Biomedical subjects

H R MacDonald

Publications and source records attributed to H R MacDonald.

At least 109 records · Page 6Linked to original sources

PubMed1994

Differential effects of superantigen-induced "anergy" on priming and effector stages of a T cell-dependent antibody response.

The in vitro T cell nonresponsiveness or anergy to restimulation with staphylococcal enterotoxin B (SEB) following the in vivo injection of the superantigen is well characterized. Here we use mice transgenic for a V beta 8.2+ T cell receptor (TcR) (reactive with SEB) to establish a large population of anergic T cells in vivo. As expected, peripheral T cells from the SEB injected transgenic mice failed to proliferate or produce interleukin (IL)-2 following restimulation with the superantigen in vitro. However, in this system superantigen reactivity could be restored by either addition of exogenous IL-2, or stimulation with immobilized anti-TcR antibody. To evaluate the effects of superantigen-induced anergy in vivo, SEB-injected or noninjected control transgenic mice were immunized and boosted with the T cell-dependent antigen tetanus toxin (TT). SEB injection of the V beta 8.2+ transgenic mice 5 days prior to the TT immunization inhibited the anti-TT antibody response as measured over a 100-day period, whereas injection of a superantigen which does not interact with the V beta 8.2% TcR (such as SEA) did not. Furthermore, SEB injection of control nontransgenic mice did not interfere with the induction of a high titer anti-TT antibody response. In contrast to the inhibition seen when SEB was given prior to TT immunization, injection of transgenics with SEB either after the priming TT immunization or after the recall booster injection did not significantly influence the titers of anti-TT antibodies produced. These results demonstrate that the establishment of peripheral T cell anergy to superantigens inhibits the specific antigenic priming of helper T cells in vivo, but does not prevent primed T cells from helping B cells to mount an effective antibody response.

Animals↗

PubMed1994

Selective expansion of activated V delta 4+ cells during experimental infection of mice with Leishmania major.

Previous work from this laboratory has revealed that infection of mice with Leishmania major leads to an expansion of gamma delta+ T cells in the spleen. Further examination of the gamma delta+ T cells expanding in infected mice has shown that the majority of these cells in the spleen, lymph nodes, blood and liver expressed the V delta 4 gene segment. Cell cycle analysis, using propidium iodide incorporation, demonstrated that while only 1% of alpha beta+ T cells in the spleen were in either S + G2/M phase, up to 10% of the gamma delta+ T cells were in cycling phase 8 weeks after infection. Comparison of the state of activation of the two populations in different organs after infection, confirmed that gamma delta+ T cells are actively dividing in lymph nodes, liver and blood, but not in the thymus or among intraepithelial lymphocytes. Examination of the expression of different activation markers on the surface of gamma delta+ T cells in the spleen of both normal and chronically infected BALB/c mice by FACS analysis, revealed increased expression of LFA-1, CD25, CD44, 4F2, CD28 and the heat-stable antigen, whereas Thy-1 and CD5 decreased. Collectively, these results suggest an oligoclonal expansion and activation of gamma delta+ T cells in response to L. major infection.

Animals↗

PubMed1994

Interleukins (IL)-1 and IL-2 control IL-2 receptor alpha and beta expression in immature thymocytes.

Functional high-affinity interleukin-2 receptors (IL-2R) contain three transmembrane proteins, IL-2R alpha, beta and gamma. We have investigated the expression of IL-2R alpha and beta genes in immature mouse thymocytes. Previous work has shown that during differentiation these cells transiently express IL-2R alpha on their surface. Stimulation of IL-2R alpha+ and IL-2R alpha- immature thymocytes with phorbol 12-myristate 13-acetate and calcium ionophore induces synthesis of IL-2R alpha and IL-2R beta mRNA. Most of this response depends on autocrine stimulation by IL-2. IL-1 synergizes with IL-2 to induce a 120-fold increase in IL-2R alpha mRNA and a 14-fold increase in IL-2R beta mRNA levels. A large proportion of the stimulated cells contains both transcripts. These interleukins do not induce any differentiation to more mature phenotypes. Collectively, these results show that IL-2 plays a major role in the regulation of IL-2R expression in normal immature thymocyte. We suggest that this response to interleukins may be part of a homeostatic mechanism to increase the production of immature thymocytes during stress.

