Vasoactive intestinal peptide as a modulator of lymphocyte and immune function

Homeostatic and therapeutic roles of VIP in smooth muscle function: myo-neuroimmune interactions

We tested the hypothesis that spontaneous release of vasoactive intestinal peptide (VIP) from enteric neurons maintains homeostasis in smooth muscle function in mild inflammatory insults and that infusion of exogenous VIP has therapeutic effects on colonic smooth muscle dysfunction in inflammation. In vitro experiments were performed on human colonic circular smooth muscle tissues and in vivo on rats. The incubation of human colonic circular smooth muscle strips with TNF-alpha suppressed their contractile response to ACh and the expression of the pore-forming alpha(1C) subunit of Ca(v)1.2 channels. VIP reversed both effects by blocking the translocation of NF-kappaB to the nucleus and its binding to the kappaB recognition sites on halpha(1C)1b promoter. The translocation of NF-kappaB was inhibited by blocking the degradation of IkappaBbeta. Induction of inflammation by a subthreshold dose of 17 mg/kg trinitrobenzene sulfonic acid (TNBS) in rats moderately decreased muscularis externa concentration of VIP, and it had little effect on the contractile response of circular smooth muscle strips to ACh. The blockade of VIP and pituitary adenylate cyclase-activating peptide receptors 1/2 during mild inflammatory insult significantly worsened the suppression of contractility and the inflammatory response. The induction of more severe inflammation by 68 mg/kg TNBS induced marked suppression of colonic circular muscle contractility and decrease in serum VIP. Exogenous infusion of VIP by an osmotic pump reversed these effects. We conclude that the spontaneous release of VIP from the enteric motor neurons maintains homeostasis in smooth muscle function in mild inflammation by blocking the activation of NF-kappaB. The infusion of exogenous VIP mitigates colonic inflammatory response and smooth muscle dysfunction.

Immunocytochemical investigation of immune cells within human primary and permanent tooth pulp

AIM

The aim of this study was to determine whether there are any differences in the number and distribution of immune cells within human primary and permanent tooth pulp, both in health and disease.

DESIGN

The research took the form of a quantitative immunocytochemical study. One hundred and twenty-four mandibular first permanent molars and second primary molars were obtained from children requiring dental extractions under general anaesthesia. Following exodontia, 10-microm-thick frozen pulp sections were processed for indirect immunofluorescence. Triple-labelling regimes were employed using combinations of the following: (1) protein gene product 9.5, a general neuronal marker; (2) leucocyte common antigen (LCA); and (3) Ulex europaeus I lectin, a marker of vascular endothelium. Image analysis was then used to determine the percentage area of immunostaining for LCA.

RESULTS

Leucocytes were significantly more abundant in the pulp horn and mid-coronal region of intact and carious primary teeth, as compared to permanent teeth (P < 0.05, anova). Both dentitions demonstrated the presence of well-localized inflammatory cell infiltrates and marked aborization of pulpal nerves in areas of dense leucocyte accumulation.

CONCLUSIONS

Primary and permanent tooth pulps appear to have a similar potential to mount inflammatory responses to gross caries The management of the compromised primary tooth pulp needs to be reappraised in the light of these findings.

Novel mechanisms of class II major histocompatibility complex gene regulation

Class II MHC molecules present processed peptides from exogenous antigens to CD4+ helper T lymphocytes. In so doing, they are central to immunity, driving both the humoral and cell mediated arms of the immune response. Class II MHC molecules, and the genes encoding them, are expressed primarily in cells of the immune system (B cells, thymic epithelial cells, activated T cells and professional antigen presenting cells). The expression is also under developmental control. Research over the past 20 years have provided a clear understanding of the cis-elements and transcription factors that regulate the expression of Class II MHC genes. Perhaps the most critical advance has been the discovery of CIITA, a non- DNA binding activator of transcription that is a master control gene for class II gene expression. Current research is focused on understanding the situations where class II MHC gene expression occurs in a CIITA-independent pathway, and the molecular basis for this expression. Finally, significant emphasis is being placed on targeting class II MHC transcription factors to either inhibit or stimulate the immune response to transplanted tissue or in cell based vaccines. This communication outlines recent advances in this field and discusses likely areas for future research.

