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M Coulombe

Publications and source records attributed to M Coulombe.

At least 19 recordsLinked to original sources
PubMed2001

The basis of immunogenicity of endocrine allografts.

Two signals are required for optimal T-cell activation: the engagement of the antigen-specific receptor and the provision of a second non-antigen-specific inductive signal, or costimulator (CoS). Regarding allograft immunity, two primary pathways of donor antigen presentation can fulfill this two-signal requirement, resulting in cellular immunity to a transplant: (1) "direct" (donor MHC-restricted) presentation in which the antigen-presenting cells (APCs) resident within the transplant directly activate host T lymphocytes and (2) "indirect" (host MHC-restricted) presentation in which host-derived APCs acquire donor antigens that are then presented to host T lymphocytes. It appears that endocrine allografts, such as pancreatic islets and thyroid, are highly dependent on donor-derived APCs, or "passenger leukocytes," to trigger acute graft rejection. Tissue pretreatment aimed at selectively eliminating APCs within endocrine tissues can result in indefinite allograft survival in immune-competent recipients. Although such results implicate the "direct" pathway as the predominant route of host sensitization, the role of donor APCs in rejection appears to be more complex. Recently, we have found that indirect, CD4 T-cell-dependent reactivity can contribute to islet allograft rejection. However, such indirect recognition nevertheless requires donor-derived APCs as a source of antigen. Thus, whereas the donor-type APC is a critical limiting step for initiating islet allograft rejection, such cells can trigger both direct and indirect forms of immune responses that can result in graft rejection. That is, donor hematopoietic cells, rather than tissue parenchymal cells, probably play a major role in providing antigens that stimulate cellular immunity.

Animals↗
PubMed2000

Synaptic connectivity in hippocampal neuronal networks cultured on micropatterned surfaces.

Embryonic rat hippocampal neurons were grown on patterned silane surface in order to organize synapse formations in a controlled manner. The surface patterns were composed of trimethoxysilylpropyl-diethylenetriamine (DETA) lines separated by tridecafluoro-1,1,2,2-tetrahydrooctyl-1-dimethylchlorosilane (13F) spaces. Pre- and post-synaptic specializations were identified by immunostaining for synapsin I and microtubule-associated protein-2 (MAP-2). Functional synaptic connections were examined by recording simultaneously from pairs of neurons using the whole-cell configuration of the patch-clamp technique. Spontaneous and evoked synaptic currents were recorded in neurons cultured for 2-14 days. The formation of functional connections was accompanied by the appearance of spontaneous synaptic currents (SSCs), which could be detected after approximately 3 days in culture in the absence of evoked synaptic currents (ESCs). ESCs were detected only after approximately 7 days in culture, mostly in the form of unidirectional synaptic connections. Other forms of synaptic connectivity, such as bidirectional and autaptic connections, were also identified. Both transient GABAergic and glutamatergic signals mediated the transmissions between communicating cells. These results demonstrate the combination of various types of synaptic connections forming simple and complex networks in neurons cultured on line (DETA)-space (13F) patterns. Finally, precisely synchronized SSCs were recorded in neuron pairs cultured on pattern indicating the existence of a fast-acting feedback mechanism mediated by pre-synaptic GABA(A) receptors.

Alkanes↗
PubMed2000

Anti-LFA-1 therapy induces long-term islet allograft acceptance in the absence of IFN-gamma or IL-4.

