and 48 h after treatment. The ex vivo effects on neutrophil function, neutrophil apoptosis, and hematological parameters were examined, as was the effect on percentage lung consolidation. Neutrophil function assays included random migration under agarose, cytochrome C reduction, iodination, Staphylococcus aureus ingestion, chemotaxis, and antibody-dependent and antibody-independent cell-mediated cytotoxicity. Apoptosis was determined using a cell death detection kit. Killing was performed at 72 h after treatment. Statistical comparisons were made among the three groups of challenged-treated animals: saline, danofloxacin, and tilmicosin. Comparisons were also made between nonchallenged nontreated animals (NCH) and challenged saline-treated animals. There were no significant differences for any of the neutrophil function assays or neutrophil apoptosis among the challenged-treated groups. This suggests that danofloxacin and tilmicosin have no clinically significant effects on neutrophil function or apoptosis. There were also no significant differences in percentage lung consolidation among the challenged-treated groups. Significant differences were found between the NCH calves and the challenged saline-treated calves in several neutrophil assays, which were attributed to effects of P. haemolytica infection.     

Alterations in bovine neutrophil function during the periparturient period

Neutrophils from 8 Holstein heifers were evaluated for function during the periparturient period. Random migration, ingestion of bacteria, superoxide anion production, native (nonenhanced) chemiluminescence, iodination, and antibody-dependent, cell-mediated cytotoxicity by neutrophils were determined. Foremilk samples were evaluated for bacteria. Significant (P less than 0.05) increases in random migration of neutrophils, iodination, and chemiluminescence were evident 2 weeks before parturition and then decreased dramatically by the first week after parturition. These impairments of neutrophil function after parturition may be manifested as a severe cumulative deficit in the native defenses afforded by the neutrophil.     

Suppression of neutrophil and lymphocyte function induced by a vaccinal strain of bovine viral diarrhea virus with and without the administration of ACTH

Effects of a modified live vaccine (MLV) strain of bovine viral diarrhea virus (BVD) on lymphocyte and neutrophil function were determined in cattle with and without increased plasma cortisol (hydrocortisone) concentrations. Cattle were given MLV-BVD vaccine IM and intranasally. Cattle given ACTH received 200 IU every 12 hours for 10 doses. The MLV-BVD virus when administered alone caused no apparent clinical signs or body temperature response. Of 4 MLV-BVD-treated calves that were also given ACTH, 2 developed increased body temperature and respiratory distress. The MLV-BVD virus caused a decrease in circulating lymphocytes and neutrophils, whereas administration of ACTH and MLV-BVD induced a neutrophilia and lymphopenia. The MLV-BVD virus and ACTH when administered separately or in combination caused a depression of lymphocyte blastogenesis in response to selected mitogens. Neutrophils were separated from the peripheral blood and their function was evaluated, using the following procedures: (i) random migration under agarose, (ii) ingestion of 125I-labeled Staphylococcus aureus, (iii) quantitative nitroblue tetrazolium reduction, (iv) iodination, and (v) antibody-dependent cell-mediated cytotoxicity (ADCC). The MLV-BVD virus produced a significant (P less than 0.05) suppression of neutrophil iodination and ADCC. Neutrophils from cattle given MLV-BVD virus and ACTH had enhanced random migration, enhanced S aureus ingestion, suppressed iodination, and suppressed ADCC activity.     

Effects of infection with parainfluenza-3 virus and infectious bovine rhinotracheitis virus on neutrophil functions in calves

Calves were challenge exposed in separate experiments with parainfluenza-3 (PI-3) virus or infectious bovine rhinotracheitis (IBR) virus. Blood neutrophils were assayed for functional activity every other day for at least 3 weeks by random migration, Staphylococcus aureus ingestion, antibody-dependent cell-mediated cytotoxicity, cytochrome-c reduction, iodination, and native chemiluminescence. Exposure to PI-3 virus resulted in a brief febrile response and no other clinical signs. Alterations in total or differential WBC counts were not detected. Chemiluminescence and iodination activities were reduced from activities before exposure. Exposure to IBR virus resulted in mild clinical signs and a febrile response of several days' duration. Total WBC and mononuclear cell counts were reduced. Random migration was reduced, whereas S aureus ingestion was enhanced. We concluded that infection of calves with IBR virus and PI-3 virus might directly or indirectly result in alterations of neutrophil function. The functional alterations apparently are different for each virus. These virus-induced alterations in neutrophil function might predispose calves to secondary bacterial pneumonia.     

