Granzyme B, a new player in activation-induced cell death, is down-regulated by vasoactive intestinal peptide in Th2 but not Th1 effectors

Following antigenic stimulation and differentiation, Th1 and Th2 effector cells contribute differently to cellular and humoral immunity. Vasoactive intestinal peptide (VIP) induces Th2 responses by promoting Th2 differentiation and survival. In this study, we investigate the mechanisms for the protective effect of VIP against activation-induced cell death (AICD) of Th2 effectors. Surprisingly, microarray and protein data indicate that VIP prevents the up-regulation of granzyme B (GrB) in Th2 but not Th1 effectors. This is the first report of GrB expression in Th cells and of its involvement in activation-induced apoptosis. The enhanced responsiveness of Th2 cells to VIP is probably due to the higher expression of VIP receptors. The effect of VIP on Th2 survival and GrB expression is mediated through the VIP receptors 1 and 2 and cAMP signaling through exchange protein activated by cAMP and, to a lesser degree, protein kinase A. In addition to effects on GrB, VIP also down-regulates Fas ligand (FasL) and perforin (Pfr) expression. The extrinsic Fas/FasL pathway and the intrinsic GrB-dependent pathway act independently in inducing AICD. The mechanisms by which GrB induces cell death in Th1/Th2 effectors include both fratricide and suicide. Fratricide killing, prevalent in wild-type cells, is calcium and Pfr dependent, whereas the cell death of Pfr-deficient Th cells involves Fas and GrB but is calcium independent. This study identifies GrB as a new significant player in Th1/Th2 AICD and characterizes two mechanisms for the protective effect of VIP on Th2 survival, i.e., the down-regulation of GrB and FasL expression.

Role of vasoactive intestinal peptide in inflammation and autoimmunity

Vasoactive intestinal peptide (VIP), a peptide produced by immune cells, exerts a wide spectrum of immunological functions that control the homeostasis of the immune system. In the last decade, VIP has been clearly identified as a potent anti-inflammatory factor, both in innate and adaptive immunity. In innate immunity, this peptide inhibits the production of inflammatory cytokines and chemokines from macrophages, microglia and dendritic cells. In addition, VIP reduces the expression of co-stimulatory molecules on antigen-presenting cells, and therefore reduces stimulation of antigen-specific CD4 T-cells. In terms of adaptive immunity, VIP promotes T-helper (Th)2-type responses, and reduces inflammatory Th1-type responses. Several of the molecular mechanisms involved in the inhibition of cytokine and chemokine expression, and in the preferential development and/or survival of Th2 effectors are known. Therefore, VIP and its analogs have been proposed as promising alternative candidates to existing therapies for the treatment of acute and chronic inflammatory and autoimmune diseases. The aim of this review is to update knowledge of the cellular and molecular events that are relevant to VIP function in the immune system. The central functions that VIP plays in cellular processes is being recognized and attention is being focused on this important peptide with regard to exciting new candidates for therapeutic intervention and drug development.

Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibit chemokine production in activated microglia

Microglia react to even minor disturbances in CNS homeostasis and function as critical regulators of CNS inflammation. Activated microglia secrete inflammatory mediators such as cytokines and chemokines, which contribute to the pathophysiological changes associated with several neuroimmunologic disorders. Microglia-derived inflammatory chemokines recruit various populations of immune cells, which initiate and maintain the inflammatory response against foreign antigens. Entry and retention of activated immune cells in the CNS is a common denominator in a variety of traumatic, ischemic, and degenerative diseases. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two structurally related neuropeptides that function as potent anti-inflammatory factors in the periphery. Here we investigated the effects of VIP and PACAP on chemokine production by activated microglia. VIP and PACAP inhibit the expression of the microglia-derived CXC chemokines MIP-2 and KC, and of the CC chemokines MIP-1alpha, -1beta, MCP-1, and RANTES. The inhibition of chemokine gene expression correlates with an inhibitory effect of VIP/PACAP on NFkB binding. The VIP/PACAP inhibition of both chemokine production and of NFkB binding is mediated through the specific receptor VPAC1 and involves a cAMP-dependent intracellular pathway. Of biological significance is the fact that the inhibition of chemokine production by VIP/PACAP leads to a significant reduction in the chemotactic activity generated by activated microglia for peripheral leukocytes, i.e., neutrophils, macrophages, and lymphocytes. Because reduction in the number and activation of infiltrating leukocytes represents an important factor in the control of inflammation in the CNS, VIP and/or PACAP released by neurons during an inflammatory response could serve as neuronal survival factors by limiting the inflammatory process.