Animals↗

PubMed1994

Double-negative thymocyte subsets in CD3 zeta chain-deficient mice: absence of HSA+CD44-CD25- cells.

Double-negative (DN) thymocyte subsets were examined in mice deficient in the CD3 zeta chain (zeta-/-). The HSA+CD44-CD25- subset was found to be missing, and DN thymocytes seemed to differentiate directly from HSA+CD25+CD44- cells to double-positive (DP) cells. When fetal thymic ontogeny was examined, we found a marked difference between zeta-/- embryos and heterozygous littermates from embryonic day 17.5, in terms of CD25, CD4 and CD8 expression, and thymus size. The zeta-/- thymocytes failed to down-regulate CD25 and to expand exponentially. The cell cycle status of adult thymocyte subsets indicated that although the HSA+CD25-CD44- subset was missing, the CD25+ DN population contained normal numbers of cycling cells, and the CD25+ DP cells (which were not detectable in normal mice) contained 5-10% cells in G2/M+S. Taken together these data suggest that the CD3 zeta chain might have a specific role in the control of proliferation of DN thymocytes during T cell development. Our data clearly show that one can dissociate the signal for a CD25+ DN cell to differentiate (which occurs in the absence of CD3 zeta), from a signal to proliferate and from loss of cell surface CD25.

Animals↗

PubMed1994

Heterogeneity in P-glycoprotein (multidrug resistance) activity among murine peripheral T cells: correlation with surface phenotype and effector function.

P-glycoprotein (P-gly) is the transmembrane efflux pump responsible for multidrug resistance in tumor cells. Functional P-gly activity can be conveniently assessed microfluorometrically using the fluorescent dye rhodamine 123 (Rh123), which is an artificial substrate for the P-gly transporter. Here we assess P-gly activity in subsets of mouse peripheral T lymphocytes using the Rh123 efflux assay. Our data indicate that virtually all CD8+ cells extrude Rh123 efficiently, whereas only a subset of CD4+ cells exhibit P-gly activity. Correlation of P-gly activity in CD4+ cells with the expression of a panel of surface markers revealed that cells bearing an "activated/memory" phenotype (CD45RB-, CD44hi, CD62L-, CD25+, CD69+) were exclusively found in the fraction that can extrude Rh123. In contrast "naive" phenotype CD4+ cells (CD45RB+, CD44lo, CD62L+, CD25-, CD69-) could be further subdivided into two major subsets based on P-gly activity. In functional studies of sorted cell populations the Rh123-extruding subset of "naive" CD4+ cells proliferated more strongly and secreted higher levels of interleukin (IL)-2 than its Rh123-retaining counterpart when activated by a variety of polyclonal stimuli. Furthermore, this subset produced detectable levels of interferon (IFN)-gamma upon stimulation but no IL-4 or IL-10. As expected, the Rh123-retaining "naive" subset produced only IL-2 after stimulation, whereas the "memory" subset produced IFN-gamma, IL-4 and IL-10 in addition to low levels of IL-2. Collectively, our data indicate that P-gly activity is a novel parameter that can be used to distinguish a subset of "preactivated" CD4+ cells that would be considered as naive on the basis of their surface phenotype.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1994

The murine interleukin-2 receptor gamma chain gene: organization, chromosomal localization and expression in the adult thymus.

