Dagmar E. Frank

Effect of bovine immunodeficiency-like virus infection on immune function in experimentally infected cattle

Bovine immunodeficiency-like virus (BIV) is a bovine lentivirus that has antigenic and genetic homology with the human immunodeficiency virus. Little work has been reported on the effect of BIV infection on bovine immune function. This study was designed to evaluate lymphocyte blastogenesis, mononuclear cell subset numbers, neutrophil function, hematology, and clinical signs in three groups of cattle. These groups were evaluated at 0-2 months post inoculation (PI, Group 1), 4-5 months PI (Group 2), or 19-27 months PI (Group 3). BIV infected animals were inoculated with the R-29 isolate of BIV in tissue culture cells, peripheral blood mononuclear cells from a R-29 infected calf, or a molecular clone of the R-29 isolate. Most inoculated animals seroconverted to BIV by Western immunoblot. BIV was reisolated from most of the animals inoculated. BIV infection was associated with an increase in the lymphocyte blastogenic response to the mitogen phytohemagglutinin in Groups 2 and 3. Neutrophil antibody dependent cell mediated cytotoxicity and neutrophil iodination were decreased (P < 0.05) in BIV infected cattle (Groups 2 and 3 and Group 3, respectively). All animals were clinically normal during the evaluation periods. Notable differences were not observed in the other assessments performed. Work with additional BIV isolates and over longer time frames is warranted.

Longitudinal studies of immune function in cattle experimentally infected with bovine immunodeficiency-like virus and/or bovine leukemia virus

The effects of single or dual infection with bovine immunodeficiency-like virus (BIV) and/or, bovine leukemia virus (BLV) on bovine immune function were examined over a 4 year period. Holstein calves were infected with BIV (four calves), BLV (five calves), BIV and BLV (five calves), or sham inoculated (three calves). Lymphocyte blastogenesis to mitogens, seven tests of neutrophil function, and mononuclear cell subset analysis by flow cytometry (BoCD4, BoCD8, BoCD2, BoWC1, sIgM+, and monocytes) were performed at regular intervals to 49 months post-infection. These data were analyzed for main effects of each virus and interaction as a 2 x 2 factorial. BIV infected cattle had lower neutrophil antibody-dependent cell-mediated cytotoxicity and iodination responses during 2 of the 4 years post-infection (P < 0.05). BIV infection was not associated with any long-term significant changes in lymphocyte blastogenesis to mitogens or changes in mononuclear cell subset numbers in blood. There was a tendency for animals infected with BIV alone to have decreased lymphocyte blastogenic responses to mitogens, but this was not statistically significant. BLV infection caused an increase in total mononuclear cells with no dramatic shift in the relative proportions of the various subsets. Co-infection with BIV and BLV did not consistently cause a different response than either virus did individually. One BIV infected animal died of non-BLV lymphosarcoma 7 months after infection. All other animals had no unusual clinical signs. In summary, infection with BIV caused a significant, temporary decrease in neutrophil function with no consistent statistically significant alteration in lymphocyte blastogenesis or mononuclear cell numbers during the first 4 years after infection. BLV infection caused an increase in lymphocyte numbers, and there appeared to be no synergism between the viruses.

The Effects of Ascorbic Acid on In Vitro Heterophil Function

As a feed additive, ascorbic acid has been shown to have a protective effect against bacterial and viral diseases and to reduce the impact of detrimental stress in chickens. This study examined the effect of ascorbic acid treatment on in vitro heterophil function by examining random migration and phagocytosis and bacterial killing of Staphylococcus aureus. Heterophils were evaluated in broiler chickens ranging from 5 to 16 wk of age, and age differences were seen. Significant increases in bacterial killing were found in heterophils treated with ascorbic acid, and this difference tended to be greater in chickens from 5 to 10.5 wk of age. No significant differences were found in phagocytosis or random migration, but ascorbic acid tended to decrease random migration. The most significant effect on in vitro heterophil function was an increase in bacterial killing.