Functional and ultrastructural evaluation of neutrophils from foals and lactating and nonlactating mares

Neutrophils from 4 pony foals, 3 lactating pony mares, and 3 nonlactating mares were evaluated ultrastructurally and by in vitro function tests. Neutrophils from foals had significantly (P = 0.05) less random migration than neutrophils from mares; values in tests for iodination and Staphylococcus aureus ingestion were also lower with foal neutrophils. Neutrophils from lactating mares had lower responses to iodination, antibody-dependent cell-mediated cytotoxicity, and random migration tests than did neutrophils from nonlactating mares. Ultrastructurally, granule concentration did not differ significantly among groups. A slight decrease in primary granules and a corresponding increase in granules with a flocculent matrix indicates partial spontaneous neutrophil degranulation in foals and lactating mares.     

Variation of neutrophil function with age in calves

Neutrophil function was evaluated on 2 occasions in 5 calves from each of the following age groups: 4 to 5 weeks, 9 to 11 weeks, 16 to 19 weeks, and 12 to 14 months. Of the neutrophil functions examined, the iodination reaction, which evaluates the activity of the myeloperoxidase-hydrogen peroxide-halide antibacterial system of the neutrophil, reflected the most marked differences among age groups. The iodination values for the 2 youngest age groups were approximately 52% of the value for the oldest cattle. This difference could not be attributed to the amount of myeloperoxidase in the neutrophil granules. Antibody-dependent cell-mediated cytotoxicity also tended to be lower in neutrophils from the 3 younger age groups. Nitroblue tetrazolium reduction, a measure of superoxide anion generation by neutrophils, was lower in the youngest age group only. The capability of neutrophils to ingest Staphylococcus aureus was higher in the 3 youngest groups of calves than in the oldest group. The observed differences in neutrophil function in young vs older calves may be partially responsible for the increased susceptibility of young calves to infectious disease.     

Effects of dexamethasone, levamisole, and dexamethasone-levamisole combination on neutrophil function in female goats

Effects of dexamethasone, levamisole, or combined dexamethasone-levamisole administration on polymorphonuclear neutrophil (PMN) function in healthy, adult female goats were studied. Goats were assigned to treated (n = 6) and control (n = 6) groups. In experiment 1, treated goats were given levamisole (6 mg/kg of body weight, IM). In experiment 2, treated goats were given 0.1 mg of dexamethasone/kg, IV, for 3 consecutive days, 1 mg of dexamethasone/kg, IV, for 6 consecutive days, and 6 mg of levamisole/kg, IM, with a 4th injection of 1 mg of dexamethasone/kg. All injections were administered 12 hours before blood collection. The PMN were evaluated for random migration and chemotaxis under agarose, ingestion of Staphylococcus aureus, cytochrome C reduction, iodination, and antibody-dependent cell-mediated cytotoxicity. Levamisole alone did not alter the function of caprine PMN. Both doses of dexamethasone caused increased random migration and decreased cytochrome C reduction and iodination. Dexamethasone resulted in no changes in chemotaxis, S aureus ingestion, and antibody-dependent cell-mediated cytotoxicity. Random migration and cytochrome C reduction returned toward base line in cells from dexamethasone and levamisole-treated goats. Although iodination activity in cells from dexamethasone-treated goats remained significantly (P less than 0.05) lower than those of controls after levamisole administration, a rebound toward base-line activity occurred.     

In vivo effect of ascorbic acid on neutrophil function in healthy and dexamethasone-treated cattle

Ascorbic acid (20 mg/kg of body weight) administered subcutaneously to otherwise nontreated cattle resulted in enhancement of neutrophil oxidative metabolism and capability of neutrophils to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). Random migration, bacterial ingestion, and iodination by neutrophils was unaffected. Three dosage levels of ascorbic acid (10 mg/kg, 20 mg/kg, and 40 mg/kg) were examined for their effects on neutrophil function in cattle treated with dexamethasone (0.04 mg/kg). Dexamethasone administration caused an enhancement of neutrophil random migration and a suppression of neutrophil oxidative metabolism, iodination, and ADCC. None of the dosage levels of ascorbic acid had an effect on the alterations in the WBC count induced by dexamethasone. The ascorbic acid did tend to reverse the effects of dexamethasone on neutrophil random migration, oxidative metabolism, and ADCC in a dose-dependent manner, with the lowest dose having no discernible effect. Ascorbic acid administration also tended to enhance Staphylococcus aureus ingestion by bovine neutrophils. These results indicate that ascorbic acid should be further investigated for its potential to reduce the susceptibility of stressed or glucocorticoid-treated cattle to infective processes.     

