Biomedical subjects

W C Davis

Publications and source records attributed to W C Davis.

At least 19 recordsLinked to original sources

PubMed1999

Bovine leukemia virus transmembrane protein gp30 physically associates with the down-regulatory phosphatase SHP-1.

In B lymphocytes, the down-regulatory phosphatase SHP-1 associates with CD22 and CD32b (also known as FcgammaRIIB) and acts as a critical negative regulator of B-cell receptor signaling. Bovine leukemia virus, a retrovirus of the HTLV/BLV group, causes persistently increased numbers of peripheral blood B lymphocytes, known as persistent lymphocytosis (PL) and, in some animals, progression to B-cell leukemia and/or lymphoma. Here, we show that SHP-1 associates with the bovine leukemia virus transmembrane protein, gp30. This interaction is either direct or indirect. The interaction is dependent on tyrosine phosphorylation, and the interaction increases after cell stimulation with sodium pervanadate. The gp30-SHP-1 interaction is seen in all of the BLV-infected, PL animals tested, but is not seen in uninfected animals or in most BLV-infected, non-PL animals, which do not express significant quantities of gp30. However, one BLV-infected, non-PL animal expressed large quantities of gp30, yet no gp30-SHP-1 interaction was detected, suggesting that there may be other factors in cells from the PL animals that facilitate the gp30-SHP-1 interaction. The association of gp30 and SHP-1 suggests the hypothesis that gp30 may act as a decoy to sequester SHP-1, resulting in up-regulation of B-cell receptor signaling. The implication of this could be a novel mechanism of viral activation of lymphocytes by removal of a down-regulatory phosphatase.

Amino Acid Sequence↗

PubMed1999

Unique superantigen activity of staphylococcal exfoliative toxins.

Certain strains of Staphylococcus aureus express one or both of two related, but immunologically distinct, exfoliative toxins (ETA and ETB). These toxins induce the symptoms associated with staphylococcal scalded skin syndrome. Both ETs have been shown to stimulate T cell proliferation. Recently, it was reported that ETA is a superantigen that stimulates T cells bearing human Vbeta2 or several murine Vbetas. However, other investigators have proposed that the superantigenicity reported for ETA resulted from contaminants in commercial preparations. This present study addresses those conflicting reports by assessing the biological and immunologic activities of highly purified rETs. ETA and ETB required APCs to induce selective polyclonal expansion of several human Vbetas (huVbetas), although, neither toxin expanded huVbeta2. ETB induced expansion of murine T cells bearing Vbetas 7 and 8, those that have the highest homology to the huVbetas expanded by ETA and ETB. Although flow cytometry of ETB-stimulated T cells matched PCR results, stimulation by ETA reduced percentages of T cells positive for several huVbetas that had been shown to have increased levels of mRNA transcripts. ETA and ETB induced contrasting reactions in vivo. In rabbits, ETB was moderately pyrogenic and enhanced susceptibility to lethal shock, while ETA lacked both activities. Predictions based on comparisons with other superantigens suggest molecular regions potentially involved in receptor binding in the ETA crystal structure and a modeled ETB three-dimensional structure. These results show that ETs are superantigens with unique properties that could account for the discrepancies reported.

Animals↗

PubMed1999

Phenotypic comparison of ileal intraepithelial lymphocyte populations of suckling and weaned calves.

Ileal intraepithelial lymphocyte (IEL) suspensions from suckling calves (1-3 weeks old) and weaned calves (3-6 months old) were phenotyped to determine whether there were differences in the lymphocyte populations consistent with postnatal maturation of the mucosal immune system. Flow cytometric comparisons of IEL from the two age groups revealed the presence of significantly larger proportions of CD4+ T lymphocytes and CD8+ T cells in the weaned animals. In contrast, there was a significantly larger proportion of B-B2+ IEL in the suckling calves. Freshly isolated IEL from both groups of calves expressed mRNA for TNF-alpha and IFN-gamma, but not IL-4 or IL-10. The B-B2+ IEL population was more closely examined by flow cytometry. These cells co-expressed IgM and CD21. However, they did not express IgA, IgG1, nor any of several additional leukocyte differentiation molecules. Immunohistochemical data confirmed the presence of IgM+ lymphocytes, and the paucity of IgA+ and IgG1+ lymphocytes in suckling calf ileum. However, substantial numbers of IgA+ and IgG1+ cells were observed in weaned calf ileum. Together, the data are consistent with ongoing postnatal maturation of the gut mucosal immune system.

