Role of cAMP in regulating cytotoxic T lymphocyte adhesion and motility

Bone marrow-derived mesenchymal stromal cells obstruct AML-targeting CD8+ clonal effector and CAR T-cell function while promoting a senescence-associated phenotype

Bone marrow mesenchymal stromal cells (MSCs) have been described as potent regulators of T-cell function, though whether they could impede the effectiveness of immunotherapy against acute myeloid leukemia (AML) is still under investigation. We examine whether they could interfere with the activity of leukemia-specific clonal cytotoxic T-lymphocytes (CTLs) and chimeric antigen receptor (CAR) T cells, as well as whether the immunomodulatory properties of MSCs could be associated with the induction of T-cell senescence. Co-cultures of leukemia-associated Wilm's tumor protein 1 (WT1) and tyrosine-protein kinase transmembrane receptor 1 (ROR1)-reactive CTLs and of CD123-redirected switchable CAR T cells were prepared in the presence of MSCs and assessed for cytotoxic potential, cytokine secretion, and expansion. T-cell senescence within functional memory sub-compartments was investigated for the senescence-associated phenotype CD28-CD57+ using unmodified peripheral blood mononuclear cells. We describe inhibition of expansion of AML-redirected switchable CAR T cells by MSCs via indoleamine 2,3-dioxygenase 1 (IDO-1) activity, as well as reduction of interferon gamma (IFNγ) and interleukin-2 (IL-2) release. In addition, MSCs interfered with the secretory potential of leukemia-associated WT1- and ROR1-targeting CTL clones, inhibiting the release of IFNγ, tumor necrosis factor alpha, and IL-2. Abrogated T cells were shown to retain their cytolytic activity. Moreover, we demonstrate induction of a CD28loCD27loCD57+KLRG1+ senescent T-cell phenotype by MSCs. In summary, we show that MSCs are potent modulators of anti-leukemic T cells, and targeting their modes of action would likely be beneficial in a combinatorial approach with AML-directed immunotherapy.

Regulatory T cells suppress the motility of cytotoxic T cells in Friend retrovirus-infected mice

Antiviral immunity often requires CD8+ cytotoxic T lymphocytes (CTLs) that actively migrate and search for virus-infected targets. Regulatory T cells (Tregs) have been shown to suppress CTL responses, but it is not known whether this is also mediated by effects on CTL motility. Here, we used intravital 2-photon microscopy in the Friend retrovirus (FV) mouse model to define the impact of Tregs on CTL motility throughout the course of acute infection. Virus-specific CTLs were very motile and had frequent short contacts with target cells at their peak cytotoxic activity. However, when Tregs were activated and expanded in late-acute FV infection, CTLs became significantly less motile and contacts with target cells were prolonged. This phenotype was associated with development of functional CTL exhaustion. Tregs had direct contacts with CTLs in vivo and, importantly, their experimental depletion restored CTL motility. Our findings identify an effect of Tregs on CTL motility as part of their mechanism of functional impairment in chronic viral infections. Future studies must address the underlying molecular mechanisms.

Influence of exercise on quantity and deformability of immune cells in multiple sclerosis

Objective

The study aimed to investigate the effect of exercise on immune cell count and cell mechanical properties in people with multiple sclerosis (pwMS) on different disease-modifying treatments (DMT) vs. healthy controls (HCs).

Methods

A cohort of 16 HCs and 45 pwMS, including patients with lymphopenia (alemtuzumab and fingolimod) as well as increased lymphocyte counts (natalizumab), was evaluated for exercise-mediated effects on immune cell counts and lymphocyte deformability. As exercise paradigms, climbing stairs at normal speed or as fast as possible and cycling were used, while blood samples were collected before, immediately, and 20 as well as 60 min post-exercise. Immune cell subtypes and lymphocyte deformability were analyzed using multicolor flow cytometry and real-time deformability cytometry.

Results

An increase in lymphocytes and selected subsets was observed following exercise in HCs and all pwMS on different DMTs. Patients with lymphopenia exhibited an increase in absolute lymphocyte counts and immune cell subsets till just below or into the reference range. An increase above the upper limit of the reference range was detected in patients on natalizumab. Exercise-induced alterations were observable even in low and more pronounced in high-intensity physical activities. Lymphocyte deformability was found to be only mildly affected by the investigated exercise regimes.

Conclusion

People with multiple sclerosis (PwMS) treated with alemtuzumab, fingolimod, and natalizumab respond to acute exercise with a comparable temporal pattern characterized by the increase of immune cell subsets as HCs. The magnitude of response is influenced by exercise intensity. Exercise-mediated effects should be considered when interpreting laboratory values in patients on immunomodulatory therapy. The impact of exercise on biophysical properties should be further elucidated.

Cell contractile force measured using a deformable hollow capsule

There are several possible ways to measure the contraction of cells in vitro. Here, we report measurements of the contractile properties of 3T3-L1 cells grown to confluence on 3D hollow capsules. The capsules were fabricated using the layer-by-layer polyelectrolyte deposition technique on a polymer core. After the polyelectrolyte film was completed, the core was dissolved to leave the hollow capsule. The contractile force of the cells was determined from the deformation in the capsule size induced by interruption of the actin cytoskeleton of the cells that adhered to the outer surface of the hollow capsules, using prior measurements of the elastic modulus of the capsule. From the measurements of the compressive modulus for the capsules (of 6.52 μN), those capsule deformations indicate that the forskolin relaxed the layer of cells by 19.6 μN and the cytochalasin-D relaxed the layer of cells by 45.6 μN. The density of cells in the layer indicated that the force associated with the forskolin-induced relaxation of a single cell is 3.2 nN and the force associated with the cytochalasin-D-induced relaxation of a single cell is 7.5 nN. The mechanism of action of forskolin through second messenger pathways to disrupt the assembly of actin stress fibres also explains its reduced effect on cell contraction compared to that for cytochalasin-D, which is a compound that directly inhibits the polymerization of F-actin filaments.

Noncoding RNAs link metabolic reprogramming to immune microenvironment in cancers

Altered metabolic patterns in tumor cells not only meet their own growth requirements but also shape an immunosuppressive microenvironment through multiple mechanisms. Noncoding RNAs constitute approximately 60% of the transcriptional output of human cells and have been shown to regulate numerous cellular processes under developmental and pathological conditions. Given their extensive action mechanisms based on motif recognition patterns, noncoding RNAs may serve as hinges bridging metabolic activity and immune responses. Indeed, recent studies have shown that microRNAs, long noncoding RNAs and circRNAs are widely involved in tumor metabolic rewiring, immune cell infiltration and function. Hence, we summarized existing knowledge of the role of noncoding RNAs in the remodeling of tumor metabolism and the immune microenvironment, and notably, we established the TIMELnc manual, which is a free and public manual for researchers to identify pivotal lncRNAs that are simultaneously correlated with tumor metabolism and immune cell infiltration based on a bioinformatic approach.

cAMP Bursts Control T Cell Directionality by Actomyosin Cytoskeleton Remodeling

T lymphocyte migration is an essential step to mounting an efficient immune response. The rapid and random motility of these cells which favors their sentinel role is conditioned by chemokines as well as by the physical environment. Morphological changes, underlaid by dynamic actin cytoskeleton remodeling, are observed throughout migration but especially when the cell modifies its trajectory. However, the signaling cascade regulating the directional changes remains largely unknown. Using dynamic cell imaging, we investigated in this paper the signaling pathways involved in T cell directionality. We monitored cyclic adenosine 3′-5′ monosphosphate (cAMP) variation concomitantly with actomyosin distribution upon T lymphocyte migration and highlighted the fact that spontaneous bursts in cAMP starting from the leading edge, are sufficient to promote actomyosin redistribution triggering trajectory modification. Although cAMP is commonly considered as an immunosuppressive factor, our results suggest that, when transient, it rather favors the exploratory behavior of T cells.

