We investigated the effects of different neuropeptides on human dendritic cells (DC) maturation. Immature DC, derived from monocytes cultured for 6 days with IL-4 plus GM-CSF, have been exposed to somatostatin, substance P, or vasoactive intestinal peptide (VIP). Among these neuropeptides, only VIP induces the production of bioactive IL-12 and the neoexpression of CD83 on a fraction of the DC population, with an effect significant at 100 and 10 nM, respectively. These effects of VIP are dose-dependent, unaffected by polymixin B, and partly prevented by a VIP receptor antagonist. Although the effects of VIP alone remain modest, it synergizes with TNF-α to induce DC maturation. In the presence of a suboptimal concentration of TNF-α, which has no detectable effect on DC by itself, VIP induces the production of high levels of bioactive IL-12, the neoexpression of CD83 on almost all the DC population (with an effect significant at 10 and 0.1 nM, respectively), and the up-regulation of various adhesion and costimulatory molecule expression. Moreover, DC exposed to VIP plus a suboptimal concentration of TNF-α are as potent as mature DC obtained by treatment with an optimal concentration of TNF-α in stimulating allogenic T cell proliferation. Our data suggest that, in inflammatory sites, VIP may cooperate with proinflammatory mediators, such as TNF-α, to induce DC maturation.

The nervous and immune systems are intimately related. The interactions between both systems are facilitated by anatomical connections and are mediated by soluble factors, such as neuropeptides and cytokines, recognized by both systems. Numerous neuropeptides released peripherally by primary sensory neurons, such as vasoactive intestinal peptide (VIP),3 somatostatin (SOM), and substance P (SP), have potent regulatory activity on immune and inflammatory reactions (1). Of particular interest is VIP, a 28-aa peptide, widely distributed in both central and peripheral nervous systems (1, 2). VIP-containing nerve fibers have been identified in the primary and secondary lymphoid organs, the blood vessels throughout the body, the intestinal and respiratory tracts, and the skin (1). VIP is released in functionally relevant amounts in numerous regional immune/inflammatory responses. The concentrations of VIP are increased in the serum of patients with septic shock, in nasal secretions, and in bronchoalveolar lavage fluids of allergic patients after challenge. Furthermore, VIP levels are higher in the skin of patients with atopic dermatitis and psoriasis as compared with normal skin. VIP exerts its effects through two high affinity G protein-associated receptors (VIP-RI and VIP-RII) expressed on immune cells (3). By increasing vasodilatation and venular-capillary permeability, VIP participates in the inflammatory process. VIP also affects several important aspects of the immune response including leukocyte recruitment and activation. It modulates lymphokine production by T cells (4, 5, 6, 7), inhibits IL-6, IL-12, and TNF-α production by LPS-stimulated monocytes and macrophages (8, 9, 10), and protects mice from endotoxemia through the inhibition of IL-6 and TNF-α production (11). VIP also modulates Ig production by B cells (12, 13), induces mast cell degranulation (14), and is mitogenic for connective tissue, epithelial cells, and keratinocytes (15, 16).

Dendritic cells (DC) are crucial for the initiation of a primary immune response. They are distinguishable from other APC by their potent Ag-presenting capacity. In peripheral nonlymphoid sites, resident DC are immature and highly effective at processing foreign Ags (17, 18, 19). After Ag challenge in vivo or stimulation with inflammatory stimuli, resident DC capture Ag and migrate to the secondary lymphoid organs (17, 18, 19, 20). During their migration, DC are thought to undergo modulations of phenotype and function, referred to as DC maturation. They increase in size, express increased levels of surface Ags important in T cell activation (such as CD40, CD54, CD58, CD86, and MHC class I/II), produce cytokines (such as TNF-α and IL-12), neoexpress some molecules (such as CD83 on human cells), and lose their capacity to process Ag (i.e., decrease of uptake and proteolytic digestion of Ags and disappearance of the class II compartment) (17, 18, 19, 21). In the T cell-dependent areas of the lymphoid organs, myeloid migratory DC have potent immunostimulatory properties and sensitize recirculating naive Ag-specific T cells (17, 18, 19).

In the present work, we have investigated the effect of different neuropeptides, SOM, SP, and VIP on human immature DC function. We show that VIP induces DC maturation. Although the effect of VIP by its own remains moderate, VIP synergizes with TNF-α in inducing DC maturation.

