Differences in responsiveness to CD3 stimulation between naive and memory CD4+ T cells cannot be overcome by CD28 costimulation

Blockade of Cd40-Cd154 Interferes with Human T cell Engraftment in Scid Mice

Antibodies to the ligand for CD40 (CD154) have been shown to exert profound effects on the development of cell-mediated immune responses in mice. The present study shows that an antibody to human CD154 (hCD40L) inhibits in vivo Tetanus toxoid (TT) specific secondary antibody responses in hu-PBL-scid mice, as well as the expansion of xenoreactive human T cells in the scid mice. A possible cause for the reduced expansion of xenoreactive, human T cells, was the decreased expression of murine B7.1 and B7.2 caused by the administration of anti-hCD40L. Therefore, it may be that defective maturation of murine antigen-presenting cells impeded the priming and expansion of human xenoreactive T cells.

Role of acid sphingomyelinase bioactivity in human CD4+ T-cell activation and immune responses

Acid sphingomyelinase (ASM), a lipid hydrolase enzyme, has the potential to modulate various cellular activation responses via the generation of ceramide and by interaction with cellular receptors. We have hypothesized that ASM modulates CD4⁺ T-cell receptor activation and impacts immune responses. We first observed interactions of ASM with the intracellular domains of both CD3 and CD28. ASM further mediates T-cell proliferation after anti-CD3/CD28 antibody stimulation and alters CD4⁺ T-cell activation signals by generating ceramide. We noted that various pharmacological inhibitors of ASM or knockdown of ASM using small hairpin RNA inhibit CD3/CD28-mediated CD4⁺ T-cell proliferation and activation. Furthermore, such blockade of ASM bioactivity by biochemical inhibitors and/or molecular-targeted knockdown of ASM broadly abrogate T-helper cell responses. In conclusion, we detail immune, pivotal roles of ASM in adaptive immune T-cell responses, and propose that these pathways might provide novel targets for the therapy of autoimmune and inflammatory diseases.

The modulation of PPARγ1 and PPARγ2 mRNA expression by ciglitazone in CD3/CD28-activated naïve and memory CD4+ T cells

Given their roles in immune regulation, the expression of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) 1 and 2 isoforms was investigated in human naïve (CD45RA+) and memory (CD45RO+) CD4+ T cells. Stimulation of both types of cells via the CD3/CD28 pathway resulted in high expression of both PPARγ receptors as measured by real-time PCR. Treatment with the PPARγ agonist, ciglitazone, increased PPARγ1 expression but decreased PPARγ2 expression in stimulated naïve and memory cells. Furthermore, when present, the magnitude of both PPARγ receptors expression was lower in naïve cells, perhaps suggesting a lower regulatory control of these cells. Similar profiles of selected proinflammatory cytokines were expressed by the two cell types following stimulation. The induction of PPARγ1 and suppression of PPARγ2 expressions in naïve and memory CD4+ T cells in the presence of ciglitazone suggest that the PPARγ subtypes may have different roles in the regulation of T-cell function.

Protection from graft-versus-host disease with a novel B7 binding site–specific mouse anti–mouse CD28 monoclonal antibody

We studied the role of CD28 in T-cell biology and T cell–mediated pathology using a novel mouse anti–mouse CD28 antibody, E18, which recognizes an epitope close to the B7 binding site. In vitro, this antibody completely blocked binding of B7 molecules to CD28 expressed on mouse thymocytes but enhanced anti-CD3–induced proliferation of peripheral T cells. Injections of E18 monoclonal antibody into normal BALB/c mice in vivo, however, led to a reversible reduction in Treg cell frequencies among CD4+ cells, both in the thymus and in secondary lymphoid organs, suggesting that E18 acted as an inhibitor of CD28 signaling under these conditions. Antagonistic activity of E18 in vivo was further implied by suppressed responses of conventional CD4+ T cells to stimulation with the superantigen staphylococcal enterotoxin B and in a model of acute graft-versus-host disease. In contrast to healthy mice, intact monoclonal antibody E18, but not its nonstimulatory Fab fragment, increased the frequencies of Treg cells among CD4+ T cells in these pro-inflammatory settings allowing for efficacious protection from acute graft-versus-host disease. Thus, the agonistic signal generated by conventional, ie, nonsuperagonistic, anti-CD28 antibodies is important for their immunotherapeutic potential in vivo.