Targeting Adenosine in Cancer Immunotherapy to Enhance T-Cell Function

T cells play a critical role in cancer control, but a range of potent immunosuppressive mechanisms can be upregulated in the tumor microenvironment (TME) to abrogate their activity. While various immunotherapies (IMTs) aiming at re-invigorating the T-cell-mediated anti-tumor response, such as immune checkpoint blockade (ICB), and the adoptive cell transfer (ACT) of natural or gene-engineered ex vivo expanded tumor-specific T cells, have led to unprecedented clinical responses, only a small proportion of cancer patients benefit from these treatments. Important research efforts are thus underway to identify biomarkers of response, as well as to develop personalized combinatorial approaches that can target other inhibitory mechanisms at play in the TME. In recent years, adenosinergic signaling has emerged as a powerful immuno-metabolic checkpoint in tumors. Like several other barriers in the TME, such as the PD-1/PDL-1 axis, CTLA-4, and indoleamine 2,3-dioxygenase (IDO-1), adenosine plays important physiologic roles, but has been co-opted by tumors to promote their growth and impair immunity. Several agents counteracting the adenosine axis have been developed, and pre-clinical studies have demonstrated important anti-tumor activity, alone and in combination with other IMTs including ICB and ACT. Here we review the regulation of adenosine levels and mechanisms by which it promotes tumor growth and broadly suppresses protective immunity, with extra focus on the attenuation of T cell function. Finally, we present an overview of promising pre-clinical and clinical approaches being explored for blocking the adenosine axis for enhanced control of solid tumors.

Establishing a dose-response relationship between acute resistance-exercise and the immune system: Protocol for a systematic review

Exercise immunology research has traditionally focussed on aerobic-exercise, however it has become apparent in more recent years that resistance-exercise can also considerably affect host immunobiology. To date however, no systematic process has been used to establish a dose-response relationship between resistance-exercise and the immune system. The present systematic review was thus conducted to determine the dose-response effects of a bout of resistance-exercise on acute leukocyte counts. In accordance with the PRISMA guidelines, a systematic literature search was conducted in the electronic databases, PubMed, Web of Science, and Google Scholar, over the date range of 1989-2016. Following the PICO elements, eligibility criteria included: i) participants: healthy humans aged 18-40; ii) intervention: a single bout of resistance-exercise; iii) comparator: at least one comparator group; iv) outcome: acute measures of circulating leukocyte counts. Specific exclusion criteria were also applied. Risk of bias and quality of evidence was assessed using the PEDro scale. Due to the individual designs of the admitted studies, a qualitative analysis (systematic narrative synthesis) was employed in the present review. The results of the present review demonstrate that a single bout of resistance-exercise induces an acute monocytosis, neutrophilia, and lymphocytosis. It became apparent that the reviewed literature either does not consistently specify, or does not describe with sufficient detail, the time-course between the onset of exercise and the collection of blood. We recommend that researchers consider addressing this in future studies, and also collect blood measures during exercise to aid with comparison of temporal effects. Regarding the determination of a dose-response relationship, an acute neutrophilia, monocytosis and lymphocytosis appears to occur more rapidly and to a greater magnitude following a single bout of high-dose vs low-dose resistance-exercise. Mechanistically, exercise-induced cell trafficking changes are associated with mechanical, metabolic and endocrine factors. Physical aptitude of the host may also affect resistance-exercise-induced lymphocyte trafficking responses.

Murid Gammaherpesvirus Latency-Associated Protein M2 Promotes the Formation of Conjugates between Transformed B Lymphoma Cells and T Helper Cells

Establishment of persistent infection in memory B cells by murid herpesvirus-4 (MuHV-4) depends on the proliferation of latently infected germinal center B cells, for which T cell help is essential. Whether the virus is capable of modulating B-T helper cell interaction for its own benefit is still unknown. Here, we investigate if the MuHV-4 latency associated M2 protein, which assembles multiprotein complexes with B cell signaling proteins, plays a role. We observed that M2 led to the upregulation of adhesion and co-stimulatory molecules in transduced B cell lines. In an MHC-II restricted OVA peptide-specific system, M2 polarized to the B-T helper contact zone. Furthermore, it promoted B cell polarization, as demonstrated by the increased proximity of the B cell microtubule organizing center to the interface. Consistent with these data, M2 promoted the formation of B-T helper cell conjugates. In an in vitro competition assay, this translated into a competitive advantage, as T cells preferentially conjugated with M2-expressing B cells. However, expression of M2 alone in B cells was not sufficient to lead to T cell activation, as it only occurred in the presence of specific peptide. Taken together, these findings support that M2 promotes the formation of B-T helper cell conjugates. In an in vivo context this may confer a competitive advantage to the infected B cell in acquisition of T cell help and initiation of a germinal center reaction, hence host colonization.

Polyunsaturated Fatty Acid-derived lipid mediators and T cell function

Fatty acids are involved in T cell biology both as nutrients important for energy production as well as signaling molecules. In particular, polyunsaturated fatty acids are known to exhibit a range of immunomodulatory properties that progress through T cell mediated events, although the molecular mechanisms of these actions have not yet been fully elucidated. Some of these immune activities are linked to polyunsaturated fatty acid-induced alteration of the composition of cellular membranes and the consequent changes in signaling pathways linked to membrane raft-associated proteins. However, significant aspects of the polyunsaturated fatty acid bioactivities are mediated through their transformation to specific lipid mediators, products of cyclooxygenase, lipoxygenase, or cytochrome P450 enzymatic reactions. Resulting bioactive metabolites including prostaglandins, leukotrienes, and endocannabinoids are produced by and/or act upon T leukocytes through cell surface receptors and have been shown to alter T cell activation and differentiation, proliferation, cytokine production, motility, and homing events. Detailed appreciation of the mode of action of these lipids presents opportunities for the design and development of therapeutic strategies aimed at regulating T cell function.

Regulation of immune responses by prostaglandin E2

PGE(2), an essential homeostatic factor, is also a key mediator of immunopathology in chronic infections and cancer. The impact of PGE(2) reflects the balance between its cyclooxygenase 2-regulated synthesis and 15-hydroxyprostaglandin dehydrogenase-driven degradation and the pattern of expression of PGE(2) receptors. PGE(2) enhances its own production but suppresses acute inflammatory mediators, resulting in its predominance at late/chronic stages of immunity. PGE(2) supports activation of dendritic cells but suppresses their ability to attract naive, memory, and effector T cells. PGE(2) selectively suppresses effector functions of macrophages and neutrophils and the Th1-, CTL-, and NK cell-mediated type 1 immunity, but it promotes Th2, Th17, and regulatory T cell responses. PGE(2) modulates chemokine production, inhibiting the attraction of proinflammatory cells while enhancing local accumulation of regulatory T cells cells and myeloid-derived suppressor cells. Targeting the production, degradation, and responsiveness to PGE(2) provides tools to modulate the patterns of immunity in a wide range of diseases, from autoimmunity to cancer.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Effects of intracellular calcium and actin cytoskeleton on TCR mobility measured by fluorescence recovery

BACKGROUND

The activation of T lymphocytes by specific antigen is accompanied by the formation of a specialized signaling region termed the immunological synapse, characterized by the clustering and segregation of surface molecules and, in particular, by T cell receptor (TCR) clustering.

METHODOLOGY/PRINCIPAL FINDINGS

To better understand TCR motion during cellular activation, we used confocal microscopy and photo-bleaching recovery techniques to investigate the lateral mobility of TCR on the surface of human T lymphocytes under various pharmacological treatments. Using drugs that cause an increase in intracellular calcium, we observed a decrease in TCR mobility that was dependent on a functional actin cytoskeleton. In parallel experiments measurement of filamentous actin by FACS analysis showed that raising intracellular calcium also causes increased polymerization of the actin cytoskeleton. These in vitro results were analyzed using a mathematical model that revealed effective binding parameters between TCR and the actin cytoskeleton.

CONCLUSION/SIGNIFICANCE

We propose, based on our results, that increase in intracellular calcium levels leads to actin polymerization and increases TCR/cytoskeleton interactions that reduce the overall mobility of the TCR. In a physiological setting, this may contribute to TCR re-positioning at the immunological synapse.