Consequences of intestinal inflammation on the enteric nervous system: neuronal activation induced by inflammatory mediators

The ENS is responsible for the regulation and control of all gastrointestinal functions. Because of this critical role, and probably as a consequence of its remarkable plasticity, the ENS is often relatively well preserved in conditions where the architecture of the intestine is seriously disrupted, such as in IBD. There are structural and functional changes in the enteric innervation in animal models of experimental intestinal inflammation and in IBD. These include both up and down regulation of transmitter expression and the induction of new genes in enteric neurons. Using Fos expression as a surrogate marker of neuronal activation it is now well established that enteric neurons (and also enteric glia) respond to inflammation. Whether this "activation" is limited to a short-term functional response, such as increased neuronal excitability, or reflects a long-term change in some aspect of the neuronal phenotype (or both) has yet to be firmly established, but it appears that enteric neurons are highly plastic in their response to inflammation.

Evidence for neural regulation of inflammatory synovial cell functions by secreting calcitonin gene-related peptide and vasoactive intestinal peptide in patients with rheumatoid arthritis

OBJECTIVE

To elucidate the possible involvement of the nervous system in the regulation of pathophysiologic responses in patients with rheumatoid arthritis (RA), we examined the expression of peripheral nerves containing the neuropeptides calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) in RA synovium and their effects on RA synovial cell functions.

METHODS

The effects of CGRP and VIP on proinflammatory cytokine and matrix metalloproteinase (MMP) production by RA synovial cells were estimated by enzyme-linked immunosorbent assay, and their messenger RNA (mRNA) expression by reverse transcription-polymerase chain reaction (RT-PCR) using limiting dilutions of the complementary DNA. Expression of CGRP receptors (CGRPRs) and VIP receptors (VIPRs) on RA synovial cells was assessed by RT-PCR and radioreceptor assays. The functions of CGRPRs and VIPRs of the synovial cells were studied by using a CGRPR antagonist and a VIPR antagonist, respectively.

RESULTS

CGRP and VIP inhibited the proliferation of, and the proinflammatory cytokine and MMP production by, RA synovial cells at the level of mRNA expression. Expression of CGRPR and VIPR on RA fibroblast-like synovial cells was confirmed by RT-PCR and radioreceptor assays. Functions of the neuropeptide receptors were inhibited by their receptor antagonists. CGRP and VIP inhibited nuclear translocation and phosphorylation of the transcription factor cAMP response element binding protein in RA synovial cells.

CONCLUSION

CGRP and VIP inhibited excessive synovial cell functions, which suggests neural regulation of inflammatory responses in patients with RA and possible clinical application of the neuropeptides.

Thymosin alpha 1 interacts with the VIP receptor-effector system in rat and mouse immunocompetent cells

Thymic peptide thymosin alpha 1 (10(-11) to 10(-6) M) is shown to interact with the VIP receptor-effector system in rat and mouse peritoneal macrophages, and both rat peripheral blood lymphocytes and spleen lymphocytes. In all models, thymosin alpha 1 inhibits 125I-VIP binding with a potency that is in a range 1000-1700 times lower than that of the native VIP. Interaction of thymosin alpha 1 with VIP receptors is compared with that of some structurally VIP-related peptides such as helodermin, PHI, secretin, and glucagon. The order of potency in inhibiting 125I-VIP binding was VIP > helodermin > PHI > secretin > thymosin alpha 1. Thymosin alpha 1 (10(-10) to 10(-6) M) was weak in stimulating adenylyl cyclase activity. Its efficacy is in a range 900-1800 times lower than that of native VIP in all cell types studied. The analysis of the sequence of both complete and N-terminal portion of thymosin alpha 1 reveals close structural and physicochemical similarities with the members of the so-called VIP family of polypeptides. Taken together, experimental data support that thymosin alpha 1 must be included like the lowest partial agonist of the VIP family of polypeptides and it is a VIP receptor antagonist with weak intrinsic activity.

The disodium salt of EDTA inhibits the binding of vasoactive intestinal peptide to macrophage membranes: endodontic implications

The purpose of this study was to investigate the effect of the disodium salt of ethylenediamine tetraacetate (EDTA), a calcium ion chelator used in the root canal therapy, on vasoactive intestinal peptide (VIP) binding to macrophage membranes (MM's). Binding assays were conducted at 15 degrees C in 0.5 ml of 50 mM Tris-HCl buffer (pH 7.5) containing 1.6% (w/v) bovine serum albumin, 1.2 mg/ml of bacitracin, and different EDTA concentrations, using 45 pM of [125I]VIP as tracer. Results showed that EDTA inhibits VIP binding to MM's in a dose-dependent manner, with an IC50 value of 5.4 mM (p < 0.01). EDTA concentrations equal or higher than 100 mM of abolished VIP-MM interaction. Taking into account that the macrophage plays an essential role in inflammatory reactions and the immune response, we conclude that the apical extrusion of EDTA during root canal therapy could modify VIP-macrophage interaction modulating the inflammatory mechanisms involved in periapical lesions.

