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Biomedical subjects

W C Davis

Publications and source records attributed to W C Davis.

At least 73 records · Page 4Linked to original sources
PubMed1998

Activation of bovine lymphocyte subpopulations by staphylococcal enterotoxin C.

Staphylococcus aureus is a major mastitis-causing pathogen in cattle. The chronic nature of bovine staphylococcal mastitis suggests that some products or components of S. aureus may interfere with the development of protective immunity. One class of molecules that could be involved are superantigens (SAgs). Although a significant number of mastitis isolates produce SAgs, the effect of these molecules on the bovine immune system is unresolved. To determine if immunosuppression caused by SAgs could play a role in pathogenesis, we monitored bovine lymphocytes exposed to staphylococcal enterotoxin C1 (SEC1). Activation of bovine lymphocytes by either SEC1 or concanavalin A (ConA) was influenced by the gammadelta/alphabeta T-cell ratio in the culture. Compared to ConA-induced stimulation, cultures stimulated with SEC1 generated small numbers of CD4+ alphabeta T cells expressing high levels of interleukin-2 receptor alpha chain (IL-2R alpha) and major histocompatibility complex class II (MHCII), suggesting that SAg exposure does not lead to full activation of these cells. This state of partial activation was most pronounced in cultures with a high gammadelta/alphabeta ratio. In contrast, significant numbers of CD8+ alphabeta T cells expressed high levels of IL-2R alpha and MHCII, regardless of the gammadelta/alphabeta ratio and the stimulant used. CD8+ blasts in cultures stimulated with SEC1 also expressed another activation marker, ACT3, previously detected predominantly on thymocytes and CD4+ T cells. Although gammadelta CD2- and CD2+ T cells expressed MHCII and IL-2R alpha following stimulation with SEC1, only a few cells increased to blast size, suggesting that they were only partially activated. The results suggest ways in which SAgs might facilitate immunosuppression that promotes the persistence of bacteria in cattle and contributes to chronic intramammary infection.

Animals↗
PubMed1998

B-lymphocyte proliferation during bovine leukemia virus-induced persistent lymphocytosis is enhanced by T-lymphocyte-derived interleukin-2.

Bovine leukemia virus (BLV)-induced persistent lymphocytosis is characterized by a polyclonal expansion of CD5+ B lymphocytes. To examine the role of the cytokine microenvironment in this virus-induced B-lymphocyte expansion, the expression of interleukin-2 (IL-2), IL-4, IL-10, and gamma interferon (IFN-gamma) mRNA, was measured in stimulated peripheral blood mononuclear cells from persistently lymphocytotic BLV-infected cows, nonlymphocytotic BLV-infected cows, and uninfected cows. IL-2 and IL-10 mRNA expression and IL-2 functional activity were significantly increased when peripheral blood mononuclear cells from persistently lymphocytotic cows were stimulated with concanavalin A (ConA). Additionally, during persistent lymphocytosis, peak IL-2 and IL-10 mRNA expression was delayed, and elevated expression was prolonged. To determine the potential biologic importance of increased IL-2 and IL-10 expression, the response of isolated B lymphocytes from persistently lymphocytotic cows to human recombinant cytokines and to cytokine-containing supernatants from isolated T lymphocytes was examined. While recombinant human IL-10 (rhIL-10) did not consistently induce detectable changes, rhIL-2 increased viral protein (p24) and IL-2 receptor expression in isolated B lymphocytes from persistently lymphocytotic cows. Additionally, rhIL-2 and supernatant from ConA-stimulated T lymphocytes enhanced B-lymphocyte proliferation. The stimulatory activity of the T-lymphocyte supernatant could be completely inhibited with a polyclonal anti-rhIL-2 antibody. Finally, polyclonal anti-rhIL-2 antibody, as well as anti-BLV antibody, inhibited spontaneous proliferation of peripheral blood mononuclear cells from persistently lymphocytotic cows, demonstrating that the spontaneous lymphoproliferation characteristic of BLV-induced persistent lymphocytosis is IL-2 dependent and antigen dependent. Collectively, these findings strongly suggest that increased T-lymphocyte expression of IL-2 in BLV-infected cows contributes to development and/or maintenance of persistent B lymphocytosis.