Adrenergic inhibition of innate anti-viral response: PKA blockade of Type I interferon gene transcription mediates catecholamine support for HIV-1 replication

Type I interferons (IFN-alpha and -beta) play a key role in anti-viral immunity, and we sought to define the molecular mechanisms by which the sympathetic nervous system (SNS) inhibits their effects. In peripheral blood leukocytes and plasmacytoid dendritic cells (pDC2), induction of interferon anti-viral activity by double-stranded RNA (poly-I:C) or CpG DNA was substantially inhibited by norepinephrine and by pharmacologic activation of the cAMP/PKA signaling pathway. This effect was specific to Type I interferons and driven by PKA-mediated repression of IFNA and IFNB gene transcription. Luciferase reporter analyses identified tandem interferon response factor-binding sites in positive regulatory domains I and III of the IFNB promoter as a key target of PKA inhibition. PKA suppression of Type I interferons was associated with impaired transcription of interferon response genes supporting the "anti-viral state", and was sufficient to account for norepinephrine-induced enhancement of HIV-1 replication. Given the ubiquitous role of Type I interferons in containing viral replication, PKA-mediated inhibition of IFN transcription could explain the stimulatory effects of catecholamines on a broad range of viral pathogens.

Enhanced replication of simian immunodeficiency virus adjacent to catecholaminergic varicosities in primate lymph nodes

Clinical and in vitro studies have shown that activity of the autonomic nervous system (ANS) can stimulate lentivirus replication. To define the potential anatomical basis for this effect, we analyzed the spatial relationship between catecholaminergic neural fibers and sites of simian immunodeficiency virus (SIV) replication in lymph nodes from rhesus macaques experimentally infected with SIVmac251. Viral replication was mapped by in situ hybridization for SIV env, gag, and nef RNA, and catecholaminergic varicosities from the ANS were mapped by sucrose phosphate glyoxylic acid chemofluorescence. Spatial statistical analyses showed that the likelihood of active SIV replication increased by 3.9-fold in the vicinity of catecholaminergic varicosities (P < 0.0001). The densities of both ANS innervation and SIV replication differed across cortical, paracortical, and medullary regions of the lymph node, but analyses of each region separately continued to show increased replication of SIV adjacent to catecholaminergic varicosities. Ancillary analyses ruled out the possibility that SIV-induced alterations in lymph node architecture might create a spurious spatial association. These data support human clinical studies and in vitro molecular analyses showing that catecholamine neurotransmitters from the ANS can increase lentiviral replication by identifying a specific anatomic context for interactions between ANS neural fibers and replication of SIV in lymphoid tissue.

Phosphodiesterase 8 (PDE8) regulates chemotaxis of activated lymphocytes

The immune system depends on chemokines to recruit lymphocytes to tissues in inflammatory diseases. This study identifies PDE8 as a new target for inhibition of chemotaxis of activated lymphocytes. Chemotactic responses of unstimulated and concanavalin A-stimulated mouse splenocytes and their modulation by agents that stimulate the cAMP signaling pathway were compared. Dibutyryl cAMP inhibited migration of both cell types. In contrast, forskolin and 3-isobutyl-1-methylxanthine each inhibited migration of unstimulated splenocytes, with little effect on migration of stimulated splenocytes. Only dipyridamole alone, a PDE inhibitor capable of inhibiting PDE8, strongly inhibited migration of stimulated and unstimulated splenocytes and this inhibition was enhanced by forskolin and reversed by a PKA antagonist. Following concanavalin A stimulation, mRNA for PDE8A1 was induced. These results suggest that in employing PDE inhibitor therapy for inflammatory illnesses, inhibition of PDE8 may be required to inhibit migration of activated lymphocytes to achieve a full therapeutic effect.

beta-Adrenoreceptors reactivate Kaposi's sarcoma-associated herpesvirus lytic replication via PKA-dependent control of viral RTA

Reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) lytic replication is mediated by the viral RTA transcription factor, but little is known about the physiological processes controlling its expression or activity. Links between autonomic nervous system activity and AIDS-associated Kaposi's sarcoma led us to examine the potential influence of catecholamine neurotransmitters. Physiological concentrations of epinephrine and norepinephrine efficiently reactivated lytic replication of KSHV in latently infected primary effusion lymphoma cells via beta-adrenergic activation of the cellular cyclic AMP/protein kinase A (PKA) signaling pathway. Effects were blocked by PKA antagonists and mimicked by pharmacological and physiological PKA activators (prostaglandin E2 and histamine) or overexpression of the PKA catalytic subunit. PKA up-regulated RTA gene expression, enhanced activity of the RTA promoter, and posttranslationally enhanced RTA's trans-activating capacity for its own promoter and heterologous lytic promoters (e.g., the viral PAN gene). Mutation of predicted phosphorylation targets at RTA serines 525 and 526 inhibited PKA-mediated enhancement of RTA trans-activating capacity. Given the high catecholamine levels at sites of KSHV latency such as the vasculature and lymphoid organs, these data suggest that beta-adrenergic control of RTA might constitute a significant physiological regulator of KSHV lytic replication. These findings also suggest novel therapeutic strategies for controlling the activity of this oncogenic gammaherpesvirus in vivo.

Activation of Th1 and Tc1 cell adenosine A2A receptors directly inhibits IL-2 secretion in vitro and IL-2-driven expansion in vivo

To evaluate the direct effect of adenosine on cytokine-polarized effector T cells, murine type 1 helper T cells (Th1) and type 1 cytotoxic T lymphocytes (Tc1) and Th2/Tc2 cells were generated using an antigen-presenting cell (APC)-free method. Tc1 and Tc2 cells had similar adenosine signaling, as measured by intracellular cyclic AMP (cAMP) increase upon adenosine A(2A) receptor agonism by CGS21680 (CGS). CGS greatly reduced Tc1 and Tc2 cell interleukin 2 (IL-2) and tumor necrosis factor alpha (TNF-alpha) secretion, with nominal effect on interferon gamma (IFN-gamma) secretion. Tc2 cell IL-4 and IL-5 secretion was not reduced by CGS, and IL-10 secretion was moderately reduced. Agonist-mediated inhibition of IL-2 and TNF-alpha secretion occurred via A(2A) receptors, with no involvement of A(1), A(2B), or A(3) receptors. Adenosine agonist concentrations that abrogated cytokine secretion did not inhibit Tc1 or Tc2 cell cytolytic function. Adenosine modulated effector T cells in vivo, as CGS administration reduced CD4(+)Th1 and CD8(+)Tc1 cell expansion to alloantigen and, in a separate model, reduced antigen-specific CD4(+) Th1 cell numbers. Remarkably, agonist-mediated T-cell inhibition was abrogated by in vivo IL-2 therapy. Adenosine receptor activation therefore preferentially inhibits type I cytokine secretion, most notably IL-2. Modulation of adenosine receptors may thus represent a suitable target primarily for inflammatory conditions mediated by Th1 and Tc1 cells.

Uterine response to infectious bacteria in estrous cyclic ewes

PROBLEM

Luteal-phase uteri are susceptible to infections, and PGE2 and exogenous progesterone can down-regulate, whereas PGF2alpha can up-regulate, uterine immune functions.

METHOD OF STUDY

Uteri of follicular- or luteal-phase ewes were inoculated with either saline or bacteria (Arcanobacterium pyogenes and Escherichia colt). Vena caval blood was collected for the next 3 days, and progesterone, PGE2, and PGF2alpha were measured. The effects of 10(-7) M PGE2 (Experiment 1), 10(-7) M PGF2alpha (Experiment 2), 10(-7) M indomethacin (INDO), and diluent on proliferation of lymphocytes from the vena caval blood in response to mitogens was quantified.

RESULTS

Experiment 1: Progesterone was greater (P < 0.01) in luteal than in follicular ewes (3.4 versus 0.4 ng/mL), and only luteal ewes inoculated with bacteria developed infections.Lymphocyte proliferation was least (P = 0.08) in follicular ewes (2.6 versus 4.5 pmol for follicular and luteal, respectively). Concanavalin A (Con A)-stimulated proliferation was less (P < 0.05) for ewes inoculated with bacteria and for cells cultured with diluent (5.9 versus 3.1 pmol for saline and bacteria, respectively) or with INDO (6.6 versus 2.8 pmol for saline and bacteria, respectively). Also, Con A-stimulated lymphocytes from ewes inoculated with bacteria tended to proliferate less (P < 0.1) when cultured with PGE2 (4.9 versus 3.7 pmol for saline and bacteria, respectively) or PGE2 + INDO (5.5 versus 3.8 pmol for saline and bacteria, respectively). Experiment 2: Progesterone was greater (P < 0.01) in luteal than in follicular ewes (6.5 versus 1.2 ng/mL), and only luteal ewes inoculated with bacteria developed infections. Con A-stimulated lymphocyte proliferation was greater (P < 0.001) for follicular ewes (4.1 versus 3.1 pmol for follicular and luteal, respectively). Proliferation of lymphocytes collected from follicular ewes was greater (P < 0.01) when cells were cultured with PGF2alpha (3.5 versus 2.7 pmol for follicular and luteal, respectively), but INDO did not affect unstimulated or mitogen-stimulated proliferation.