Effect of recombinant human cytokines on porcine neutrophil function

The activity of four recombinant human cytokines on porcine neutrophils was evaluated. Porcine neutrophils were treated with varying doses of recombinant human tumour necrosis factor-alpha (rHu-TNF), interferon-gamma (rHu-IFN), interleukin-8 (rHu-lL-8), or granulocyte-macrophage colony-stimulating factor (rHu-GM-CSF). The function of treated neutrophils was compared with that of non-treated controls in the following assays: antibody-independent neutrophil cytotoxicity (AINC), antibody-dependent cell-mediated cytotoxicity (ADCC), iodination, Staphylococcus aureus ingestion, cytochrome C reduction, random migration, and chemotaxis. Treatment with rHu-TNF produced significant (P < 0.05) depression of neutrophil random migration (2.5, 25, and 250 ng ml-1 rHu-TNF) and iodination (250 ng ml-1) and a near significant (P = 0.08) depression in ADCC (250 ng ml-1). Treatment with 25,000 U ml-1 of rHu-IFN caused a significant increase in AINC. At lower doses of rHu-IFN, there was a trend (0.05 < P < or = 0.08) toward depression of AINC (250 U ml-1) and ADCC (25 U ml-1) and enhancement of iodination (250 U ml-1). Treatment with 50 ng ml-1 of rHu-IL-8 caused a near significant increase (P = 0.06) in AINC. There were no significant differences noted when porcine neutrophils were treated with rHu-GM-CSF (2.5-2500 U ml-1). No synergism was noted between rHu-TNF and rHu-IFN.

Alteration of Neutrophil Function in BCG-Treated and Non-Treated Swine after Exposure to Salmonella typhimurium

Salmonella typhimurium infection in swine causes an enterocolitis followed by a persistent carrier state, but little is known about the mechanisms that allow this organism to colonize and persist in host tissues. Neutrophils provide a first line of defense against invading pathogens such as Salmonella typhimurium. The purpose of this study was to evaluate porcine neutrophil function after in vivo exposure to Salmonella and to determine if the immunomodulator, bacillus Calmette Guerin (BCG), exerts any effect on neutrophil function or on the colonization and persistence of S. typhimurium in the pig. Compared to negative controls, neutrophils from pigs exposed to S. typhimurium exhibited significantly decreased iodination, cytochrome-C reduction, antibody-dependent cell-mediated cytotoxicity, random migration, and chemotaxis (P less than or equal to 0.05). Neutrophil bactericidal activity against S. typhimurium was significantly enhanced. Most of the significant differences were noted in the first two days after exposure to Salmonella. Often the functional alterations were biphasic, peaking again 7-10 days after exposure. BCG alone significantly depressed random migration and cytochrome-C reduction in unstimulated neutrophils. The clinical course, colonization pattern, and persistence of Salmonella were similar between pigs receiving BCG and untreated pigs. These data suggest that S. typhimurium infection causes a depression in oxidative metabolism and motility, yet an increase in overall bactericidal activity against S. typhimurium in circulating porcine neutrophils. It also appears that BCG treatment, as reported here, does not enhance resistance of pigs to S. typhimurium colonization or reduce the number of persistent organisms in the porcine ileum.

