Vasoactive intestinal peptide differentially modulates human immunoglobulin production

Sensory neurons regulate stimulus-dependent humoral immunity

Sensory neurons sense pathogenic infiltration, serving to inform immune coordination of host defense. However, sensory neuron-immune interactions have been predominantly shown to drive innate immune responses. Humoral memory, whether protective or destructive, is acquired early in life - as demonstrated by both early exposure to streptococci and allergic disease onset. Our study further defines the role of sensory neuron influence on humoral immunity in the lung. Using a murine model of Streptococcus pneumonia pre-exposure and infection and a model of allergic asthma, we show that sensory neurons are required for B-cell and plasma cell recruitment and antibody production. In response to S. pneumoniae , sensory neuron depletion resulted in a larger bacterial burden, reduced B-cell populations, IgG release and neutrophil stimulation. Conversely, sensory neuron depletion reduced B-cell populations, IgE and asthmatic characteristics during allergen-induced airway inflammation. The sensory neuron neuropeptide released within each model differed. With bacterial infection, vasoactive intestinal polypeptide (VIP) was preferentially released, whereas substance P was released in response to asthma. Administration of VIP into sensory neuron-depleted mice suppressed bacterial burden and increased IgG levels, while VIP1R deficiency increased susceptibility to bacterial infection. Sensory neuron-depleted mice treated with substance P increased IgE and asthma, while substance P genetic ablation resulted in blunted IgE, similar to sensory neuron-depleted asthmatic mice. These data demonstrate that the immunogen differentially stimulates sensory neurons to release specific neuropeptides which specifically target B-cells. Targeting sensory neurons may provide an alternate treatment pathway for diseases involved with insufficient and/or aggravated humoral immunity.

Association of neuropeptides with Th1/Th2 balance and allergic sensitization in children

BACKGROUND

Among neurogenic factors, the neuropeptides have an important regulatory influence on immune system activity and may lead to allergic sensitization.

OBJECTIVE

The aim of our study was to investigate the relationship of the neuropeptides vasoactive intestinal peptide (VIP), somatostatin (SOM) and substance P (SP) on modulation of Th1/Th2 balance and allergic sensitization in children.

METHODS

Within the LISAplus (Life style-Immune system-Allergy) study, blood samples of 321 six-year-old children were analysed for concentration of neuropeptides, Th1 and Th2 cytokines, transcription factors for T cell regulation and suppressors of cytokine signalling. In addition, samples were screened for specific IgE against inhalant and food allergens.

RESULTS

Children with high SOM values showed a Th2 polarization and a reduced expression of FOXP3, the marker for regulatory T cells. High (VIP) levels correlated inversely with the expression of T cell transcription factors (Tbet and SOCS3). In contrast, elevated levels of SP were associated with reduced GATA3 and SOCS3 expression and with increased IFN-gamma concentrations. Allergic sensitization was more prevalent in children with higher SOM and VIP concentrations but not associated with SP levels.

CONCLUSION

Our data reveal an association between neuropeptides and modulatory effects on immune cells in vivo, especially on Th1/Th2 balance with a correlation to allergic sensitization in children. We suggest that elevated SOM and VIP concentrations and the inducing factors should be considered as allergy risk factors.

Molecular makeup of HIV-1 envelope protein

A broad range of structural, functional, and immunological similarities between HIV-1 gp120 and human proteins, especially those participating in immune responses, highlight gp120 as a pleiotropic protein that can in different ways affect many important functions of the human immune system. Here we described some of these properties of HIV-1 gp120 that represent the main obstacle in the development of effective and safe AIDS vaccine.

Vasoactive intestinal peptide (VIP) inhibits TGF-beta1 production in murine macrophages

Vasoactive intestinal peptide (VIP) and the structurally related neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), produced and/or released in the lymphoid microenvironment act primarily as macrophage- and T cell-deactivating agents. In the present study we investigate the effect of VIP and PACAP on the production of TGF-beta1 in the macrophage cell line Raw 264.7 and in peritoneal macrophages. The two neuropeptides do not affect the baseline TGF-beta1 production by unstimulated macrophages, but reduce dramatically TGF-beta1 production by LPS-stimulated macrophages. The effects are mediated through the specific receptors VPAC1, VPAC2, and PAC1. The effect of VIP is mediated primarily through the cAMP pathway, whereas PACAP activates both the cAMP and the protein kinase C pathway. VIP reduces the TGF-beta1 steady-state mRNA levels in both peritoneal macrophages and Raw 264.7 cells treated with LPS. A similar effect is observed upon the in vivo administration of VIP. This report adds VIP and PACAP to the only other neuropeptide, substance P, known to regulate TGF-beta1 production in immune cells.

The neuropeptides VIP and PACAP inhibit IL-2 transcription by decreasing c-Jun and increasing JunB expression in T cells

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) act as macrophage and T-cell deactivators. Previously we established that VIP/PACAP limit T-cell activation directly, by inhibiting interleukin 2 (IL-2), and indirectly, by reducing the macrophage costimulatory functions. The nature of the IL-2 transcriptional factors affected by VIP/PACAP has not been elucidated. Here we investigate the effect of VIP on the AP-l complexes bound to several regulatory sites. VIP/PACAP downregulate c-Jun, and upregulate JunB mRNA and protein. The reduction in c-Jun correlates with the inhibition of the c-Jun N-terminal kinase (JNK). The effects of VIP/PACAP on c-Jun and JunB expression lead to changes in the composition of the AP-l complexes, from c-Jun/Fos to JunB/Fos dimers, with a subsequent decrease in DNA binding and loss of transactivating activity.