CONCLUSIONS

Prostaglandin F2alpha enhanced lymphocyte proliferation, whereas bacterial inoculation and in vitro treatment with PGE2 suppressed lymphocyte proliferation. This may signify the involvement of bacterial products and prostaglandins in regulation of uterine immunity.

The actin cytoskeleton and cytotoxic T lymphocytes: evidence for multiple roles that could affect granule exocytosis-dependent target cell killing

One important mechanism cytotoxic T lymphocytes (CTLs) use to kill virus-infected, transplanted or tumour targets is exocytosis of granules that contain cytotoxic agents such as perforin and granzymes. Granule exocytosis-dependent target cell killing is a complex process, involving initial T-cell receptor (TCR)-dependent signalling that includes Ca2+ influx and activation of protein kinase C, shape changes that serve to bind the CTL to the target and, finally, exocytosis of lytic granules at the site of contact with the target cell. Although there is reason to propose that multiple steps in the lytic process could involve the actin cytoskeleton of CTLs, few studies have examined this issue, and those that have do not allow the specific step(s) involved to be determined. We have used the potent membrane-permeant actin cytoskeleton-modifying drugs jasplakinolide and latrunculin A to investigate the actin dependence of defined processes that are expected to be important for granule exocytosis-dependent killing. Our results, obtained using TALL-104 human leukaemic CTLs as a model system, are consistent with the idea that a functional actin cytoskeleton is required for TCR/CD3-dependent signalling, for activation of store-dependent Ca2+ influx and for CTL shape changes. When cells were stimulated with solid-phase anti-CD3 antibodies, treatment with either jasplakinolide or latrunculin A abolished granule exocytosis. However, when cells were stimulated in a manner that bypasses TCR/CD3-dependent signalling, granule exocytosis was not significantly altered, suggesting that the actin cytoskeleton does not function as a barrier to exocytosis.

Rapid up-regulation of alpha4 integrin-mediated leukocyte adhesion by transforming growth factor-beta1

The alpha4 integrins (alpha4beta1 and alpha4beta7) are cell surface heterodimers expressed mostly on leukocytes that mediate cell-cell and cell-extracellular matrix adhesion. A characteristic feature of alpha4 integrins is that their adhesive activity can be subjected to rapid modulation during the process of cell migration. Herein, we show that transforming growth factor-beta1 (TGF-beta1) rapidly (0.5-5 min) and transiently up-regulated alpha4 integrin-dependent adhesion of different human leukocyte cell lines and human peripheral blood lymphocytes (PBLs) to their ligands vascular cell adhesion molecule-1 (VCAM-1) and connecting segment-1/fibronectin. In addition, TGF-beta1 enhanced the alpha4 integrin-mediated adhesion of PBLs to tumor necrosis factor-alpha-treated human umbilical vein endothelial cells, indicating the stimulation of alpha4beta1/VCAM-1 interaction. Although TGF-beta1 rapidly activated the small GTPase RhoA and the p38 mitogen-activated protein kinase, enhanced adhesion did not require activation of both signaling molecules. Instead, polymerization of actin cytoskeleton triggered by TGF-beta1 was necessary for alpha4 integrin-dependent up-regulated adhesion, and elevation of intracellular cAMP opposed this up-regulation. Moreover, TGF-beta1 further increased cell adhesion mediated by alpha4 integrins in response to the chemokine stromal cell-derived factor-1alpha. These data suggest that TGF-beta1 can potentially contribute to cell migration by dynamically regulating cell adhesion mediated by alpha4 integrins.

BDCA-2, a novel plasmacytoid dendritic cell-specific type II C-type lectin, mediates antigen capture and is a potent inhibitor of interferon alpha/beta induction

Plasmacytoid dendritic cells are present in lymphoid and nonlymphoid tissue and contribute substantially to both innate and adaptive immunity. Recently, we have described several monoclonal antibodies that recognize a plasmacytoid dendritic cell-specific antigen, which we have termed BDCA-2. Molecular cloning of BDCA-2 revealed that BDCA-2 is a novel type II C-type lectin, which shows 50.7% sequence identity at the amino acid level to its putative murine ortholog, the murine dendritic cell-associated C-type lectin 2. Anti-BDCA-2 monoclonal antibodies are rapidly internalized and efficiently presented to T cells, indicating that BDCA-2 could play a role in ligand internalization and presentation. Furthermore, ligation of BDCA-2 potently suppresses induction of interferon alpha/beta production in plasmacytoid dendritic cells, presumably by a mechanism dependent on calcium mobilization and protein-tyrosine phosphorylation by src-family protein-tyrosine kinases. Inasmuch as production of interferon alpha/beta by plasmacytoid dendritic cells is considered to be a major pathophysiological factor in systemic lupus erythematosus, triggering of BDCA-2 should be evaluated as therapeutic strategy for blocking production of interferon alpha/beta in systemic lupus erythematosus patients.

Impaired response to HAART in HIV-infected individuals with high autonomic nervous system activity

Neurotransmitters can accelerate HIV-1 replication in vitro, leading us to examine whether differences in autonomic nervous system (ANS) activity might promote residual HIV-1 replication in patients treated with highly active antiretroviral therapy. Patients who showed constitutively high levels of ANS activity before highly active antiretroviral therapy experienced poorer suppression of plasma viral load and poorer CD4(+) T cell recovery over 3-11 months of therapy. ANS activity was not related to demographic or behavioral characteristics that might influence pathogenesis. However, the ANS neurotransmitter norepinephrine enhanced replication of both CCR5- and CXCR4-tropic strains of HIV-1 in vitro via chemokine receptor up-regulation and enhanced viral gene expression, suggesting that neural activity may directly promote residual viral replication.

FD-891, a structural analogue of concanamycin A that does not affect vacuolar acidification or perforin activity, yet potently prevents cytotoxic T lymphocyte-mediated cytotoxicity through the blockage of conjugate formation

FD-891 belongs to a group of 18-membered macrolides, and is a structural analogue of a specific inhibitor of vacuolar type H+-ATPase, concanamycin A (CMA). In our previous work, we have shown that CMA specifically inhibits perforin-dependent cytotoxic T lymphocyte (CTL)-mediated cytotoxicity through the degradation and inactivation of perforin, although CMA does not affect Fas ligand (FasL)-dependent cytotoxicity. Here, we show that FD-891 potently prevents not only perforin-dependent but also FasL-dependent CTL-mediated killing pathways by blocking CTL-target conjugate formation. In contrast to CMA, FD-891 was unable to inhibit vacuolar acidification and only slightly decreased the perforin activity in lytic granules. FD-891 blocked granule exocytosis in response to anti-CD3, mainly owing to the lack of CTL binding to immobilized anti-CD3. The conjugate formation was markedly inhibited only when effector cells were pretreated with FD-891. Consistent with these observations, fluorescence-activated cell sorter (FACS) analysis for cell surface receptors revealed that FD-891 significantly reduced the expression of the T-cell receptor (TCR)/CD3 complex. These data suggest that the blockage of conjugate formation and subsequent target cell killing might be at least partly owing to FD-891-induced down-regulation of the TCR/CD3 complex.