Animals↗
PubMed1998

Characterization of staphylococcal bovine mastitis isolates using the polymerase chain reaction.

A polymerase chain reaction (PCR) assay was adapted to detect toxin genes of staphylococcal isolates from cases of bovine mastitis. Samples were obtained from three geographical areas: Korea and Idaho and Washington in the northwest United States. Samples from Korea and Washington were randomly chosen. Idaho samples were from a prospective study of mastitis etiology. Forty-one milk samples from 25 commercial farms in south-central Idaho were collected from cows with symptoms of mastitis. Although Staphylococcus aureus constituted 37.5% of mastitis isolates, these isolates lacked genes for staphylococcal enterotoxins (SEs), toxic shock syndrome toxin, and exfoliative toxins. In contrast, 4 of 13 isolates from Washington and 6 of 20 isolates from South Korea expressed SEs. These results suggest that PCR may be an effective means of screening bovine isolates for toxins. They also emphasize the potential for significant geographic differences in mastitis etiology.

Animals↗
PubMed1998

Induction of type 2 cytokines by a staphylococcal enterotoxin superantigen.

Persistent intramammary infections of dairy cows with Staphylococcus aureus may involve immunosuppression mediated by bacterial toxins such as enterotoxins and other super-antigens (SAgs). Previously we found that stimulation of bovine PBMC with staphylococcal enterotoxin C (SEC) induced a unique phenotype of activated CD8+ T cells expressing a newly identified activation molecule, ACT3. In the present study we found that SEC induced the expression of interleukin (IL)-4 and IL-10 mRNAs, two cytokines associated with type 2 responses. Elevated levels of IL-4 and IL-10, observed between day 0 and day 4 of culture, were associated with temporary inhibition of proliferative responses of T cells, evidenced by a decrease in numbers of CD4+ T cells and a small increase in numbers of CD8+ T cells. Vigorous proliferation of T cells occurred between days 4 and 7 of culture and with a bias towards CD8+ T cells. Acquisition of the ACT3+ phenotype by CD8+ T cells was preceded by induction of IL-4 mRNA. Thus, in the bovine system, SAgs may hinder protective responses by inducing type 2 cytokines, which interfere with immune clearance of many microbial pathogens. The results of the study are consistent with the hypothesis that SAgs are involved in immunosuppression, and suggest possible immunomodulatory mechanisms.

Animals↗
PubMed1997

Macrophage-parasite relationship in theileriosis. Reversible phenotypic and functional dedifferentiation of macrophages infected with Theileria annulata.

Theileria annulata is a tick-transmitted protozoan parasite of cattle, which transforms cells of macrophage (Mphi) or B cell lineage. Bone marrow cells, bone marrow cell-derived, and monocyte-derived Mphi were infected with T. annulata sporozoites, and the resulting cell lines were assessed for surface marker expression and function. Transformed lines expressed histocompatibility complex (MHC) class-I and II, CD44, CD45, and the myeloid marker DH598-surface markers CD14, CD11b, M-M7, TH57A, and to a lesser extent CD11a/CD18, CD11c, and ACT(B), were down-regulated. Likewise, transformed cells failed to express Mphi functions (Fc-receptor-mediated phagocytosis, phorbol myristate acetate-induced oxidative burst, lipopolysaccharide-induced tumor necrosis factor alpha, and nitric oxide generation and procoagulant activity up-regulation). Mphi origin was assured by homogeneity of the starting population, cloning of cells by limiting dilution, and repeated microscopic and flow cytometric monitoring of the cell lines. Elimination of the parasite by treatment with BW720c resulted in the re-acquisition of monocyte lineage properties, as evidenced by up-regulation of CD14, and by re-acquisition of the capacity to ingest opsonized sheep red blood cells and bacteria. Thus, Mphi transformed by T. annulata appear to undergo a process of parasite-induced dedifferentiation but reassume the differentiated phenotype upon elimination of the parasite.