PBMC were isolated from healthy volunteers by standard density gradient centrifugation on Ficoll-Paque (Pharmacia Biotech, Uppsalla, Sweden). Monocytes were purified from PBMC by positive selection using a magnetic cell separator (MACS; Miltenyi Biotex, Bergisch Gladbach, Germany) according to the manufacturer’s instructions. Purity assessed by FACS analysis using a FITC-labeled anti-CD13 mAb (Cymbys, Hants, U.K.) was >95%. Monocytes were cultured in culture medium (CM) consisting in RPMI 1640 medium supplemented with 10% FCS, 2 mM l-glutamine, 50 U/ml penicillin, 50 μg/ml streptomycin, 10 mM HEPES, and 0.1 mM nonessential amino acids (all from Life Technologies, Cergy Pontoise, France) at 5 × 106 cells/5 ml/well in 6-well tissue culture plates (Costar, Cambridge, MA) with 20 ng/ml IL-4 and 20 ng/ml GM-CSF (R&D Systems, Abingdon, U.K.). On day 6, cells were analyzed by FACS, as described above; only the homogeneous immature DC population characterized by high levels of CD1a (mean fluorescence intensity (MFI) from 100 to 800) and no CD83 expression was used. DC were then recultured at 105 cells/200 μl/well in 96-well flat-bottom tissue culture plates (Costar) in cytokine-containing CM with or without different concentrations of the following neuropeptides: VIP (Calbiochem, La Jolla, CA), SP, or SOM (both from Sigma, St. Louis, MO). In some experiments, DC were also stimulated with TNF-α (R&D Systems) or LPS (from Escherichia coli isotype 0111:B4) (Sigma). In other experiments, immature DC have been exposed to VIP in the presence of 5 μg/ml polymyxin B sulfate or of 10−6 M of a VIP receptor antagonist (VIP6–28, reference V4508) (both from Sigma) (22).

FACS analysis was performed using a FACSvantage cytofluorometer (Becton Dickinson, Erembodegem, Belgium) with the following mAbs: FITC-labeled anti-CD1a (Immunoquality Products, Groningen, The Netherlands), anti-CD80 and anti-CD86 (both from PharMingen, San Diego, CA), anti-CD54 and anti-HLA-DR (both from Becton Dickinson), and anti-CD40 (Serotec, Oxford, U.K.) mAbs. The binding of the anti-CD83 mAb (Immunotech, Marseille, France) was revealed by FITC-labeled anti-mouse IgG Ab (Silenus, Hauworth, Australia). Control isotype mAbs were from Becton Dickinson. Results are expressed in MFI values after subtraction of the MFI obtained with the control mAb or as a percentage of positive cells.

Day 6 DC were incubated for 48 h with various stimuli, as described above, and the biologically active IL-12 p40/p35 heterodimer (IL-12 p75) was measured in cell-free culture supernatants by ELISA using a commercial kit (R&D Systems) according to the manufacturer’s recommendations (sensitivity of 0.5 pg/ml). Results are expressed in pg/ml.

Day 6 DC were washed, recultured at 2.5 × 105 cells/5 ml/well in 6-well culture plates in cytokine-containing CM and were either unstimulated or stimulated with 0.2 ng/ml TNF-α, 10−6 M VIP, 0.2 ng/ml TNF-α plus 10−6 M VIP, or 20 ng/ml TNF-α. After 4 days, DC were washed two times in CM, irradiated (3000 rad), and cultured in quintuplicate at 104 cells/200 μl/well in 96-well flat-bottom culture plates with 5 × 104 allogenic T cells. T cells were purified from PBMC from healthy volunteers by rosetting with sheep RBCs; the purity assessed by FACS analysis using a FITC-labeled anti-CD3 mAb (Immunotech) was >95%. After 5 days, cells were pulsed during the last 16 h with [3H]thymidine (0.25 μCi/well) (Amersham, Amersham, U.K.). Results are expressed in cpm (mean ± SD of quintuplicate values) or in proliferation index (PI) defined as follows: A/B, where A and B are the cpm values obtained in the presence or absence of stimulus, respectively.