The fungal metabolite gliotoxin: immunosuppressive activity on CTL-mediated cytotoxicity

Gliotoxin, a potential etiologic agent which is synthesized by Aspergillus fumigatus and other pathogenic fungi, exhibits a variety of immunosuppressive activities. We have found that gliotoxin markedly inhibits both perforin-dependent and Fas ligand-dependent cytotoxic T-lymphocyte (CTL)-mediated cytotoxicity. Gliotoxin blocked granule exocytosis and the production of inositol phosphates in response to anti-CD3 stimulation. Apparently, activation signals were not efficiently received by the gliotoxin-treated CTL clone, perhaps because gliotoxin profoundly disturbed CTL cell attachment to immobilized anti-CD3. Although the expression of surface molecules of the CTL clone such as CD3 was unaffected by gliotoxin, the effector/target conjugate formation was inhibited dose-dependently by gliotoxin treatment of the effector CTL clone. These results suggest that gliotoxin prevents CTL from interacting with target cells.

Differential Expression and Regulation of Cyclooxygenase Isozymes in Thymic Stromal Cells

Prostaglandins (PGs) are lipid-derived mediators of rapid and localized cellular responses. Given the role of PG in supporting thymic T cell development, we investigated the expression of the PG synthases, also known as cyclooxygenases (COX)-1 and -2, in the biosynthesis of PGs in thymic stromal cell lines. The predominant isozyme expressed in cortical thymic epithelial cells was COX-1, while COX-2 predominated in the medulla. IFN-γ up-regulated expression and activity of COX-2 in medullary cells, in which COX-2 was expressed constitutively. In contrast, IFN-γ down-regulated COX-1 activity, but not expression, in cortical cells. Stromal cells support T cell development in the thymus, although the mediators of this effect are unknown. Selective inhibition of COX-2, but not COX-1, blocked the adhesion of CD4+CD8+ and CD4+CD8− thymocytes to medullary cell lines. No effect of the inhibitors was observed on the interactions of thymocytes with cortical epithelial lines. These data further support the differential regulation of COX-1 and COX-2 expression and function in thymic stromal cells. PGs produced by COX-2 in the medullary thymic stroma may regulate the development of thymocytes by modulating their interaction with stromal cells.

Type IV phosphodiesterase inhibition in experimental allergic encephalomyelitis of Lewis rats: sequential gene expression analysis of cytokines, adhesion molecules and the inducible nitric oxide synthase

Type IV phosphodiesterase inhibitors are able to suppress EAE. To investigate the effects of this therapy in the central nervous system, we serially analyzed from days 7 to 17 postinoculation the gene expression pattern of tumor necrosis factor (TNF), lymphotoxin, interferon-gamma, interleukin-1beta, the inducible nitric oxide synthase (iNOs), interleukin-10, the vascular cell adhesion molecule-1 (VCAM-1) and the intercellular adhesion molecule-1 (ICAM-1) in the spinal cord of Lewis rats with actively induced EAE, treated with Rolipram. Treated rats had a delayed and milder disease, and reduced numbers of infiltrates in the nervous tissue. The gene expression profile was similar to that of untreated rats, although delayed, with no evidence of IL-10 upregulation during the observation period. The delayed inflammation was not associated with changes in the expression of VCAM-1 and ICAM-1. In peripheral blood mononuclear cells, TNF mRNA levels were decreased and interleukin-10 was unchanged. This therapy did not alter the proliferative ability of T lymphocytes against myelin basic protein. The encephalitogenic potential of splenocytes from treated animals was also unaffected. The high levels of both iNOs mRNA and nitric oxide (NO) found before the appearance of clinical signs, suggests that NO generation might be a contributing factor to the therapeutic benefit achieved by Rolipram in the rat.

Signaling through the tetraspanin CD82 triggers its association with the cytoskeleton leading to sustained morphological changes and T cell activation

In this report, we provide new evidence of a crosstalk between T cell activation and adhesion processes through a functional cytokeleton. We show that CD82 signaling induces long-lasting adhesion, spreading and development of membrane extensions, involving actin polymerization. Addition of various co-stimuli (phorbol 12-myristate 13-acetate or monoclonal antibodies to CD3 or CD2) increases the CD82-induced morphological alterations and, reciprocally, CD82 engagement synergizes with these stimuli to induce T cell activation as indicated by both primary tyrosine phosphorylation and IL-2 production. Different kinases are involved in both processes. CD82 co-signaling involves src kinases including p56 Ick. On the other hand, the CD82-induced alterations of cell morphology are negatively regulated by cAMP-dependent kinases independently of activation of src kinases. Simultaneously with cytoskeletal rearrangements, we observed an inducible association of CD82 with the cytoskeletal matrix. In addition, the potentiating and stabilizing effects induced by CD82 cross-linking on tyrosine phosphorylation were abolished by cytoskeleton-disrupting agents. These results suggest that the actin polymerization triggered by CD82, through its ability to associate with the cytoskeletal matrix, is the primary step involved in the CD82 induced co-stimulatory activity. Our data provide further evidence for a direct role of the actin cytoskeleton as a major component for sustained signal transduction in T cells and suggest that tetraspanins could be "membrane organizers" connecting both surface and intracellular molecules.

Evidence for differences in the mechanisms by which antibodies against CD44 promote adhesion of erythroid and granulopoietic progenitors to marrow stromal cells

Adhesive interactions between haemopoietic progenitor cells and stromal elements involve a number of different molecules, some of which may be progenitor- lineage- and stage-specific. CD44 is one such molecule, although little is known about the mechanism(s) by which it is involved. In this study, several anti-CD44 monoclonal antibodies (mAb) increased the adherence of clonogenic cells, without affecting the total number of types of progenitors recoverable from the adhesion cultures. All of these mAb recognized epitopes on the globular head of CD44. In contrast, two mAb that recognized other regions of CD44 reduced progenitor adhesion to stroma. The mechanism by which one of the anti-CD44 mAb (L178) enhanced progenitor adhesion did not involve CD44-crosslinking, and was independent of VLA-4-, VLA-5- or LFA-1-mediated interactions, Ca or Mg cations, or accessory cells. In addition, CD44 expression on both progenitors and stromal cells contributed to L178-enhanced progenitor adhesion. Baseline adherence of erythroid progenitors to stroma required tyrosine kinase activity, whereas that of granulopoietic progenitors did not. However, the increase in adhesion did require tyrosine kinase activation. Additional experiments suggested that enhanced adhesion of CFU-GM to stroma may also be adenylate cyclase-dependent. Taken together, the present studies indicate both similarities and differences in the mechanisms of CD44-mediated adhesion of erythroid and granulopoietic progenitors to stromal cells.

Propentofylline and iloprost suppress the production of TNF-alpha by macrophages but fail to ameliorate experimental autoimmune encephalomyelitis in Lewis rats

Intracellular cAMP levels can be elevated by activation of cAMP-generating adenylate cyclase (AC) or inhibition of cAMP-cleavage by phosphodiesterases. Elevation of intracellular cAMP levels in immune cells inhibits production of some Th1-cytokines, particularly TNF-alpha, and results mainly in downregulation of the immune response. Experimental autoimmune encephalomyelitis (EAE) of Lewis rats is a disease mediated by type 1 T helper lymphocytes and macrophages and serves as a model of multiple sclerosis. In EAE we therefore tested the immunomodulatory potency of an AC-activating, stable prostacyclin analogue, iloprost, and of a potent and non-selective inhibitor of phosphodiesterases, propentofylline, which also has neuroprotective properties. Preventive treatment of Lewis rats with propentofylline (2 x 10 or 12.5 mg/ kg/d), iloprost (2 x 10 or 12.5 micrograms/kg/d), or both did not significantly ameliorate clinical or histological signs of EAE actively induced by immunization with myelin basic protein (MBP) in complete Freund's adjuvant. Furthermore, adoptive transfer EAE (AT-EAE), passively induced by injection of encephalitogenic MBP-specific Th1 lymphocytes, was not altered in its course by the combined application of iloprost (2 x 10 micrograms/kg/d) and propentofylline (2 x 20 mg/kg/d) starting on the day of cell transfer. In vitro assays demonstrated that iloprost strongly and propentofylline moderately inhibited the production of TNF-alpha by macrophages and that iloprost in vivo similarly suppressed TNF-alpha secretion, although this effect was limited to a few hours after a single injection. In contrast to macrophages, TNF-alpha production by antigen-activated encephalitogenic T helper line cells in vitro was completely resistant to modulation by these agents. In addition, the presence of iloprost, propentofylline, or both drugs during activation of the line cells in vitro did not impair their encephalitogenicity in vivo. The findings delineate immunomodulatory effects of both substances, particularly of iloprost, but fail to support a possible therapeutic role of these agents in autoimmune inflammation of the central nervous system.

