Biomedical subjects

W C Davis

Publications and source records attributed to W C Davis.

At least 145 records · Page 8Linked to original sources

PubMed1994

CD4+ T-cell clones obtained from cattle chronically infected with Fasciola hepatica and specific for adult worm antigen express both unrestricted and Th2 cytokine profiles.

The well-established importance of helper T (Th)-cell subsets in immunity and immunoregulation of many experimental helminth infections prompted a detailed study of the cellular immune response against Fasciola hepatica in the natural bovine host. T-cell lines established from two cattle infected with F. hepatica were characterized for the expression of T-cell surface markers and proliferative responses against F. hepatica adult worm antigen. Parasite-specific T-cell lines contained a mixture of CD4+, CD8+, and gamma/delta T-cell-receptor-bearing T cells. However, cell lines containing either fewer than 10% CD8+ T cells or depleted of gamma/delta T cells proliferated vigorously against F. hepatica antigen, indicating that these T-cell subsets are not required for proliferative responses in vitro. Seventeen F. hepatica-specific CD4+ Th-cell clones were examined for cytokine expression following concanavalin A stimulation. Biological assays to measure interleukin-2 (IL-2) or IL-4, gamma interferon (IFN-gamma), and tumor necrosis factor and Northern (RNA) blot analysis to verify the expression of IL-2, IL-4, and IFN-gamma revealed that the Th-cell clones expressed a spectrum of cytokine profiles. Several Th-cell clones were identified as Th2 cells by the strong expression of IL-4 but little or no IL-2 or IFN-gamma mRNA. The majority of Th-cell clones were classified as Th0 cells by the expression of either all three cytokines or combinations of IL-2 and IL-4 or IL-4 and IFN-gamma. No Th1-cell clones were obtained. All of the Th-cell clones expressed a typical memory cell surface phenotype, characterized as CD45Rlow, and all expressed the lymph node homing receptor (L selectin). These results are the first to describe cytokine responses of F. hepatica-specific T cells obtained from infected cattle and extend our previous analysis of Th0 and Th1 cells from cattle immune to Babesia bovis (W. C. Brown, V. M. Woods, D. A. E. Dobbelaere, and K. S. Logan, Infect. Immun. 61:3273-3281, 1993) to include F. hepatica-specific Th2 cells.

Animals↗

PubMed1994

Enhanced B-lymphocyte expression of IL-2R alpha associated with T lymphocytosis in BLV-infected persistently lymphocytotic cows.

Peripheral blood lymphocytes from bovine leukemia virus (BLV)-negative and BLV-infected, aleukemic cows with persistent lymphocytosis were evaluated for expression of B and T lymphocyte subset-specific molecules and co-expression of the interleukin-2 receptor alpha (IL-2R alpha) molecule. Results demonstrate enhanced mitogen-induced expression of the IL-2R alpha molecule on B lymphocytes from BLV-infected, lymphocytotic cows. Lymphocyte subset analyses further demonstrate that BLV-infected, lymphocytotic cows are not only characterized by sustained elevations in CD5+ B lymphocytes, but also show significantly elevated numbers of CD3+, CD4+, and CD8+ T lymphocytes. These results provide evidence suggesting that B lymphocytes from BLV-infected, lymphocytotic cows are more sensitive to activation signals and up-regulation of the IL-2 signaling pathway than lymphocytes from clinically normal BLV-free cows, and that T lymphocytes may be involved in the aberrant regulatory pathways underlying BLV-induced persistent B lymphocytosis.

Animals↗

PubMed1994

Association of GP51 expression and persistent CD5+ B-lymphocyte expansion with lymphomagenesis in bovine leukemia virus infected sheep.

Alterations in the circulating CD5+ B-lymphocyte population, in vitro GP51 expression, and in vivo tax/rex expression that may precede lymphomagenesis were characterized prospectively in ten experimentally BLV-infected sheep. Infection with pathogenetic BLV resulted in a significant expansion of the circulating CD5+ B-lymphocyte population in six infected sheep. Of the remaining four infected sheep that did not have persistently elevated CD5+ B-lymphocyte counts, three developed lymphoid neoplasia within 14 months post-inoculation. Neoplastic cells from two of these three sheep were CD5- B-lymphocytes, while cells from the third were CD5+ B-lymphocytes. In vitro GP51 expression was a consistent feature of circulating lymphocytes from all three sheep developing tumors, but high level tax/rex gene transcription was not detected in circulating lymphocytes prior to lymphomagenesis. Neither in vitro GP51 expression nor high level tax/rex gene transcription was associated with expansion of the CD5+ B-lymphocyte population in sheep with significantly elevated CD5+ B-lymphocyte counts. These observations indicate that BLV infection in sheep results in expansion of the circulating CD5+ B-lymphocyte population, and that this expansion is not required for the subsequent development of BLV-associated lymphoid neoplasia.

