PubMed Health⌕ Search

Biomedical subjects

B E Torbett

Publications and source records attributed to B E Torbett.

At least 19 recordsLinked to original sources
PubMed1994

Cloned human CD8+ cytotoxic T lymphocytes protect human peripheral blood leukocyte-severe combined immunodeficient mice from HIV-1 infection by an HLA-unrestricted mechanism.

The ability to infect human peripheral blood leukocyte-reconstituted severe combined immunodeficient (hu-PBL-SCID) mice with HIV has allowed evaluation of several strategies for preventing or treating infection. In one study, hu-PBL-SCID mice derived from HIV gp160-vaccinated donors were shown to resist HIV infection, and resistance correlated best with in vitro assays of cellular immunity. We have assessed directly the importance of cellular immunity to HIV in the present experiments by the adoptive transfer of HLA-A3-restricted HIV-1 Nef-specific or HLA-B14-restricted Gag-specific CD8+ CTL clones to SCID mice bearing HLA-matched or mismatched PBL grafts. Multiple inoculations of CTL before and after HIV-1 exposure protected HLA-matched hu-PBL-SCID mice from infection, but initiation of CTL therapy on the same day as HIV infection was much less effective. However, at the high numbers of CTL required for complete protection from HIV infection, many HLA-mismatched hu-PBL-SCID mice were also protected by pre-exposure CTL transfer. Transfer of CTL with a different specificity (HTLV-1 Tax) to HLA-matched hu-PBL-SCID mice also afforded partial protection. These results suggest that HLA-restricted cytotoxicity may be less important than other nonspecific effector mechanisms for the inhibition of HIV-1 infection in vivo.

Animals↗
PubMed1994

Human immunodeficiency virus type 1 infection of neonatal severe combined immunodeficient mice xenografted with human cord blood cells.

In these studies, neonatal C.B-17 severe combined immunodeficient (nSCID) mice were reconstituted with human cord blood leukocytes (hu-CBLs). The resulting hu-CBL-nSCID mice contained readily detectable human CD3+ T lymphocytes and CD20+ human B cells, and produced substantial levels of human IgM and IgG (including all subclasses). Human cells persisted in lymphoid organs and peripheral blood for at least 8 weeks, and CD4+ T cells outnumbered CD8+ T cells. Engraftment of human cells in peripheral lymphoid organs and blood was much greater than that seen in adult SCID mice grafted with adult peripheral blood leukocytes (PBLs). Hu-CBL-nSCID mice were susceptible to infection with laboratory-adapted and fresh clinical human immunodeficiency virus type 1 (HIV-1) isolates. Following infection with HIV-1, virus could be recovered by the coculture of spleen, lymph node, peritoneal cavity, liver, and plasma samples from hu-CBL-nSCID mice with fresh human peripheral blood mononuclear cells, and proviral copies were detectable following amplification using the polymerase chain reaction (PCR). HIV p24 core antigen levels in hu-CBL-nSCID mouse plasma were consistent with ongoing viral replication and high viral burdens. Rapid CD4+ T cell depletion occurred following infection with laboratory isolates of HIV-1 or a syncytium-inducing clinical isolate, but a non-syncytium-inducing clinical isolate caused expansion of CD8+ T cells, leading to an inversion of the CD4:CD8 ratio with only a transient decrease in CD4+ T cells. These results suggest that the hu-CBL-nSCID mouse system has unique features that mimic certain aspects of pediatric HIV infection, and distinguish it from other animal models of HIV infection, including the related hu-PBL-SCID model.

Animals↗
PubMed1994

Physiological T-cell death: susceptibility is modulated by activation, aging, and transformation, but the mechanism is constant.