Animals↗
PubMed1997

Modulation of bovine leukemia virus-associated spontaneous lymphocyte proliferation by monoclonal antibodies to lymphocyte surface molecules.

Both human T lymphotropic virus (HTLV) and bovine leukemia virus (BLV) infections are characterized by in vitro proliferation of peripheral blood lymphocytes in the absence of exogenous antigens or mitogens. Differential expression of lymphocyte surface molecules in HTLV and BLV infection suggests that lymphocyte dysregulation may involve signaling through surface molecules involved in immune regulation. We examined the expression of adhesion and major histocompatibility (MHC) molecules on circulating lymphocytes from BLV-infected cows with persistent lymphocytosis and the ability of monoclonal antibodies to these molecules to modulate spontaneous lymphocyte proliferation. The integrin molecule, CD11c, and both MHC class I and MHC class II molecules were upregulated on B and T lymphocytes from PL cows. Anti-CD11c antibody was stimulatory to lymphocyte proliferation regardless of BLV status and had a greater stimulatory effect on spontaneously proliferating lymphocytes from persistently lymphocytotic cows than on normal bovine lymphocytes. Antibodies to bovine class I and class II inhibited spontaneous lymphocyte proliferation. Results suggest that lymphocyte dysregulation in BLV-induced persistent lymphocytosis involves upregulation of and signaling through lymphocyte surface molecules which are involved in immune activation of lymphocytes.

Animals↗
PubMed1997

Further analysis of the phenotype and distribution of tumor cells in sporadic B-cell and T-cell lymphomas in the lymph node and spleen of cattle.

Immunohistologic studies were performed to identify the phenotype and distribution of neoplastic lymphocytes in the spleens of BLV-negative animals examined by PCR and diagnosed as having sporadic bovine leukosis. Tumor cells from three cases of sporadic bovine leukosis were identified as of B-cell lineage. Tumor cells from three additional cattle were identified as CD3+ CD4- CD8+, CD3+ CD4- CD8-, and CD3+ CD4- WC1+, respectively. The last case was diagnosed as a gamma/delta T-cell lymphoma. Differences in morphology proliferative characteristics were recognized between B- and T-cell type lymphomas. The tumor cells in B-cell type lymphoma were characterized as follows: medium or large in size, round or polymorphic nucleus with rough chromatin with some tumor cells containing a convoluted nucleus. These tumor cells of B-cell type lymphoma were present in the red pulp and periarteriolar lymphoid sheath. Tumor cells of the T-cell type lymphoma were uniformly smaller than B-cell type and present around arteries or replaced red pulp of the spleen.

Animals↗
PubMed1997

Detection of Mycobacterium bovis infection in cattle using an immunoassay for bovine soluble interleukin-2 receptor-alpha (sIL-2R-alpha) produced by peripheral blood T-lymphocytes following incubation with tuberculin PPD.

After activation of T-lymphocytes with antigen there is an increase in the expression of interleukin-2 receptor-alpha (IL-2R-alpha) followed by the release of a soluble form of the molecule (sIL-2R-alpha) from the membrane of the stimulated cells. The present study investigates the novel use of the release of sIL-2R-alpha from activated T-lymphocytes as a marker of cell-mediated immunity (CMI) in cattle infected with Mycobacterium bovis. An enzyme immunoassay was used to detect sIL-2R-alpha produced following incubation of bovine peripheral blood mononuclear cells with mycobacterial antigens. Using this assay, 63/67 cattle naturally infected with M. bovis were identified whereas only 1/51 uninfected animals were considered to give a positive result. This assay is more convenient to use than lymphocyte proliferation assays which involve the use of radionucleosides. It should prove useful for monitoring the immunological activation of bovine T-lymphocytes in a variety of situations including the development of CMI responses in cattle to novel mycobacterial antigens or potential vaccines.

Animals↗
PubMed1997

Cell-mediated cytolysis of equine herpesvirus-infected cells by leukocytes from young vaccinated horses.