Animals↗

PubMed1999

Differential effects of type I IFNs on the growth of WC1- CD8+ gamma delta T cells and WC1+ CD8- gamma delta T cells in vitro.

Type I IFNs have a broad array of immunoregulatory functions that include up-regulation of type 1 immune responses through enhancing differentiation and activation of CD8+ T cells and CD4+ Th1 cells. Ovine trophoblast IFN-tau is a recently described type I IFN with the potential for therapeutic use, based on its potent antiviral activity yet low toxicity. Studies were designed to determine the immunoregulatory effects of IFN-tau on Ag-stimulated T cells, and a novel effect of type I IFNs on gammadelta T cells was observed. In cultures of parasite Ag-stimulated bovine T cells that contained a mixture of alphabeta and gammadelta T cells, both IFN-tau and IFN-alpha suppressed the expansion of WC1+ CD2- CD6- CD8- gammadelta T cells, yet stimulated the growth of WC1- CD2+ CD6+ CD8+ gammadelta T cells and CD8+ alphabeta T cells. The CD8+ gammadelta T cell subset expressed high levels of the IL-2R alpha-chain. Furthermore, we showed that type I IFN enhanced IL-2 production by these Ag-stimulated T cell lines. In short term cultures of PBMC, IL-2 stimulated an expansion of WC1- CD6+ CD8+ gammadelta T cells, which was significantly increased by IFN-tau, even though IFN-tau alone did not support cell survival. These studies demonstrate for the first time that type I IFNs differentially modulate the proliferation of different subsets of gammadelta T cells, which appears to act in part via IL-2.

Animals↗

PubMed1999

Role of CD8+ and WC-1+ gamma/delta T cells in resistance to Mycobacterium bovis infection in the SCID-bo mouse.

The role of various effector T cell populations in the bovine immune response to Mycobacterium bovis infection is poorly understood. This is largely due to the difficulties associated with performing in vivo challenge studies in the natural host species. In this report, we utilized a fetal bovine-severe combined immunodeficient (SCID-bo) xenochimeric mouse model to study the protective role of two putative effector cell types, CD8+ T cells and a subpopulation of gamma/delta T cells that express WC-1, a member of the cysteine-rich scavenger receptor superfamily (CRSR). We demonstrate that CD8+ T cells play a key role in protection and contribute substantially to bovine IFN-gamma mRNA levels at 30 days post-infection. The role of WC-1 bearing cells to protection was less definitive but our results suggest that this population may play a pivotal role early in infection. Granuloma architecture was altered in anti-WC-1 (ILA29) but not anti-CD8 (ILA51) -treated animals, suggesting that this population may be involved in recruitment of various cell types to sites of infection.

Animals↗

PubMed1999

Bovine monocytoid cells transformed to proliferate cease to exhibit lineage-specific functions.

Bovine cell lines of the monocyte-Mphi lineage were tested for surface marker expression and were characterized with respect to functions. Cell lines tested encompassed an SV40-transformed cell line (Bo-Mac), a spontaneously emerging monocytoid cell line (M617), and T. annulata-transformed lines derived from bovine Mphi. All lines failed to express surface markers expressed by 1 degrees Mphi, with the exception of CD44, WC9 and the DH59 myleoid cell marker. T. annulata-derived lines expressed, in addition, CD45 and MHC-class-II molecules. Except for nonspecific esterase staining, none of the typical macrophage functions were expressed by any of the cell lines. These included phagocytosis of opsonized E. coli bacteria and of IgG-treated erythrocytes, eliciting of an oxidative burst, the ability to express type-I-interferon (IFN) and to respond to lipopolysaccharide, as determined by four different effector functions (nitric oxide synthesis, tumor necrosis factor (TNF) secretion, IFN production and procoagulant activity upregulation). When transformation induced by T. annulata was reversed by chemical elimination of the parasite, cells ceased to proliferate but started to acquire some of the phenotypic characteristics of Mphi. This suggests that regardless of their origin, exponentially growing bovine cells of the monocyte-Mphi lineage poorly represent a lineage-specific phenotype and should be used with caution in immunological studies.