mAb therapy directed against a variety of cell surface accessory molecules has been effectively utilized to prolong allograft acceptance in various models of tissue and organ transplantation. The purpose of this study was to determine whether transient therapy directed against the adhesion molecule LFA-1 (CD11a) was sufficient to induce donor-specific tolerance to pancreatic islet allografts. Anti-LFA-1 monotherapy was found to be efficacious in inducing long-term islet allograft acceptance in multiple donor-recipient strain combinations. Graft acceptance following anti-LFA-1 therapy was not simply due to clonal ignorance of donor Ags in that the majority of recipients bearing established islet allografts resisted rejection induced by immunization with donor-type APCs. Furthermore, donor-specific tolerance from anti-LFA-1-treated animals could be transferred to secondary immune-deficient animals. Taken together, these results indicated that transient anti-LFA-1 monotherapy resulted in donor-specific tolerance. In vitro, functionally tolerant animals retained normal anti-donor reactivity as assessed by proliferative, cytotoxic, and cytokine release assays that demonstrated that tolerance was not secondary to general clonal deletion or anergy of donor-reactive T cells. Finally, anti-LFA-1 treatment was effective in both IL-4-deficient and IFN-gamma-deficient recipients, indicating that neither of these cytokines are universally required for allograft acceptance. These results suggest that anti-adhesion-based therapy can induce a nondeletional form of tolerance that is not overtly dependent on the prototypic Th1 and Th2 cytokines, IFN-gamma and IL-4, respectively, in contrast to results in other transplantation models.

Adoptive Transfer↗
PubMed1999

Tolerance to antigen-presenting cell-depleted islet allografts is CD4 T cell dependent.

Pretreatment of pancreatic islets in 95% oxygen culture depletes graft-associated APCs and leads to indefinite allograft acceptance in immunocompetent recipients. As such, the APC-depleted allograft represents a model of peripheral alloantigen presentation in the absence of donor-derived costimulation. Over time, a state of donor-specific tolerance develops in which recipients are resistant to donor APC-induced graft rejection. Thus, persistence of the graft is sufficient to induce tolerance independent of other immune interventions. Donor-specific tolerance could be adoptively transferred to immune-deficient SCID recipient mice transplanted with fresh immunogenic islet allografts, indicating that the original recipient was not simply "ignorant" of donor antigens. Interestingly, despite the fact that the original islet allograft presented only MHC class I alloantigens, CD8+ T cells obtained from tolerant animals readily collaborated with naive CD4+ T cells to reject donor-type islet grafts. Conversely, tolerant CD4+ T cells failed to collaborate effectively with naive CD8+ T cells for the rejection of donor-type grafts. In conclusion, the MHC class I+, II- islet allograft paradoxically leads to a change in the donor-reactive CD4 T cell subset and not in the CD8 subset. We hypothesize that the tolerant state is not due to direct class I alloantigen presentation to CD8 T cells but, rather, occurs via the indirect pathway of donor Ag presentation to CD4 T cells in the context of host MHC class II molecules.

Adoptive Transfer↗
PubMed1998

Neuronal and glial epitopes and transmitter-synthesizing enzymes appear in parallel with membrane excitability during neuroblastoma x glioma hybrid differentiation.

The membrane excitability and the presence of neural proteins, including neuronal and glial markers and neurotransmitter-synthesizing enzymes, were examined in parallel while the NG108-15 cell line was maintained in a serum-free medium. Whole-cell recordings in voltage-clamp or current-clamp configurations were used to evaluate the membrane excitability, and immunostaining was done with a panel of well-characterized antibodies against NSE, NF150, S-100 beta, GFAP, ChAT and TH. Culture for 4 to 10 days led to a striking rise in neurite outgrowth, electrical excitability and expression of neural proteins in type I neuron-like cells, which were of both neuronal and glial character, and expressed both cholinergic and adrenergic traits. After about 2 weeks, type II cells which lack neurite processes began to emerge. The type II cells proliferated, as revealed by BrdU uptake, and gradually overgrew differentiated cell types. They exhibited little or no membrane excitability and absence of immunoreactivity for the neuronal and glial specific proteins tested. These measurements indicate that the presence of these neural proteins at crucial stages of membrane excitability development is an important characteristics of NG108-15 cell differentiation, providing insights into the neural development and the reversible nature of neoplasia in the nervous system.

Animals↗
PubMed1996

Tissue immunogenicity: the role of MHC antigen and the lymphocyte costimulator B7-1.