Identification of G-proteins coupling to the vasoactive intestinal peptide receptor VPAC(1) using immunoaffinity chromatography: evidence for precoupling

VPAC(1) receptor subtype-specific G-protein interactions were identified using a strategy that exploits an essential initial signaling event, namely the functional and physical association of the receptor with G-protein. An immunoaffinity purification column was constructed using a previously characterized antibody that had been raised against the first extracellular loop of the VPAC(1) receptor. VPAC(1)/G-protein complexes were solubilized from membranes and copurified. Receptor and Galpha-proteins were detected in eluates using (125)I-VIP labeling and immunoblotting, respectively. Human VPAC(1) transfected in HEK293 cells couples to Gs but not Gi3, Gi1/2, or Gq. Rat VPAC(1) in brain membranes is coupled to Gs and Gi3. Rat VPAC(1) in lung membranes couples to Gs, Gi3, and Gq. Pretreatment of membranes with VIP increased the level of all G-proteins copurifying with VPAC(1). Immunoaffinity chromatography also revealed VPAC(1) receptor precoupling to G-protein in the absence of VIP pretreatment. This was confirmed using a cross-linking procedure to capture VIP receptor/G-protein complexes in the native membrane milieu prior to solubilization. Precoupling suggests that there is a significant basal level of VPAC(1) receptor activity especially in cells, such as some human malignant tumor cells, that express high levels of receptor.

Vasoactive intestinal peptide in the immune system: potential therapeutic role in inflammatory and autoimmune diseases

Vasoactive intestinal peptide (VIP), a neuropeptide that is produced by lymphoid as well as neural cells, exerts a wide spectrum of immunological functions, controlling the homeostasis of the immune system through different receptors expressed in various immunocompetent cells. In the last decade, VIP has been clearly identified as a potent anti-inflammatory factor, which acts by regulating the production of both anti- and pro-inflammatory mediators. In this sense, VIP has been described to prevent death by septic shock, an acute inflammatory disease with a high mortality. In addition, VIP regulates the expression of co-stimulatory molecules, this being an action that may be related to modulating the shift toward Th1 and Th2 differentiation. We have recently reported that VIP prevents the deleterious effects of an experimental model of rheumatoid arthritis, by downregulating both inflammatory and autoimmune components of the disease. Therefore, VIP has been proposed as a promising candidate alternative treatment for acute and chronic inflammatory and autoimmune diseases such as septic shock, arthritis, multiple sclerosis, Crohn disease, or autoimmune diabetes.

Enhanced delayed-type hypersensitivity and diminished immediate-type hypersensitivity in mice lacking the inducible VPAC(2) receptor for vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) and its G protein-coupled receptors, VPAC(1)R and VPAC(2)R, are prominent in the immune system and regulate many aspects of T cell-dependent immunity. In mouse T cells, VPAC(1)R is expressed constitutively, whereas VPAC(2)R is induced by immune stimuli. VPAC(2)R-null (VPAC(2)R(-/-)) mice on a C57BL/6 background are shown here to have normal basic immune characteristics, including serum Ig concentrations, blood levels of all leukocytes, and spleen number of total T cells (CD3(+)) and T cells bearing CD4, CD8, and CD28. Hapten-evoked cutaneous delayed-type hypersensitivity (DTH) was significantly enhanced in VPAC(2)R-null mice compared with age- and sex-matched wild-type mice. In contrast, generation of IgE anti-hapten antibodies and active cutaneous anaphylaxis were > or =70% lower in VPAC(2)R-null mice than in wild-type controls. Cytokine production by splenic CD4(+) T cells, stimulated with adherent anti-CD3 plus anti-CD28 antibodies, revealed higher levels of IL-2 (mean = 3-fold) and IFN-gamma (mean = 3-fold), and lower levels of IL-4 (mean = one-fifth) in VPAC(2)R-null mice than wild-type controls. Loss of VIP-VPAC(2)R maintenance of the normal ratio of Th2/Th1 cytokines thus leads to a state of enhanced DTH and depressed immediate-type hypersensitivity, which may alter both host defense and susceptibility to immune-mediated diseases.

Anti-inflammatory properties of the type 1 and type 2 vasoactive intestinal peptide receptors: role in lethal endotoxic shock

Vasoactive intestinal peptide (VIP) is a neuropeptide that can modulate several immune aspects. Previous reports showed that VIP attenuates the deleterious consequences of septic shock by inhibiting the production of pro-inflammatory agents and stimulating the production of anti-inflammatory cytokines in activated macrophages. In this study, by using selective VIP agonists, we investigated the differential involvement of the VIP receptors in the anti-inflammatory role of VIP. Both the type 1 VIP receptor (VPAC1) agonist, [K(15), R(16), L(27)] VIP 1-7-GRF 8-27, and the type 2 VIP receptor (VPAC2) agonist, Ro25-1553, protected mice from lethal endotoxemia by inhibiting the macrophage-derived pro-inflammatory mediators IL-6, TNF-alpha, IL-12 and NO, and by stimulating the production of the anti-inflammatory cytokine IL-10. In addition, both VIP and VPAC1 agonist, but not the VPAC2 agonist, reduced in vitro and in vivo the expression of the co-stimulatory B7. 1/B7.2 molecules, and the subsequent stimulatory activity for T helper cells in stimulated macrophages. The higher effectiveness of the VPAC1 agonist compared with the VPAC2 agonist suggests that VPAC1 is the major mediator of the anti-inflammatory action of VIP. Since VIP and the two agonists appear to affect multiple cytokines and inflammatory factors, they might provide a more efficient therapeutical alternative to the use of specific cytokine antibodies or antagonists.