The significance of vasoactive intestinal polypeptide (VIP) in immunomodulation

Evidence for VIP influences on immune function comes from studies demonstrating VIP-ir nerves in lymphoid organs in intimate anatomical association with elements of the immune system, the presence of high-affinity receptors for VIP, and functional studies where VIP influences a variety of immune responses. Anatomical studies that examine the relationship between VIP-containing nerves and subpopulations of immune effector cells provide evidence for potential target cells. Additionally, the presence of VIP in cells of the immune system that also possess VIP receptors implies an autocrine function for VIP. The functional significance of VIP effects on the immune system lies in its ability to help coordinate a complex array of cellular and subcellular events, including events that occur in lymphoid compartments, and in musculature and intramural blood circulation. Clearly, from the work described in this chapter, the modulatory role of VIP in immune regulation is not well understood. The pathways through which VIP can exert an immunoregulatory role are complex and highly sensitive to physiological conditions, emphasizing the importance of in vivo studies. Intracellular events following activation of VIP receptors also are not well elucidated. There is additional evidence to suggest that some of the effects of VIP on cells of the immune system are not mediated through binding of VIP to its receptor. Despite our lack of knowledge regarding VIP immune regulation, the evidence is overwhelming that VIP can interact directly with lymphocytes and accessory cells, resulting in most cases, but not always in cAMP generation within these cells, and a subsequent cascade of intracellular events that alter effector cell function. VIP appears to modulate maturation of specific populations of effector cells, T cell recognition, antibody production, and homing capabilities. These effects of VIP are tissue-specific and are probably dependent on the resident cell populations within the lymphoid tissue and the surrounding microenvironment. Different microenvironments within the same lymphoid tissue may influence the modulatory role of VIP also. Effects of VIP on immune function may result from indirect effects on secretory cells, endothelial cells, and smooth muscle cells in blood vessels, ducts, and respiratory airways. Influences of VIP on immune function also may vary depending on the presence of other signal molecules, such that VIP alone will have no effect on a target cell by itself, but may greatly potentiate or inhibit the effects of other hormones, transmitters, or cytokines. The activational state of target cells may influence VIP receptor expression in these cells, and therefore, may determine whether VIP can influence target cell activity. Several reports described in this chapter also indicate that VIP contained in neural compartments is involved in the pathophysiology of several disease states in the gut and lung. Release of inflammatory mediators by cells of the immune system may destroy VIP-containing nerves in inflammatory bowel disease and in asthma. Loss of VIPergic nerves in these disease states appears to further exacerbate the inflammatory response. These studies indicate that altered VIP concentration can have significant consequences in terms of health and disease. In addition, the protective effects of VIP from tissue damage associated with inflammatory processes described in the lung also may be applicable to other pathological conditions such as rheumatoid arthritis, anaphylaxis, and the swelling and edema seen in the brain following head trauma. While VIP degrades rapidly, synthetic VIP-like drugs may be developed that interact with VIP receptors and have similar protective effects. Synthetic VIP-like agents also may be useful in treating neuroendocrine disorders associated with dysregulation of the hypothalamic-pituitary-adrenal axis, and pituitary release of prolactin.

Homologous regulation of vasoactive intestinal peptide (VIP) receptors on rat peritoneal macrophages

In the present study, we examined the effect of pretreatment with VIP and various peptides structurally related to VIP such us PHI, helodermin, and secretin on VIP receptor number and affinity, as well as VIP-stimulated cyclic AMP production in rat peritoneal macrophages. Short-term (5-30 min) exposures of rat peritoneal macrophages to 0.1 microM VIP induced a rapid reduction in specific binding. Pretreatment for 15 and 30 min caused 26% (SEM = 6) and 48% (SEM = 4) reduction in specific binding, respectively. The maximal effect was observed at 120 min, causing a decrease of 67% (SEM = 6) in specific binding. Pretreatment with 0.1 microM VIP for 15, 30, and 120 min caused 23% (SEM = 9), 52% (SEM = 4), and 76% (SEM = 4) reduction in cyclic AMP production, respectively. Only VIP concentrations at the nanomolar level and higher were shown to be effective. The potency of VIP and related peptides to desensitize was similar to their potency to occupy receptors and to activate cyclic AMP production. The internalization of radioiodinated VIP was also studied. It was shown that receptor-bound ligand is internalized during the downregulation process. However, the diminution in VIP binding to macrophages was not completely explained by internalization.