Pancreatic islet transplantation represents a potential treatment for insulin-dependent diabetes mellitus. One approach to circumvent the requirement for recipient immune suppression is to reduce or eliminate the immunogenicity of the donor graft prior to transplantation. In this study, we have examined the relative contributions of graft MHC Ag expression and donor-derived costimulatory (CoS) activity to the rejection of islet allografts. Depletion of donor hemopoietic APCs from islet tissue facilitated long-term allograft survival even when donor class I MHC Ag expression was greatly increased by IFN-gamma treatment prior to grafting. Conversely, islet allografts from transgenic mice expressing the CoS molecule B7-1 (CD80) on islet beta cells were acutely rejected even when hemopoietic APCs were eliminated. Thus, B7-1 is sufficient to confer the capacity of islet parenchymal cells to stimulate allorejection. Taken together, these results point towards donor-derived CoS activity as a primary target of intervention therapy to modulate tissue immunogenicity.

Animals↗
PubMed1996

T lymphocyte indifference to extrathymic islet allografts.

Although the deletion of self-reactive T cells maturing in the thymus is well documented, the nature of tolerance to Ags expressed exclusively on peripheral (extrathymic) tissues is less clear. Numerous studies have examined T cell reactivity to transgene-encoded Ags expressed in the periphery through tissue-specific promoters. These studies have yielded varied results concerning the degree and nature of tolerance induced to these Ags, ranging from T cell clonal deletion or inactivation to clonal "ignorance" of the peripheral transgene-encoded Ag. Furthermore, the relationship of these findings to the generation and maintenance of transplantation tolerance to extrathymic tissue allografts remains unclear. Whereas transgenic studies represent a developmental form of tolerance, grafted tissues are introduced into adult, nontolerant recipients. To relate these two model systems, we determined whether extrathymic tissue allografts could induce a developmental form of tolerance. As a model of extrathymic alloantigen expression, pancreatic islet allografts, depleted of donor APCs, were established in the periphery of severe combined immune-deficient (SCID) mice. We then examined the potential donor reactivity of adoptively transferred bone marrow-derived T cell precursors maturing in the presence of the established peripheral allograft. Such T cells were neither activated nor tolerized either in vitro or in vivo, suggesting that T cells are indifferent to Ags expressed by extrathymic islet allografts when presented in the absence of a second costimulatory signal.

Animals↗
PubMed1996

Autoimmune destruction of islet grafts in the NOD mouse is resistant to 15-deoxyspergualin but sensitive to anti-CD4 antibody.

Islet allografts transplanted into Type I diabetic recipients may be destroyed by allorejection or recurrent autoimmune diabetes. We studied islet transplantation in three murine models in order to determine the relative sensitivity of autoimmunity and alloimmunity to two immunosuppressive agents that may be useful in clinical islet transplantation: 15-deoxyspergualin (DSG) and anti-CD4 antibody (GK 1.5). In the model in which only allorejection occurs (BALB/c islets transplanted into streptozotocin-induced diabetic CBA or streptozotocin-induced diabetic NOD recipients), both DSG and anti-CD4 antibody treatment led to indefinite survival of allogeneic islets (>100 days in both treatments). In the second model in which only recurrent autoimmunity can destroy islet grafts (islets from NOD donors transplanted into spontaneously diabetic NOD recipients), only anti-CD4 treatment caused prolonged graft survival [MST 36.7 +/- 6.8 days vs 9.8 +/- 1.8 days (controls), P < 0.0002]. Treatment with DSG did not cause any increase in graft survival (MST 12.6 +/- 5.4 days, NS). Finally, using a model in which both autoimmunity and allorejection may occur (BALB/c to spontaneously diabetic NOD mice), treatment with anti-CD4 caused marked graft prolongation [42.0 +/- 14.5 days vs 7.2 +/- 0.8 days (control), P < 0.002] while DSG again did not prolong graft survival with respect to untreated recipients (9.8 +/- 3.0, NS). We conclude that recurrent autoimmunity in the NOD mouse involves a CD4+ T cell that is not sensitive to DSG. Anti-CD4 antibody may be useful in human clinical islet transplantation trials because it seems to prevent both allorejection and recurrent autoimmunity.

