PubMed Health⌕ Search

Biomedical subjects

C L Baldwin

Publications and source records attributed to C L Baldwin.

At least 55 records · Page 3Linked to original sources
PubMed1989

Characterization of buffalo-derived theilerial parasites with monoclonal antibodies and DNA probes.

The characteristics of intra-lymphocytic Theileria isolated from African buffalo and from cattle that were infected with buffalo-derived parasites were evaluated using anti-schizont monoclonal antibodies (mAbs) and DNA probes. Antigenic differences were revealed by the reactivities of 27 mAbs with the buffalo-derived parasites isolated from different animals. Antigenic diversity was also seen with Theileria-infected lymphoblastoid cell isolates taken from the lymph nodes and lambda gt11, showed specific hybridization to parasite DNA in Southern blots of restriction enzyme-digested, lymphoblastoid cells infected with buffalo-derived theilerial parasites. Genotypic differences between the buffalo-derived parasites were revealed by the restriction fragment length polymorphisms seen with hybridization of those probes to DNA from cloned and uncloned Theileria-infected cell lines. The evaluation of theilerial parasites derived from buffalo and from cattle which underwent typical T. p. lawrencei reactions, after being infected with buffalo-derived theilerial parasites, did not show any specific phenotypic or genotypic characteristics of these parasites that would distinguish them from T. p. parva and T. p. bovis parasites. The validity of these subspecies distinctions is discussed.

Animals↗
PubMed1988

An update of respiratory cancer and occupational exposure to arsenicals.

Mortality was updated through 1982 for 611 arsenic-exposed employees originally studied through 1973. In the earlier report, total mortality was observed to have been below the comparable U.S. population; however, mortality was significantly elevated for respiratory cancer. The focus of the update was on respiratory cancer and of special interest was whether the risk of respiratory cancer remained in excess for individuals alive as of the end of the last study. In the update, 9 additional respiratory cancers were observed subsequent to 1973, the end of the follow-up in the original study, versus 7.8 expected. The risk ratio for the time-interval 1974-1982 (standardized mortality ratio SMR = 116) was diminished compared to that reported in the original study (SMR = 330). When the entire study period was analyzed, the risk of respiratory cancer did not appear to decline with interval since exposure cessation. Analyses by duration of arsenic exposure and interval since first exposure did not reveal any obvious dose-response relationships.

Arsenic↗
PubMed1988

T-cell clones in immunoparasitology.

Cell-mediated immunity (CMI) is important in many parasitic infections. Stimulation by parasite-specific antigens can induce clonal expansion of parasite-specific T-cells which may act by direct cytotoxic action or by indirect effects on other cells such as natural killer cells or antibody-producing B-cells (Box 1). In many cases however, the precise effector functions and the identity of antigens that elicit protective responses in parasitic infections are poorly defined. Analysis of proliferative and cytotoxic activities of subcloned cultures of T-cells stimulated with parasite antigens can provide some clues about the importance of CMI, but, as this review shows, much more precise information can be obtained by analysis of the response of cloned T-cell cultures.

Journal Article↗
PubMed1988

Evaluation of cytotoxic lymphocytes and their parasite strain specificity from African buffalo infected with Theileria parva.

Theileria parva-reactive cytotoxic lymphocytes and their precursors were examined in the blood of African buffalo infected with T. parva and uninfected African buffalo. Peripheral blood mononuclear cells (PBM) from eight of 11 infected buffalo were found to have potent cytotoxic activity after stimulation with autologous parasitized cells for 6 days in vitro, while PBM from uninfected buffalo or PBM from infected buffalo not stimulated in vitro had no cytotoxic activity. The cytotoxic activity was specific for parasitized cells and genetically restricted since there was no killing on uninfected autologous lymphoblasts and a lower percentage of killing on parasitized allogeneic lymphocytes than on targets of autologous parasitized cells. The cytotoxic cells tested for parasite strain specificity were shown to kill autologous cells transformed with different stocks of both cattle-derived (T. parva parva) and buffalo-derived (T. parva lawrencei) parasites.

Animals↗
PubMed1988

Bovine T cells, B cells, and null cells are transformed by the protozoan parasite Theileria parva.