Receptor-independent mechanisms are involved in the priming of neutrophil's oxidase by vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) primed the respiratory burst of human neutrophils induced by phorbol myristate acetate (PMA) and by the chemotactic peptide N-formyl-Met-Leu-Phe (fMLP). The sigmoidal-shaped curve of the priming effect of VIP differs for both agonist since the Hill coefficient was close to three in the case of neutrophil activation by fMLP whereas the corresponding value for PMA was close to one. The priming effect of VIP was enhanced when neutrophils were stimulated by FMLP in the presence of sphinganine, a protein kinase C inhibitor, at concentrations which almost abolished the response to PMA. VIP failed to increase resting cytosolic free calcium and to modify the transient increase in [Ca2+]i induced by fMLP. The described results point out that the mechanism of the priming of neutrophils by VIP is also independent of calcium and protein kinase C. The absence of VIP receptors in plasma membrane of neutrophils suggests that a receptor-independent mechanism modulates the agonist-triggered signaling pathway. The priming of neutrophils by VIP can not be considered as a pharmacological effect, as may be deduced from the required VIP concentration; it should be rather considered that the enhancement of the formation of reactive oxygen metabolites by VIP may be interesting in the understanding of the neuroimmune axis.

Immunohistochemical localization of peptidergic nerve fibers and neuropeptide receptors in Peyer's patches of the cat ileum

This study examined the distribution of peptidergic nerve fibers in Peyer's patches to determine whether appropriate receptors were present. Vasoactive intestinal peptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and receptors for VIP and SP were localized in lymphoid follicles of the cat ileum using a combined indirect horseradish peroxidase and streptavidin-biotin method. The margins of follicles were innervated by nerve fibers containing VIP, SP and CGRP. Nerve fibers were predominantly around lymphatics and high endothelial venules at the edges of follicles. Specific receptors for VIP and SP were present at the margins of follicles and in the lamina propria around crypts. VIP receptors were numerous on T cells within and around high endothelial venules and lymphatic vessels and at the margins of follicles. SP receptors were identified on a small number of T and B cells, granulocytes and macrophages, restricted to the margins of follicles. The defined distribution in ileal lymphoid tissue of nerve fibers containing VIP and SP and the corresponding localization of their appropriate receptors support immunoregulatory roles for neuropeptides in mucosal immunity.

Priming effect of vasoactive intestinal peptide on the respiratory burst of neutrophils non-mediated by plasma membrane receptors

Vasoactive intestinal peptide (VIP) primed the respiratory burst of human neutrophils in response to phorbol myristate acetate. Maximal and half-maximal effects were achieved at 10 and 0.5 nM VIP respectively. The absence of plasma membrane receptors to VIP in neutrophils suggests that priming of the respiratory burst should be considered as a side effect of VIP. However, from the above indicated concentration range, the priming of the neutrophil by VIP cannot be considered as a pharmacological effect. The enhancement of the formation of reactive oxygen metabolites by VIP may be important in the pathology of VIP-producing tissues.

Molecular cloning and functional characterization of a human liver vasoactive intestinal peptide receptor

We have isolated a cDNA from a human liver library which is 2349 base pairs in length and encodes a near-full length seven transmembrane receptor (432 amino acids), 85% homologous to the amino acid sequence for the rat vasoactive intestinal peptide (VIP) receptor. Northern blot analysis identifies a major species at 3.3 kb in lung, and to a lesser extent in brain, heart and liver. In order to confirm the identity of this human clone, double-stranded oligonucleotides encoding the signal peptide of the rat VIP receptor were constructed by polymerase chain reaction and attached to the 5' end of the human clone. COS cells transiently transfected with this human VIP receptor chimera, express a single binding site for 125I-VIP with a Kd of 9.2 +/- 2 nM. Related peptides displace 125I-VIP with a relative potency of VIP = PACAP > helodermin >> PHM > secretin, which is similar to the binding profile seen in human tissues. This human chimeric receptor is functionally coupled to the stimulation of adenylyl cyclase in transfected COS cells, as evidenced by a dose-dependent increase in intracellular cAMP accumulation. These studies indicate that this cDNA encodes a human liver VIP receptor which is functionally coupled to the activation of adenylyl cyclase.