The objective of this study was to determine whether the administration of modified-live equine herpesvirus (EHV-1) to young horses with residual maternal antibodies stimulated EHV-specific cytolytic responses, and whether these responses were crossreactive between EHV-1 and EHV-4. Eighteen clinically normal Belgian cross-foals were used in the study and were commingled in two adjacent pens. Skin biopsies were harvested from 16 foals within 24 h of birth and fibroblast cultures were established, expanded and cryopreserved. Beginning at approximately 10 weeks of age, 10 randomly chosen foals were inoculated on days 0, 21, and 43 of the study with a vaccine containing modified-live EHV-1. Blood mononuclear leukocytes were obtained on days 0, 32, and 50 for the assessment of EHV-specific cytolytic activity using 5 h and 18 h chromium release assays. EHV-1-specific antibodies were assessed by enzyme-linked immunosorbent assay using serum collected on days -21, 0, 32, and 50 of the study. Lymphocyte blastogenic tests and bioassays for interferon activity were conducted on day 50. After two vaccinations, mononuclear leukocytes from seven of ten vaccinated foals had cytolytic activity against autologous EHV-1 cells and leukocytes from six of ten lysed EHV-4-infected cells when tested in an 18 h assay. This activity was enhanced by exogenous interleukin 2 and was markedly reduced using target cells from unrelated horses. Cytotoxicity was not detected in a 5 h assay following in vitro stimulation of leukocytes. After three vaccinations, blood leukocytes from 6/6 vaccinated foals and 0/6 unvaccinated foals had proliferative responses EHV-1. There were no significant differences in interferon production by leukocytes from these foals. Twelve foals tested had low concentrations of (maternal) EHV-1-specific antibody prior to vaccination. Five of eight foals tested had increases in EHV-specific antibodies, while 4/4 commingled unvaccinated foals had a decrease or no change in EHV-specific antibodies. These results demonstrate cytotoxic cellular immune responses can be induced in young horses with maternal antibodies following administration of modified-live vaccine.

Animals↗
PubMed1997

Cytokine RNA expression in an equine CD4+ subset differentiated by expression of a novel 46-kDa surface protein.

Two monoclonal antibodies (MAb), HB65A (IgG2a) and HB86A (IgGI), recognize a unique cell surface molecule on equine T-lymphocytes. The molecule, designated EqWC4, identified by these MAbs is present on a subpopulation of CD4+ equine lymphocytes (6.3-10.2% of Arabian lymphocytes CD4+ WC4+) and a smaller population of CD8+ lymphocytes (0.5% to 1.2% of Arabian lymphocytes CD8+ WC4+). EqWC4 is absent from B-lymphocytes, granulocytes, and macrophages. Both MAbs bound to a 46-kDa protein following immunoprecipitation reactions with lysates of surface labeled thymocytes. Immunoaffinity purification using HB65A yielded two molecules of 46 kDa and 52 kDa under reducing conditions and a third 92-kDa molecule was present in nonreduced conditions. Activation by mitogen did not increase expression of EqWC4 on equine lymphocytes. Lymphocytes from Arabian, Pony, and Thoroughbred breeds showed a common distribution of EqWC4 among leukocytes. However, there were significantly fewer Pony lymphocytes bound to HB65A and HB86A when compared to Arabian and Thoroughbred breeds. Using reverse transcriptase-polymerase chain reaction (RT-PCR), magnetically enriched populations (to 80% of cells isolated) of EqWC4+ lymphocytes expressed a cytokine RNA profile dominated by -interleukin2 (IL-2) and interferon-gamma (IFN-gamma) for unstimulated cells. Upon mitogen stimulation, IL-4 was also expressed at low levels while the IL-2 levels decreased and the IFN-gamma levels increased relative to unstimulated cells. EqWC4 is similar to CD28 in molecular weight and its formation of dimers and could therefore be the equine orthologue. However, because of the differences in CD28 expression, EqWC4 probably represents a previously uncharacterized equine lymphocyte marker.

