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L N Ruben

Publications and source records attributed to L N Ruben.

At least 37 records · Page 2Linked to original sources
PubMed1987

Corticosteroid regulation of IL-1 production may be responsible for deficient immune suppressor function during the metamorphosis of Xenopus laevis, the South African clawed toad.

Thymus immune suppressor function is deficient during the metamorphosis of Xenopus laevis, the South African clawed toad. Thymuses of antigen-activated metamorphic larvae were tested for restoration of suppressor function by co-culture with matched fragments of spleens from immunized, antibody-producing young adults. The inhibition of unusually high endogenous corticosteroid levels in metamorphic larvae with metyrapone restores suppressor function. Dexamethasone counteracts this effect. Since corticosteroids can inhibit clonal expansion of thymus-derived (T) immunocytes by effecting lymphokines in mammals, we tested recombinant DNA-produced human interleukin-1 (rIL-1) and interleukin-2 (rIL-2), and the lectin concanavalin A in vivo. All restore thymus suppressor function in metamorphosing larvae. When metyrapone, dexamethasone and rIL-2 are injected together into antigen-activated larvae their thymuses will suppress splenic antibody production. Moreover, since rIL-1 and rIL-2 are able to restore thymic suppression in antigen-activated metamorphic larvae, endogenous corticosteroid does not effect their function. The basis for the lack of suppressor function during metamorphosis of Xenopus laevis may be endogenous corticosteroid regulation of IL-1 production to create IL-2 deficiency, thereby inhibiting T cell clonal expansion.

Adrenal Cortex Hormones↗
PubMed1987

The characterization of the toad splenocytes which bind mouse anti-human IL-2 receptor antibody.

We have utilized two depletion protocols to characterize the spleen cells of the South African clawed toad, which bind specifically mouse-anti-human IL-2 receptor (anti-Tac) antibody and recombinant DNA produced IL-2. When the selectively lymphotoxic reagent, N-CH3-N-nitrosourea (NMU), is injected into adult toads, it removes the thymic cortex and lymphocytes throughout the body required for helper and cytotoxic cell functions. We have also used a monoclonal mouse anti-Xenopus IgM antibody to deplete toad splenocyte populations of surface (s) Ig+ cells. Freshly biopsied and cultured spleen cells were compared with respect to their capacity to bind fluorescent (Fl*-) anti-Tac antibody and its ligand, rIL-2, after a depletion protocol. The results clearly show that a phytohemagglutinin (PHA)/IL-2 sensitive splenocyte population is removed by NMU injection. While many of the remaining NMU insensitive, previously cultured cells are Tac+, they fail to bind rIL-2. Freshly biopsied spleen cells with constitutive IL-2 receptors are found in both the sIg- (T cell enriched) and sIg+ (B cell enriched) populations following panning. Moreover, both populations are able to bind the ligand with equal efficiency. Thus, constitutive IL-2 receptor bearing cells are not restricted to either the T or B cell populations. The predominant PHA activatable, rIL-2 binding cell populations of the toad appear to be T cells which are involved with helper and cytotoxic functions.

Animals↗
PubMed1987

Toad splenocytes bind human IL-2 and anti-human IL-2 receptor antibody specifically.

Human r-DNA IL-2 and fluorescent (Fl) mouse anti-human IL-2 receptor antibody have been tested separately and in competition with each other for their capacities to bind to the splenocytes of Xenopus laevis, the South African clawed toad. Binding by Fl*-mouse anti-DNP antibody of the same subclass (IgG1, kappa) was used as a control. The results of visual tests using rIL-2 coated fluorescent Covaspheres demonstrate that the human mediator will bind cells of the toad spleen. Moreover, the mediator inhibits binding of the antibody against the human IL-2 receptor, as detected by cytofluorimetry. Some of the IL-2 receptors on the toad cells appear to be constitutive, since they are expressed on freshly biopsied lymphocytes. Activation of these cells in vitro will increase the percentage of those cells able to bind both the anti-receptor antibody and rIL-2. Since the human mediator is only able to modulate in vivo immune activity in antigen-activated toads, it appears that in spite of having some constitutive IL-2 receptors, a quantitative increase in receptor expression is required before immunological behavior can be effected. More stringent controls of receptor expression may have provided an additional regulatory level as mammalian mechanisms evolved.

Animals↗
PubMed1987

Compromised T-cell regulatory functions during anuran metamorphosis: the role of corticosteroids.