Characteristics of receptors for VIP in rat peritoneal macrophage membranes

Vasoactive intestinal peptide (VIP) receptors were investigated in rat peritoneal macrophage membranes (RPMM) using [125I]VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on time, temperature, and membrane concentration. The Scatchard analysis of binding data was consistent with the existence of two classes of VIP binding sites with Kd values of 0.60 +/- 0.08 and 275 +/- 39 nM and binding capacities of 580 +/- 71 and 72,500 +/- 810 fmol VIP/mg protein, respectively. The interaction showed a high degree of specificity, as suggested by competitive displacement experiments with several peptides structurally or not structurally related to VIP. These pharmacological studies showed the following order of potency: VIP (IC50 = 1 nM) > rGRF (IC50 = 13 nM) > PHI (IC50 = 421 nM) >> secretin. Glucagon, somatostatin, insulin octapeptide of cholecystokinin [CCK(26-33)], and pancreastatin were ineffective at concentrations up to 1 microM. Binding of [125I]VIP to membranes is markedly reduced by increasing the ionic strength of incubation medium. Treatment of membranes with dithiothreitol, trypsin, and phospholipases A2 and C resulted in a loss of the ability of these membranes to bind VIP. However, treatment with phospholipase D did not affect binding of VIP by membranes. The molecular characterization of VIP receptors in RPMM was performed after [125I]VIP cross-linking to membranes using the cross-linker dithiobis (succinimidyl propionate). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membrane proteins revealed specific [125I]VIP-protein complexes of M(r) 55,000 +/- 1700, 35,000 +/- 900, and 22,000 +/- 500.

Vasoactive intestinal peptide inhibits fMLP-induced respiratory burst in human lymphocytes

N-Formyl-Methionyl-Leucyl-Phenylalanine (fMLP) induced in lymphocytes the production of reactive oxygen intermediates in a process which was inhibited by the presence of Vasoactive Intestinal Peptide (VIP) in a dose-dependent response at VIP concentrations in the range 10(-10)-10(-7) M. The dissociation constant for the high-affinity receptors of VIP agrees with the ID50 of the activation of adenylate cyclase which are close to 0.2 nM VIP, whereas the ID50 for the inhibition by VIP of fMLP-induced chemiluminescence approaches to 5 nM VIP. Both IBMX and Forskolin produced in lymphocytes an inhibition of fMLP-induced chemiluminescence. The degree of inhibition was ascertained to be additive in the presence of the above indicated agents and suboptimal concentrations of VIP. The saturation by cAMP of its putative target, the regulatory subunit of protein kinase A, appears to be required for the onset of the inhibitory effect of VIP. This study provides evidence of the molecular signal, namely cAMP, which provokes an inhibitory effect on chemoatractant-stimulated human lymphocytes and further support a role for VIP as a mediator in the neuroimmune system.

Vasoactive intestinal peptide (VIP) inhibits substrate adherence capacity of rat peritoneal macrophages by a mechanism that involves cAMP

In this study, vasoactive intestinal peptide (VIP) is shown to inhibit substrate adherence capacity of rat peritoneal macrophages. The inhibitory response occurred in the 0.1-1,000 nM range of VIP concentrations and it was a time-dependent process. At 15 min, half maximal inhibition (IC50) was obtained at 0.37 +/- 0.26 nM and maximal inhibition (53.8%) at 10(-6) M VIP. The inhibitory effect of VIP was correlated with the stimulation by this peptide of cyclic AMP (cAMP) production in rat peritoneal macrophages. Moreover, agents that inhibited VIP-stimulated cAMP production, such as the VIP-antagonist [4-Cl-D-Phe6, Leu17]-VIP and somatostatin, also decreased the inhibitory effect of VIP on substrate adherence capacity of macrophages. On the contrary, the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) and the lipid-soluble derivative of cAMP N6,2'-O-dibutyryl cAMP (Bu-cAMP) inhibited the adherence of macrophages to substrate and potentiated the inhibitory action of VIP. These results demonstrate that VIP inhibits substrate adherence capacity of rat peritoneal macrophages by a mechanism that involves cAMP, and show, for the first time, an action of VIP on the function of peritoneal macrophages.

Norepinephrine and vasoactive intestinal peptide induce IL-6 secretion by astrocytes: synergism with IL-1 beta and TNF alpha

Resident glial cells and invading inflammatory cells are responsible for cytokine production within the brain. Astrocytes are known to secrete a variety of cytokines upon stimulation with cytokines themselves, protein kinase C activators, bacterial or viral constituents. Astrocytes also have surface receptors for a wide number of neurotransmitters and neuropeptides and some of these substances affect astrocyte immune functions, such as major histocompatibility complex (MHC) class II antigen expression. To elucidate the activity of neuromediators on cytokine secretion by glial cells, we studied the secretion of interleukin-6 (IL-6) by cultured rat astrocytes after incubation with various neurotransmitters and neuropeptides. Norepinephrine (NE) and the beta-adrenergic agonist isoproterenol (IPT) induced IL-6 secretion in a dose-dependent fashion. NE effect was predominantly mediated by beta 2-adrenergic receptors with a minor contribution of alpha 1-adrenergic receptors. The induction of IL-6 release by dibutyryl-cAMP indicated that IL-6 secretion secondary to beta 2-adrenergic receptor activation probably occurs through cAMP signalling pathways. Vasoactive intestinal peptide (VIP) was the sole neuropeptide able to induce IL-6 secretion. NE and VIP promoted IL-6 mRNA synthesis and both substances synergized with interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) in inducing IL-6 release. Our findings provide further evidence that neurons modulate astrocyte cytokine production and thereby regulate central nervous system immune functions.