CD8(+) T-cell autoreactivity to an HLA-B27-restricted self-epitope correlates with ankylosing spondylitis

HLA-B27 is highly associated with ankylosing spondylitis (AS), but the mechanism is unknown. Among the HLA-B27 alleles, B*2709, which differs by one amino acid from the susceptible B*2705, is not associated with the disease. Here, we analyze the reactivity, in patients with AS and in healthy controls carrying the B*2709 or B*2705 alleles, to an EBV epitope derived from LMP2 (236-244) and to a sequence-related self-peptide from vasoactive intestinal peptide receptor 1 (VIP1R 400-408). We found that both B*2705(+) and B*2709(+) subjects possess LMP2 236-244-specific, HLA-B27-restricted T cells, whereas only the B*2705(+) individuals respond significantly to VIP1R 400-408. These results prompted us to compare, by IFN-gamma ELISPOT analysis, the T-cell response to VIP1R 400-408 in patients with AS versus B*2705 healthy controls. The data show that VIP1R 400-408-specific reactivity is a major feature of the patients with AS. These findings show, for the first time to our knowledge, a widespread reactivity in patients with AS against a self-epitope that exhibits some features of a putative "arthritogenic" peptide.

Immunohistochemical localization and distribution of VIP/PACAP receptors in human lung

VIP and PACAP are distributed in nerve fibers throughout the respiratory tract acting as potent bronchodilators and secretory agents. By using RT-PCR and immunoblotting techniques, we have previously shown the expression of common VIP/PACAP (VPAC(1) and VPAC(2)) and specific PACAP (PAC(1)) receptors in human lung. Here we extend our aims to investigate by immunohistochemistry their localization and distribution at this level. A clear immunopositive reaction was obtained in human lung sections by using either anti-VPAC(1) or -VPAC(2) receptor antibodies but not with anti-PAC(1) receptor antibody. However, PAC(1) receptor (and VPAC(1) and VPAC(2) receptors) could be identified in lung membranes by immunoblotting which supports that the PAC(1) receptor is expressed at a low density. Both VPAC(1) and VPAC(2) receptors showed similar immunohistochemical patterns appearing in smooth muscle cells in the wall of blood vessels and in white blood cells (mainly in areas with inflammatory responses). The results agree with previous evidence on the importance of both peptides in the immune system and support their anti-inflammatory and protective roles in lung.

Differential expression of vasoactive intestinal peptide receptors 1 and 2 (VIP-R1 and VIP-R2) mRNA in murine lymphocytes

Vasoactive intestinal peptide (VIP), a neuropeptide present in the lymphoid microenvironment, modulates cytokine expression and affects T cell proliferation. Recent molecular studies identified two VIP receptors. VIP-R1 and VIP-R2, primarily in nonlymphoid cells. In this study, we investigate the expression of VIP-R1 and VIP-R2 mRNA in unstimulated and stimulated lymphocytes and thymocytes, and in various lymphocyte subpopulations. In contrast to VIP-R1 which is constitutively expressed, the expression of VIP-R2 is induced only following stimulation through the TCR-associated CD3 complex. Both CD4+ and CD8+ T cells express VIP-R1 and VIP-R2. Two T cell lines, EL-4.IL-2 and D10.G4.1 express exclusively VIP-R2. VIP induces the expression of the VIP-R2 gene in the absence of additional stimuli. Differential expression and regulation of the two VIP receptors in T lymphocytes suggests different physiological roles in mediating the immunomodulatory activities of VIP and related neuropeptides.

Specific recognition of the human neuroendocrine receptor for vasoactive intestinal peptide by anti-peptide antibodies

Rabbit polyclonal IgG antibodies were generated to three distinct synthetic peptide substituents of the human neuroendocrine-type 7 transmembrane-domain receptor for vasoactive intestinal peptide (VIP), including a portion of the amino-terminus, first extracellular loop, and carboxyl-terminus. Immunofluorescent staining of both human K293 cell transfectants, expressing recombinant VIP receptors, and HT-29 human intestinal epithelial cells, bearing native VIP receptors, was observed with each of the antibodies and was eliminated specifically after absorption of antibodies with the respective peptide immunogen. Each of the antibodies recognized the same approximately 70-kDa membrane proteins, extracted from both K293 cell transfectants and HT-29 cells, in sodium dodecyl sulfate-polyacrylamide gel electrophoresis blots. Neither IgG nor Fab preparations of the antibodies inhibited VIP binding to cellular receptors at a concentration of 1 microgram/ml, that yielded optimal immunofluorescence, or at 5-300 micrograms/ml. In contrast, 5-200 micrograms/ml of anti-peptide antibodies as IgG, but not Fab, significantly inhibited the increase in concentration of cyclic AMP in HT-29 cells elicited by 1 nM VIP, without affecting the greater increase evoked by 100 nM VIP or alone altering the level of cyclic AMP. Antibodies to several peptide substituents thus bind specifically to VIP receptors in immunoblots and permeabilized cells, and may affect the cellular functions of VIP receptors with sufficient selectivity to reduce transduction of signals, without altering the binding of VIP.