A common inhibitory receptor for major histocompatibility complex class I molecules on human lymphoid and myelomonocytic cells

Natural killer (NK) cell-mediated lysis is negatively regulated by killer cell inhibitory receptors specific for major histocompatibility complex (MHC) class I molecules. In this study, we characterize a novel inhibitory MHC class I receptor of the immunoglobulin-superfamily, expressed not only by subsets of NK and T cells, but also by B cells, monocytes, macrophages, and dendritic cells. This receptor, called Ig-like transcript (ILT)2, binds MHC class I molecules and delivers a negative signal that inhibits killing by NK and T cells, as well as Ca2+ mobilization in B cells and myelomonocytic cells triggered through the B cell antigen receptor and human histocompatibility leukocyte antigens (HLA)-DR, respectively. In addition, myelomonocytic cells express receptors homologous to ILT2, which are characterized by extensive polymorphism and might recognize distinct HLA class I molecules. These results suggest that diverse leukocyte lineages have adopted recognition of self-MHC class I molecules as a common strategy to control cellular activation during an immune response.

Elevation of intracellular cAMP inhibits RhoA activation and integrin-dependent leukocyte adhesion induced by chemoattractants

Chemoattractant receptors of the serpentine, heterotrimeric Galphai protein-linked family can activate leukocyte integrins and in this role regulate leukocyte traffic and cell-cell interactions in immune and inflammatory responses. Using a mouse lymphoid cell line transfected with human formyl peptide or interleukin-8 receptors and normal human neutrophils as models, we show that cAMP functions as a gating element on the chemoattractant-induced rho-dependent signaling pathway leading to leukocyte integrin activation and adhesion. cAMP, acting through protein kinase A, inhibits chemoattractant-triggered integrin-dependent leukocyte adhesion. cAMP also prevents guanine nucleotide exchange on RhoA, a small GTP-binding protein of the rho subfamily, which is activated in seconds by chemoattractants. In contrast, chemoattractant-triggered intracellular calcium elevation is unaffected by cAMP, and cAMP has no effect on rho-dependent adhesion and RhoA guanine nucleotide exchange triggered through the independent protein kinase C pathway. These data suggest that cAMP-induced inhibition of rho activation may be responsible for the anti-adhesive effect of cAMP and may contribute to the anti-inflammatory activity of cAMP elevating agonists and drugs. Moreover, the findings extend the concept of cyclic nucleotide gating as a broadly important mechanism in the regulation of intracellular signaling pathways and the cellular activities they control.

A novel inhibitory receptor (ILT3) expressed on monocytes, macrophages, and dendritic cells involved in antigen processing

Immunoglobulin-like transcript (ILT) 3 is a novel cell surface molecule of the immunoglobulin superfamily, which is selectively expressed by myeloid antigen presenting cells (APCs) such as monocytes, macrophages, and dendritic cells. The cytoplasmic region of ILT3 contains putative immunoreceptor tyrosine-based inhibitory motifs that suggest an inhibitory function of ILT3. Indeed, co-ligation of ILT3 to stimulatory receptors expressed by APCs results in a dramatic blunting of the increased [Ca2+]i and tyrosine phosphorylation triggered by these receptors. Signal extinction involves SH2-containing protein tyrosine phosphatase 1, which is recruited by ILT3 upon cross-linking. ILT3 can also function in antigen capture and presentation. It is efficiently internalized upon cross-linking, and delivers its ligand to an intracellular compartment where it is processed and presented to T cells. Thus, ILT3 is a novel inhibitory receptor that can negatively regulate activation of APCs and can be used by APCs for antigen uptake.

Dexamethasone alters rapidly actin polymerization dynamics in human endometrial cells: evidence for nongenomic actions involving cAMP turnover

Glucocorticoids, in addition to their well characterized effects on the genome, may affect cell function in a manner not involving genomic pathways. The mechanisms by which the latter is achieved are not yet clear. A possible means for this action may involve the actin cytoskeleton, since the dynamic equilibrium of actin polymerization changes rapidly following exposure to several stimuli, including hormones. The aim of the present work was to find out if glucocorticoids exert rapid, nongenomic effects on actin polymerization in Ishikawa human endometrial cells, which represent a well characterized in vitro cell model expressing functional glucocorticoid receptors. Short term exposure of the cells to the synthetic glucocorticoid dexamethasone resulted in an overall decrease of the G/total-actin ratio in a time- and dose-dependent manner. Specifically, in untreated Ishikawa cells the G/total-actin ratio was 0.48 +/- 0.01 (n = 26). It became 0.35 +/- 0.01 (n = 13, P < 0.01) following exposure to 10(-7) M dexamethasone for 15 min. This was induced by a significant decrease of the cellular G-actin level, without affecting the total actin content, indicating a rapid actin polymerization. This conclusion was fully confirmed by direct fluorimetry measurements, that showed a significant increase of the F-actin content by 44% (n = 6, P < 0.001) in cells treated with dexamethasone (10(-7)M, 15 min). The rapid dexamethasone-induced alterations of the state of actin polymerization were further supported by fluorescence microscopy. The latter studies showed that the microfilaments of cells pretreated with 10(-7)M dexamethasone for 15 min were more resistant to various concentrations of the antimicrofilament drug cytochalasin B, compared to untreated cells, implying microfilament stabilization. The action of dexamethasone on actin polymerization seems to be mediated via specific glucocorticoid binding sites, since the addition of the glucocorticoid antagonist RU486 completely abolished its effect. Moreover, it appears to act via non-transcriptional pathways, since actinomycin D did not block the dexamethasone-induced actin polymerization. In addition, cell treatment with 10(-7)M dexamethasone for 15 min fully reversed the forskolin-, but not the 8-bromo-cAMP-induced actin depolymerization. In line with these findings, the cAMP content of Ishikawa cells was decreased by 29.2% after a 15 min treatment with 10(-7)M dexamethasone (n = 4, P < 0.01). In conclusion, our results showed that dexamethasone induces rapid, time-, and dose-dependent changes in actin polymerization dynamics in Ishikawa cells. This action seems to be mediated via cAMP, involving probably nongenomic pathways. The above findings offer new perspectives for the understanding of the early cellular responses to glucocorticoids.

Preventive but not therapeutic application of Rolipram ameliorates experimental autoimmune encephalomyelitis in Lewis rats

Experimental autoimmune encephalomyelitis (EAE) in Lewis rats, an animal model mimicking some aspects of multiple sclerosis, was treated with the type IV-specific phosphodiesterase inhibitor Rolipram. Actively induced EAE evoked by immunization with myelin basic protein (MBP) in complete Freund's adjuvant was delayed but only slightly ameliorated in its maximal severity by preventive treatment with Rolipram (2 x 3 mg/kg per day) starting on the day of immunization. Therapeutic administration of Rolipram (2 x 5 mg/kg per day) was begun within hours after onset of first clinical signs of EAE but could not modify the further course of the disease. Both doses had significant side effects. Injection of 5 mg Rolipram/kg provoked transient slackening and unsteady gait while chronic application of 6 mg/kg/day strongly accelerated the weight gain in adolescent rats. EAE adoptively transferred by injection of encephalitogenic T line blasts was shortened and significantly suppressed in its severity by application of Rolipram (2 x 5 mg/kg per day) starting on the day of cell transfer. In corresponding lumbar spinal cord sections density of inflammatory infiltration by T cells and macrophages was reduced. Rolipram did not prevent generation of an antigen-specific immune response in vivo. In vitro the drug inconsistently inhibited MBP-induced activation of encephalitogenic T cells. TNF-alpha secretion by encephalitogenic T cells was limited only when T cell proliferation was also affected. In contrast, TNF-alpha production by LPS-activated macrophages was consistently and markedly suppressed by Rolipram. However, since the encephalitogenic T line cells produced at least 100 times more TNF-alpha than the same number of Rolipram-sensitive macrophages, the impact of Rolipram on the total amount of TNF-alpha synthesized in EAE may be limited. Together with our histological findings, the data suggest that relevant immunosuppressive mechanisms of Rolipram may be the inhibition of migration of leukocytes into the central nervous system and to some extent its inhibitory effect on T cell proliferation and macrophage activity. The downregulatory effects of Rolipram may be partially counteracted by its augmenting impact on the production of nitric oxide by macrophages.