The target cells for infection and transformation by Theileria parva were investigated. Peripheral blood mononuclear cells were reacted with monoclonal antibodies specific for bovine leukocyte differentiation antigens, sorted into subpopulations with a fluorescence-activated cell sorter, and infected in vitro with T. parva sporozoites. Infected cells were cultured at limiting dilution, and transformed clones were screened with monoclonal antibodies. The results indicated that B cells, T cells (including BoT4+ and BoT8+ cells), and null cells but not monocytes or neutrophils were transformed in vitro after infection with T. parva. After transformation, peripheral blood T cells and T-cell clones retained expression of most or all of the T-cell differentiation antigens including the mature T-cell marker recognized by monoclonal antibody IL-A27, BoT2, and BoT4 or BoT8, and some cells acquired a low level of expression of BoT4, BoT8, or the null cell marker recognized by monoclonal antibody IL-A29. T. parva-transformed null cells retained expression of the IL-A29 determinant and acquired expression of BoT2 and BoT8 but not the IL-A27 determinant or BoT4. T. parva-transformed B cells in most instances lost expression of surface immunoglobulin and never acquired expression of the IL-A27 determinant, BoT2, BoT4, or BoT8, although some cells acquired a low level of expression of the null cell marker recognized by monoclonal antibody IL-A29. Further studies on cell lines and clones grown in vitro from populations isolated from T. parva-infected cattle suggested that the majority of the in vivo T. parva-transformed cells were of T-cell origin.

Animals↗
PubMed1988

Monoclonal antibodies which react with bovine T-lymphocyte antigens and induce blastogenesis: tissue distribution and functional characteristics of the target antigens.

In this study we report on the tissue distribution and functional characteristics of bovine T-cell differentiation antigens recognized by the monoclonal antibodies (mAbs) IL-A26, IL-A27, and IL-A28. All three mAbs are able to stimulate proliferation of peripheral blood mononuclear cells (PBM) and inhibit proliferation of responder cells in mixed leucocyte cultures (MLC). MAbs IL-A27 and IL-A28 are believed to react with the same molecule, which is different to that recognized by IL-A26 as determined by a number of criteria. MAbs IL-A27 and IL-A28 inhibit binding of one another, but not of IL-A26. MAbs IL-A27 and IL-A28 react with 25% of thymocytes confined to the medulla, whereas IL-A26 reacts with approximately 80% of thymocytes, including medullary and cortical populations. MAbs IL-A27 and IL-A28 react with thymocytes which express BoT4 or BoT8 singularly, whereas IL-A26 reacts with all cells which express BoT4 or BoT8, either singularly or dually, in addition to all thymocytes which react with IL-A27/28. Only IL-A26 inhibits spontaneous sheep erythrocyte (E)-rosette formation by bovine T cells. Based on tissue distribution and functional characteristics, IL-A26 is believed to recognize the bovine homologue of CD2, designated BoT2, whereas IL-A27/28 reacts with a mature T-cell antigen. Cells reactive with the mAbs constitute approximately 60% of bovine PBM. Using these mAbs in dual immunofluorescence analyses, at least three populations of bovine T cells are demonstrable in PBM. The majority of T cells are BoT4+ or BoT8+ and also react with IL-A26/27/28. A second small population of PBM is negative for BoT4 and BoT8 but is IL-A26/27/28+. A third population (less than 5%) is BoT4-/BoT8-/ILA27/28- but reacts with IL-A26.

Animals↗
PubMed1988

Bovine pan T-cell monoclonal antibodies reactive with a molecule similar to CD2.

Monoclonal antibodies (mAb) CH128A and CH61A react with molecules of 50,000-60,000 MW. They are expressed by all T cells in cattle, comprising 44-69% of peripheral blood mononuclear leucocytes (PBM), the majority of lymphocytes in T-dependent areas of lymph node, and 75-80% of cells derived from the thymus including both cortical and medullary thymocytes. The molecule recognized by these mAbs is not expressed on B lymphocytes, monocytes/macrophages, or granulocytes. Both mAb inhibit spontaneous rosette formation by sheep erythrocytes and bovine lymphocytes. We postulate that these mAb see the bovine homologue of the human sheep red blood cell receptor CD2 and has been named BoT2.

Animals↗
PubMed1987

Alloreactive T cell clones transformed by Theileria parva retain cytolytic activity and antigen specificity.