Animals↗

PubMed1999

Phenotypic analysis of bronchoalveolar lavage fluid lymphocytes in horses with chronic pulmonary disease.

A panel of specific antibodies against CD3, CD4, CD5, CD8, MHC I and II was used in single and two colour flow cytometry to define T cell subpopulations in bronchoalveolar lavage fluid of horses affected with chronic obstructive pulmonary disease and of healthy controls. According to the results of the clinical examination including bronchoscopy and cytology of the tracheal aspirate the horses were divided into four groups (healthy, subclinically to mildly affected; moderately affected, and severely affected). All groups of horses had a similar percentage of CD3+ cells in the BALF. Compared to controls, severely affected horses had a significantly increased number of CD4+ cells in the BALF, but a similar percentage of CD4+ cells whereas mildly and moderately affected horses had a decreased percentage. The percentage and number of CD8+ cells and the percentage of CD8+/MHCII+ cells in the BALF was found to be higher than normal and varied according to the disease state. This novel finding raises the possibility that not only the CD4+ cells but also the CD8+ cells are involved in the pathogenesis of COPD. The percentage and the number of CD8+ cells in BALF might be of diagnostic value to detect subclinical to mild cases of COPD.

Animals↗

PubMed1999

Theileria annulata in CD5(+) macrophages and B1 B cells.

Theileria parasites infect and transform bovine leukocytes. We have analyzed laboratory-established Theileria sp.-infected leukocyte lines and observed that transformed macrophages express CD5. Low-level expression of CD5 by macrophages was further confirmed on three independent Theileria annulata clinical isolates from Tunisia. Interestingly, the fourth CD5(+) clinical isolate (MB2) was morphologically different, expressed surface immunoglobulin M (IgM) and BoLA class II, and had rearranged Ig light-chain genes. To demonstrate that MB2 did indeed contain CD5(+) B cells, individual clonal lines were obtained by limiting dilution, and CD5 expression and Ig gene rearrangement were confirmed. This suggests that in natural infections T. annulata can invade and transform CD5(+) B cells.

Animals↗

PubMed1999

Bovine gammadelta T-cell responses to the intracellular protozoan parasite Theileria parva.

T cells bearing the gammadelta antigen receptor (gammadelta T cells) can constitute up to 50% of T cells in the peripheral blood and lymphoid organs of young cattle. We present data showing that gammadelta T cells are involved in immune responses against Theileria parva. gammadelta T cells isolated from peripheral blood mononuclear cells (PBMC) of T. parva-naive and -immune cattle proliferated in the presence of fixed or unfixed autologous T. parva-infected lymphoblasts (TpL) and heat-stressed concanavalin A (ConA)-induced blasts (ConA blasts) but not untreated ConA blasts. The specificity of response was further evaluated with a panel of gammadelta T-cell lines and clones. T-cell reactivity was blocked by GB21A, a monoclonal antibody (MAb) specific for the gammadelta T-cell receptor, but not by MAbs specific for class I and class II major histocompatibility complex (MHC) molecules. In addition, TpL but not ConA blasts from a variety of MHC-mismatched animals induced proliferation of the gammadelta T-cell lines and clones. These gammadelta T cells were found to respond to TpL infected with several different parasite stocks and failed to recognize TpL after elimination of the parasite by the theilericidal drug BW 720C. Assays for cytotoxic activity of gammadelta T cells sorted from bulk cultures of immune PBMC restimulated several times with autologous TpL demonstrated that effector cells whose specificity is similar to that of proliferating cells are generated. These results suggest that bovine gammadelta T cells are activated by and lyse T. parva-infected cells by recognizing conserved parasite-induced or parasite-derived antigens in an MHC-unrestricted fashion.