Defects in the interleukin-2 receptor gamma (IL-2R gamma) chain in the man result in an X-linked severe combined immunodeficiency, SCIDX1, characterized by an absence of T-cell differentiation. This phenotype may result from pertubations in IL-2, IL-4-, IL-7- or IL-15-mediated signaling, as the IL-2R gamma chain forms an integral component of these receptor systems. We have isolated and characterized cDNA and genomic clones for the murine IL-2R gamma. The gene (Il2rg) is well conserved between mouse and man with respect to overall structure and size, and contains regions of high conservation in the promoter region as well. Il2rg maps to mouse X chromosome region 40, in a region of synteny with human Xq12-13.1. We have also explored the expression of the IL-2R gamma during thymocyte development. IL-2R gamma transcripts are detected in the earliest thymocyte precursor cells and persist throughout intrathymic development into the mature peripheral compartment. Genomic clones for the murine IL-2R gamma will allow for further studies on the regulation and function of this gene in vivo.

Amino Acid Sequence↗

PubMed1994

CD4/CD8 lineage commitment in T cell receptor transgenic mice: evidence for precommitment of CD4+ CD8+ thymocytes.

CD4+ and CD8+ mature T cells arise from CD4+ CD8+ thymic precursors by a process of positive selection that ultimately requires interaction of the T cell receptor (TCR) with self major histocompatibility complex (MHC) molecules. The mechanism of commitment of immature CD4+ CD8+ thymocytes to CD4 or CD8 lineages is controversial. Using TCR transgenic mice, we present evidence that CD4+ CD8+ thymocytes are precommitted to either the CD4 or CD8 lineage, prior to positive selection and independently of TCR specificity for MHC. This lineage precommitment model places important constraints on signaling via CD4 or CD8 coreceptor molecules.

Animals↗

PubMed1994

Superantigens and retroviral infection: insights from mouse mammary tumor virus.

Superantigens induce a vigorous immune response by stimulating T cells that express particular T-cell receptor V beta chains. Mouse mammary tumor virus is a milk-transmitted retrovirus that encodes such a superantigen. Paradoxically, as discussed by Werner Held and colleagues, the strong superantigen-induced immune response permits the survival of the virus via T-cell dependent clonal expansion of infected B cells.

Animals↗

PubMed1994

MHC class II hierarchy of superantigen presentation predicts efficiency of infection with mouse mammary tumor virus.

Superantigens (SAgs) encoded by infectious mouse mammary tumor viruses (MMTVs) play a crucial role in the viral life cycle. Their expression by infected B cells induces a proliferative immune response by SAg-reactive T cells which amplifies MMTV infection. This response most likely ensures stable MMTV infection and transmission to the mammary gland. Since T cell reactivity to SAgs from endogenous Mtv loci depends on MHC class II molecules expressed by B cells, we have determined the ability of MMTV to infect various MHC congenic mice. We show that MHC class II I-E+ compared with I-E- mouse strains show higher levels of MMTV infection, most likely due to their ability to induce a vigorous SAg-dependent immune response following MMTV encounter. Inefficient infection is observed in MHC class II I-E- mice, which have been shown to present endogenous SAgs poorly. Therefore, during MMTV infection the differential ability of MHC class II molecules to form a functional complex with SAg determines the magnitude of the proliferative response of SAg-reactive T cells. This in turn influences the degree of T cell help provided to infected B cells and therefore the efficiency of amplification of MMTV infection.

Animals↗

PubMed1993

Precommitment of CD4+CD8+ thymocytes to either CD4 or CD8 lineages.

CD4+ and CD8+ mature T cells arise from CD4+CD8+ precursors in the thymus. During this process, cells expressing T-cell receptors (TCRs) reactive with self major histocompatibility complex (MHC) class I or II molecules are positively selected to the CD8 or CD4 lineage, respectively. It is controversial whether lineage commitment of CD4+CD8+ thymocytes is controlled directly by TCR specificity for MHC (instructional model) or, alternatively, by processes that operate independently of TCR specificity (stochastic model). We show here that CD4+CD8+ thymocytes bearing a MHC class I-restricted transgenic TCR can be subject to two alternative developmental fates. One population of CD4+CD8+ cells is positively selected by MHC class I molecules to the CD8 lineage as expected, whereas the other CD4+CD8+ population rearranges endogenous TCR genes and is positively selected by MHC class II molecules to the CD4 lineage. Blocking TCR-MHC class II interactions in vivo does not interfere with the generation of CD4+CD8+ cells expressing endogenous TCRs but does prevent their subsequent maturation to CD4+ cells. These data support a version of the stochastic model in which CD4+CD8+ thymocytes are precommitted to the CD4 or CD8 lineage independently of TCR specificity for MHC and prior to positive selection.