Sources of variation introduced into a phagocytosis assay as a result of the isolation of neutrophils from bovine blood

A study was conducted to examine sources of variation introduced into a phagocytosis assay as a result of the isolation of neutrophils from bovine blood, including variation attributable to isolation of neutrophils from blood, variation between duplicate determinations of percentage phagocytosis, and the variation in the ability of neutrophils isolated from blood (over repeated collections from the jugular vein) to phagocytose. For the phagocytosis assay, jugular venous blood from each of 4 cows was divided into 2 equal portions. The neutrophils were isolated by lysis of red blood cells with 0.2% sodium chloride. The neutrophils (2 x 10(7)) were incubated in duplicate with 32P-labeled Staphylococcus aureus ([32P]SA; 2 x 10(8)) in skimmed milk samples (2.5% final concentration) prepared from 4 cows. This process was repeated thrice on neutrophils isolated from 4 cows at 2-week intervals. The proportions of variation in percentage of 32P-labeled S aureus phagocytosed between duplicate neutrophil isolations and between duplicate assay determinations were 0 and 1%. Differences among skimmed milk sources and among runs, using blood neutrophils taken at different times from the same donor cow, accounted for 62 and 36% of the total variation. The results indicated that variation arising from blood neutrophil isolation introduced into a phagocytosis assay within a single-day trial is of no concern. The large variation among skimmed milk sample sources indicated differences among cows in the ability of their milk to support phagocytosis. The variation in neutrophil isolations over time for any cow was considered too large to allow for evaluation of physiologic and environmental effects on phagocytosis of neutrophils isolated from blood.     

Effects of human IL-8 isoforms on bovine neutrophil function in vitro

Interleukin 8 (IL-8) is a potent chemotactic and activating agent for human neutrophils and bovine IL-8 is chemotactic for bovine neutrophils; however, it is unclear whether IL-8 activates bovine neutrophils. Two isoforms of human recombinant (hr) IL-8 protein (77 and 72 amino acid) were used to stimulate bovine neutrophils in vitro. Bovine neutrophils exhibited significant migration in the presence of 0.1, 0.5, 1.0 and 5.0ngml(-1) hr IL-8 when incubated for 30min at 37 degrees C in a modified Boyden chamber assay. Both the 77 and 72 aa forms were equally effective in inducing migration in this assay. At the highest doses of IL-8 examined (1 and 5ngml(-1)), migration was similar to migration in the presence of 20% zymosan-activated serum (ZAS) or 12h lipopolysaccharide (LPS)-stimulated blood monocyte supernatants (CM). Significant (p<0. 05) release of alkaline phosphatase (ALK-P) (from specific granules) occurred but myeloperoxidase (MPO) release and superoxide anion production were not enhanced in bovine neutrophils by either form of hrIL-8 at any of the doses tested. Significant (p<0.05) alkaline phosphatase release was observed in the presence of 10 and 100ngml(-1) for the 72 aa form of IL-8 and only at the higher dose for the 77 aa form of IL-8. The ZAS and CM significantly enhanced neutrophil degranulation of ALK-P and MPO as well as inducing superoxide anion production. These results suggest that IL-8 may play a role in both neutrophil recruitment and activation during bovine inflammatory processes.     

Association of class I bovine lymphocyte antigen complex alleles with in vitro blood neutrophil functions, lymphocyte blastogenesis, serum complement and conglutinin levels in dairy cattle

Ninety-eight lactating Holstein cows from two genetic lines selected for high and average milk production were used in the study. Five peripheral blood samples were collected over a 60-day period from each cow for evaluation of neutrophil function, lymphocyte blastogenesis, leukocyte count, and serum complement and conglutinin levels. Blood samples were typed for antigens encoded by alleles at the bovine major histocompatibility complex (BoLA) A locus. Alleles w14(w8), w20A, and w19(w6) were the most frequent of 14 alleles present in this herd. Association of BoLA type with immune function results was examined by using gene substitution models including and ignoring sire effects. Alleles w15(w8) and w16 were associated with greater circulating mononuclear cell and total leukocyte numbers, while w27(w10), w11, and w20A were associated with lower numbers of these cell types. Alleles EU28D and w20A were positively and negatively associated with granulocyte percentage, respectively. Allele w16 was associated with greater antibody-independent neutrophil cytotoxicity, unstimulated lymphocyte proliferation, serum conglutinin activity, and with lower antibody-dependent neutrophil cytotoxicity. Allele w19(w6) was associated with decreased conglutinin activity and decreased neutrophil iodination. Increased antibody-dependent neutrophil cytotoxicity was observed for animals bearing allele w14(w8), and decreased neutrophil iodination, serum conglutinin, and nonstimulated lymphocyte blastogenesis were observed in individuals carrying w20A or EU28D. Significance of both sire and BoLA complex effects suggests that both major histocompatibility complex genes and background genes of the sire significantly affect immune function. This research suggests BoLA-A locus genes may be major genes or markers for closely linked major genes involved in regulation of nonspecific immune function.     