The role of CD4 T cells in the pathogenesis of multiple sclerosis

T lymphocytes play a central role in the pathogenesis of multiple sclerosis (MS) (Zhang et al., 1992). Both CD4+ and CD8+ T cells have been demonstrated in MS lesions, with CD4+ T cells predominating in acute lesions and CD8+ T cells being observed more frequently in chronic lesions (Raine, 1994). Additionally, T cells are found in all four of the described histopathologic subtypes of MS (Lucchinetti et al., 2000). Activated myelin‐reactive CD4+ T cells are present in the blood and cerebrospinal fluid (CSF) of MS patients; in contrast, only nonactivated myelin‐reactive T cells are present in the blood of controls (Zhang et al., 1994). The success of several T‐cell‐targeted therapies in MS reinforces the importance of the role of the T cell in MS pathogenesis. Here, we outline basic concepts in CD4+ T‐cell immunology and summarize the current understanding of the role of CD4+ T cells in the pathogenesis of MS.

Similar potential to become activated and proliferate but differential kinetics and profiles of cytokine production of umbilical cord blood T cells and adult blood naive and memory T cells

Low alloreactivity of umbilical cord blood (UCB) T-cells may explain diminished graft-versus-host-disease after UCB transplantation. We investigated whether UCB T-cells have an intrinsic lower capacity to become activated. T-cells from UCB or adult blood (AB) were stimulated with anti-CD3 and anti-CD28 antibodies. On days 1-3 after stimulation, T-cell activation was determined by CD25 expression, proliferation was measured, and kinetics of cell division were analyzed by staining with CFSE. UCB and AB T cells exhibited similar numbers of activated and proliferating cells, but the extent of activation was lower in UCB T-cells. Enzyme-linked immunospot analysis showed lower levels and slower kinetics of IL-2, IL-4, IL-10, and IFN-gamma secreting cells for UCB T-cells. Comparison of UCB T-cells with CD45RA+ naive or CD45RO+ memory T cells purified from AB showed relatively low numbers of IL-4 and IL-10 secreting T cells in CD45RA+ AB T-cells and UCB T-cells as compared with CD45RO+ AB T cells. Numbers of IL-2 or IFN-gamma secreting cells in adult CD45RA+ T-cells were lower than in CD45RO+ T-cells but higher than in UCB T-cells. Thus diminished reactivity of UCB T-cells was not caused by a lower capacity to become activated and proliferate but may be explained by a lower extent of activation in UCB T cells, the absence of memory T cells in UCB, and differences between naive T cells from UCB and AB.

LFA-1 is a key determinant for preferential infection of memory CD4+ T cells by human immunodeficiency virus type 1

Memory CD4+ T cells are considered a stable latent reservoir for human immunodeficiency virus type 1 (HIV-1) and a barrier to eradication of this retroviral infection in patients under therapy. It has been shown that memory CD4+ T cells are preferentially infected with HIV-1, but the exact mechanism(s) responsible for this higher susceptibility remains obscure. Previous findings indicate that incorporation of host-derived intercellular adhesion molecule 1 (ICAM-1) in HIV-1 increases virus infectivity. To measure the putative involvement of virus-anchored ICAM-1 in the preferential infection of memory cells by HIV-1, quiescent and activated naive and memory T-cell subsets were exposed to isogenic virions either lacking or bearing ICAM-1. Memory CD4+ T cells were found to be more susceptible than naive CD4+ T cells to infection with ICAM-1-bearing virions, as exemplified by a more important virus replication, an increase in integrated viral DNA copies, and a more efficient entry process. Interactions between virus-associated host ICAM-1 and cell surface LFA-1 under a cluster formation seem to be responsible for the preferential HIV-1 infection of the memory cell subset. Altogether, these data shed light on a potential mechanism by which HIV-1 preferentially targets long-lived memory CD4+ T cells.