It is not surprising that the recent explosion of interest in physiological cell death has been centered particularly on lymphocytes. Physiological cell death responses are singularly important in the biology of T lymphocytes, especially in the establishment and maintenance of a diverse, non-autoreactive, and self-limiting repertoire. Cell death responses can be triggered in T cells by a variety of stimuli; sensitivity to these inducers is altered as a function of differentiation, activation, aging, and transformation. The elimination of autoreactive T cells occurs by a process that involves comitogenic stimulation at high dose with antigenic and/or mitogenic agents. The control of susceptibility to this activation-driven cell death with differentiation and with prior activation provides a mechanistic explanation for the development of central and peripheral tolerance. Enhanced lymphocyte activation with aging also leads to an augmented activation-driven cell death response. However, aging does not alter cell death responses generally, and aging-associated changes in cell death responses cannot account for aging-associated immunopathology. Oncogenic transformation also alters the activation-driven cell death response by supplanting one of the required signals for activation-driven cell death. This difference provides a rationale for selective anti-tumor therapy. A single mechanism underlies all cases of physiological cell death and involves out-of-phase mitotic activity. We now know that of the two hallmarks of cell death, genome digestion is dispensable and mitotic-like events associated with cell cycle arrest are critical. T cells triggered to undergo physiological cell death arrest in a post-mitotic compartment of the cell cycle and die when they attempt a precocious and abortive mitosis.

Aging↗
PubMed1993

Rapid loss of CD4+ T cells in human-PBL-SCID mice by noncytopathic HIV isolates.

Human immunodeficiency virus (HIV) isolates differ in cell tropism, replication, pathogenicity, and syncytial induction in vitro. CD4+ T cells were enumerated in severe combined immunodeficient mice transplanted with human peripheral blood leukocytes (hu-PBL-SCID mice) and infected with HIV isolates with different in vitro cytopathicity. Two noncytopathic, macrophage-tropic strains, HIV-1SF162 and HIV-2UC1, induced extensive CD4+ T cell depletion, whereas HIV-1SF33, which is highly cytopathic for T cells in vitro, caused little CD4+ T cell depletion at equivalent virus burden. In vitro cytopathicity assays therefore do not predict CD4 depletion in the hu-PBL-SCID model.

Animals↗
PubMed1993

Patterns of cytokine gene expression by CD4+ T cells from young and old mice.

We have analyzed the patterns of induced cytokine gene expression and cell cycle activity by CD4+ cells from mice, and have examined how these response patterns change during the aging process. CD4+ cells were isolated from spleens of young adult and old C57BL/6NNia mice and were stimulated in vitro with plate-bound anti-CD3 epsilon mAb. The cells were then assessed over time for the capacity to accumulate transcripts for IL-1 alpha, IL-1 beta, IL-2, IL-3, IL-4, IL-5, IL-6, IFN-gamma, TNF-alpha, and TNF-beta; to secrete IL-2, IL-3, IL-4, IL-5, IL-6, and IFN-gamma; and to progress through S phase. Before the first major cell division in culture (< 32 h), stimulated CD4+ cells of the old group contained similar peak levels of IL-2, TNF-alpha, and TNF-beta transcripts relative to young adult controls, whereas IL-3, IL-4, IL-5, and IFN-gamma transcripts accumulated to significantly higher peak levels in the old group. These findings were consistent with the patterns of cytokine secretion later in culture (24 to 72 h): the peak IL-2 levels were similar between age groups, but the old group exhibited an enhanced capacity to release IL-3, IL-4, IL-5, and IFN-gamma. In contrast, CD4+ cells of the young group were superior in the hyper-expression of the housekeeping gene, rpL32, before cell division and in the levels of S phase activity throughout 3-day cultures. Similar analyses of CD4+ cells from mice of intermediate ages showed that the alterations in cytokine profiles occurred gradually from young adulthood to old age, whereas the reductions in proliferative capacity were late life changes. Consistent with previous reports, we found that the splenic CD4+ cell group also underwent a progressive, age-dependent increase in the proportions of cells expressing high levels of membrane CD44 (a phenotype associated with memory or effector cells). Moreover, the analysis of IL-3, IL-5, and IFN-gamma production by isolated CD4+CD44lo and CD4+CD44hi cells revealed that the capacity to produce these cytokines segregated predominantly with the CD44hi subset, regardless of donor age. Taken together, our data suggest that gradual age-associated shifts in the subset composition of the splenic CD4+ cell pool underlie progressive changes in the patterns of cytokine gene expression by this cell group.

