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Biomedical subjects

S Macrae

Publications and source records attributed to S Macrae.

13 recordsLinked to original sources
PubMed1988

Colonization of Tomato Plants by Two Agrocin-Producing Strains of Agrobacterium tumefaciens.

For a bacterium to be a successful biocontrol agent against crown gall disease, it must produce an effective agrocin specific for Agrobacterium tumefaciens and be able to colonize host plants efficiently. The colonization abilities of K84 and J73, successful and potential biocontrolling strains, respectively, were compared both in vivo and in vitro. Both strains produced fibrils attaching them to tomato root surfaces and had similar colonization efficiencies up to 14 days after inoculation. However, the ability of J73 to colonize plants for longer periods was significantly less than that of K84. Thus, the presence of fibrils is not sufficient to ensure colonization. No correlation was found between hydrophobicity and colonization.

Journal Article↗
PubMed1986

Rubber production in guayule: determination of rubber producing potential.

Optimum conditions for the rapid, efficient, nondestructive determination of rubber producing potential in guayule (Parthenium argentatum) were established. The rubber producing potential may be defined as the ability of the plant material to synthesize rubber from a precursor under specified conditions. To achieve this, stem slices taken from the first 5 centimeters of branches were incubated with [(14)C]acetate as precursor in 0.1 molar phosphate buffer (pH 6.5) at 26 degrees C for 16 hours in the light. The (14)C from labeled acetate and acetyl coenzymeA were efficiently incorporated into rubber whereas the (14)C from both mevalonic acid (MVA) and isopentenylpyrophosphate (IPP) were poorly incorporated. Incorporation of 68.6% of the (14)C from labeled IPP into the acetone extractable material suggests that most of the IPP was channeled down the lower terpenoid branch of the polyisoprene biosynthetic pathway. The incorporation of (14)C from labeled acetate into rubber was most efficient at temperatures between 20 and 25 degrees C. The rubber producing potential was also found to be dependent on light intensity. The roots which represent about one-third of the plant biomass not only had the highest rubber producing potential but also contained the highest amount of rubber (7.6%), indicating that the root system could be a major source of rubber. The mature stem bark also had a high rubber content and rubber producing potential, whereas the young stem had a low rubber content and a lower potential for producing rubber. The leaves showed little potential to incorporate labeled acetate into rubber and no more than 0.5% rubber was found in guayule leaves.

Journal Article↗
PubMed1985

Possible adrenal involvement in hydroxyurea toxicity defense mechanisms.

Changes in blood biochemistry, resembling adrenocortical hyperfunction, induced by oral administration with hydroxyurea (HYD) at a dosage of 800 mg/Kg/d for 5 days (K+ and total protein decrease, total cholesterol increase) are not modified or enhanced (total protein) by adrenalectomy. Adrenalectomy dramatically enhanced the decrease of WBC and neutrophils normally induced by HYD. Replacement therapy with corticosterone attenuated and/or delayed the above changes. Normally-functioning adrenocortical tissue may play a role in protection against HYD haematological toxicity in the rat and the drug-induced hypothalamus pituitary mediated adrenocortical activation seems to represent a mechanism capable of counteracting drug toxicity.

Adrenalectomy↗
PubMed1982

Conditioned immune response associated with allogeneic skin grafts in mice.

Groups of CBA mice were given sham skin grafts (conditioned stimulus, CS) or alloantigen only (unconditioned stimulus, US; C57BL/6 lymphoid cells inoculated i.p.). A further group of animals received simultaneous US and CS (alloantigen (US), in this case actually given in the context of a C57BL/6 skin graft). The peripheral blood leukocyte (PBL) pool of all animals was analyzed in tissue culture for the frequency of cytotoxic T lymphocyte precursors (CTLp) specific for alloantigens on the grafted tissue. After three "conditioning" trials, spaced at intervals to allow recovery in all groups of the CTLp frequency to that of naive control mice, individuals in all groups were sham-grafted (given CS alone). PBL of these mice were tested 2 days after removal of the casts. Only group CS + US, and only some 50 to 60% of these, were able to show a "conditioned" increase in the CTLp frequency specific for alloantigens of the grafted tissue after sham-grafting. When these "responder" mice were subdivided into two groups that were subsequently given two trials of CS only or CS + US, followed by retesting with CS alone, either extinction or reinforcement of the previously conditioned response was observed.

Animals↗
PubMed1981

Microheterogeneity in regulatory circuits for T-cell alloresponsiveness.

Mixed leucocyte cultures of responder spleen cells from individual B10 mice, challenged with irradiated allogeneic B10.D2 or B10.BR spleen cells, were used to generate discrete pools of cytotoxic T lymphocytes (CTL) with which to immunize (B10 x B10.D2)F1 or (B10 x B10.BR)F1 animals. Aliquots of the original donor B10 spleen cells were stored at -70 degrees. Eighteen days after immunization of the F1 animals, spleen and serum preparations from these mice were tested, in reciprocal fashion, for their ability to affect the development of CTL from the thawed donor B10 spleen lymphocytes in fresh cultures challenged with either the original or a third party allogeneic stimulus. Evidence for individual specific suppression by F1-T lymphocytes or by F1-serum (antibody) molecules was obtained. By priming (B10 x B10.D2)F1 mice with B10 lymphoid cells the F1 animals can also be shown to resist the otherwise lethal GvHD induced by sublethal whole body irradiation followed by intravenous challenge with B10 lymphoid cells. Using F1 mice primed and subsequently challenged with lymphocytes prepared from individual donors, self-preference in the regulation of GvHD was also seen. A similar fine specificity of regulatory cells was observed using suppressor cells from individual mice rendered neonatally tolerant of histocompatible cells (by inoculation of F1 hybrid cells within 24 hr of birth). These findings suggest that the mouse T cell alloreceptor repertoire is subject to a process of somatic diversification during normal ontogenesis. By examining the regulation of alloresponsiveness in T lymphocytes of B10.Br origin which differentiate from the appropriate stem cells in a B10 or B10.Br host, we have uncovered evidence that the T-cell alloreceptor repertoire is, in part at least, determined by the host MHC environment.