Animals↗
PubMed1996

Pancreatic islet allograft immunity and tolerance: the two-signal hypothesis revisited.

The principle assumption of this discussion is that costimulation (CoS) forms the primary stimulus that compels T cells to mount a response to their specific antigen. However, this response can be either positive or negative, depending on the developmental stage of the T cell and the microenvironment in which the antigen and CoS are received. Thus, both immunity and tolerance may represent different outcomes of a two-signal process. We would emphasize that CoS is a functional term and not a strict molecular definition. While many molecular interactions have been described as providing CoS activity, notably those involving the B-7 family of cell surface molecules, it is not yet clear what combination(s) of non-antigen-specific signals may fulfil this function. This point is important because many studies have achieved tolerance through strategies designed to inhibit specific CoS molecules. However, it may be that differential signaling through distinct CoS molecules, rather than a global inhibition of CoS per se, plays a role in the generation of active tolerance in such studies (Bluestone 1995). A corollary of this notion is that antigen (signal 1) delivery to T cells is a null event and so is not an inherently paralysing signal. Of course, if signal 1 is not itself a tolerogenic signal, then other mechanisms are necessary to explain many empirical observations of tolerance to allogeneic or self antigens. This is best illustrated by those forms of functional tolerance to either alloantigens or self antigens that do not appear to be the result of clonal deletion/inactivation. It would be relatively simple to invoke a model of tolerance whereby the relevant tissue-destructive cell is eliminated or inactivated; such a model would preclude the necessity to suggest active regulatory mechanisms of tolerance. However, in several model systems, including our own observations concerning tolerance induction to APC-depleted islet allografts, tissue-destructive T cells can persist in recipients tolerant to allogeneic or self antigens. Furthermore, there are key examples in which tolerance demonstrates a dominant phenotype; that is, tolerant cells can regulate the activity of naive, non-tolerant cells. This latter observation points to the function of an active, regulatory form of tolerance. As such, we would emphasize that tolerance should not be defined as unresponsiveness since the tolerant state is the consequence of very active immune reactions.

Animals↗
PubMed1995

Donor antigen-presenting cell-independent rejection of islet xenografts.

Donor-derived antigen-presenting cells (APC) are thought to serve as major stimulators for triggering the rejection of tissue allografts. However, the capacity of APC to stimulate xenogeneic T cells is generally deficient relative to the corresponding response from allogeneic T cells. For this reason, the contribution of donor-type APC to xenogeneic graft rejection remains unclear. Using a concordant species combination (rat to mouse), we examined the requirement for donor-type APC in triggering islet xenograft rejection. While the depletion of donor-type APC resulted in indefinite allograft survival, similar depletion of APC from xenogeneic rat islets resulted in only modest graft prolongation. Furthermore, APC-depleted rat xenografts were rejected by a CD8+ T cell-independent mechanism, as determined by appropriate depletion of T cell subsets through monoclonal antibody therapy. This contrasts with the dependence of islet allograft rejection on both CD4+ and CD8+ T cells. Although in vitro experiments show that rat APC can directly stimulate mouse T cells, rat APC do not appear to be required for xenograft immunity in vivo. We conclude that the mechanisms of islet allograft and xenograft rejection differ both in the dependence on donor-type APC and in the role of T cell subsets in the response.

Animals↗
PubMed1994

Tolerance induction to cultured islet allografts. I. Characterization of the tolerant state.