Aging↗
PubMed1993

Homozygous scid/scid;beige/beige mice have low levels of spontaneous or neonatal T cell-induced B cell generation.

The autosomal recessive scid mutation results in defective immunoglobulin and T cell receptor gene rearrangement. The scid mutation occurred in the allotype congenic C.B-17 line, and up to 25% of C.B-17 scid mice spontaneously produce both T cells and immunoglobulin, a phenotype known as "leaky." Moreover, introduction of neonatal T cells into C.B-17 scid mice leads to immunoglobulin production by 100% of animals. We have produced mice homozygous for both the scid and beige mutations. By contrast with C.B-17 scid mice, BALB/c scid.beige mice have a < 2% incidence of "leakiness." This percentage does not increase with age, and introduction of neonatal T cells fails to rescue immunoglobulin production. This suggests that a gene (or genes) closely linked to the beige locus regulates B and/or T cell development.

Animals↗
PubMed1993

The expression of CD45RB on antigen-responsive CD4+ lymphocytes: mouse strain polymorphism and different responses to distinct antigens.

The levels of CD45RB expression by HGG-specific CD4+ cells residing in the Ag-draining lymph nodes of HGG-primed CBA/CaJ mice were analyzed. When sorted populations of CD4+, CD45RBhi, and CD4+, CD45RBlo cells were cultured with HGG and Ag-presenting cells, the majority of the proliferative response was found in the CD45RBlo fraction early after in vivo priming (Day 6), and this pattern remained stable through 12 days postpriming. To determine whether this segregation of responsiveness was consistent in other mouse strains, HGG-primed C57BL/6J mice were similarly analyzed. In contrast to findings with the CBA/CaJ strain, the CD4+, CD45RBhi cell fraction obtained from C57BL/6J mice was the predominant responding population early after in vivo priming (Day 6); however, there was a parallel increase in responsiveness of CD4+, CD45RBhi, and CD4+, CD45RBlo cells by Day 12. Thus, there was not a decrease in CD45RBhi expression with a concommitant increase in CD45RBlo expression in CD4+ cells proliferating to HGG. Despite the heterogeneity in CD45RB expression by the primed CD4+ cells of the two strains, the entire proliferative response to HGG early after priming resided in the fraction bearing high levels of membrane CD44, thus arguing for the existence of CD45RBhi, CD44hi and CD45RBlo, CD44hi cells during the early phase of the response. In both mouse strains the CD4+, CD45RBhi subset of primed lymph node cells produced significant levels of IL-2 in response to HGG and APC, whereas no significant IL-2 or IL-4 production was detectable in HGG-stimulated CD45RBlo cells of either strain. The CD4+, CD45RBhi subset also proliferated more vigorously in response to polyclonal activation than the CD4+ CD45RBlo fraction. To examine whether the patterns of CD45RB expression on HGG-primed cells from C57BL/6J mice were common to other antigens, the response profiles were examined after in vivo priming with a second antigen, KLH. In contrast to studies with HGG as the Ag, the proliferative response to KLH in C57BL/6J mice was evenly divided among the CD45RBhi and CD45RBlo fractions on Day 8 after priming, but shifted markedly to the CD45RBlo fraction by Day 12 after priming. Taken together, these data show that the patterns of CD45RB expression on primed populations of CD4+ cells can exhibit mouse strain polymorphism and can differ depending on the choice of antigen for immunization.

Animals↗
PubMed1992

CD4 is expressed on murine pluripotent hematopoietic stem cells.