Guanine nucleotide regulation of VIP binding to rat peritoneal macrophage membranes

In the present study, we have examined the effect of guanine nucleotides on VIP binding to rat peritoneal macrophage membranes. Both guanosine 5'-triphosphate (GTP) and its nonhydrolizable analog guanosine 5'-beta, Y-imidotriphosphate [Gpp(NH)p] inhibited, in a dose-dependent manner, the VIP binding to its specific binding sites. Half-maximal inhibition (IC50) was observed at 5.4 +/- 0.5 microM GTP. The inhibitory effect of GTP was due to an increase of the dissociation rate of peptide bound to membranes. The specificity of the binding inhibition was assessed from the lack of action of the other nucleotides tested. These results directly suggest the coupling of VIP binding sites with guanine nucleotide binding proteins in rat peritoneal macrophage membranes.

Structural requirements for the occupancy of pituitary adenylate-cyclase-activating-peptide (PACAP) receptors and adenylate cyclase activation in human neuroblastoma NB-OK-1 cell membranes. Discovery of PACAP(6-38) as a potent antagonist

In these structure activity studies, the 46 analogs of the 27-amino-acid form of the pituitary-adenylate-cyclase-activating peptide, PACAP(1-27), and the 38-amino-acid form, PACAP(1-38), were either monosubstituted or bisubstituted at positions 1-3, 20 and 21 or N-terminally shortened. All analogs were compared on human neuroblastoma NB-OK-1 cell membranes for their ability to occupy 125I-[AcHis1]PACAP(1-27)-labelled receptors (AcHis, N alpha-acetylhistidine) and to activate adenylate cyclase (in terms of potency and intrinsic activity). The monophasic slope of dose/effect curves on both parameters suggested interaction with one class of PACAP receptor. Residues 28-38 in the C-terminally extended peptide, PACAP(1-38), played a favorable role in recognition, in that receptors coupled to adenylate cyclase were, in general, more sensitive to PACAP(1-38) analogs than to the corresponding PACAP(1-27) analogs. At variance with PACAP(6-27), PACAP(6-38) was well recognized and acted as a potent competitive antagonist (Ki 1.5 nM). Residues 1-3 were all important in enzyme activation: modification of the beta-turn potential gave full agonists (the LAla2 and DAla2 derivatives) or partial agonists (LPhe2 and DPhe2; LArg2 and DArg2; Glu3 and Asn3). Finally, a proper alpha-helix was also important: the combined substitution of Lys21/Lys22 by Gly21/Gly22 decreased the binding affinity sharply.

Modulation of human natural killer activity by vasoactive intestinal peptide (VIP) family. VIP, glucagon and GHRF specifically inhibit NK activity

Vasoactive intestinal polypeptide (VIP) is a neuropeptide, which also modulates some immune functions. Natural killer (NK) cell activity was already found to be diminished by VIP. In the present paper we report that VIP is able to decrease NK cell activity of human large granular lymphocytes (LGL), showing maximal inhibition at doses ranging from 10(-8) to 10(-6) M. Some neuropeptides, belonging to the VIP family (secretin, glucagon, peptide histidine isoleucine, PHI and human growth hormone releasing factor, GHRF), were also tested. Among these peptides, secretin and PHI were shown to be uneffective on NK cell activity whereas glucagon and GHRF were inhibitory. The D50 of GHRF was similar to that of VIP (10(-9) M), the D50 of glucagon was 10(-8) M. A recently synthesized VIP-antagonist (4Cl-D-Phe6-Leu17) was then used to assess its ability to reverse the VIP-mediated inhibition of NK activity. The antagonist was able to completely reverse the inhibitory effect of VIP on NK activity. The VIP-antagonist was also able to reverse the inhibitory effect of glucagon and GHRF, even though to a lesser extent than for VIP. Our data provide a new physiological observation regarding the functional activity of LGL, supporting the presence of a receptor for VIP on human LGL with NK activity.