Animals↗

PubMed1999

Bovine leukemia virus-induced persistent lymphocytosis in cattle does not correlate with increased ex vivo survival of B lymphocytes.

Bovine leukemia virus (BLV) is an oncogenic retrovirus associated with B-cell lymphocytosis, leukemia, and lymphosarcoma in the ovine and bovine species. We have recently reported that in sheep, BLV protects the total population of peripheral blood mononuclear cells (PBMCs) from ex vivo spontaneous apoptosis. This global decrease in the apoptosis rates resulted from both direct and indirect mechanisms which allow extension of cell survival. Although sheep are not natural hosts for BLV, these animals are prone to develop virus-induced leukemia at very high frequencies. Most infected cattle, however, remain clinically healthy. This difference in the susceptibilities to development of leukemia in these two species might be related to alterations of the apoptotic processes. Therefore, we designed this study to unravel the mechanisms of programmed cell death in cattle. We have observed that PBMCs from persistently lymphocytotic BLV-infected cows were more susceptible to spontaneous ex vivo apoptosis than cells from uninfected or aleukemic animals. These higher apoptosis rates were the consequence of an increased proportion of B cells exhibiting lower survival abilities. About one-third of the BLV-expressing cells did not survive the ex vivo culture conditions, demonstrating that viral expression is not strictly associated with cell survival in cattle. Surprisingly, culture supernatants from persistently lymphocytotic cows exhibited efficient antiapoptotic properties on both uninfected bovine and uninfected ovine cells. It thus appears that indirect inhibition of cell death can occur even in the presence of high apoptosis rates. Together, these results demonstrate that the protection against spontaneous apoptosis associated with BLV is different in cattle and in sheep. The higher levels of ex vivo apoptosis occurring in cattle might indicate a decreased susceptibility to development of leukemia in vivo.

Animals↗

PubMed1999

Regulation of the immunoglobulin G1 receptor: effect of prolactin on in vivo expression of the bovine mammary immunoglobulin G1 receptor.

Induction of colostrogenesis in non-pregnant cows was used to evaluate the relationship between prolactin (PRL) and mammary immunoglobulin G1 (IgG1) receptor expression. Six of eleven non-pregnant, non-lactating Holstein cattle responded to a standard lactation induction protocol by development of elevated IgG1 concentrations in mammary secretions. In order to increase the diversity in PRL concentrations, two of the six cattle were treated with bromocriptine, and two others were treated with recombinant bovine PRL. Serum alpha-lactalbumin, serum PRL and mammary secretion IgG1 concentrations were measured throughout the experiment. Biopsies of mammary tissue were collected after induction of lactation, and after treatments to alter serum PRL. Immunohistochemistry was used to evaluate IgG1 receptor expression. Administration of recombinant bovine (rbPRL) was associated with increased lactogenic activity, decreased secretion IgG1 concentrations, and decreased IgG1 receptor expression. Decreased serum PRL, due to bromocriptine, was associated with decreased lactogenic activity and maintenance of IgG1 receptor expression. Results of this experiment are consistent with an effect of PRL in decreasing the expression of the bovine mammary IgG1 receptor at the onset of lactogenesis.

Animals↗

PubMed1998

Concanavalin A-stimulated proliferation of T cell subset-depleted lymphocyte populations isolated from Fasciola hepatica-infected cattle.

Over 14 weeks, peripheral blood lymphocytes (PBL) were isolated from eight adult cattle which had been orally infected with Fasciola hepatica via trickle infection over a 10-day period. Two age, breed and sex-matched cattle served as controls. CD4+, CD8+ and gammadelta+ T cells were depleted from whole PBL populations by magnetic bead depletion. Lymphocyte proliferation assays demonstrated a transient, but marked elevation in responsiveness to Concanavalin A (Con A) between weeks 2 and 4 post-infection in PBL from infected animals. Proliferative responses to Con A were significantly greater in PBL from infected cattle than uninfected/control cattle over the initial period of the experiment. Con A-stimulated proliferation of PBL isolated from infected cattle followed a similar pattern to PBL responses to F. hepatica antigen. In both whole and subset-depleted lymphocyte populations from infected cattle, proliferative responses to Con A decreased from day 28 post-infection. Depletion of CD4+, CD8+ and gammadelta+ T cell subpopulations significantly augmented responses soon after infection. These findings suggest that the capacity of bovine PBL to proliferate in response to Con A stimulation, was in some way attenuated by F. hepatica infection and proliferative responses due to non-specific activation was suppressed by the coordinated activities of various lymphocyte subsets.