Glucocorticoid receptor concentrations, which are undetectable before metamorphosis, increase to a maximum during the metamorphic period and decline to toadlet levels thereafter. The generation of a high concentration of receptors, imparting enhanced glucocorticoid sensitivity particularly to the lymphoid tissues of metamorphic larvae suggests the possibility that increasing endogenous levels could be responsible for the compromised T-cell functions which have been described for these stages of development (Ruben et al, 1985a).

Adrenal Cortex Hormones↗
PubMed1987

Signals provided in vivo by human rIL-2 and Con A can switch hapten-specific tolerance from unresponsiveness to responsiveness in the South African clawed toad.

Injection in vivo of trinitrobenzene sulphonic acid (TNBS) will conjugate trinitrophenyl (TNP) to the cells and proteins of rodents, and induce hapten-specific tolerance to this epitope. However, the induction of hapten-specific tolerance by this method in the South African clawed toad, Xenopus laevis, is restricted to its subsequent presentation on Ficoll or polyvinylpyrrolidone (PVP). This restricted tolerance depends on the stimulation of an N-methyl-N-nitrosourea (NMU)-insensitive, cyclophosphamide (CyP)-sensitive hapten-specific (suppressor) population that is functionally demonstrable in vitro. Unresponsiveness to TNP-Ficoll can be switched to responsiveness by injection in vivo of recombinant DNA-produced human IL-2 (rIL-2) or the plant-derived lectin, concanavalin A (Con A). Responsiveness to TNP-Ficoll requires thymic presence, although thymic extracts from rIL-2- or Con A-injected toads will suffice. Unresponsiveness to TNP-PVP can also be broken by these reagents, but thymic presence is not required with this immunogen. TNP-Ficoll responses are thymus requiring, while those to TNP-PVP are not, in the toad. Since TNBS failed to stimulate hapten-specific tolerance to a secondary challenge to TNP-Ficoll, we suggest that the suppressor function involved in the establishment of the unresponsive state may act on the differentiation, rather than on the function, of the relevant B cells.

Animals↗
PubMed1986

Recombinant DNA produced human IL-2, injected in vivo, will substitute for carrier priming of helper function in the South African clawed toad, Xenopus laevis.

The studied included in this report tested the ability of a recombinant DNA produced human lymphokine (rIL-2) to serve as a substitute for the carrier priming required for the in vivo generation of anti-hapten responses, in young adults of Xenopus laevis, the South African clawed toad. Heterologous erythrocyte carriers were used. Immune reactivity was monitored with hapten-specific antigen binding cells (ABC) in spleen cell suspensions, 8 days after injection i.p. of trinitrophenylated sheep erythrocytes (TNP-SRBC) or rIL-2 or the two together. No substantial anti-hapten responses were generated by either TNP-SRBC or rIL-2 alone. However, a greatly (9X) enhanced anti-TNP response was produced after co-injection. By varying the time between injection of the rIL-2 and the TNP-SRBC challenge, it was found that the effectiveness of this mediator would last for up to three hours in this animal. When rIL-2 was co-injected with an optimal priming dose of SRBC, two days prior to TNP-SRBC challenge, it did not enhance the level of helper function generated by carrier priming. Therefore, it is likely that the rIL-2 acts on the same cells affected by carrier priming which is maximally efficient in this regard. Thus, cells, which participate in the generation of helper function in this primitive species, are sensitive to human rIL-2. The universality of an immune regulatory molecule of this kind is considered.

Animals↗
PubMed1986

The phylogeny of macrophage function: antigen uptake and degradation by peritoneal exudate cells of two amphibian species and CAF1 mice.

Equal numbers of thioglycollate mobilized peritoneal exudate cells (PEC) of the newt, Notophthalmus viridescens, the South African clawed toad, Xenopus laevis, and CAF1 mice were compared with respect to their capacity to take up and degrade soluble 14C-ovalbumin (OVA). PEC of the newt failed to take up the labeled antigen, while those of the toad incorporated only one-half as much as those of the mice. Moreover, the toad PEC degraded only 42% of the immunogen which was taken up, while PEC of the mice degraded 78% of the immunogen they had ingested during the 60-min period. Paraformaldehyde treatment of the PEC prevented antigen uptake, while chloroquine treatment prevented degradation with both species, and thus, active processes were involved. While newt PEC were unable to ingest soluble OVA, they were able to ingest and degrade OVA conjugated to sepharose during the same time period. The failure of primitive vertebrates to respond immunologically to soluble proteins appears to be due to their failure to ingest soluble immunogen.