Stimulatory effect of vasoactive intestinal peptide (VIP) on cyclic AMP production in rat peritoneal macrophages

Vasoactive intestinal peptide (VIP) stimulated cyclic AMP production in rat peritoneal macrophages. The stimulatory effect of VIP was dependent on time, temperature and cell concentration, and was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). At 15 degrees C, the response occurred in the 0.1-1000 nM range of VIP concentrations. Half maximal stimulation of cellular cyclic AMP (ED50) was obtained at 1.2 +/- 0.5 nM VIP, and maximal stimulation (about 3-fold basal level) was obtained between 100-1000 nM. The cyclic AMP system of rat peritoneal macrophages showed a high specificity for VIP. The order of potency observed in inducing cyclic AMP production was VIP greater than rGRF greater than hGRF greater than PHI greater than secretin. Glucagon, insulin, pancreastatin and octapeptide of cholecystokinin did not modify cyclic AMP levels at concentrations as high as 1 microM. The beta-adrenergic agonist isoproterenol increased the cyclic AMP production and show additive effect with VIP. Somatostatin inhibits the accumulation of cyclic AMP in the presence of both vasoactive intestinal peptide and isoproterenol. The finding of a VIP-stimulated cyclic AMP system in rat peritoneal macrophages, together with the previous characterization of high-affinity receptors for VIP in the same cell preparation, strongly suggest that VIP may be involved in the regulation of macrophage function.

Vasoactive intestinal peptide enhances phorbol myristate acetate-induced chemiluminescence in human lymphocytes

Phorbol-myristate-acetate (PMA) induced in lymphocytes the production or reactive oxygen intermediates in a process which was stimulated by the presence of vasoactive intestinal peptide (VIP) in a dose-dependent response at VIP concentrations in the range 10(-11)-10(-8) M. The dissociation constant for the high-affinity receptors of VIP agreed with the ID50 of the activation of adenylate cyclase, and the ID50 for the stimulation by VIP of PMA-induced chemiluminescence, which were close to 0.2 nM VIP. Forskolin produced in lymphocytes an effect quite similar to VIP. A comparison of the response to VIP and forskolin of lymphocytes and monocytes showed that, in contrast to forskolin, VIP failed to induce the above described effect in monocytes. A possible mechanism involving protein kinase C, which is activated by PMA, and an intracellular signal linked to VIP receptors is pointed out. This study further supports a role for VIP as a mediator in the neuroimmune system.

Increased plasma levels of vasoactive intestinal polypeptide in pre-eclampsia

OBJECTIVE

To investigate the plasma vasoactive peptide (VIP) levels in pregnancies complicated by pre-eclampsia.

DESIGN

A prospective clinical study.

SETTING

University Department of Obstetrics, Tromsø, Norway.

SUBJECTS

18 women with untreated gestational proteinuric hypertension between 32 and 40 weeks gestation (13 primigravid) and 8 women with normal pregnancies of similar gestational age.

INTERVENTIONS

Fasting blood samples on two occasions, 10 min apart.

MAIN OUTCOME MEASURES

Plasma VIP measured by radioimmunoassay.

RESULTS

Mean maternal plasma VIP was 13.9 (SEM 1.7) pmol/l in those with pre-eclampsia and 4.4 (SEM 0.5) pmol/l in normal pregnancies (P less than 0.0001).

CONCLUSION

The increased levels of VIP in pre-eclampsia may represent a powerful compensatory mechanism to restore vascular perfusion of various organs, including the uterus and placenta.

Glucocorticoids upregulate the high affinity receptors for vasoactive intestinal peptide (VIP) on human mononuclear leucocytes in vitro

Glucocorticoids were shown to induce a time- and dose-dependent increment of specific [125I]VIP-binding on human mononuclear leucocytes in culture. Cortisol (0.5 microM) increased specific [125I]VIP-binding to 132% of control after 48 h preincubation, to 162% after 96 h, and to 175% after 144 h. Dexamethasone (0.5 microM) increased specific [125I]VIP-binding to 140%, 194% and 210% after the same time periods. Analysis of the binding data revealed an increase in Bmax to 119% by cortisol (0.5 microM, 48 h) and to 194% by dexamethasone (0.5 microM, 48 h), and no change in Kd for the high affinity receptor after preincubation. The number of low affinity binding sites for VIP was also increased by glucocorticoids. However, in contrast to the high affinity receptor, low affinity binding sites were initially downregulated in culture, and glucocorticoids induced a restitution to number and affinity close to those obtained for freshly isolated leucocytes. This increase in low affinity binding sites was blocked by actinomycin D, in contrast to the high affinity receptor upregulation which was independent of de novo protein synthesis. Furthermore, corresponding to the glucocorticoid induced high affinity receptor upregulation, an increase in VIP stimulated cyclic AMP production was observed. The results of this study suggest that leucocyte responsiveness to VIP can be influenced by glucocorticoids.