Aging↗

PubMed1993

Superantigen-induced immune stimulation amplifies mouse mammary tumor virus infection and allows virus transmission.

Endogenous and infectious mouse mammary tumor viruses (MMTVs) encode in their 3' long terminal repeat a protein that exerts superantigen activity; that is, it is able to interact with T cells via the variable domain of the T cell receptor (TCR) beta chain. We show here that transmission of an infectious MMTV is prevented when superantigen-reactive cells are absent through either clonal deletion due to the expression of an endogenous MTV with identical superantigen specificity or exclusion due to expression of a transgenic TCR beta chain that does not interact with the viral superantigen. A strict requirement for superantigen-reactive T cells is also seen for a local immune response following MMTV infection. This immune response locally amplifies the number of MMTV-infected B cells, most likely owing to their clonal expansion. Collectively, our data indicate that a superantigen-induced immune response is critical for the MMTV life cycle.

Animals↗

PubMed1993

Peripheral T cell activation and deletion induced by transfer of lymphocyte subsets expressing endogenous or exogenous mouse mammary tumor virus.

Murine T cell reactivity with products of the minor lymphocyte stimulatory (Mls) locus correlates with the expression of particular variable (V) domains of the T cell receptor (TCR) beta chain. It was recently demonstrated that Mls antigens are encoded by an open reading frame (ORF) in the 3' long terminal repeat of either endogenous or exogenous mouse mammary tumor virus (MMTV). Immature thymocytes expressing reactive TCR-V beta domains are clonally deleted upon exposure to endogenous Mtv's. Mature T cells proliferate vigorously in response to Mls-1a (Mtv-7) in vivo, but induction of specific anergy and deletion after exposure to Mtv-7-expressing cells in the periphery has also been described. We show here that B cells and CD8+ (but not CD4+) T cells from Mtv-7+ mice efficiently induce peripheral deletion of reactive T cells upon transfer to Mtv-7- recipients, whereas only B cells stimulate specific T cell proliferation in vivo. In contrast to endogenous Mtv-7, transfer of B, CD4+, or CD8+ lymphocyte subsets from mice maternally infected with MMTV(SW), an infectious homologue of Mtv-7, results in specific T cell deletion in the absence of a detectable proliferative response. Finally, we show by secondary transfers of infected cells that exogenous MMTV(SW) is transmitted multidirectionally between lymphocyte subsets and ultimately to the mammary gland. Collectively our data demonstrate heterogeneity in the expression and/or presentation of endogenous and exogenous MMTV ORF by lymphocyte subsets and emphasize the low threshold required for induction of peripheral T cell deletion by these gene products.

Animals↗

PubMed1993

Oligoclonal expansion of major histocompatibility complex class I-restricted cytolytic T lymphocytes during a primary immune response in vivo: direct monitoring by flow cytometry and polymerase chain reaction.

Previous T cell receptor (TCR) sequence analysis of a panel of 23 H-2Kd restricted cytotoxic T lymphocyte (CTL) clones recognizing the decapeptide HLA-CW3 170-179 revealed a striking conservation of TCR structure, in that all clones examined used V beta 10 and J alpha pHDS58 segments. We show here that the primary response in vivo after intraperitoneal injection of DBA/2 mice with HLA-CW3 expressing transfectants of syngeneic P815 (H-2d) tumor cells is characterized by a dramatic expansion of CD8+ V beta 10+ CTL in the peritoneal cavity and draining (mesenteric) lymph node, as well as in peripheral blood. Additional analysis of TCR on HLA-CW3 immune populations by flow cytometry and polymerase chain reaction further indicates that the vast majority of responding CD8+ cells express restricted V alpha domains, a dominant J alpha segment (pHDS58), and a conserved CDR3 length for both alpha and beta chains. This novel system provides a unique opportunity to directly monitor an oligoclonal primary antigen specific immune response in vivo at the single cell level independently of functional assays.