Animals↗
PubMed1986

The development of inducer and effector immune suppressor cell function in Xenopus laevis, the South African clawed toad: the effect of metamorphosis.

Thymic capacity to induce suppression of antibody production by immunized Xenopus laevis toadlet spleen fragments was tested in co-cultures for different developmental stages (Nieuwkoop, P.D. and J. Faber: Normal Table of Xenopus laevis (Daudin) (North Holland, Amsterdam) 1967). While thymuses of stages 52-54 (premetamorphosis) induced suppression, those of stages 58-62 (metamorphosis) did not. This capacity returned in metamorphic climax (stages 63-65). Tests of lectin-induced suppressor function in spleens of different developmental stages exposed the same pattern of compromised activity during metamorphosis. To test whether larval thymuses could effect suppression, rather than just induce it, antigen-activated thymuses from the different stages were co-cultured with immunized toadlet spleen fragments which had been suppressor-depleted by cyclophosphamide. Only thymuses from premetamorphic larvae suppressed. Thus, when thymic capacity to induce suppression returned in metamorphic climax, it was adult-like: it lacked effector suppressor cells.

Animals↗
PubMed1986

Two cellular pathways regulate the response to TNP-Ficoll in Xenopus laevis.

The initiation of the anti-TNP response to TNP-Ficoll in the amphibian Xenopus laevis has been studied. Although the response to this antigen is thymus independent in mammals, it is thymus dependent for the first three days following immunization in Xenopus. This thymus regulation is not MHC restricted, since it can be substituted for by thymus xenografts, and by prior or co-injection of heterologous red blood cells or Concanavalin A. The pathway which is activated by the Con A to substitute for the thymus is NMU sensitive, unlike the thymic pathway. The peripheralised alternative pathway is activated by particulate but not soluble TNP-Ficoll. The thymus-dependent and alternative pathways are discussed in terms of their possible nature, regulation and evolutionary significance.

Animals↗
PubMed1986

Thymic involvement in memory responses after primary challenge with TNP-Ficoll in Xenopus laevis, the South African clawed toad.

Memory to TNP-Ficoll in Xenopus laevis is demonstrable as a more rapid secondary response rather than an augmented response. While adult thymectomy abrogates ability to respond to both primary and secondary challenge with soluble TNP-Ficoll, memory to this antigen can be revealed in thymectomized animals by challenge with TNP-Ficoll on bentonite beads. Memory to TNP-Ficoll cannot be revealed by secondary challenge with TNP-LPS or TNP-RBC, but memory to TNP-LPS is revealed by TNP-Ficoll challenge. These results are consistent with the hypothesis that, whereas B1 cells (capable of responding to TI-2 antigens) can develop from a pool of B1 and B2 memory cells (generated in response to TD or TI-1 antigens), initial challenge with TI-2 antigen does not produce a pool containing both B-cell subsets.

Animals↗
PubMed1985

Murine and human interleukin 2 can substitute for the thymus in immune responses to TNP-Ficoll in Xenopus laevis, the South African clawed toad.

Extirpation of the thymuses of Xenopus laevis abrogates the capacity to respond to trinitrophenol (TNP)-Ficoll regardless of the age of the animal. This thymus requirement can be substituted for by a variety of treatments which stimulate thymus-derived (T)cell activity in the periphery, such as the rejection of allogeneic skin grafts, immunologic challenge with thymus-dependent immunogens, (e.g., heterologous erythrocytes), or plant-derived lectins (e.g., concanavalin A). Here we report that interleukin 2 (IL-2), a T-cell-produced hormone of mammalian origin also substitutes for this thymus requirement in thymectomized toads.

Animals↗
PubMed1985

Suppression in Xenopus laevis: thymus inducer, spleen effector cells.