Prostaglandin E2 and monoclonal antibody to lymphocyte function-associated antigen-1 differentially inhibit migration of T lymphocytes across microvascular retinal endothelial cells in rat

Lymphocyte-transendothelial cell migration is a complex event, and although much is known about the receptor-ligand interactions involved, little is understood about the intracellular events which accompany these interactions, or their regulation by inflammatory mediators. In this study we have shown that activation of T lymphocytes increased the proportion of cells migrating across monolayers of cultured retinal microvascular endothelial cells by both lymphocyte function-associated antigen-1 (LFA-1)-dependent and LFA-1-independent mechanisms. In preliminary experiments, it was found that activation of T cells with mitogens such as concanavalin (Con A) increased significantly T-cell migration across the endothelial monolayers. In contrast, activation of the endothelial monolayer with interferon-gamma (IFN-gamma) (96 hr) had no effect on transendothelial migration. Investigation of adhesion molecule requirements for transendothelial migration indicated that LFA-1 was necessary (P < 0.02) but that intracellular adhesion molecule-1 did not appear to be involved. Investigation of the role of prostaglandins in transendothelial migration revealed that, while prostaglandin E2 (PGE2) did not affect adhesion molecule expression on endothelial cells or T cells, treatment of either cell significantly blocked transendothelial migration (P < 0.05). Pretreatment with PGE2 combined with LFA-1 blockade had an additive effect on inhibition of T-cell transendothelial migration, indicating that two independent mechanisms were operative. PGE2 also had a direct inhibitory effect on T-cell adhesion to the endothelium. These results highlight the importance of considering non-adhesion receptor-mediated mechanisms, perhaps involving cytoskeletal and/or motility, in the migration of T cells across endothelial monolayers.

Dissection of lymphocyte function-associated antigen 1-dependent adhesion and signal transduction in human natural killer cells shown by the use of cholera or pertussis toxin

The effect of the guanosine triphosphate-binding protein (G-protein) inhibitors cholera toxin (Ctx) and pertussis toxin (Ptx) has been analyzed on lymphocyte function-associated antigen 1 (LFA-1)-dependent adhesion and signal transduction in human natural killer (NK) cells. Ctx, but not Ptx, inhibited the LFA-1-dependent adhesion of NK cells to tumor target cells which constitutively express the intercellular cell adhesion molecule-1 (ICAM-1) and to NIH/3T3 mouse fibroblasts stably transfected with human ICAM-1. This effect was detectable only by the use of the entire Ctx but not of the Ctx B subunit. In addition, Ctx could inhibit both NK cell binding and spreading to purified ICAM-1 protein. NK cell treatment with Ctx modified neither the surface expression of LFA-1 nor its Mg2+ binding site. These findings, together with the absence of any detectable effect of Ctx on the constitutive phosphorylation of LFA-1 alpha, suggests that this toxin modifies the avidity of LFA-1 for ICAM-1 by acting on LFA-1-cytoskeletal protein association. Unlike Ctx, Ptx did not affect NK cell adhesion. The effects of Ctx and Ptx are unlikely to depend on intracellular levels of cyclic adenosine 3',5'-monophosphate (cAMP), since a strong increase of cAMP was induced by both toxins. Moreover, this was confirmed by the observation that the LFA-1-dependent adhesion was not inhibited by the adenylate cyclase activator forskolin (FSK), the phosphodiesterase inhibitor isobutyl-1-methylxanthine (IBMX), or both, which increase intracellular cAMP levels. Unlike the differential effect on cell adhesion, both the intracellular calcium [Ca2+]i increase and phosphoinositide breakdown mediated via LFA-1 were consistently inhibited in a dose-dependent manner by both Ctx and Ptx. Also in this case, the inhibitory effect did not depend on an increase of intracellular cAMP as indicated by NK cell treatment with FSK, IBMX, or both. Further evidence of the involvement of G-proteins in LFA-1-mediated signal transduction was the inhibitory effect of the GDP analog guanosine-5'-O-2-thiodiphosphate (GDP beta S) on LFA-1-mediated calcium mobilization. Taken together, our data provide evidence that the LFA-1-mediated NK cell adhesion and signal transduction are partially independent phenomena which may be regulated by different G-proteins.

CD31-triggered rearrangement of the actin cytoskeleton in human natural killer cells

In this report, we analyze whether CD31, also known as platelet-endothelial cell adhesion molecule-1 (PECAM-1), can transduce an outside-in signal in human natural killer (NK) lymphocytes in vitro. We show that CD31, but not HLA class-I cross-linking triggers an outside-in transmembrane signal in NK lymphocytes, mediating cell spreading and cytoskeletal rearrangement. These phenomena are Mg2+, but not Ca2+ dependent, suggesting that signal transduction elicited by CD31 cross-linking may involve an associated integrin. Two possible candidates would be alpha v and alpha L, whose function is known to depend on Mg2+. However, the CD31-induced cytoskeletal rearrangement was not reduced by the use of alpha v- or alpha L-specific F(ab')2, suggesting that CD31 could transduce a signal by itself or by association with a still-undefined integrin. Moreover, talin, but not vinculin or tubulin, appears to co-localize with actin microfilaments in the membrane ruffles of NK cells that undergo cytoskeleton rearrangement following CD31 cross-linking. Both spreading and cytoskeletal rearrangement appear to be regulated by intracellular cyclic-3',5'-adenosine monophosphate (cAMP). Indeed, the activator of the adenylyl cyclase, forskolin, inhibited cell spreading and cytoskeletal rearrangement induced by CD31 cross-linking. This phenomenon was also observed using the membrane-permeants cAMP analog Sp adenosine-3', 5' -cyclic monophosphothioate (Sp-cAMPS), but not its inactive isomer Rp-cAMPS. Likewise, adhesion of NK lymphocytes to NIH/3T3 murine fibroblasts transfected with the cDNA encoding human CD31 was blocked by increasing intracellular cAMPS levels. We suggest that intracellular cAMP may be involved in CD31-mediated signal transduction, and may regulate NK-endothelial cell adhesion and possibly, the tissue localization of NK cells.

Exogenous and endogenous opioids as biological response modifiers

Narcotic opioid compounds are among the most widely prescribed drug interventions for individuals suffering pain. Among the unwarranted side effects of respiratory depression, constipation, and physical dependence are the immunosuppressive qualities, particularly those which affect cell-mediated immunity. The immunosuppressive characteristics of opioid narcotics (e.g., morphine) have recently come into focus with the advent of acquired immune deficiency syndrome (AIDS) and the putative causative agent, human immunodeficiency virus type 1 (HIV-1). Specifically, a vast reservoir of HIV-1-infected individuals exists among drug abusers. Moreover, experimental evidence would suggest narcotic opioids may increase viral load in infected individuals by modifying the cellular machinery of activated leukocytes. Likewise, investigators have shown that opioids modify tumor growth and development. In this review, a comparison between endogenous opioid peptides and exogenous opiates on cell-mediated immunity and its relationship to viral infection and tumors is described.

Beneficial effect of amrinone on murine cardiac allograft survival

Amrinone is a non-glycoside positive inotropic agent with an inhibitory effect on a cyclic adenosine monophosphate (AMP) phosphodiesterase isoenzyme. In the present study, we examined the immunosuppressive action of amrinone, since several other cyclic AMP-elevating agents have been shown to suppress T lymphocyte activation. First, the in vivo effects of amrinone were investigated. Oral amrinone treatment, at 40 mg/kg per day, significantly prolonged median cardiac allograft survival compared with non-treated controls (22.0 days versus 10.5 days, P < 0.01) when DBA/2 mouse hearts (H-2d) were heterotopically transplanted into C57B1/6 mice (H-2b). Histopathological examination showed that there was less prominent cellular infiltration in the amrinone-treated than in the non-treated allografts. Plasma amrinone concentrations of mice after a single oral dose of 40 mg/kg were within the range of clinical relevance. To clarify the mechanism of action, in vitro studies were done. The generation of specific cytotoxic T lymphocytes after mixed lymphocyte culture was significantly suppressed by addition of amrinone to the culture medium at 5 micrograms/ml. The production of IL-2 and the interferon-gamma during mixed lymphocyte culture was also suppressed by amrinone at 5 micrograms/ml. However, the level of intracellular cyclic AMP in mouse splenic lymphocytes was not affected significantly by the same dose of amrinone. In conclusion, amrinone has immunosuppressive actions at the therapeutic doses, and it may be a beneficial agent for therapy against acute cardiac allograft rejection.