Animals↗

PubMed1998

Real-time analysis of immunogen complex reaction kinetics using surface plasmon resonance.

Real-time biospecific interactions of immunogens, measured via BIAcore, were used to verify qualitatively a biosensor design which relies on analyte binding competition reactions to open cross-linked receptor channels. The complexes of importance are: (1) cardiac troponin I (TnI) and monoclonal mouse anti-TnI IgG mAb 265, (2) TnI and bispecific antibodies (BsAbs) which on one end recognize TnI while the other end recognizes nicotinic acetylcholine receptors (nAChRs), (3) nAChRs and rat anti-nAChR IgG mAb 148, (4) nAChRs and BsAbs, (5) nAChRs and Fab'148-TnI biopolymers, and (6) mAb 265 and Fab-TnI biopolymers. A commonly used sensor chip, CM5, was employed to immobilize TnI by covalent amine coupling, while bilayer membrane-associated protein, nAChR, was noncovalently sequestered on a HPA sensor chip via hydrophobic adsorption of membrane lipids. The epitopes of membrane-bound nAChRs were still available to immunogens after being immobilized. Kinetic rate constants and affinities of these systems were calculated from BIAcore sensorgrams. The order of magnitude for dissociation rate constants of the BsAb/TnI linker complex and biopolymer/mAb 265 complex is 10(-2) s-1, which provides an opportunity for competitive binding of free analyte in the sensing systems.

Animals↗

PubMed1998

IL-4 protects adult C57BL/6 mice from prolonged Cryptosporidium parvum infection: analysis of CD4+alpha beta+IFN-gamma+ and CD4+alpha beta+IL-4+ lymphocytes in gut-associated lymphoid tissue during resolution of infection.

Resistance of adult C57BL/6 mice to severe Cryptosporidium parvum infection is dependent on CD4+alpha beta+ TCR lymphocytes. In this study, we demonstrated that treatment with anti-IFN-gamma mAb extended oocyst excretion 18 days longer, and anti-IL-4 mAb extended oocyst excretion at least 11 days longer than isotype control mAb treatment. Analysis of the specific activity of anti-IFN-gamma mAb present in treated mouse sera suggested that IFN-gamma may have a limited role in the resolution phase of infection. Changes were also documented in numbers of CD4+alpha beta+IFN-gamma+ and CD4+alpha beta+IL-4+ lymphocytes in Peyer's patches and intraepithelium of adult C57BL/6 mice during resolution of C. parvum infection. Resistance to initial severe infection was associated with CD4+alpha beta+IFN-gamma+ lymphocytes, and eventual resolution of infection was associated with CD4+alpha beta+IL-4+ lymphocytes. Analysis of cytokine expression following in vitro stimulation with C. parvum Ags during resolution of infection demonstrated consistent increases in CD4+alpha beta+IL-4+ lymphocytes, but not CD4+alpha beta+IFN-gamma+ lymphocytes. The relevance of CD4+alpha beta+IL-4+ lymphocytes in protection against C. parvum was then evaluated in C57BL/6 IL-4 gene knockout mice (IL-4(-/-)). Adult IL-4(-/-) mice excreted oocysts in feces approximately 23 days longer than IL-4(+/+) mice. Further, anti-IFN-gamma mAb treatment increased the severity and the duration of infection in IL-4(-/-) mice compared with those in IL-4(+/+) mice. Together, the data demonstrated that IFN-gamma was important in the control of severity of infection, and either IFN-gamma or IL-4 accelerated termination of infection. However, neither IL-4 nor IFN-gamma was required for the final clearance of infection from the intestinal tract of adult mice.