Animals↗

PubMed1994

Characterization of caprine microglial cells and in vitro infection with caprine arthritis-encephalitis lentivirus.

BACKGROUND: Similar to human immunodeficiency virus-1 and simian immunodeficiency virus-1, microglial cells in brain tissue are a major cell target for infection with caprine arthritis-encephalitis lentivirus (CAEV) in vivo. These observations have raised interest in the role of microglial cells in the development of lentivirus-induced neurologic lesions. To initiate in vitro studies into the pathogenesis of encephalomyelitis caused by CAEV, we characterized primary cultures of caprine microglia, determined their susceptibility to virus infection, and examined the effect of virus infection on class I and class II major histocompatibility complex antigen expression. EXPERIMENTAL DESIGN: Microglia were examined as adherent cells in purified cultures and as nonadherent cells in mixed glial cell cultures, which also contained astrocytes and oligodendroglia. The cultured cells were investigated with regard to their phenotype, class I and II major histocompatibility complex antigen expression, and susceptibility to infection with CAEV using light and electron microscopy, enzyme and lectin cytochemistry, immunocytochemistry, flow cytometry, and kinetic analysis of virus replication. RESULTS: The cultured microglia had a typical macrophage morphology, were actively phagocytic, and expressed macrophage-like markers including non-specific esterase, complement receptor CR3, and Ricinis communis agglutinin-1. Microglia were highly permissive to CAEV infection in vitro as indicated by induction of syncytial cells, formation of lentivirus particles, expression of viral antigens, and release of high titered infectious virus into culture supernatants. CAEV selectively infected microglia in mixed glial cultures but replicated less efficiently than in purified microglial cultures; productive infection of astrocytes or oligodendrocytes was not detected. There was constitutive expression of class I and class II major histocompatibility complex antigens on microglia in purified and mixed cultures that was not altered significantly by CAEV infection alone. CONCLUSIONS: These observations demonstrated that cultured caprine microglial cells had a macrophage-like phenotype and were highly permissive to productive CAEV infection in vitro. This primary brain culture system is a valuable tool to study lentivirus-microglial interactions in the central nervous system.

Animals↗

PubMed1993

The cellular immunology of bovine paratuberculosis: immunity may be regulated by CD4+ helper and CD8+ immunoregulatory T lymphocytes which down-regulate gamma/delta+ T-cell cytotoxicity.

In a previous investigation, we obtained evidence that the major histocompatibility complex (MHC)-restricted proliferative response of CD4+ lymphocytes to Mycobacterium paratuberculosis antigens was depressed in naturally infected and immunized animals. Findings suggested that depression of the response was attributable to an abrogation in the ability of CD4+ cells to respond to specific antigens and/or the actual loss of antigen-reactive cells. In vitro cell experiments indicated that the depression was associated with the presence of gamma/delta+ T cells that modulated CD4+ cell function. Examination of additional animals confirmed and extended these observations and showed that the ability of gamma/delta+ T cells to regulate CD4+ responses were blocked by the presence of CD8+ cells. CD4+ T cells from some exposed animals incorporated [3H]-thymidine in the presence of CD8+, gamma/delta+ cells and/or antigen and antigen-presenting cells, but CD4+ cell proliferation was abrogated when CD8+ were excluded from the assays. Likewise, gamma/delta+ T-cell proliferation was abrogated when CD8+ cells were present. The mechanism by which CD8+ cells blocked gamma/delta+ T-cell responses could not be determined, however, the observed effect resembled the veto cell phenomenon. The data suggest that the development of protective immunity against M. paratuberculosis may be dependent on the capacity of CD8+ cells to modulate the regulatory activity of gamma/delta+ T populations.

Animals↗

PubMed1993

Suppression of proliferative response of BoCD4+ T lymphocytes by activated BoCD8+ T lymphocytes in the mammary gland of cows with Staphylococcus aureus mastitis.