Animals↗
PubMed1979

Effect of gold sodium thiomalate on murine lymphocyte functions.

The in vitro effects of gold sodium thiomalate (GTM) on various murine splenic lymphocytic functions were tested. The presence of GTM in cultures of splenic cells suppressed anti-hapten responses to both thymus-independent and thymus-dependent antigens. GTM also suppressed the in vitro generation of cytotoxic effector cells as well as the mitogenic response to both T cell and B cell mitogens. This suppression could not be reversed by the addition of irradiated spleen cells. Spleen cells exposed to GTM for 4 hr prior to culture also exhibited similarly suppressed functions, although their functional capacity could be fully restored by the addition of irradiated spleen cells. These results show that GTM inhibits both humoral and cellular immune mechanisms and appears to act primarily at the accessory (macrophage) cell level, with perhaps a secondary effect on T lymphocytes.

Animals↗
PubMed1979

Differentiation of functionally active mouse T lymphocytes from functionally inactive bone marrow precursors. III. Induction of T-cell activities by growth of bone marrow on feeder layers prepared from mouse thymocytes.

The ability of small and large T precursor cell pools to differentiate into mature functional T lymphocytes on thymus feeder cell layers or in the presence of a supernatant prepared from such feeder layers was compared. Evidence was obtained showing that the small cell pool differentiated as effectively in the presence of soluble factors prepared from the thymus cultures as in the presence of the thymus cells themselves. In contrast, large stem cells apparently needed cellular contact with the thymus feeder cultures in order to promote differentiation, though a time point could be found at which further differentiation from this precursor pool would also occur in the presence of the thymus culture supernatant only. These data concurred with evidence from in vivo experiments for two pools of T-cell precursors which differentiated in thymectomized or thymus-intact recipients respectively.

Animals↗
PubMed1979

Differentiation of functionally active mouse T lymphocytes from functionally inactive bone marrow precursors. IV. Recovery of T-cell function from bone marrow precursors in a histo-incompatible environment.

Regeneration of T-cell activities in vivo or in vitro from mouse bone marrow precursors differentiating in the presence of an allogeneic thymus was investigated. The data indicated that T-depleted bone marrow cells fail to affect long-term reconstitution of allogeneic recipients unless a pool of rapidly maturing T-precursor cells is also removed (post-thymic pool). Animals reconstituted with pre-thymic bone marrow stem cells become stable chimaeras in which cells capable of generating an in vitro CML response to host antigens, as well as cells capable of suppressing that response, could be demonstrated. Similar data (CML directed against the H-2 antigens of the 'host' thymus feeder layer and cells capable of inhibiting that response) were obtained when pre-thymic bone marrow cells were grown in vitro on allogeneic thymus feeder cells. When cytotoxic T-lymphocyte precursor (CTLp) and helper (CTLh) cells were separately investigated, a restriction in their co-operation for an anti-host response was observed when precursor cells differentiated in an allogeneic environment. Only CTLp and CTLh differentiating in the presence of the same allogeneic thymus source (whether in vivo or in vitro) could co-operate to generate CTL directed to H-2 antigens of that thymus source.

Animals↗
PubMed1979

MHC restriction of murine T lymphocyte reactivity analysed by growth of bone marrow cells in vitro on thymus epithelial monolayers.

Mature mouse T lymphocytes, derived from long-term culture of bone marrow cells on thymus epithelial monolayers, were analysed with respect to their ability to co-operate with B cells (for antibody production) or T cells (in the generation of cytotoxic cells) when the bone marrow T precursor cells and the thymus epithelial cells differ at defined regions of the major histocompatibility complex. A pool of more mature bone marrow T-cell precursors gave rise to T cells interacting only with T/B lymphocytes sharing MHC determinants with the strain of origin of the bone marrow cells used. In contrast, a more immature bone marrow T-cell precursor pool produced T lymphocytes which had acquired MHC restriction (in terms of co-operativity with T/B cells) as defined by the MHC determinants of the thymus epithelium, and not those MHC determinants of the cultured bone marrow population. In addition, some evidence was obtained for Ir gene control (mapping in the MHC region) in the development of the repertoire of T cells involved in production of cytotoxic responses in vitro to TNP-modified self antigens.

Animals↗
PubMed1978

Analysis of mechanisms of maintenance of neonatally induced tolerance to foreign alloantigens.

Mice made tolerant to allogeneic tissues in neonatal life have been examined at different times for their ability to respond to the tolerizing determinants in a variety of assays (in vitro CML, MCL and in vivo GvH assays). All animals were tolerant in terms of their inability to produce CTL to the relevant determinants, and to induce GvH in lethally irradiated F1 recipients. Nevertheless, some mice also showed a normal MLC proliferative response and contained antigen-specific serum inhibitory factors, while other mice contained apparently antigen-specific suppressor cells. The pool of the latter, futhermore, was expanded considerably upon adoptive transfer of tolerant cells (with tolerizing antigens) to lethally irradiated syngeneic recipients. The data are compatible with the notion that suppression of clonal expansion represents the primary mechanism of tolerance maintenance (induction), and that the infrequently observed serum reactivity in such tolerant mice represents a vestige of the means whereby-cell mediated suppression was induced.

Animals↗