The immune tolerance network and rheumatic disease: immune tolerance comes to the clinic

The development of effective, new, biologically based therapies for RA has created real excitement and justifiable optimism in recent years among rheumatologists and among patients with rheumatic diseases. Recent advances in our understanding of the mechanisms of immune activation and immune tolerance provide further cause for optimism. Against this background, the establishment of the ITN is an important step. However, significant hurdles remain to be cleared. First, despite dramatic scientific progress, restoration of immune tolerance in the face of an established autoimmune response is still an elusive goal, even in the laboratory. Not only does the ITN face this fundamental scientific challenge, but it also faces daunting practical and political challenges. For example, can the ITN influence the research agenda of the pharmaceutical and biotechnology industries? This question and other important questions will only be answered as the ITN matures. Autoimmune disease, although individually uncommon, affects more than 2% of Americans. The rheumatologist is especially aware of the devastating potential of autoimmune diseases. If the ITN succeeds in linking basic research into the mechanisms of autoimmunity with clinical trials of promising new therapies, it can be expected to play a critical role in advancing the practice of clinical rheumatology.

HIV gp120 plus specific peptides are recognized in a similar manner to specific HLA plus peptide by HLA-restricted antigen-specific T-cell lines

HIV induces disease only following chronic activation of the immune system. Other retroviruses such as the mouse mammary tumour virus (MMTV) activate a large percentage of T cells by encoding a superantigen (SAg). To date there is no evidence that HIV encodes a SAg. An alternative way to induce pan-activation of the immune system is by allogeneic stimulation, which occurs following transplantation. Here we extend previous work which demonstrated that HIVpg120 could bind peptides in a similar manner to HLA, by demonstrating that human antigen presenting cells (APCs) expressing gp120 (but not DR1) can present a DR1-restricted peptide to induce proliferation of a DR1-restricted peptide-specific T-cell line in a similar manner to the same peptide presented by a DR1 expressing APC. Our data provide strong support for the hypothesis that the HLA-like regions of gp120 encode functional properties shared with HLA, and could explain the extraordinary clinical and immunological similarities between AIDS and chronic graft versus host disease.

T cell memory: heterogeneity and mechanisms

Immunological memory is manifested by the body's ability to enjoy long-term protection against specific pathogens previously encountered through illness or vaccination. This memory response resides in the long-lived, previously activated memory T and B lymphocytes that are believed to exist in a quiescent state. Recent advances in studies on T cell memory have revealed heterogeneity in the T cells that mediate memory responses that may have implications for the generation and maintenance of these cells over time. This review will present these recent findings on memory T cells in the context of past research and current models for the generation and persistence of memory T cells.

The p55 TNF-alpha receptor plays a critical role in T cell alloreactivity

TNF-alpha is known to be an important mediator of tissue damage during allograft rejection and graft-vs-host disease (GVHD), but its role in supporting T cell responses to allogeneic Ags is unclear. We have studied this question by comparing normal mice with those lacking the p55 (p55 TNFR-/-) or p75 (p75 TNFR-/-) TNF-alpha receptors as donors in well-defined bone marrow transplant (BMT) models. Recipients of p55 TNFR-/- cells had significantly reduced mortality and morbidity from GVHD compared with the other two sources of T cells. In vitro, T cells lacking the p55 (but not the p75) TNF-alpha receptor exhibited decreased proliferation and production of Th1 cytokines in MLC. This defect was only partially restored by exogenous IL-2 and affected both CD4+ and CD8+ populations. CD8+ p55 TNFR-/- proliferation was impaired independently of IL-2 whereas CTL effector function was impaired in an IL-2-dependent fashion. Inhibition of TNF-alpha with TNFR:Fc in primary MLC also impaired the proliferation and Th1 differentiation of wild-type T cells. BMT mixing experiments demonstrated that the reduced ability of p55 TNFR-/- donor cells to induce GVHD was due to the absence of the p55 TNFR on T cells rather than bone marrow cells. These data highlight the importance of TNF-alpha in alloreactive T cell responses and suggest that inhibition of the T cell p55 TNF-alpha receptor may provide an additional useful therapeutic maneuver to inhibit alloreactive T cell responses following bone marrow and solid organ transplantation.