Investigations were conducted to determine the mechanisms that account for differences in the responses of BoCD4+ lymphocytes from mammary gland secretions (MGS) in healthy cows and in cows with Staphylococcus aureus infection. The proliferative response to lectins and S. aureus antigens of mammary gland lymphocytes from healthy, S. aureus immunized cows was less than the response of peripheral blood lymphocytes. The lower responses of mammary gland lymphocytes were attributable both to less efficient antigen presentation by mammary gland antigen-presenting cells (APC) than by peripheral blood APC, and to lower responsiveness of mammary gland lymphocytes to lectins and antigen. In addition, the proliferative response of infected mammary gland lymphocytes was less than the response of uninfected mammary gland lymphocytes. This difference resulted from decreased proliferation of BoCD4+ lymphocytes in infected MGS. Flow cytometric analysis revealed that infected MGS contained increased numbers of BoCD8+ cells which coexpressed an activation molecule, ACT2, relative to BoCD8+ cells from uninfected MGS. Removal of BoCD8+, ACT2+ lymphocytes resulted in increased antigen responsiveness by lymphocytes from infected mammary glands. Also, when purified BoCD4+ lymphocytes were stimulated with antigen in the presence of varying numbers of ACT2+, BoCD8+ lymphocytes, antigen responsiveness was decreased in a dose-related manner. These data demonstrate that hyporesponsiveness of mammary gland lymphocytes to lectins and S. aureus antigen is, in part, mediated by activated BoCD8+ lymphocytes and suggest that this population enhances persistent intramammary infection by S. aureus.

Animals↗

PubMed1993

Identification of a monoclonal antibody reactive with the bovine orthologue of CD3 (BoCD3).

A monoclonal antibody (mAb), MM1A, that identifies a molecule expressed on a large percentage of bovine lymphocytes (60-80%) was examined to determine its specificity. Two and three colour immunofluorescence analysis using flow cytometry revealed the molecule is highly expressed on all CD4+ and CD8+ lymphocytes and lymphocytes that express WC1 and the gamma/delta TCR. In contrast to mAbs reactive with BoCD5, MM1A did not react with B lymphocytes. Biochemical analysis revealed that the mAb immunoprecipitates a molecular complex comprising a set of peptides with M(r) approximately 12, 16, 22, 32, 36, and 44 kDa under reducing conditions and an additional 96 kDa peptide complex under non-reducing conditions. The data indicate that MM1A recognizes the bovine orthologue of CD3 (BoCD3).

Animals↗

PubMed1993

Analysis of the gamma/delta T cell restricted antigen WC1.

The nine antibodies (mAbs) which clustered with the standard WC1 mAb CC15 in temporary cluster TC22 were analysed by immunoprecipitation, flow cytometry and immunohistology. Two forms of the molecule, with molecular weights of 205 and 215 kDa, were identified by immunoprecipitation and SDS-PAGE, the expression of which correlated with subclusters generated by flow cytometric analysis. Immunohistological data, however, did not reveal any tissue specific distribution. We propose the existence of at least two isoforms of WC1 which may prove to identify subpopulations of CD2- CD4- CD8- gamma/delta T cells.

Animals↗

PubMed1993

Expression of T19 (WC1) molecules by ovine lymphocytes.

Workshop clusters WC1 and WC2 monoclonal antibodies (mAbs) were tested for their reactivity with ovine peripheral blood mononuclear cells (PBMC). The populations of ovine lymphocytes defined by these mAbs were found to be part of the population of T19+ (WC1+) cells, and the gamma/delta T cell receptor (TCR) (WC2) expressing T cells. The expression of cell surface WC1 antigens following mitogen stimulation of ovine PBMC was studied. Whilst the size of the WC1 populations increased during culture with concanavalin A, the changes in the ratio of WC1:gamma/delta TCR percentages observed suggested either a loss of WC1 molecules or a selective expansion of WC1- cells.

Animals↗

PubMed1993

Clustering of monoclonal antibodies recognizing different members of the WC1 gene family.

Mouse L cell lines expressing two different bovine WC1 glycoproteins were produced by transfection of the cells with the corresponding cDNAs. The cell lines were used to analyze the reactivities of 67 monoclonal antibodies (mAbs) which recognize bovine gamma/delta T cells. The results indicated that preliminary clustering of mAbs can be achieved based on their recognition of epitopes expressed on all gene products, or of epitopes encoded by individual members of the gene family. The studies also showed that at least three members of the WC1 gene family are expressed, although it is not yet known how many can be expressed by individual bovine gamma/delta T cells. Final clustering of the WC1 mAbs will not be possible until the exact number of expressed gene products is known, and the reactivities of the mAbs with these products have been analyzed.