Animals↗

PubMed1993

Superantigen-reactive CD4+ T cells are required to stimulate B cells after infection with mouse mammary tumor virus.

Superantigens are defined by their ability to stimulate a large fraction of T cells via interaction with the T cell receptor (TCR) V beta domain. Endogenous superantigens, classically termed minor lymphocyte-stimulating (Mls) antigens, were recently identified as products of open reading frames (ORF) in integrated proviral copies of mouse mammary tumor virus (MMTV). We have described an infectious MMTV homologue of the classical endogenous superantigen Mls-1a (Mtv-7). The ORF molecules of both the endogenous Mtv-7 and the infectious MMTV(SW) interact with T cells expressing the TCR V beta 6, 7, 8.1, and 9 domains. Furthermore, the COOH termini of their ORF molecules, thought to confer TCR specificity, are very similar. Since successful transport of MMTV from the site of infection in the gut to the mammary gland depends on a functional immune system, we were interested in determining the early events after and requirements for MMTV infection. We show that MMTV(SW) infection induces a massive response of V beta 6+ CDC4+ T cells, which interact with the viral ORF. Concomitantly, we observed a B cell response and differentiation that depends on both the presence and stimulation of the superantigen-reactive T cells. Furthermore, we show that B cells are the main target of the initial MMTV infection as judged by the presence of the reverse-transcribed viral genome and ORF transcripts. Thus, we suggest that MMTV infection of B cells leads to ORF-mediated B-T cell interaction, which maintains and possibly amplifies viral infection.

Animals↗

PubMed1993

A role for gamma delta + T cells during experimental infection of mice with Leishmania major.

To assess the importance of gamma delta + T lymphocyte responses in experimental murine cutaneous leishmaniasis, the expression of gamma delta + TCR on the surface of lymphocytes in spleen and draining lymph nodes of mice infected with Leishmania major was examined. In both susceptible BALB/c and resistant CBA/J mice, an increase in gamma delta + T cells was observed after s.c. infection. Whereas in chronically infected BALB/c mice, these cells can represent up to 35% of the CD3+ cells in the spleen, in CBA/J mice the percentage of gamma delta + T cells returns to a lower level after resolution of lesions. Further experiments, in which the disease outcome was modified in susceptible BALB/c and in resistant CBA/J mice by chemotherapy or immunointervention, have confirmed that a correlation existed between the multiplication of the parasites and the expansion of gamma delta + T cells in the spleen. Interestingly, in BALB/c mice infected for 4 mo, these gamma delta + T cells represent 80% of the activated blast population and a large proportion of them express the alpha-chain of the CD8 molecule. In an attempt to assess a potential role for the gamma delta + T cells in the control of infection with L. major, the effect of injection of mAb against gamma delta TCR on the course of infection was studied. In both BALB/c and CBA/J mice, blocking of the gamma delta TCR resulted in the development of larger lesions that contained increased numbers of parasites. This treatment significantly delayed the healing of cutaneous lesions in otherwise resistant CBA/J mice. Taken together these results indicate that gamma delta + T cells are expanded during experimental infection of mice with L. major and could be involved in host defense against this parasite.

Animals↗

PubMed1993

Peripheral clonal deletion of superantigen-reactive T cells is enhanced by cortisone.