We show here for the first time that pluripotent hematopoietic stem cells express the CD4 antigen. CD4+ cells isolated from mouse marrow repopulated all hematopoietic lineages in both the long-term repopulation assay and the competitive repopulation assay. This finding indicates that the CD4+ population contains primitive stem cells with extensive repopulation capacity. Interestingly, the CD4- population had significant life-sparing activity, even though this population was depleted of long-term repopulating stem cells when compared with CD4+ cells. The majority of the cells that respond to the stroma in Whitlock-Witte cultures with B-cell differentiation were recovered in the CD4- population. Thus, this bone marrow (BM)-derived B-cell precursor lacks CD4, which is in contrast to myeloid precursors and thymus-derived lymphoid precursors that reportedly express CD4. We show further that the CD4 molecule expressed on BM cells is similar in molecular weight and epitope makeup to the CD4 antigen found on thymocytes. Detection of CD4 on BM cells is dependent on using high concentrations of antibodies. Thus, it is not surprising that expression of CD4 on pluripotent stem cells has been missed previously. Taken together, our data suggest that the CD4 molecule may play an important role in lineage definition in early hematopoietic differentiation.

Animals↗
PubMed1992

EBV-induced human B cell lymphomas in hu-PBL-SCID mice.

Epstein-Barr virus (EBV) infection is associated with Burkitt's lymphoma (BL) in normal individuals and immunoblastic B cell lymphomas in immunosuppressed or HIV-infected individuals. SCID mice reconstituted with human peripheral blood leukocytes (hu-PBL-SCID) from EBV-seropositive donors also may develop spontaneous B cell lymphomas which histologically and phenotypically resemble post-transplant tumors, and are distinct from BL. These tumors always contain EBV DNA. We have noted three different reproducible outcomes depending upon the EBV-seropositive donor used for generation of hu-PBL-SCID mice: (i) no tumors appear; (ii) tumors appear in a fraction of hu-PBL-SCID mice with a 10-20 wk. latent period; or (iii) tumors appear in all hu-PBL-SCID mice within 6-10 wk. Southern blot analysis of late versus early tumors using a probe specific for the EBV terminal repeat sequences (BamNJ), which allows distinction between circular latent and linear replicating genomes, shows that late tumors do not involve active EBV replication but that early tumors do show replicating genomes. In addition, EBV genomes were monoclonal in late tumors but polyclonal in early tumors. These data suggest two mechanisms for EBV lymphomagenesis, slow outgrowth of rare latently-infected B cells, and more rapid transformation of uninfected bystander B cells by replicating virus. The latter process may be highly amenable to therapy in patients at risk for EBV-related lymphomas. In addition, prospective screening of EBV-seropositive transplant recipients in the hu-PBL-SCID model may predict the risk of post-transplant lymphoma development.

Animals↗
PubMed1991

Break for SCIDs.

Explore the source record for details and available documents.

Animals↗
PubMed1991

Cell proliferation and cytokine production by CD4+ cells from old mice.

Splenocytes from young adult or old C57BL/6NNia mice were stimulated in vitro with the anti-CD3 epsilon mAb, 145-2C11, in either soluble (2C11s) or plate-bound (2C11i) form. In the young group, each mode of cell activation resulted in peak DNA synthesis at approximately 48 h of culture; at this time point, the old group exhibited response levels to 2C11s or 2C11i that were approximately 40% of those in the young group. However, in the presence of 2C11i, splenocytes from old donors showed a delayed peak response which approached the peak levels attained in the young group. To analyze the responsiveness of the CD4+ T cell subpopulation, this cell type was isolated from spleens of young or old mice and was stimulated in vitro with 2C11s or 2C11i, in the presence or absence of added accessory cells (T cell-depleted, irradiated splenocytes). The induction of DNA synthesis by 2C11s was accessory cell dependent, and the response in the old group were markedly reduced in comparison to those in the young group. In contrast, stimulation of DNA synthesis with 2C11i was relatively accessory cell independent, resulted in higher response levels in both age groups, and lessened the disparity between age groups. The analysis of IL-2 and IL-4 secretion by stimulated CD4+ cells revealed that, in response to 2C11s and accessory cells, only IL-2 accumulation was detectable and the levels in the young group were approximately 10-fold higher than the IL-2 levels in the old group. However, stimulation of CD4+ cells with 2C11i and accessory cells yielded improved IL-2 production and a detectable IL-4 response in the old group, whereas the young group exhibited a response profile similar to that induced by 2C11s. Further analysis of the IL-2, IL-4, and IFN gamma mRNA levels in 2C11i-stimulated CD4+ cells revealed that old donor cells accumulated similar levels of IL-2 transcripts, but higher levels of IL-4 and IFN gamma transcripts, than young donor CD4+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

Differences in the expression profiles of CD45RB, Pgp-1, and 3G11 membrane antigens and in the patterns of lymphokine secretion by splenic CD4+ T cells from young and aged mice.