Expression of the costimulator molecules, CD80, CD86, CD28, and CD152 on lymphocytes from neonates and young children

The expression of CD80, CD86, CD28, and CD152 were examined on peripheral blood lymphocytes from adults, neonates (cord blood lymphocytes) and young children (2-20 months of age). There was no difference in the expression of CD80 or CD86 between adult and neonatal B cells, either resting or activated. A higher percentage of resting T cells expressed CD28 in neonates and young children compared to adults. CD28 expression was similar on adult and neonatal T cells activated with PMA and ionomycin. However, CD28 was expressed at greater intensity on a higher percentage of neonatal T cells than adult T cells stimulated with CD3. CD152 expression was lower on neonatal T cells than adult T cells stimulated with PMA and ionomycin and undetectable on neonatal T cells stimulated with CD3. In contrast, intracellular CD152 was equivalent in adult and neonatal T cells stimulated with PMA and ionomycin, suggesting trafficking of CD152 to the cell surface may be differentially regulated in neonatal T cells. Since the T cell response is determined by the balance of signals received from CD28 and CD152, high levels of CD28 expression and lower surface expression of CD152 on neonatal T cells may represent specialisation to promote activation of neonatal T cells.

Endothelial cells modify the costimulatory capacity of transmigrating leukocytes and promote CD28-mediated CD4(+) T cell alloactivation

Activated vascular endothelial cells (ECs) express major histocompatibility complex (MHC) class II molecules in vitro and in vivo in acute and chronic allograft rejection. However, human ECs may be limited in their ability to effectively activate CD4(+) T cells, because they do not express members of the B7 family (CD80 and CD86) of costimulatory molecules. In this study, we show that ECs promote the full activation of CD4(+) T cells via trans-costimulatory interactions. By reverse transcriptase polymerase chain reaction, Western blot, and FACS((R)) analysis, we could not detect the expression of CD80 and CD86 on activated ECs and found minimal expression on purified CD4(+) T cells. In contrast, both CD80 and CD86 were expressed in allogeneic CD4(+) T cell-EC cocultures. Expression of CD86 peaked at early times between 12 and 24 h after coculture, whereas CD80 was not expressed until 72 h. Addition of anti-CD86 but not anti-CD80 monoclonal antibodies to cocultures inhibited IL-2 production and the proliferation of CD4(+) T cells to allogeneic donor human umbilical vein ECs (HUVECs), as well as to skin and lung microvascular ECs. Furthermore, we found that interferon gamma-activated ECs but not untreated ECs induced mRNA and cell surface expression of CD80 and CD86 on CD4(+) T cells, and these T cells were functional to provide a trans-costimulatory signal to autologous CD4(+) T cells. Blockade of MHC class II and lymphocyte function-associated antigen 3 but not other EC cell surface molecules on IFN-gamma-activated ECs inhibited the induction of CD86 on CD4(+) T cells. Transmigration of purified populations of monocytes across EC monolayers similarly resulted in the induction of functional CD86, but also induced the de novo expression of the cytokines interleukin (IL)-1alpha and IL-12. In addition, EC-modified monocytes supported enhanced proliferation of allogeneic and autologous CD4(+) T cells. Taken together, these data define the ability of the endothelium to modify CD4(+) T cells and monocytes for trans-costimulatory events. This unique function of the endothelium in alloimmune T cell activation has functional consequences for the direct and the indirect pathways of allorecognition.