Age Factors↗

PubMed1998

Comparison of the unique characteristics of the immune system in different species of mammals.

The current interpretation of how cytokines regulate immune responses is based largely on studies conducted in humans and rodents. As summarized here, comparative studies have revealed significant differences in the composition of the immune system in other species. The difference noted emphasize that it will not be possible to fully understand the role of cytokines in immune regulation without comparative studies that include analysis of cytokine function in additional species.

Animals↗

PubMed1998

The equine homologue of LFA-1 (CD11a/CD18): cellular distribution and differential determinants.

The equine homologue of the leucocyte integrin LFA-1 (CD11a/CD18) has been characterized using a panel of four monoclonal antibodies (mAbs). The antibodies labelled almost all leukocytes, thymocytes and lymph node cells from normal horses, and immunoprecipitated two noncovalently associated polypeptides with molecular weights of 180 kDa and 100 kDa, respectively. The antigen recognized by one mAb could be precipitated by another in this cluster in a sequential immunoprecipitation assay. The mAbs, however, did not block the activities on lymphocyte function of one another. A mAb to the beta subunit of human LFA-1 cross-reacted with equine LFA-1, but an antibody to its alpha subunit did not, suggesting that the beta subunit of the leukocyte integrin may be more highly-conserved. Functionally, H20A and a human CD18 antibody (MHM23) inhibited phorbol ester-mediated homotypic lymphocyte aggregation, whereas mAb CZ3.2 induced rather than inhibited the homotypic cell aggregation. The formation of lymphocyte aggregates induced by CZ3.2 was not blocked by the inhibitory antibodies H20A or MHM23. CZ3.1 seemed to have little inducible or inhibitory effects on homotypic cell aggregation. The mAb CZ3.1 defined a unique LFA-1 determinant present on granulocytes, but absent on lymphocytes in members of an extended horse family, in contrast to the other antibodies which labelled both granulocytes and lymphocytes from these animals. In all other horses tested, no differences in reactivity of CZ3.1 and the other LFA-1 antibodies were observed when the antibodies were tested on lymphocytes or granulocytes. Our results indicate that common epitopes are shared' between human and equine LFA-1, and that the described panel of monoclonal antibodies identifies distinct determinants present on the equine LFA-1 molecule. The following monoclonal antibodies used in this study were given official workshop designations at the Second International Workshop on Equine Leukocyte Antigens (Lunn et al., 1998) CZ3.1 (Cor) = W45; CZ3.2 (Cor) = W77.

Animals↗

PubMed1998

The distribution of lymphocyte subsets in normal ovine skin.

The distribution of lymphocyte subsets in the skin of clinically normal sheep was studied using monoclonal antibodies to OvCD5, OvCD4, OvCD8, WC1, and CD45RA. Four different anatomical sites were examined in each of 38 sheep. Four different age groups ranging from 7 to 10-day-old lambs to 12 to 14-month-old adults were represented. The majority of lymphocytes in all age groups and at all sites were angiocentrically located within the superficial dermis. Total lymphocyte numbers at each site increased with age. The predominant cell type identified at all sites was WC1+ and the proportion of lymphocytes of this phenotype was significantly higher at wooled sites. Only occasional CD45RA +/- cells were present in any section.

Aging↗

PubMed1998

Characterisation of a monoclonal antibody recognising the CD3epsilon chain of the bovine T cell receptor complex.

We describe the characterisation of a monoclonal antibody (mAb), designated MM1A, which reacts with an antigen molecule on the surface of bovine alphabeta and gammadeltaTcR+ T cells. The mAb immunoprecipitated a series of polypeptides of 21 kDa, 22 kDa, 32 kDa, 36 kDa and 44 kDa which is consistent with it recognising the TcR/CD3 complex. COS cells, transfected with a cDNA encoding the bovine CD3epsilon chain, reacted with mAb MM1A indicating that the epitope recognised is on the epsilon chain of the complex and confirming that the mAb recognised bovine CD3.

Animals↗