Theileria parva is a protozoan parasite which infects and transforms bovine lymphocytes. This study examined the effects of Theileria-induced transformation on phenotype and function, in terms of cytolytic potency and specificity, of class I and class II-specific alloreactive T cell clones. Alloreactive T cell clones infected with T. parva (Muguga) retained expression of the T cell differentiation antigens BoT2, BoT4, BoT8 and the mature T cell antigen recognized by monoclonal antibody IL-A27, as well as cytolytic function and antigen specificity, over a period of 3-4 months in continuous culture. These features were identical to those expressed by the uninfected parent clones. During this period, neither antigenic stimulation nor exogenous growth factors were required for the maintenance of proliferation, function or antigen specificity. Thereafter, cytolytic activity declined and was eventually lost, which may reflect degenerative changes normally associated with T cell senescence rather than result from parasitization per se.

Animals↗
PubMed1987

Phenotypic and functional characteristics of bovine T lymphocytes.

Monoclonal antibodies have been derived which detect the bovine equivalents of the human pan-T cell marker CD2 and the T lymphocyte subpopulation markers CD4 and CD8. We refer to the bovine analogues as BoT2, BoT4 and BoT8. Monoclonal antibodies have also been derived which detect an antigen(s) with similarities to CD3, although the precise nature of the target molecule(s) in this instance remains to be elucidated. In general there is close similarity between the tissue distributions and, where these have been determined, the molecular masses of the BoT2, BoT4, BoT8 and putative BoT3 entities and their counterparts in other species. BoT2 is expressed on a majority of peripheral blood T lymphocytes and thymocytes and BoT2+ cells are found in both thymic cortex and medulla. In contrast, the putative BoT3 marker is expressed by a minority of thymocytes which are moreover, largely restricted to medulla. Monoclonal antibodies detecting BoT2 determinants have been shown to precipitate 55 kDa molecules. Antibodies to the BoT2 and BoT3 entities have been shown to induce proliferation in peripheral blood mononuclear cells of some cattle, and to be capable of inhibition of antigen-driven proliferative responses and cytolytic function. The BoT4 and BoT8 markers are expressed in a mutually exclusive manner by bovine peripheral blood mononuclear cells but they are coexpressed on a large population of thymocytes. Monoclonal antibodies have been used to precipitate molecules of 52 and 55 kDa in the case of those detecting BoT4 and 34 and 35 kDa in the case of an antibody reactive with a BoT8 determinant. The BoT4 and BoT8 markers have been associated with specificity for, and restriction by, MHC class II and class I molecules respectively.

Animals↗
PubMed1987

Bovine helper T-cell clones specific for lymphocytes infected with Theileria parva (Muguga).

T-cell clones specific for lymphocytes infected with Theileria parva were derived from animals immunized by infection with T. parva (Muguga). These clones were non-cytolytic and had the BoT4+ BoT8- surface phenotype, BoT4 and BoT8 being the bovine analogues of human CD4 and CD8 molecules. The clones proliferated in response to irradiated autologous lymphoblasts infected with T. parva (Muguga) but not to autologous uninfected lymphoblasts or monocytes. They were parasite strain-specific, in that they did not respond to autologous lymphoblasts infected with another parasite stock, T. parva (Marikebuni). The clones proliferated in the absence of exogenous T-cell growth factor (TCGF) and produced TCGF when stimulated with concanavalin A. Induction of proliferation of the cloned T-cells was genetically restricted, and evidence was obtained which indicated that they were restricted by determinants on class II major histocompatibility complex (MHC) molecules. These findings demonstrate that infections with T. parva stimulate antigen-specific MHC-restricted T-cells with the properties of T-helper cells. The results also provide further evidence for the expression of a parasite strain-specific antigen on the surface of T. parva-infected lymphocytes.

Animals↗
PubMed1986

Characterization of a subset of bovine T lymphocytes that express BoT4 by monoclonal antibodies and function: similarity to lymphocytes defined by human T4 and murine L3T4.