Endothelial antigen presentation: stimulation of previously activated but not naïve TCR-transgenic mouse T cells

In vitro experiments have shown that endothelial cells can function as antigen-presenting cells to CD4(+) T lymphocytes. The studies presented here address the question of whether naïve versus previously activated CD4(+) helper T cells differ in their responses to endothelial antigen presentation. TCR-transgenic mice were used as a source of naive T cells of defined antigen specificity. These cells were stimulated in vitro with antigen and splenic antigen-presenting cells to generate populations of T lymphocytes with a previously activated/memory phenotype. Two different types of mouse endothelial cells were used as antigen-presenting cells, including the SVEC4-10 line derived from lymph node endothelium and primary murine pulmonary microvascular endothelium. Monolayer cultures of both types of endothelium were capable of antigen-dependent stimulation of previously activated TCR-transgenic CD4(+) cells. In contrast, neither endothelial type could activate naïve CD4(+) T cells. When costimulatory signals were provided in trans by the addition of MHC-mismatched mouse spleen cells, activation of naïve T cells by endothelial antigen presentation could be demonstrated. The expression of ICAM-1 or VCAM-1 on the endothelial cells was not sufficient to activate naïve T cells. Furthermore, the mouse lung endothelium constitutively expresses B7-1, and therefore, the inability of endothelium to stimulate naïve T cells could not be attributed to a lack of CD28-ligands. These studies suggest that the potential role of endothelial antigen presentation in immune responses is restricted to promoting responses by T cells which have previously encountered antigen presented by other antigen-presenting cells.

Low CD3+CD28-induced interleukin-2 production correlates with decreased reactive oxygen intermediate formation in neonatal T cells

The capacity of neonatal T cells to secrete interleukin-2 (IL-2) has been reported to be variable. We analysed IL-2 production in purified neonatal and adult T cells using polyclonal activator phorbol ester + calcium ionophore (PDBu + iono) or receptor-mediated anti-CD3/anti-CD3+ anti-CD28 stimulation. PDBu + iono induced equally high IL-2 levels in both groups and, when stimulated with plate-bound anti-CD3 monoclonal antibody (mAb), the IL-2 secretion by neonatal cells was undetectable and adult cells produced low amounts of IL-2 (mean 331 +/- 86 pg/ml). The addition of anti-CD28 mAb to anti-CD3-stimulated cells markedly increased IL-2 production in both cell types, but levels of IL-2 in neonatal T cells remained clearly lower than those of adult T cells (respective mean values: 385 +/- 109 pg/ml and 4494 +/- 1199 pg/ml). As NF-kappa B is a critical transcription factor in the control of IL-2 expression, we next analysed its nuclear translocation in neonatal and adult T cells using the electrophoretic mobility shift assay and, because induction of reactive oxygen intermediates (ROI) is required for the activation of NF-kappa B, we also analysed levels of intracellular ROI in these cells using the ROI-reactive fluorochrome DCFH-DA and flow cytometry. In neonatal T cells NF-kappa B activation and ROI formation after anti-CD3 stimulation were low compared with adult T cells and, although addition of anti-CD28 mAb increased induction of NF-kappa B and ROI formation, levels similar to those of adults were not achieved. After PDBu + iono stimulation, the cells showed similar ROI formation and IL-2 secretion. Our results suggest that reduced IL-2 production by neonatal T cells is specific for anti-CD3 and anti-CD3+ anti-CD28-mediated stimulation and that these activators cannot effectively activate the ROI-NF-kappa B signalling pathway in neonatal T cells.