Studies were carried out on suppressor function in the amphibian Xenopus laevis, the South African clawed toad. Suppression by the thymus of haemagglutinin (HA) production by spleen is antigen-dependent, partially specific and not MHC-restricted in this species (Ruben, Buenafe & Seivert, 1983). Three questions were considered in this study. Does the thymus effect suppression by stimulating peripheralized spleen effector cells, or do effector cells reside within the thymus? Do macrophages participate in the induction and/or expression of thymus-dependent suppressor function? Can thymus suppressor and helper functions be distinguished by using irradiation treatment? The capacity of immunized thymus to suppress HA when co-cultured with spleen fragments from immunized, cyclophosphamide (CyP)-injected animals was tested. Immunized thymus failed to suppress the high levels of HA production by spleen fragments from CyP-treated, immunized donors. Colloidal carbon injection resulted in blockade of macrophage function, and both the capacity of thymuses to suppress and of spleens to be suppressed in co-cultures. Finally, the effect of thymus exposure to gamma-irradiation in vitro was tested using autogeneic thymus/spleen combinations. This enabled the visualization of thymic helper function, which is MHC-restricted in Xenopus (Bernard et al., 1981). Four dosages of irradiation were tested after antigen challenge. The highest HA titres were produced by spleen co-cultures with thymuses which had received 1000 rads. We conclude that suppression of HA production in spleen is not the result of thymus suppressor effector cells, but that suppressor function is mediated by thymus inducer cells which stimulate suppressor effectors in spleen. Both the thymic inducers and effectors in the spleen are sensitive to CyP and macrophage blockade. Our studies further suggest that we are able to distinguish between the thymic functions of help and suppression in Xenopus by taking advantage of their differential sensitivities to irradiation. While it has been postulated, on other grounds, that suppression was one of the earliest thymic regulatory functions to have evolved (L.N. Ruben & R.H. Clothier, submitted), here we suggest the presence of sequential activities of more than one cellular subset, as early in evolution as the primitive anuran (tail-less) amphibia.

Animals↗
PubMed1985

Lectin effects on thymic suppression of hemagglutinin production in vitro by spleen fragments from Xenopus laevis, the South African clawed toad.

Suppression of hemagglutinin (HA) production was studied in co-cultures of thymus and spleen fragments from the South African clawed toad, Xenopus laevis. Concanavalin (Con)A and peanut (PNA) and wheatgerm (WGA)agglutinins were tested in conjunction with, or as a substitute for antigenic induction of thymus suppression. While thymuses from animals injected with PNA or WGA and antigen expressed suppressor function, those treated with Con A and antigen did not. Spleen fragments from animals challenged with PNA or WGA and antigen were resistant to suppression by normal thymus in reciprocal co-cultures; those receiving Con A and antigen alone were equally suppressible. All three lectins can substitute for antigen in the induction of thymus suppression. However, only PNA and WGA induce suppressor function in Xenopus spleen. Since WGA can induce splenic suppression in adult thymectomized animals, it is now possible to distinguish thymic and peripheral aspects of suppression of HA in this primitive vertebrate.

Animals↗
PubMed1984

Immunologic reactivity to TNP-Ficoll during development and ageing in Xenopus laevis, the South African clawed toad.

The immunological response of Xenopus laevis to haptenated Ficoll was examined throughout development. The capacity to respond to TNP-Ficoll originated with the first appearance (at stage 48, 8 days post-fertilisation) of mature thymic lymphocytes, and preceded the ability to respond to heterologous erythrocytes. During premetamorphosis the response increased, while during prometamorphosis , particularly at stages 57-58, there was a marked reduction. The response recovered during the metamorphic climax and immature adult stages, increasing further at the onset of sexual maturity. The reduced response during prometamorphosis parallels the reported reduction in other thymus-dependent responses.

Aging↗
PubMed1984

Genetic limits of thymic immunosuppression of anti-hapten antibody production in Xenopus laevis laevis, the South African clawed toad.

Thymic immunosuppression in adult Xenopus laevis laevis, the South African clawed toad, is antigen-dependent and antigen-specific, but it is not genetically restricted. In this report, we show that combination in vitro with a thymus from an immunized Xenopus laevis laevis can suppress antibody production to a hapten from spleen fragments, if the spleen fragments are derived from a subspecies of Xenopus laevis or a species of Xenopus which shares the same diploid chromosome number (2N = 36). Some aspects of the evolution of thymic immunosuppression are considered in the light of these results.

Animals↗
PubMed1984

Lectins and substitution for helper function in anti-hapten responses in Xenopus laevis.

Substitution by lectins for the carrier-priming requirement in thymus-dependent, antigen-binding responses in Xenopus laevis has been examined. Concanavalin A (Con A) was found to substitute for carrier priming in control, early-thymectomized and adult-thymectomized animals, but not in animals given a single, high dose of N-methyl-N-nitrosourea, which has a permanent effect on certain thymus-dependent functions in this species. Lipopolysaccharide and other lectins, such as peanut agglutinin and wheat germ agglutinin, were unable to substitute for carrier priming. These effects of Con A are discussed in terms of substitution via amplifier T cells or a helper T cell subset.

Age Factors↗