Role of the cervical lymphatics in the Th2-type hierarchy of CNS immune regulation

CNS immune regulation is intimately dependent on the dynamics of cerebral extracellular fluid circulation. Animal models indicate that following the introduction of antigen into the CNS, normal circulation of interstitial and cerebrospinal fluids provides the opportunity for (a) delivery of CNS-derived antigen to lymphoid organs, as well as, (b) retention of immunologically significant amounts of antigen within the CNS. Thus, even in the absence of disease, CNS-derived antigen can induce antigen-specific activation of naive lymphocytes in lymphoid organs and specific reactivation of lymphoblasts that have migrated into the CNS. The initial peripheral immune response to CNS-derived antigen is induced in cervical lymph nodes and is characterized by a strong antibody response, no delayed-type hypersensitivity, and only priming for cytotoxic T-cell responses. This Th-2 type hierarchy of immune regulation is reinforced within the antigen-stimulated CNS where specific B lymphoblasts are permitted to develop their effector function but cell-mediated immunity is inhibited. Developing a paradigm for CNS immune regulation is important in understanding how CNS disorders in humans are induced, perpetuated, and may be manipulated.

VIP1 and VIP2 receptors but not PVR1 mediate the effect of VIP/PACAP on cytokine production in T lymphocytes

Neuropeptides such as VIP and PACAP produced or released within the lymphoid microenvironment modulate the immune response through their effect on immune cells bearing specific receptors. In response to antigenic stimulation, CD4+ T cells, and to a lesser degree CD8+ T cells, produce cytokines that play essential roles in the initiation and amplification of various immune responses. VIP/PACAP downregulate the expression of a variety of cytokines such as IL-2, IL-4, and IL-10, by directly affecting the cytokine-producing T cells. Since three types of receptors, PVR1 (the PACAP-preferring receptor), PVR2 (VIP1), and PVR3 (VIP2) bind PACAP/VIP, this study investigated the expression of these receptors in murine T lymphocytes and their role in mediating the inhibition of cytokines. VIP1 and VIP2 agonists, but not PVR1 agonists, inhibit IL-2, IL-4, and IL-10 production, and VIP1 and VIP2, but not PVR1 mRNA, were identified in purified CD4+ and CD8+ splenic T cells. In addition, immunofluorescence studies confirmed the presence of VIP1 and VIP2 on CD4+ and CD8+ T cells. These results indicate that both subsets of peripheral T lymphocytes express VIP1 and VIP2, but not PVR1 receptors, and that the inhibitory effect of VIP/PACAP on IL-2 and IL-10 production is mediated by both VIP1 and VIP2 receptors.

Effect of vasoactive intestinal peptide (VIP) on cytokine production and expression of VIP receptors in thymocyte subsets

Intrathymic T cell precursors undergo a programmed sequence of developmental changes resulting in the production of mature, self-MHC restricted, single positive T lymphocytes which migrate to the periphery. The intrathymic T cell development is controlled by various factors, including cytokines and possibly neuroendocrine hormones. Our previous studies indicate that vasoactive intestinal peptide (VIP) inhibits IL-2 and IL-4 production in thymocytes through different molecular mechanisms. Thymocytes acquire the competence to express IL-2 and IL-2R during thymic development in a maturation-dependent manner. In this study we investigate the effect of VIP on IL-2 production, and the expression of VIP-R1 and VIP-R2 mRNA in different thymocyte subsets in comparison to T cell lines. All thymocyte subsets and T cell lines tested express VIP-R2. In contrast, only single positive, CD4+8- and CD4-8+ thymocytes express VIP-R1. VIP inhibits IL-2 production in CD4+8+ and single positive CD4+8- and CD4-8+ thymocytes and in TH1 cells stimulated through the TCR. No inhibition is observed in CD3-4-8- and single positive CD4+8- and CD4-8+ thymocytes, or in TH1 cells stimulated by a combination of calcium ionophores and phorbol esters. These findings suggest that VIP inhibits IL-2 production through VIP-R2, and that it interferes with a TCR-connected transduction pathway. We also investigate the expression of VIP mRNA in thymocyte subsets and T cell lines, and conclude that thymocytes as well as antigen-specific T cells may function as VIP sources within the lymphoid organs.

Vasoactive intestinal peptide stimulates p59fyn kinase activity in murine thymocytes

The neuropeptide VIP has immunomodulatory properties, including the inhibition of cytokine production (IL-2, IL-4, and IL-10) in T lymphocytes stimulated through their TCR. The transduction pathways involved in the inhibitory effect of VIP on IL-2 expression are not known. Here we investigate the effect of VIP on the T-cell-specific protein tyrosine kinases p56lck and p59fyn in resting and stimulated thymocytes. VIP does not affect lck or fyn activity in stimulated thymocytes and does not alter the general pattern of cellular tyrosine phosphorylation. However, VIP stimulates p59fyn, but not p56lck, kinase activity in resting thymocytes. The effect is dose dependent, exhibits a specific time course, and is reproduced by other cAMP-inducing agents such as forskolin, prostaglandin E2, and 8-bromo-cAMP, suggesting that cAMP may function as the intracellular mediator.