Characterization of functional receptors for vasoactive intestinal peptide (VIP) in rat peritoneal macrophages

Functional vasoactive intestinal peptide (VIP) receptors have been characterized in rat peritoneal macrophages. The binding depended on time, temperature and pH, and was reversible, saturable and specific. Scatchard analysis of binding data suggested the presence of two classes of binding sites: a class with high affinity (kd = 1.1 +/- 0.1 nM) and low capacity (11.1 +/- 1.5 fmol/10(6) cells), and a class with low affinity (kd = 71.6 +/- 10.2 nM) and high capacity (419.0 +/- 80.0 fmol/10(6) cells). Structural requirements of these receptors were studied with peptides structurally or not structurally related to VIP. Several peptides inhibited 125I-VIP binding to rat peritoneal macrophages with the following order of potency: VIP greater than rGRF greater than hGRF greater than PHI greater than secretin. Glucagon, insulin, somatostatin, pancreastatin and octapeptide of cholecystokinin (CCK 26-33) were ineffective. VIP induced an increase of cyclic AMP production. Half-maximal stimulation (ED50) was observed at 1.2 +/- 0.5 nM VIP, and maximal stimulation (3-fold above basal levels) was obtained between 0.1-1 microM. Properties of these binding sites strongly support the concept that VIP could behave as regulatory peptide on the macrophage function.

Effects of high in vivo levels of vasoactive intestinal polypeptide on function of circulating lymphocytes in humans

To examine the possible in vivo significance of the immunomodulatory effects of vasoactive intestinal polypeptide described in vitro, several parameters of peripheral blood lymphocyte function were studied in a patient with a pancreatic endocrine tumor and high circulating levels of vasoactive intestinal polypeptide. There was no imbalance of the circulating lymphocyte subpopulations, and the in vitro responses of the patient's lymphocytes to mitogens were normal. However, there was an increased number (32%) of peripheral lymphocytes expressing interleukin 2 receptor. Serum immunoglobulin M levels were higher than in controls, and the patient's lymphocytes exhibited a spontaneous in vitro immunoglobulin M production higher than normal. Comparable increases in both interleukin 2 receptor expression and immunoglobulin M production were induced in vitro in normal peripheral lymphocyte cultures by the addition of vasoactive intestinal polypeptide concentrations similar to that detected in the patient's plasma. These findings indicate that a modulatory effect of vasoactive intestinal polypeptide on lymphocyte activation and immunoglobulin synthesis may be operating in vivo. They also suggest that vasoactive intestinal polypeptide does not mediate major defects in peripheral blood lymphocyte function in vivo.

Somatostatin and vasoactive intestinal peptide reduce interferon gamma production by human peripheral blood mononuclear cells

There is increasing evidence that neuropeptide modulation of the immune response is an important physiological phenomenon which involves the interaction of peptidergic neuromodulators with specific neuropeptide receptors on the plasma membrane of immune effector cells. Many studies have examined the effect of neuropeptides on mitogen-induced lymphocyte proliferation and immunoglobulin synthesis but very little is known about specific lymphokine production. In this study, we describe the effect of somatostatin (SOM) and vasoactive intestinal peptide (VIP) on interferon gamma (IFN-gamma) production by normal human peripheral blood mononuclear cells (PBMC) stimulated in vitro with polyclonal T cell activator staphylococcal enterotoxin A (SEA). Our findings provide experimental evidence that both SOM and VIP reduce the IFN-gamma production by SEA-stimulated PBMC. This reduction was time- (with maximal effect at 72 h) and dose-dependent (at doses as low as 10(-11) M with maximal effect at concentrations between 10(-9) and 10(-8) M of neuropeptides). This effect was absent in resting PBMC. The meaning of inhibitory effect of VIP and SOM on IFN-gamma production and its role in immune response in vivo are discussed.

Pathogenesis of the natural killer cell deficiency in AIDS

Deficiency in natural killer (NK) cell activity is a common feature of acquired immune deficiency syndrome (AIDS). This is part of a general immune dysfunction in AIDS and may lead to progression of the disease, since NK cells are known to be involved in protection against tumors and against viral infections. The lack of immunological surveillance by NK cells of the growth of pathogens that activate the HIV-1 tat infectivity gene may also favor progression to AIDS. The pathogenesis of NK cell deficiency in AIDS is not known. Previous studies have shown that NK cells from AIDS patients are able to bind but not to lyse the target cell line K562. This results from an inability to rearrange the cytoskeleton microtubular (MT) system and to release the natural killer cytotoxic factor (NKCF). This report by Maria Caterina Sirianni and colleagues evaluates the possible mechanisms leading to this NK cell deficiency.