Previous studies indicate that the 3G11, CD45RB, and Pgp-1 determinants are differentially expressed on CD4+ T cell subsets in the mouse. We used multicolor immunofluorescence staining and flow cytofluorometric analysis to examine the expression of each of these determinants on splenic CD4+ cells from young (age 3 to 6 mo) and aged (age 24 to 26 mo) C57BL/6 mice. The CD4+ pool from aged mice contained significantly reduced numbers of 3G11+ and CD45RBhi cells, but increased numbers of Pgp-1hi cells, in comparison with the young group. Analysis of the simultaneous expression of all three subset determinants on CD4+ cells revealed that, in young mice, the major fraction (greater than 50%) was 3G11+CD45RBhiPgp-1lo. Among the less prevalent cell phenotypes, reductions in 3G11 expression correlated with decreases in CD45RB levels and increases in Pgp-1 levels. The phenotype that dominated the young group (3G11+CD45RBhiPgp-1lo) was approximately fivefold less represented in the aged group. The CD4+ pool from aged mice was characterized by increases in the 3G11-CD45RBvariablePgp-1hi and the 3G11+CD45RBloPgp-1hi phenotypes. To evaluate possible age-associated differences in cytokine secretion patterns by splenic CD4+ cells, purified CD4+ cells from each age group were stimulated in vitro with immobilized anti-CD3 epsilon mAb and accessory cells. At various times thereafter, supernatants from cultures were tested for IL-2 and IL-4 content by using the CTLL.6 and 11.6 bioassays, respectively, and the CD4+ cells were assayed for [3H]TdR uptake. Cell cultures from the aged group exhibited similar peak IL-2 accumulation and lower peak [3H]TdR uptake, but greatly increased peak IL-4 accumulation, as compared with cell cultures from the young group. The expression patterns of subset determinants, in conjunction with cytokine secretion profiles, indicate that, in aged mice, marked alterations occur in the subset composition of the splenic CD4+ cell pool. These findings are discussed in the context of previous findings on changes in T cell reactivity with advancing donor age.

Aging↗
PubMed1990

Frequencies of T cells secreting IL-2 and/or IL-4 among unprimed CD4+ populations. Evidence that clones secreting IL-2 and IL-4 give rise to clones which secrete only IL-4.

We have utilized a limiting dilution assay, involving a minimum of in vitro culture, to determine the frequencies of CD4+ T cells which have the capacity to secrete IL-2 (Th1), IL-4 (Th2) or IL-2 and IL-4 (Th0). CD4+ lymph node cells obtained from unimmunized mice were found to contain 40% Th1, 34% Th2, and 26% Th0 cells. The fact that Th0 cells could be identified in cell populations obtained from unimmunized mice suggested a possible role for Th0 in the differentiation pathways of Th1 and Th2. Antigen-specific Th0 clones were thus established and observed to convert to a Th2 phenotype after prolonged culture. The relevance of these findings is discussed in the context of current models of CD4+ T cell subsets.

Animals↗
PubMed1989

A new murine CD4+ T cell subset with an unrestricted cytokine profile.