We report the identification of a subset of bovine T cells by two monoclonal antibodies (mAb), IL-A11 and IL-A12, and some functional analyses of these cells. Both mAb precipitate two polypeptides, called BoT4, with apparent molecular mass of 52 and 55 kilodaltons. The epitopes recognized by these two mAb are different, however. BoT4 is found on approximately 70% of thymocytes and 30% of peripheral blood mononuclear cells (PBM), is not expressed by monocytes or B cells, and is found on cells in the T-dependent areas of lymph nodes. BoT4+ lymphocytes purified by a fluorescence-activated cell sorter proliferate in response to mitogenic and alloantigenic stimulation without addition of exogenous growth factors, whereas BoT4- lymphocytes do not. Monoclonal antibodies IL-A11 and IL-A12 have no effect on mitogen- (PHA and Con A) or alloantigen-induced proliferation of PBM. Monoclonal antibody IL-A12 has no inhibitory effect on the cytolytic activity of bulk populations of alloreactive T lymphocytes, and most of the cytolytic activity generated in mixed leukocyte culture is ascribable to the BoT4- population. Using cloned alloantigen-specific lymphocytes, we found that the ability of BoT4+ clones to proliferate to alloantigenic stimuli without exogenous growth factors is a characteristic of some clones, as is susceptibility to inhibition of proliferation by mAb IL-A12. These results implicate the BoT4 molecule in antigen recognition but indicate that the requirement for BoT4 is variable among clones. Our findings, together with those in the companion paper, which provides evidence that BoT4+ lymphocytes are class II restricted, indicate that BoT4+ lymphocytes are the bovine equivalent of Leu3/T4+ lymphocytes of humans and analogous lymphocytes of other species.

Animals↗
PubMed1986

Alloreactive bovine T lymphocyte clones: an analysis of function, phenotype, and specificity.

A bovine alloreactive cell population was subjected to complement-dependent lysis with monoclonal antibody (mAb) IL-A11. The original population and the population depleted of cells bearing the determinant recognized by mAb IL-A11 were cloned. Parent cultures and 21 clones were examined for cytolytic function and for expression of determinants recognized by mAb IL-A11 and two additional mAb, IL-A12 and IL-A17. Clones could be classified according to maximal achievable levels of cytolysis by using Theileria parva-infected bovine lymphoblastoid target cells. In this way, three groups were identified--one capable of high level cytolysis, one of intermediate levels, and one group comprising apparently noncytolytic clones. The clones in the first group reacted with mAb IL-A17; those in the second and third groups, with mAb IL-A11 and IL-A12. It was shown that cytotoxicity effected by IL-A17+ clones could be inhibited by this mAb and also by a mAb directed to MHC class I determinants on target cells. Conversely, cytotoxicity effected by IL-A11+/IL-A12+ clones could be inhibited by mAb IL-A11 and by a mAb directed to MHC class II determinants on target cells. The levels of expression of class I and class II determinants on target cells correlated with the levels of killing by clones of the IL-A17+ phenotype and clones of the IL-A11+/IL-A12+ phenotype, respectively. The results indicate that cytotoxic bovine T lymphocyte clones specific for class I MHC antigens and both cytotoxic and noncytotoxic clones specific for class II MHC antigens can be obtained. Further, their specificity for class I or class II antigens can be determined by phenotyping with mAb.

Animals↗
PubMed1986

Improved methods for purification and depletion of monocytes from bovine peripheral blood mononuclear cells. Functional evaluation of monocytes in responses to lectins.

We have compared different techniques for the enrichment and depletion of monocytes from bovine peripheral blood mononuclear cells. Adherence to plasma-coated gelatin was the most efficient and reproducible method for enrichment of monocytes (80% monocytes), whereas depletion of peripheral blood mononuclear cells of monocytes (0.3% monocytes and less) was best achieved by defibrination of the blood from which the PBM were separated. In both instances, purity of the cell population could be improved further by an additional step, namely, FACS sorting with a monocyte-specific monoclonal antibody to purify monocytes (97% monocytes and more), and adherence to polystyrene to remove residual monocytes from defibrinated PBM (0.1% monocytes and less). Depletion of monocytes abolished the response of PBM to concanavalin A and phytohaemagglutinin. The lectin-induced response could be restored by adding gelatin/plasma purified monocytes. This activity of monocytes could be replaced by 2-mercaptoethanol.

Animals↗
PubMed1986

Bovine cytotoxic T-cell clones specific for cells infected with the protozoan parasite Theileria parva: parasite strain specificity and class I major histocompatibility complex restriction.

We present information on the specificity of three bovine cytotoxic T-cell clones reactive with lymphoblasts infected with the protozoan parasite Theileria parva. The clones were derived from peripheral blood mononuclear cells of an animal immunized with T. parva (Muguga stock), after five stimulations in vitro with an autologous parasitized cell line. The three clones belonged to the BoT8+ subset of T cells, which is similar to the human CD8+ T-cell subset. On the basis of analysis on a panel of infected target cells originating from cattle of different major histocompatibility complex (MHC) phenotypes, killing by all three clones was found to be restricted to targets bearing the class I MHC specificity KN104, which is defined by alloantiserum KNA104 and monoclonal antibody IL-A4. This class I MHC restriction was confirmed by blocking of target cell lysis with these antibodies and monoclonal antibody w6/32, which reacts with a nonpolymorphic determinant on bovine class I MHC molecules. The three clones were parasite strain specific, in that they did not kill cells of the appropriate MHC type infected with T. parva (Marikebuni stock). These findings, taken together with previous observations that immunization of cattle with T. parva (Muguga) does not provide protection against challenge with T. parva (Marikebuni), suggest that the cytotoxic T cells recognize a cell surface antigen that may be important in induction of immunity to the parasite.