CD28 co-stimulation is intact and contributes to prolonged ex vivo survival of hyporesponsive synovial fluid T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), T cells in the inflamed joint are considered to play a crucial role in the pathogenesis. However, despite the fact that synovial T cells have an activated memory phenotype, they are functionally suppressed upon combined CD3 and CD28 stimulation. Here, we analyzed the contribution of both CD3 and CD28 to the hyporesponsiveness of synovial T cells in RA. In contrast to the low CD3 responsiveness of synovial fluid (SF) T cells compared to peripheral blood (PB) T cells, the CD28 co-stimulatory response was observed to be unaffected. Hyporesponsiveness of SF T cells has previously been associated with decreased levels of intracellular glutathione (GSH), an antioxidant and regulator of the intracellular redox state. Treatment of SF T cells with N-acetylcysteine, an antioxidant and replenisher of GSH, selectively improved CD3-induced responses, while leaving CD28 responsiveness unaffected. These data show that the CD3 pathway is highly sensitive to intracellular GSH alterations, whereas CD28 responsiveness is relatively refractory. Furthermore, in support for a functional role of CD28 co-stimulation, it was demonstrated that CD28 ligation acted in synergy with the IL-2 receptor gamma chain signaling cytokine IL-15 in the enhancement of the ex vivo survival of SF T cells. These data indicate that CD28 co-stimulatory capacity of SF T cells, in contrast to CD3 stimulation, remains intact despite an altered intracellular redox state. Thereby, CD28 stimulation may contribute to the persistence of T cells at the site of inflammation, which might be of relevance in the pathogenesis of RA.

Similar ligand densities required for restimulation and effector function of cytotoxic T cells

This study compared ligand densities on antigen-presenting cells (APCs) needed for in vitro restimulation of in vivo primed T cells and for in vitro assessed T cell effector function. Spleen cells of lymphocytic choriomeningitis virus (LCMV)-primed mice were restimulated in vitro with graded amounts of virus-derived peptides using macrophages or a cloned dendritic cell line as APCs. To test for effector function of these cytotoxic T cells, the same APCs pulsed with graded amounts of the peptides were used as target cells in an in vitro 51Cr release assay. The same peptide concentration that rendered an APC restimulatory for primed cytotoxic T lymphocytes (CTLs) also rendered it susceptible for lysis by the same CTLs. In addition, the same peptide concentrations that made macrophages susceptible for CTL-mediated lysis induced proliferative responses in vitro of in vivo primed memory CTLs. Thus, restimulation of in vivo primed T cells--measured by either proliferation or cytotoxic effector function--or sensibilization of target cells for lysis requires similar ligand densities on APCs and is therefore, contrary to expectations, governed by similar overall avidity thresholds. These results have implications for CTL memory.

Immune memory in CD4+ CD45RA+ T cells

This study addresses the question of whether human peripheral CD4+ CD45RA+ T cells possess antigen-specific immune memory. CD4+ CD45RA+ T cells were isolated by a combination of positive and negative selection. Putative CD4+ CD45RA+ cells expressed CD45RA (98.9%) and contained < 0.1% CD4+ CD45RO+ and < 0.5% CD4+ CD45RA+ CD45RO+ cells. Putative CD45RO+ cells expressed CD45RO (90%) and contained 9% CD45RA+ CD45RO+ and < 0.1% CD4+ CD45RA+ cells. The responder frequency of Dermatophagoides pteronyssinus-stimulated CD4+ CD45RA+ and CD4+ CD45RO+ T cells was determined in two atopic donors and found to be 1:11,314 and 1:8031 for CD4+ CD45RA+ and 1:1463 and 1:1408 for CD4+ CD45RO+ T cells. The responder frequencies of CD4+ CD45RA+ and CD4+ CD45RO+ T cells from two non-atopic, but exposed, donors were 1:78031 and 1:176,903 for CD4+ CD45RA+ and 1:9136 and 1:13,136 for CD4+ CD45RO+ T cells. T cells specific for D. pteronyssinus were cloned at limiting dilution following 10 days of bulk culture with D. pteronyssinus antigen. Sixty-eight clones were obtained from CD4+ CD45RO+ and 24 from CD4+ CD45RA+ T cells. All clones were CD3+ CD4+ CD45RO+ and proliferated in response to D. pteronyssinus antigens. Of 40 clones tested, none responded to Tubercule bacillus purified protein derivative (PPD). No difference was seen in the pattern of interleukin-4 (IL-4) or interferon-gamma (IFN-gamma) producing clones derived from CD4+ CD45RA+ and CD4+ CD45RO+ precursors, although freshly isolated and polyclonally activated CD4+ CD45RA+ T cells produced 20-30-fold lower levels of IL-4 and IFN-gamma than their CD4+ CD45RO+ counterparts. Sixty per cent of the clones used the same pool of V beta genes. These data support the hypothesis that immune memory resides in CD4+ CD45RA+ as well as CD4+ CD45RO+ T cells during the chronic immune response to inhaled antigen.