The T cell receptor (TcR) V beta-specific expansion, deletion and induction of nonresponsiveness among murine T cells responding to superantigens in the periphery has been well characterized. Here we demonstrate that clonal deletion of staphylococcal enterotoxin (SE) B-reactive V beta 8.2+ cells can be significantly increased when mice are injected with hydrocortisone (HC) following superantigen stimulation in vivo. The induced sensitivity to HC persists for at least 30 days after SEB injection, making it unlikely that proliferating cells were uniquely responsible for the enhanced deletion. Superantigen-induced HC sensitivity was a general phenomenon and could also be observed among V beta 11+ cells after the injection of SEA. Experiments conducted on thymectomized mice indicated that HC-sensitive, SEB-responsive cells could not be accounted for by rapidly produced, immature lymphocytes recently exported from the thymus. Further, V beta 8.1+ peripheral lymphocytes from TcR transgenic mice expressing the Mls-1a superantigen were sensitive to HC. These results imply that the majority of cells remaining after superantigen-induced clonal expansion and deletion in vivo have indeed reacted with the superantigen. Implications for differential superantigen recognition by T cells expressing the same TcR V beta domain, perhaps due to a significant V alpha contribution to the interaction in vivo, are discussed.

Animals↗

PubMed1993

Expression of the CD28 costimulatory molecule on subsets of murine intestinal intraepithelial lymphocytes correlates with lineage and responsiveness.

The CD28 antigen has been recently demonstrated to be a costimulatory molecule and is expressed by almost all thymic and peripheral T cell receptor (TcR) alpha beta+ and gamma delta+ cells in the mouse system. We show here that expression of CD28 is heterogeneous among murine intestinal intraepithelial lymphocytes (IEL). Whereas some TcR alpha beta-expressing IEL subsets such as CD4+8- and CD4-8 alpha+ beta+ cells express CD28 at the same levels as their phenotypic counterparts in lymph node, other subsets of TcR alpha beta cells (including CD4-8 alpha+ beta- and CD4+8 alpha+ beta- cells) as well as TcR gamma delta+ IEL fail to express CD28. Parallel experiments using aged BALB/c-nu/nu mice indicated that CD28 expression patterns among IEL are quite similar to those of normal BALB/c mice. Furthermore, forward light scatter analysis showed that CD28- cells are considerably larger than CD28+ cells in the gut, although cycling cells were rare in both subsets. Finally CD28- cells in the gut did not proliferate or produce IL-2 upon stimulation by anti-CD3 monoclonal antibodies (mAb) and phorbol 12-myristate 13-acetate, whereas CD28+ cells in the gut and lymph nodes responded to these stimuli. The response of the CD28+ cells was enhanced by anti-CD28 mAb. These results suggest that CD28- IEL (CD4- 8 alpha+ beta- cells, and some CD4+ 8 alpha+ beta- cells) may follow a different developmental pathway from that of CD28+ IEL in a thymus-independent environment, and that expression of CD28 correlates with responsiveness of the cells to triggering via the TcR-CD3 complex.

Animals↗

PubMed1993

Clonal anergy to staphylococcal enterotoxin B in vivo: selective effects on T cell subsets and lymphokines.

Injection of bacterial superantigens such as staphylococcal enterotoxin B (SEB) in adult mice results in initial proliferation of SEB-responsive V beta 8+ T cells followed by induction of a state of non-responsiveness frequently referred to as clonal anergy. We show here that SEB-induced anergy involves selective changes in lymphokine production and that it affects CD4+ V beta 8+ and CD8+ V beta 8+ T cells in different fashions. Whereas both CD4+ V beta 8+ and CD8+ V beta 8+ cells from anergic mice exhibit strongly reduced proliferative capacity and interleukin(IL)-2 production upon restimulation with SEB either in vivo or in vitro the CD8+ subset from SEB-injected mice produces other lymphokines (such as interferon(IFN)-gamma) at normal or slightly increased levels in response to SEB. Changes in the levels of production of IL-2 and IFN-gamma protein correlated well with mRNA accumulation both in vivo and in vitro. Collectively these data suggest that superantigen-induced anergy involves selective changes in signal transduction and/or gene regulation in T lymphocytes.

Animals↗