Animals↗
PubMed1997

Evidence for the development of macrophage-like cells in long-term culture of bovine aortic endothelial cells.

Macrophages are known to be derived from monocytes which proliferate in the bone marrow. The proliferation of monocytes may occur in other places as well. In the present study, we describe the morphological behaviour of macrophage-like cells in endothelial cell cultures obtained from bovine aorta. These cells resembled hemopoietic clones containing progenitor-like cells. Immature and mature macrophage-like cells were rich in acid phosphatase activity, and expressed the CD18 molecule using immunolocalisation. Mature cells contained intracellular lipid droplets. "Actin" globules were apparent only in the peripheral cell areas without lamellipodia or filipodia. At the ultrastructural level, the mature cells were crowded with granules which could be lysosomes, phagolysosomes, or endocytotic vesicles. Multinuclear giant cells which behaved in a different way to the macrophage-like cells were observed. The development and maintenance of macrophage-like cells appears to be dependent on the coculture with endothelial cells. It may signify that endothelial cells are involved in the proliferation of monocytes outside the bone marrow.

Acid Phosphatase↗
PubMed1997

Kinetic modeling and analysis of a vesicle system for immunosensor development.

A novel mechanism is presented for immunosensor development that uses an immunological competition reaction in a vesicle system. This system consists of a suspension of reconstituted vesicles, channel agonist, protein linker to block the channels, voltage sensitive dye and analyte to be detected. In the proposed mechanism analyte serves a catalytic role as individual analytes competitively displace multiple channel linkers through association with one channel, dissociation and new associations with other channels. When one channel opens on a vesicle a permanent Nernst potential develops for that vesicle leading to fluorescence of voltage sensitive dyes. The time constant of the redistribution from linker-channel form to analyte-channel form is 0.92/k4 (k4 is the off-rate constant for the analyte-channel association) in the region of analyte concentrations less than 10(-9) M. Kinetic analyses show that several factors, including concentration of analyte or linker, number of channels per vesicle, on-rate or off-rate constant of the linker-channel and on-rate constant of analyte-channel complexes have significant effects on the minimum signal response time.

Antigen-Antibody Reactions↗
PubMed1997

Development of a sandwich immunoassay for the detection of soluble bovine interleukin-2 receptor-alpha (sIL-2R-alpha) and its use to measure cell-mediated immunity in cattle.

Stimulation of T-lymphocytes with mitogens or antigens results in the production of the cytokine interleukin-2, which exerts its physiological effect by interacting with a specific IL-2 receptor on the cell surface. The alpha-chain of this receptor is induced and expressed on the cell surface after lymphocyte activation. Following continuous antigen stimulation, a smaller soluble form of this alpha-subunit (sIL-2R-alpha) is shed from the membrane of activated cells. This study describes a sandwich ELISA for bovine sIL-2R-alpha that was developed using monoclonal antibodies specific for bovine IL-2R-alpha (CD 25). The feasibility of using sIL-2R-alpha released by activated T-lymphocytes as an in vitro marker of cell-mediated immunity (CMI) in cattle is demonstrated. Calves were immunized with the foreign protein keyhole limpet haemocyanin (KLH) and the development of CMI was followed using sIL-2R-alpha release, IFN-gamma production and lymphocyte proliferation assay. The results showed that the release of sIL-2R-alpha by previously sensitized cells following stimulation with antigen is likely to be a useful marker of CMI in infectious diseases, and in the study of T cell antigens and/or novel vaccines. Using appropriate detection systems, the measurement of sIL-2R-alpha may also prove to be a useful marker of CMI in other species.

Animals↗
PubMed1997

Identification of two distinct subsets of bovine gamma delta T cells with unique cell surface phenotype and tissue distribution.