CD28-mediated activation of resting human T cells without costimulation of the CD3/TCR complex

Stimulation of resting human T cells by crosslinked CD28 monoclonal antibodies (mAb) induces some early signaling events but does not lead to IL-2 secretion and proliferation. The induction of these functions usually requires the delivery of additional signals such as that provided by costimulation of the T cell receptor (TCR). We analyzed the capacity of a panel of different CD28 mAb to induce cellular functions in purified human T cells. Two patterns of reactivity were observed. "Costimulatory" CD28 mAb like 9.3 required coengagement of the CD3/TCR complex for the induction of IL-2 gene transcription and proliferation. On the other hand, a "stimulatory" pathway could be defined by the use of the CD28 mAb BW 828, which triggered IL-2 synthesis, IL-2R expression, and proliferation without further requirement for additional stimuli. BW 828-induced proliferation was sensitive to inhibition by cyclosporin A and was mainly found in the CD4+CD45R0+ ("memory") T cell subset. These data suggest that T cell stimulation with mAb BW 828 defines a CD28-associated signaling pathway which leads to the induction of effector functions without the need for CD3/TCR coengagement. This pathway might play a role in antigen-independent activation and expansion of T cells.

Major histocompatibility complex class II-expressing endothelial cells induce allospecific nonresponsiveness in naive T cells

The role of endothelial cells (EC) in initiating a primary T cell response is of importance in clinical transplantation and autoimmunity since EC are the first allogeneic target encountered by the recipient's immune system and may display tissue-specific autoantigens in the context of an inflammatory response. In this study, we have investigated the antigen-presenting cell function of human umbilical vein-derived EC (HUVEC), depleted of constitutively major histocompatibility complex class II+ cells and induced to express class II molecules by interferon-gamma. The results show that HUVEC do not express B7 but can support proliferation by antigen-specific T cell clones. In contrast, they were unable to initiate a primary alloresponse using three independent HUVEC cultures and MHC class II-mismatched CD4+ T cells from eight donors. The response to HUVEC was reconstituted by trans-costimulation provided by DAP.3 transfectants expressing human B7.1. Coculture of peripheral blood T cells with EC expressing allogeneic DR molecules had markedly different effects on CD45RO+ and RA+ subsets. Subsequent reactivity of the RO+ T cells was unaffected by exposure to EC, indicating a neutral encounter. In contrast, culture with DR+ EC induced allospecific nonresponsiveness in RA+ T cells.

Functional assessment of CD2, CD3 and CD28 on the surface of peripheral blood T-cells from infants at low versus high genetic risk for atopy

Recent studies from several laboratories suggest that the rate of postnatal maturation of T-cell function(s) associated with in vitro activation may be slower in children at high genetic risk for atopy (HR), compared to their normal (low risk; LR) counterparts. The present study compared the in vitro activity of the function-associated surface molecules CD2, CD3 and CD28 in panels of 27 HR and 13 LR infants, with a reference panel of 10 adults, employing assay systems involving T-cell stimulation with MoAbs against these molecules. The response maxima induced by saturating levels of the MoAbs were equivalent in all 3 groups, but T-cells from the HR infants required 10-50 fold higher levels of anti-CD3 stimulation to attain their maximum response, relative to adults (p = 0.02); T-cells from LR infants were also less responsive to anti-CD3 than adults, but these differences were smaller and did not attain statistical significance. It is suggested that these differences are attributable to varying proportions of competent T-memory cells (which respond to low levels of anti-CD3) in PBL from these populations, the postnatal accumulation of which proceeds slowest in the HR group.