Animals↗

PubMed1993

Identification of monoclonal antibodies specific for the gamma/delta TCR.

Twelve monoclonal antibodies (mAbs) formed temporary cluster TC36. mAb CACTB6A was included as a standard antibody that reacted with the gamma/delta T cell receptor (TCR). Eight of the mAbs, CACTB6A, CACT16A, CACT17A, CACTB12A, CACTB44A, CACT71A, CACT18A and CACT61A, immunoprecipitated a 47 kDa molecule indicating that they all recognize the gamma/delta TCR. Flow cytometric studies separated these mAbs into three groups that distinguish three different gamma/delta TCR. mAb BAQ72A, which fell within TC36, immunoprecipitated a 215 kDa molecule with a similar tissue and cellular distribution to BoWC1 mAb. mAbs CACT26A, CACT63A and CACT77A reacted similarly to each other by flow cytometry and immunohistology, but were distinct from the other mAbs in TC36. These three mAbs may recognize an activation molecule and form a distinct novel mAb cluster.

Animals↗

PubMed1993

Immunohistological study on bovine small intestine including gut associated lymphoid tissue using monoclonal antibodies to WC1, TCR1 and BoCD3.

Selected antibodies (mAbs) that clustered in temporary cluster TC22 (WC1) and TC36 (TCR1) and one unclustered mAb thought to detect BoCD3 were used to compare the distribution of T and B cells and subpopulations of WC1+ or TCR1+ cells in fetal, calf, and young adult gut associated lymphoid tissue. Cells putatively positive for BoCD3 (MM1A) were detected in the interfollicular tissue similar to the pattern noted for BoCD2+ or BoCD5+ cells. WC1+ or TCR1+ cells were detected in small numbers in follicles and interfollicular tissue. Numerous WC1+ or TCR1+ cells were evident in the lamina propria and epithelia, with the highest frequency evident in tissues from animals 8 months of age.

Animals↗

PubMed1993

Cross-reactivity of workshop antibodies with cells from domestic and wild ruminants.

Reactivities of the monoclonal antibodies (mAbs) from the workshop panel with cells from cattle, sheep, goats, Cape buffalo (Syncerus caffer) and waterbuck (Kobus defassa) were tested. One hundred and sixty-nine mAbs reacted with bovine cells and 111 with sheep cells; 86 were shown to react with goat cells, 71 with buffalo cells and 70 with waterbuck cells. Some mAbs cross-reacted with all five ruminants tested, and are likely to react with epitopes that are conserved in other ruminant species. Such mAbs will obviate the need to produce mAbs panels to leukocyte antigens of other ruminants.

Animals↗

PubMed1993

Pig aortic endothelial cell antigens recognized by human IgM natural antibodies.

Human-to-pig xenoantibodies may constitute a major obstacle to the successful use of pigs as xenograft donors for human transplantation. Our studies demonstrate that normal human serum contains antibodies, primarily IgM, that are cytotoxic for pig aortic endothelial cells (PAECs). These antibodies bind to several antigens isolated from PAECs, lymphocytes, platelets, red blood cells, and the kidney. Absorption of human serum with pig lymphocytes removes the cytotoxic activity to PAECs and some, but not all, of the IgM antibodies capable of binding in an ELISA assay to the PAECs. The cytotoxic antibodies are inactivated by 2-mercaptoethanol, suggesting that they are primarily IgM. Whole cell extracts of PAEC, lymphocytes, platelets, red blood cells, and kidney were prepared and analyzed by Western blots to establish the cellular distribution of the xenoantigens that react with human IgM in pooled human serum. Results showed that several of the most intensely stained bands migrated between 24 and 66 kDa. High molecular weight bands (> 100 kDa) were observed only in kidney, platelet, and PAEC preparations. Human IgM xeniantibodies also reacted strongly in Western blots to endothelial cell membranes proteins with molecular weights of 62, 48, 42, 36, 34, 28, and 26 kDa. Absorption of human serum with pig lymphocytes removes IgM binding to all bands except for a 34-kDa Treatment of the PAEC membrane proteins with proteinase K disrupts the binding of the human IgM antibodies. Similar treatment with glycosidase F) resulted in a decrease in molecular weight of the 28- and 26-kDa bands, suggesting that these xenoantigens are glycoproteins and that antibody binding to some xenoantigens may not require glycosylation.