Regulation of interferon-gamma mRNA in a cytolytic T cell clone: Ca(2+)-induced transcription followed by mRNA stabilization through activation of protein kinase C or increase in cAMP

Activation pathways inducing the expression of the interferon (IFN)-gamma gene in a cytotoxic T lymphocyte (CTL) clone were studied for their effects on transcription and on mRNA stability. IFN-gamma was secreted by the CTL clone in response to the Ca2+ ionophore ionomycin when used in conjunction with either protein kinase C (PKC)-activating phorbol 12-myristate 13-acetate (PMA) or with agents increasing cAMP, including prostaglandin E2. We describe that ionomycin induced IFN-gamma gene transcription, which was totally inhibited in the presence of cyclosporin A (CSA), an immunosuppressant forming a calcineurin-inhibiting complex with cyclophilin. Ionomycin did not, however, permit accumulation of IFN-gamma mRNA. Activation of PKC by PMA or of cAMP-dependent protein kinase through increase in cAMP had no transcription-inducing effect, either alone or in conjunction with ionomycin, as measured in run on assays of the IFN-gamma gene. When transcription of the IFN-gamma gene, initiated in the presence of ionomycin and an agent increasing intracellular cAMP, was inhibited by CSA in the absence of PKC or cAMP-dependent protein kinase activation, the IFN-gamma mRNA was rapidly degraded (half-life = 30 min). When either PKC was activated or intracellular cAMP was increased at the time of inhibition with CSA, a stabilizing effect was observed on IFN-gamma mRNA, which led to an increase in secreted IFN-gamma. These effects were selective, they did not affect the rate of transcription of the actin gene, nor the accumulation of actin mRNA. These results show that (i) post-transcriptional events can be critical for IFN-gamma expression in activated lymphocytes, and (ii) specific stabilization of IFN-gamma mRNA can be mediated by activation of two different protein kinases involved in T cell activation.

Sustained signaling leading to T cell activation results from prolonged T cell receptor occupancy. Role of T cell actin cytoskeleton

Using antigen-specific T cell clones and peptide-pulsed antigen-presenting cells (APCs) we investigated the mechanisms that lead to sustained signaling, known to be required for activation of effector function. Four lines of evidence indicate that the T cell actin cytoskeleton plays a crucial role in T cell activation by antigen-pulsed APCs, but is not required when T cell receptor (TCR) is cross-linked by soluble antibodies. First, addition of antibodies to the major histocompatibility complex molecules recognized by the TCR aborts the ongoing intracellular calcium concentration ([Ca2+]i) increase in performed T-APC conjugates, indicating that the sustained signaling requires the continuous occupancy of TCR. Second, time-lapse image recording shows that T lymphocytes conjugated to peptide-pulsed APCs undergo a sustained [Ca2+]i increase, which is accompanied by the formation of a large and changing area of contact between the two opposing membranes. Third, drugs that disrupt the actin cytoskeleton, Cytochalasin D and and C2 Clostridium botulinum toxin induce a rapid block of [Ca2+]i rise, coincident with a block of the cyclic changes in T cell shape. Finally, the addition of Cytochalasin D or of anti-MHC antibodies to preformed conjugates inhibits interferon gamma production in an 1-antigen dose- and time-dependent fashion. These results identify T cell actin cytoskeleton as a major motor for sustaining signal transduction and possibly for driving TCR cross-linking and offer an explanation for how T cells equipped with low affinity TCR can be triggered by a small number of complexes on APCs.

Cellular mechanisms involved in morphine-mediated suppression of CTL activity

Based on a plethora of data from many laboratories, we have proposed the following mechanisms by which morphine alters immune homeostasis and immunocompetence in vivo (Fig. 2). Specifically, the administration of morphine subcutaneously via routing through blood interacts directly with opioid receptors on cells of the immune system or on receptors within the central nervous system. Although there is currently no evidence to support the direct involvement of morphine on lymphocyte opioid receptors, in vitro studies show the existence of functional, naloxone-sensitive opioid receptors (25). In addition, pharmacological and biochemical characterization of lymphocyte opioid receptors has been shown to be consistent in many instances, with the profile of neural-derived opioid receptors (25-27). Finally, recent molecular studies using oligonucleotide primers specific for the delta-class opioid receptor cloned from NG-108-15 cells (28) have been used in reverse transcription-polymerase chain reactions to generate a 400 bp product in SL which has 100% sequence homology with a published opioid receptor cloned from a brain library (35). However, future studies are necessary to establish the role of lymphocyte opioid receptors following the in vivo administration of opioids (e.g. fentanyl, methadone, and morphine). Since the administration of morphine subcutaneously appears to predominately interact with brain opioid receptors (3) located in the mesencephalon (5), other neuroendocrine systems become candidates for activation and subsequent direct modulation of immune function: (i) the HPA axis and (ii) the sympathetic nervous system (SNS).(ABSTRACT TRUNCATED AT 250 WORDS)

An inhibitor of cytotoxic functions produced by CD8+CD57+ T lymphocytes from patients suffering from AIDS and immunosuppressed bone marrow recipients

An inhibitor of the cytotoxic functions (ICF) mediated by human immunodeficiency virus (HIV)- or HLA-specific cytotoxic T lymphocytes, natural killer and lymphokine-activated killer (LAK) cells is secreted by CD8+CD57+ T lymphocytes, a subset expanded during infection with HIV and after bone marrow transplantation. We previously showed an apparent molecular mass of 20-30 kDa for this soluble glycosylated concanavalin A-binding inhibitor which is distinct from known cytokines. Here, we report a characterization of the mechanism of action of this CD8+CD57+ ICF. We show that the ICF-induced inhibition of LAK cell cytolytic activity is transient, with a spontaneous recovery of cytolytic potential after 18 h. When testing interactions of ICF with a large set of cytokines we found that the ICF-mediated inhibition of cytotoxic functions is antagonized by two cytokines: recombinant interleukin (rIL)-4 and recombinant interferon (rIFN)-gamma. Finally, we show that ICF acts at the level of cytolytic effector cells, where it induces a significant increase of cyclic AMP (cAMP) level. In contrast, no modification of either cell surface antigen expression or of target/effector cell conjugate formation could be evidenced. Addition of rIL-4 and rIFN-gamma reverses such an increase of cAMP levels and in parallel restores the cytolytic activity. Altogether, these data demonstrate that the glycoprotein ICF produced by CD8+CD57+ cells (1) inhibits cell-mediated cytotoxicity by sensitizing cytolytic effector cells to the cAMP pathway, and (2) is part of a cytokine network controlling cell-mediated cytotoxic functions.

Differential effects of cyclic adenosine 3',5'-monophosphate on T cell cytotoxicity

We have investigated natural killer cell and T cell cytotoxicity using different assays and report a dual effect of cyclic adenosine 3',5'-monophosphate (cAMP) on T cell cytotoxicity depending on the activation status of the effector cell and the test system in question. cAMP enhanced the capacity of pre-activated T cells to induce DNA fragmentation in the target cell, while it inhibited spontaneous T cell cytotoxicity and natural killer cell cytotoxicity in conventional assays based on 51Cr release. The enhancement was most likely mediated by the cAMP-dependent protein kinase type II (cAKII), which is the particular isoform in T cells associated with the centrosome and the microtubule organizing center (MTOC). We show the complete co-localization of the cAKII with the centrosome after conjugate formation. Furthermore, the reorganization of the MTOC following conjugate formation brings the type II kinase into close proximity with the T lymphocyte membrane are engaged in the effector-target interaction. Functional studies utilizing different cAMP-analog combinations further substantiate the involvement of the type II kinase.