Pigs are relatively resistant to dexamethasone induced immunosuppression

Dexamethasone administration has been widely used as a model of immunosuppression in various species. The objective of the work reported here was to evaluate immune function in pigs treated with dexamethasone. Experiment 1 pigs were assigned to either control (n = 10) or 2 mg/kg dexamethasone (n = 10) treated groups. Treatments were administered 48 and 24 h before immune function testing. The dexamethasone-treated pigs received the drug on 22 of 72 experimental days. Pigs in experiment 2 were assigned to one of three groups: control (n = 10), 2 mg/kg dexamethasone (n = 10), or 6 mg/kg dexamethasone (n = 10). Treatments were given once and immune functions were evaluated 3 and 27 h after treatment. Lymphocyte blastogenesis, total and differential white blood cell count, and several measures of in vitro neutrophil function were measured in both experiments. Antigen specific antibody production, growth rate, and organ weights at necropsy were also measured in experiment 1. There were no consistent changes in neutrophil functions in these experiments. Lymphocyte blastogenesis to concanavalin A and pokeweed mitogen was significantly (p <0.05) enhanced during experiment 1 in dexamethasone-treated pigs; antigen specific antibody production was not altered by treatment. Dexamethasone treatment (both 2 and 6 mg/kg) in experiment 2 caused a profound (p <0.02−0.01) decrease in lymphocyte blastogenesis to all three mitogens tested at 3 h after treatment. Lymphocyte proliferation returned to control levels by 27 h after treatment in experiment 2. Dexamethasone treatment was also associated with a relative neutrophilia and lymphopenia in both experiments. Dexamethasone-treated pigs in experiment 1 grew slower, had larger livers and kidneys , but smaller spleens than control animals. The transient decrease in lymphocyte blastoenesis lack of consistent , changes in neutrophil function, and unaltered antibody production despite treatment with large doses of dexamethasone indicate that pigs are remarkably resistant to immunosuppression by this drug.

An atypical T-cell lymphosarcoma in a calf with bovine immunodeficiency-like virus infection.

An 11-month-old Holstein calf experimentally infected with bovine immunodeficiency-like virus (BIV) developed T-cell lymphosarcoma 5 months postinoculation, concurrent with progressive monocytosis. Tumors were found in the thymus, multiple lymph nodes, and brain. Tumor cells were CD2+, CD4-, CD8-T cells. Infectious BIV could be recovered from splenic tissue and blood mononuclear cells. Bovine leukemia virus was not present. Because this calf was part of an ongoing experiment on the pathogenesis of BIV infection, immune function data were also available both before and after lymphosarcoma developed. Neutrophil and monocyte function were normal, but lymphocyte blastogenesis was enhanced before the development of lymphosarcoma. Follicular hyperplasia in lymphoid tissues was also seen. This case raises the possibility that BIV infection may cause or be associated with some cases of atypical T-cell lymphosarcoma, without evidence of immune suppression at the time of tumor onset.

Factors secreted by untreated and hydrocortisone-treated monocytes that modulate neutrophil function

When incubated for 1.0 hr with neutrophils isolated from bovine peripheral blood, hydrocortisone (0.05, 0.5, or 5.0 μg/ml) had no significant effect on their ability to ingest Staphylococcus aureus, to reduce nitroblue tetrazolium (NBT) or iodinate protein, or to mediate antibody‐dependent cell‐mediated cytotoxicity (ADCC) against chicken erythrocytes. Random migration was significantly enhanced by the highest concentration of hydrocortisone (HC) but was unaffected by the lower concentrations. Resting bovine monocytes were incubated for 24 hr in medium with or without added hydrocortisone (0.05,0.5, or 5.0 μg/ml). Purified bovine neutrophils were then incubated for 1.0 hr with the resulting monocyte supernatant (MS). The MS from untreated monocytes significantly enhanced neutrophil ADCC but did not affect the other neutrophil functions evaluated. Supernatants from monocytes incubated wtih 0.5 or 5.0 μg/ml hydrocortisone (HC‐treated MS) failed to enhance neutrophil ADCC but did enhance neutrophil random migration under agarose. The other parameters of neutrophil function were unaffected. Production of the factors in MS was reduced by inhibition of protein synthesis in monocytes. Their activity was reduced by exposure of MS to proteolytic enzymes, suggesting that the monocyte factors were polypeptides or proteins. Protein synthesis by the neutrophil was not necessary for its response to the monocyte‐produced ADCC‐enhancing factor but was necessary for its response to the HC‐induced monocyte factor. The results suggest that the antiinflammatory effects of glucocorticoids may be partially mediated by factors released by monocytes.