Animals↗

PubMed1993

CD8+ cytotoxic T lymphocytes against antigenic variants of caprine arthritis-encephalitis virus.

Cytotoxic T lymphocytes (CTL) specific for caprine arthritis-encephalitis virus (CAEV) were characterized using a colorimetric immunocytochemistry assay to measure surviving target cells. Peripheral blood lymphocytes from a CAEV-infected goat were cytotoxic to autologous, CAEV-infected dermal fibroblast target cells following in vitro stimulation of the lymphocytes with CAEV antigen. The lymphocytes were not cytotoxic to infected allogeneic target cells or to mock-infected autologous or allogeneic target cells. This CAEV antigen-specific, major histocompatibility complex-restricted cytotoxicity was mediated by CD8+ lymphocytes as demonstrated by selective depletion with anti-CD8 antibody and complement. CTL primed with one isolate of CAEV (CAEV-Co) had no detectable activity against target cells infected with either of two neutralization variants and diminished activity against target cells infected with three other neutralization variants. This apparent variability of CTL-sensitive epitopes among CAEV isolates may contribute to CAEV escaping immune control and may complicate vaccine design.

Animals↗

PubMed1993

Serological and biochemical detection of B-cell antigens in goats.

The production of B-cell specific alloantisera by lymphocyte transfusion between class I matched, MLR positive goats is described. Furthermore, the usefulness of preceding IEF typing is demonstrated in the selection of immunization pairs. After suitable absorptions and cluster analysis the detected B-cell specific antigens were designated BeD1-BeD6. The specificity BeD3 could also be detected by two class II-specific murine anti-H2 monoclonal antibodies. IEF class II typing of 34 animals gave concordant results between the two techniques. One additional allelic variant could be detected by IEF typing. The detected products segregated in close linkage to the earlier described caprine class I antigens. One recombinant has been found in 78 offspring. The reactivity of cells in mixed lymphocyte cultures (MLC) was correlated with the compatibility of the test cells for their B-cell specific antigens. Three of the B-cell specific sera were characterized by immunoprecipitation. The precipitated antigens corresponded in molecular weight to MHC class II products as described in other species indicating that the here described caprine products are of class II nature.

Animals↗

PubMed1993

Characterization of novel type C staphylococcal enterotoxins: biological and evolutionary implications.

The type C staphylococcal enterotoxins (SEC) are a group of highly conserved proteins with significant immunological cross-reactivity. Although three antigenically distinct SEC subtypes (SEC1, SEC2, and SEC3) have been reported in the literature, we observed that the isoelectric points of SEC from several Staphylococcus aureus isolates are different from those of any of these three subtypes. This observation led us to propose that additional SEC molecular variants exist. For assessment of this possibility, the sec genes from representative human, animal, and food isolates were cloned and sequenced. The toxins encoded by the 18 isolates used in this study included five unique SEC proteins in addition to SEC1, SEC2, and SEC3. Six of the SEC proteins (including SEC1, SEC2, and SEC3) were produced by human and food isolates. Analysis of seven bovine and ovine isolates showed that isolates from each animal species produced a unique host-specific SEC. All of the SEC caused lymphocyte proliferation, although some of the toxins differed in their ability to stimulate cells from several animal species. An explanation for these results, which is supported by our phenotypic analysis of Sec+ staphylococcal isolates, is that toxin heterogeneity is due to selection for modified SEC sequences that facilitate the survival of S. aureus isolates in their respective hosts.

Amino Acid Sequence↗

PubMed1993

Involvement of CD8+ T cells in delayed-type hypersensitivity responses against bovine leukemia virus (BLV) induced in sheep vaccinated with recombinant vaccinia virus expressing BLV envelope glycoprotein.

Delayed-type hypersensitivity responses against bovine leukemia virus (BLV) envelope glycoprotein (gp60) were induced in the skin of sheep vaccinated with recombinant vaccinia virus (RVV) expressing BLV glycoprotein. The lesions were characterized by marked infiltration of lymphocytes, slight migration of neutrophils, eosinophils, and macrophages in the dermis to hypodermis, and partial intercellular edema in the reticular layer. Immunohistochemical analysis with monoclonal antibodies demonstrated that the lymphocytic infiltrates consisted mainly of CD8+ T cells (53.7-55.8% at 48 hours post-challenge of BLV), CD4+ T cells (24.7-26.7%), and B cells (11.5-16.9%). The role of CD4+ and CD8+ T cells in suppressing BLV growth in RVV-vaccinated animals is discussed.

Animals↗