Animals↗
PubMed1986

Comparative analysis of infection and transformation of lymphocytes from African buffalo and Boran cattle with Theileria parva subsp. parva and T. parva subsp. lawrencei.

This study compared infection and transformation of peripheral blood mononuclear cells (PBM) of Boran cattle and African buffalo in vitro to determine whether differences occurred which could account for the greater susceptibility of Boran cattle to infection with Theileria parva subsp. parva and T. parva subsp. lawrencei. PBM from buffalo and cattle had a similar percentage of cells which bound T. parva subsp. parva sporozoites (24 to 34%) and in which schizonts developed during the first week after infection (18 to 23%). Using a limiting dilution culture system, it was established, however, that a significantly higher proportion of cattle PBM transformed into continuously replicating cell lines after infection with T. parva subsp. parva than did buffalo PBM. The evidence suggests that the low capacity of T. parva subsp. parva to establish infections in buffalo compared with cattle is related to the lower frequency of buffalo cells which undergo transformation. With T. parva subsp. lawrencei, however, the frequency of transformation of buffalo PBM was higher than that for cattle PBM. The frequency of cells transformed by T. parva subsp. lawrencei, therefore, cannot account for the greater resistance of buffalo to infections with T. parva subsp. lawrencei. Buffalo must have other mechanisms, either innate or acquired, which control infection with T. parva subsp. lawrencei more efficiently than in cattle.

Animals↗
PubMed1986

An update of mortality among chemical workers exposed to benzene.

Mortality was updated to the end of 1982 for 594 employees exposed to benzene who had been studied previously and for an additional 362 exposed workers not studied previously. Cause specific mortality comparisons were made using United States white male, age, and calendar year adjusted rates. Total mortality was observed to have been significantly below expectation, and this was particularly evident for deaths from accidental causes. Mortality from skin cancer was significantly raised, although there were no unusual or common characteristics among the affected individuals which would suggest a link with exposure to benzene. A non-significant excess of total deaths from leukaemia was noted based on four observed cases; however, all four were myelogenous leukaemias and this represented a significant excess in that subcategory. These and other deaths of possible interest are reviewed in detail. Analyses by work area, duration of exposure, and cumulative dose index did not show patterns suggestive of a causal association between exposure to benzene and any particular cause of death.

Adult↗
PubMed1986

Characterization by a monoclonal antibody and functional analysis of a subset of bovine T lymphocytes that express BoT8, a molecule analogous to human CD8.

Monoclonal antibody (mAb) IL-A17 characterizes a subset of bovine T lymphocytes. IL-A17 recognizes a 34,000-35,000 MW doublet, designated BoT8, which is expressed on the surface of approximately 20% of peripheral blood mononuclear leucocytes (PBM), a subpopulation of lymphocytes in T-dependent areas of lymph nodes and spleen, and about 70% of thymocytes. This molecule is not expressed on B lymphocytes, monocytes/macrophages or granulocytes. Double labelling of PBM showed that the BoT8+ population is distinct from the T lymphocyte subset expressing BoT4. BoT8+ lymphocytes purified with a fluorescence-activated cell sorter (FACS) proliferated poorly in response to mitogenic and alloantigenic stimulation in the absence of exogenous growth factors. IL-A17 had no inhibitory effect on proliferation of PBM to mitogens (Con A and PHA) or alloantigens and no measurable effect on the in vitro generation of cytolytic effector cells. However, in some experiments IL-A17 was found to block partially allospecific cytolytic function mediated by bulk effector cell populations when included in 51Cr-release assays. Fractionation of effector cells generated in an allogeneic mixed leucocyte culture (MLC) demonstrated that cytotoxic cells specific for class I major histocompatibility complex (MHC) antigens reside within the BoT8+ population. Based on these data, and information reported elsewhere on alloreactive bovine T-cell clones, BoT8 is considered to be analogous to CD8 in humans and equivalent molecules in other species.

Animals↗