CD4+ T cell clones were derived from mice immunized to keyhole limpet hemocyanin to characterize the cytokine profiles of newly isolated clones. Surprisingly, several of the clones had an unrestricted profile, producing IL-2, IL-3, IL-4, IFN-gamma, and TNF after either Con A or Ag stimulation. The coproduction of IL-2 and IL-4 was confirmed at the mRNA level. Subclones were derived which contained RNA transcripts for, as well as secreted, both IL-2 and IL-4 thus confirming the clonality of the original T cell clones. CD4+ T cell clones that expressed an unrestricted cytokine profile upon Con A stimulation were also isolated from mice immunized to other Ag (hen egg lysozyme, OVA, or type II collagen). These data indicate that CD4+ T cell clones newly isolated from immunized mice do not necessarily segregate into the Th1 and Th2 subsets. We propose this new murine CD4+ cell subset with an unrestricted pattern of cytokine production be called Th0.

Animals↗
PubMed1988

Cloned cytotoxic T lymphocytes as target cells. II. Polarity of lysis revisited.

The original polarity of lysis experiments suggested that CTL are themselves sensitive to whatever mechanism it is that CTL use to lyse their targets. This concept has placed certain limitations on possible mechanisms of lysis by CTL. Recently, we found in studies with cloned CTL as targets that cloned CTL are in fact highly resistant to lysis by other CTL, as well as to their cytotoxic granule proteins. We show here that although cloned CTL are extremely resistant to lysis by primary and cloned CTL, they are readily inactivated functionally by all primary CTL and by at least one CTL clone. Moreover, cloned CTL are also functionally inactivated by cytotoxic granule proteins. The activation of CTL, which we call inhibitin, is Ca2+ insensitive and distinct from hemolytic activity, and is, thus, unlikely to be perforin. These experiments suggest a possible alternative interpretation of the original polarity of lysis experiments.

Animals↗
PubMed1988

The role of accessory molecules in T-helper activation induced by antigen, lectin, or CD3 antibodies.

We examined the role of L3T4 and LFA-1 molecules in T-helper-cell activation, under conditions where the physical stability of T helper-accessory cell interactions was not an issue. T-helper hybridomas were activated by accessory cells coated either with concanavalin A (Con A) or with CD3 antibodies. Activation of the T helper cells was measured by microtubule-organizing center (MTOC) reorientation as an early activation event, and by interleukin-2 (IL-2) production as an indication of a fully matured response. Both parameters were strongly blocked by L3T4 and LFA-1 antibodies in the case of Con A activation. In the case of stimulation with accessory cell-bound CD3 antibody, activation was blocked by LFA-1 but not L3T4 antibody. These results support the notion that L3T4 and LFA-1 molecules play more than a simple adhesion role in T-cell activation. The differential effect of L3T4 antibody in the case of Con A activation vs CD3 activation is consistent with the possibility that L3T4 and the alpha/beta portions of the T-cell receptor must interact during antigen- and lectin-stimulated T-cell activation.

Animals↗
PubMed1986

Multiple pathways for antigen-independent activation of a T helper hybridoma.

An important question in mitogen activation of T cells is whether the T cell must interact with a major histocompatibility complex product during the activation process. The T helper hybridoma AODH 7.1 is specific for human gamma globulin in the context of IEd, and when activated secretes interleukin 2. The mitogen concanavalin A (Con A) can activate AODH 7.1 cells directly, but two other standard T cell mitogens, phytohemagglutinin (PHA) and neuraminidase-galactose oxidase, cannot. However, Con A, PHA and neuraminidase-galactose oxidase could all activate AODH 7.1 when presented on various cloned class II+ cell lines. There was an absolute requirement for the presentor cell to be class II+, and the activation signal on mitogen-treated class II+ presentor could be blocked by monoclonal antibody to the class II antigens. To determine if class II molecules were absolutely required for the presentation of a mitogen activation signal we used class II- LtK- L cells and two LtK- cell class II gene transformants as presentor cells. Only the class II+ transformants, but not the class II- LtK- cells, could present either Con A or PHA. The class II requirement cannot be bypassed through provision of soluble factors. However, when Con A was used to activate AODH 7.1 cells directly, it appeared to be acting in a transmembrane fashion. It was not the case that AODH 7.1 cells were responding to Con A on a neighboring AODH 7.1 cell, and no class II antigens were involved. These results are consistent with the idea that different routes of activation exist for T cells, at least at the level of signal recognition.

Animals↗