Lymphocyte blastogenesis and neutrophil function in cattle persistently infected with bovine viral diarrhea virus

Neutrophil function and mononuclear cell proliferative responses to mitogens were determined in healthy cattle and in cattle persistently infected with bovine viral diarrhea (BVD) virus. Uptake of [3H]thymidine by resting and mitogen-stimulated peripheral blood mononuclear cells was significantly lower in cattle persistently infected with BVD virus than in healthy cattle. Neutrophils from cattle persistently infected with BVD virus had significantly impaired capability to ingest Staphylococcus aureus, but were normal in respect to random migration under agarose, cytochrome C reduction, iodination, and antibody-dependent cell-mediated cytotoxicity. Impairment of neutrophil function in cattle persistently infected with BVD virus differs from impairment of neutrophil function reported in healthy cattle mounting an immune response to recent BVD virus infection.     

Alteration of neutrophil function associated with coccidiosis in cattle: influence of decoquinate and dexamethasone

Twenty Holstein steers subclinically infected with coccidia were allotted to 2 groups of 10 steers each. One group received a diet containing 0.5 mg of decoquinate/kg of body weight. After 25 days on the diet, there was no difference between the groups in lymphocyte blastogenic responsiveness to mitogens; however, there were differences in neutrophil function. Lymphocytes from steers of the decoquinate-fed group had decreased random migration under agarose, enhanced cytochrome C reduction, and enhanced iodination activity. Other measures of neutrophil function evaluated (chemotactic index, Staphylococcus aureus ingestion, and antibody-dependent and -independent cell-mediated cytotoxicity) were not affected. After 30 days of decoquinate feeding, half of the cattle in each group received 5 daily IM injections of dexamethasone (0.04 mg/kg of body weight). The dexamethasone-treated steers from the group that did not have decoquinate in the diet developed clinical coccidiosis, whereas the decoquinate-treated steers remained clinically normal. Lymphocyte and neutrophil function were again evaluated for a 3-day period beginning 4 days after dexamethasone treatment was halted. Neutrophils from the steers that developed clinical coccidiosis after dexamethasone administration had significantly (P less than 0.05) inhibited random migration under agarose, cytochrome C reduction, and iodination activity, but significantly (P less than 0.01) enhanced S aureus ingestion. The feeding of decoquinate prevented the inhibition of neutrophil cytochrome C reduction and lessened the inhibition of neutrophil iodination in the dexamethasone-treated group. Dexamethasone treatment was associated with an inhibition of lymphocyte blastogenic responsiveness to phytohemagglutinin in principals as well as controls.     

Effects of Moraxella bovis and culture filtrates on 51Cr-labeled bovine neutrophils

The cytotoxicity of Moraxella bovis whole cells and culture filtrates was studied, using 51Cr-labeled bovine and human blood neutrophils. The cytotoxicity of living M bovis was directly related to the concentration of bacteria in the neutrophil cultures, and was maximal at an approximate neutrophil to bacteria ratio of 1:10. Cytotoxicity was maximal by 30 minutes after living bacteria were added to the suspension of the 51Cr-labeled neutrophils. Expression of the cytotoxicity was dependent on the presence of Ca2+ in the media, and was independent of the presence of Mg2+. Cytotoxic activity was eliminated by inactivating M bovis in buffers containing formalin or sodium azide. Hemolytic and nonhemolytic isolates of M bovis were examined for cytotoxic activity. All 7 of the hemolytic isolates were cytotoxic for bovine neutrophils, but all 4 of the nonhemolytic isolates were devoid of cytotoxic activity. None of the 11 isolates were cytotoxic for human neutrophils. Sterile filtrates from 6-hour shaker cultures of a hemolytic M bovis isolate were cytotoxic for bovine neutrophils. Cytotoxicity of the filtrate was eliminated by heating, incubation with trypsin, or addition of EDTA to the media. Bacterial homogenates or sterile filtrates prepared from statistically incubated cultures of M bovis were not toxic for bovine neutrophils.