The immunogenicity of murine pancreatic islets can be reduced by culture in 95% O2 prior to transplantation. Such cultured tissue can reverse diabetes indefinitely in nonimmunosuppressed, allogeneic recipients. Although the cultured graft does not trigger a rejection response, the graft retains recognizable alloantigens in that the graft is acutely rejected when the host is immunized with donor-type antigen-presenting cells. However, over time the recipients bearing cultured islet allografts become increasingly resistant to rejecting the established graft following APC challenge. Data show that this process of graft "stabilization" is a function of time postgrafting and initial graft mass. Graft stabilization is not due to a change in the vulnerability of the graft to immune recognition--that is, stabilization cannot be accounted for by the spontaneous adaptation of the long-term graft. Rather, graft stabilization is associated with a change in host reactivity (tolerance induction). This conclusion is based on the findings that (1) recipients of long-term established grafts (> 120 days) resist rejection of both the primary and secondary donor-type grafts, and (2) donor-specific tolerance can be transferred to severe-combined-immune-deficient (scid) recipient mice.

Animals↗
PubMed1994

Tolerance induction to cultured islet allografts. II. The status of antidonor reactivity in tolerant animals.

Murine islet tissue cultured in 95% O2 to eliminate/inactivate donor antigen-presenting cells can function indefinitely and induce a state of tolerance in nonimmunosuppressed, allogeneic recipients. Such cultured grafts represent a model of antigen presentation in which antigen (signal 1) is presented without the delivery of appropriate costimulatory activity (signal 2) necessary for T cell activation. As T cell inactivation has been proposed to result from this form of antigen presentation, we determined whether the tolerance generated in response to such cultured grafts was due to a passive (clonal deletion/inactivation) mechanism. We have shown that, although tolerant in vivo, animals bearing long-term cultured islet allografts are donor-reactive in vitro as assessed by (1) CTL precursor frequency, (2) antidonor proliferative and cytotoxic responses, and (3) lymphokine production (IL-2, IL-3, TNF, and IFN-gamma). In addition, tolerance does not appear to be tissue (islet)-specific in that primed, donor-reactive T cells from tolerant animals react to islet cells in vitro and are capable of destroying donor-type islet grafts in vivo. Thus, the notion that "signal 1" antigen presentation, as represented by cultured islet allografts, leads to the clonal deletion or inactivation (anergy) of donor-reactive T cells is not supported by these results. Since this form of tolerance does not appear to be an intrinsic property of the donor-specific lymphocyte, these results are more consistent with a model of active regulatory tolerance in vivo.

Animals↗
PubMed1992

Nuclear and cytoplasmic localization of basic fibroblast growth factor in astrocytes and CA2 hippocampal neurons.

Fibroblast growth factors (FGFs) are known to stimulate mitogenesis in a variety of non-neuronal cell types and to support the survival in vitro of many neuronal cell types. The physiological role of FGFs in the CNS is currently not known. The present study determined the distribution in the rat CNS of a prominent member of the FGF family, basic FGF (bFGF). Immunohistochemical analysis showed that bFGF immunoreactivity was found predominantly in astrocytes throughout all regions of the CNS. In contrast, only a few neuronal populations were found to contain bFGF immunoreactivity, most prominent among them, neurons in the CA2 area of the hippocampus. This predominant localization of bFGF to astrocytes was confirmed by two other observations: (1) highly enriched cultures of astrocytes contained bFGF immunoreactivity and bioactivity, whereas highly enriched cultures of cerebral cortical neurons contained no detectable bFGF, and (2) neonatal rat cerebral cortex, which contains only a few differentiated astrocytes, also contained no detectable bFGF immunoreactivity and only low amounts of bFGF bioactivity. Immunocytochemical analysis also suggested that bFGF immunoreactivity was present in the nucleus as well as the cytoplasm of astrocytes and CA2 neurons. This nuclear localization was confirmed by EM analysis of the intracellular distribution of the immunoperoxidase reaction product. In addition, preparations of both nuclear and soluble fractions of brain extracts contained bFGF immunoreactivity and bioactivity. These data suggest that bFGF might be involved in mediating astrocytic influences on the late postnatal maturation and plasticity in the CNS, and that the nuclear localization of bFGF within astrocytes may play an important role in the differentiation of these cells. In addition, bFGF may play a similar role in a few specific neuronal populations, such as CA2 hippocampal neurons.

Animals↗