We describe the characterization of two subsets of bovine gamma delta T cells having distinct cell surface phenotype and tissue distribution. One population expresses the previously described 215,000 MW WC1 antigen and is negative for the cell-surface differentiation antigens CD2, CD4, and CD8. The second population expresses CD2 and CD8 but not WC1 and appears to have a T-cell receptor (TCR) rearrangement distinct from that of the WC1+ population. The WC1- population is found in large numbers in spleen and intestine. In addition, this subset is not recognized by a number of monoclonal antibodies (mAbs) specific for TCR families that are well represented in the WC1+ population. The results indicate that the gamma delta T-cell population in cattle is considerably larger than previously described and that this population can be subdivided into two distinct subsets based on cell-surface phenotype and tissue distribution.

Animals↗
PubMed1997

CD4+ T lymphocytes contribute to protective immunity induced in sheep and goats by Haemonchus contortus gut antigens.

Immunization with parasite antigens derived from the gut of adult Haemonchus contortus induces significant levels of protection against the parasite in sheep and goats. However, the mechanisms of immunity involved in this protection are not clear. Here, we investigate the requirement for CD4+ T lymphocytes in gut antigen-induced immunity against H. contortus. Gut antigen immunized animals were depleted (> 98%) of their CD4+ T lymphocytes in peripheral blood by intravenous injection of an anti-CD4 MoAb. Depletion in peripheral blood persisted for at least eight days, after which there was gradual recovery of CD4+ T lymphocytes. Serum antibody levels in gut antigen-immunized animals correlated significantly with worm parameters, suggesting a contribution by antibody to the immunity observed. By covariate analysis, using ELISA OD as the covariate, CD4+ T lymphocyte depletion was shown to partially abrogate immunity induced by gut antigen immunization, against challenge infection with H. contortus. The greatest effect of CD4+ T lymphocyte depletion was observed at 14 days post-infection with differences between CD4+ T lymphocyte depleted and intact animals less apparent between days 21 and 25. Collectively, our data indicate that CD4+ T lymphocytes contribute to immunity induced by gut antigens. Our results also suggest that antibody works synergistically with CD4+ T lymphocytes to confer this immunity.

Animals↗
PubMed1997

Expression of immunoglobulin G1 receptors by bovine mammary epithelial cells and mammary leukocytes.

The objective of this study was to identify and evaluate expression of IgG1 receptors by different cell types in mammary tissue sections and digest-dispersed cells from the bovine mammary gland. An immunohistochemical system utilizing avidin-biotin-peroxidase complex demonstrated epithelial expression of IgG1 receptors in mammary tissue sections from cows producing colostrum but not from cows in lactation. Fluorescence flow cytometry demonstrated that cells dispersed in digests from both tissues producing colostrum and lactating tissues selectively bound IgG1. Fluorescence flow cytometry, using monoclonal antibodies to cell surface molecules, cytokeratin, and IgG1, revealed that leukocytes constituted the largest percentage of cells and were the predominant cell type binding IgG1 in mammary tissue digests. Although IgG1 binding to epithelial cells predominated in the gland during colostrum production in situ, digestion and filtration to produce single cell suspensions resulted in the loss of large numbers of epithelial cells. Studies of Ig binding of cells produced by enzymatic digestion must account for the types of cells surviving the digestion process.

Animals↗
PubMed1997

Effect of prolactin on in vitro expression of the bovine mammary immunoglobulin G1 receptor.

Explants of mammary tissue from cows in late pregnancy were incubated for 72 h in serum-free, hormonally defined media to investigate the regulation of the bovine mammary IgG1 receptor. Treatments included incubation in basal medium alone, basal medium plus estradiol-17 beta, basal medium plus prolactin, or basal medium plus estradiol-17 beta and prolactin. alpha-Lactalbumin production was measured by radioimmunoassay in culture supernatants collected at 24, 48, and 72 h. Explants were examined immunohistochemically for expression of the IgG1 receptor at 24, 48, and 72 h. alpha-Lactalbumin concentrations increased, and IgG1 receptor expression decreased, by 72 h with explants cultured in the medium containing prolactin. Results suggest that, in addition to its positive lactogenic effect, prolactin decreases expression of the bovine mammary IgG1 receptor.

Animals↗