We have evaluated whether some neuropeptides may affect DC maturation. Day 6 DC were exposed to 10−10–10−6 M SOM, SP, or VIP. The neoexpression of the maturation marker CD83 (23) was evaluated 4 days later. As expected, unstimulated DC retain an immature phenotype, whereas TNF-α-treated and LPS-treated DC acquire CD83 expression (Table I and Fig. 1,A, respectively). Among the neuropeptides tested, VIP is the only one that induces CD83 expression on a fraction of DC: its effect is dose-dependent, significant at 10−8 M, and maximal at 10−6 M, the highest concentration tested (16 ± 5% and 45 ± 8% of CD83+ cells, respectively, mean ± SD, n = 5) (Fig. 1 B). PCR analysis confirmed the constitutive expression of VIP-R1 and, at a lower level, of VIP-R2 on day 6 DC (data not shown).

Table I.

VIP synergizes with TNF-α in inducing DC maturationa

StimulusCD40bCD54bCD80bCD83cCD86cHLA-DRb
%MFI%MFI
None 55 50 14 <3 26 <10 39 178 
TNF-α (0.2 ng/ml) 54 49 15 <3 27 <10 42 170 
VIP (10−6 M) 90 82 20 46 114 52 154 210 
VIP (10−6 M)+ TNF-α (0.2 ng/ml) 210 819 44 95 110 100 179 460 
TNF-α (20 ng/ml) 214 825 43 98 102 100 175 473 
StimulusCD40bCD54bCD80bCD83cCD86cHLA-DRb
%MFI%MFI
None 55 50 14 <3 26 <10 39 178 
TNF-α (0.2 ng/ml) 54 49 15 <3 27 <10 42 170 
VIP (10−6 M) 90 82 20 46 114 52 154 210 
VIP (10−6 M)+ TNF-α (0.2 ng/ml) 210 819 44 95 110 100 179 460 
TNF-α (20 ng/ml) 214 825 43 98 102 100 175 473 
a

Day 6 DC were or were not exposed to 0.2 ng/ml TNF-α, 10−6 M VIP, 0.2 ng/ml TNF-α plus 10−6 M VIP, or 20 ng/ml TNF-α. Four days later, the phenotype of the DC was determined by FACS analysis using FITC-labeled anti-CD40, anti-CD54, anti-CD80, anti-CD86, and anti-HLA-DR mAbs and unlabeled anti-CD83 mAb.

b

Results are expressed in MFI values after subtraction of the values obtained with control mAbs.

c

Results show the percentage and the MFI values of the positive cells. Data are representative of one of three separate experiments.

FIGURE 1.

A, VIP-induced CD83 expression is prevented by a VIP receptor antagonist. Day 6 DC were recultured in cytokine-containing CM and were or not stimulated by 10−6 M VIP, 0.2 ng/ml TNF-α, 10−6 M VIP plus 0.2 ng/ml TNF-α, or 100 pg/ml LPS, as described, in the absence (□) or presence of 5 μg/ml polymixin B (▧) or of 10−6 M VIP-receptor antagonist (▪). The expression of CD83 was analyzed by FACS after 4 days. Results are expressed in percentage of positive cells, mean ± SD of three separate experiments. B, VIP synergizes with TNF-α in inducing CD83 expression on human DC. Day-6 DC were recultured in cytokine-containing CM and stimulated with different concentrations of VIP in the absence (□) or presence (•) of 0.2 ng/ml TNF-α. CD83 expression was analyzed by FACS after 4 days. Data are expressed in percentage of positive cells, mean ± SD of five separate experiments.

FIGURE 1.

A, VIP-induced CD83 expression is prevented by a VIP receptor antagonist. Day 6 DC were recultured in cytokine-containing CM and were or not stimulated by 10−6 M VIP, 0.2 ng/ml TNF-α, 10−6 M VIP plus 0.2 ng/ml TNF-α, or 100 pg/ml LPS, as described, in the absence (□) or presence of 5 μg/ml polymixin B (▧) or of 10−6 M VIP-receptor antagonist (▪). The expression of CD83 was analyzed by FACS after 4 days. Results are expressed in percentage of positive cells, mean ± SD of three separate experiments. B, VIP synergizes with TNF-α in inducing CD83 expression on human DC. Day-6 DC were recultured in cytokine-containing CM and stimulated with different concentrations of VIP in the absence (□) or presence (•) of 0.2 ng/ml TNF-α. CD83 expression was analyzed by FACS after 4 days. Data are expressed in percentage of positive cells, mean ± SD of five separate experiments.

Close modal

Because VIP is released in tissues during inflammatory responses (1, 2), we tested the combined effect of VIP and LPS or TNF-α on DC maturation (17, 18, 19, 23). Day 6 DC were exposed to 10−10–10−6 M VIP in the presence of increasing concentrations of LPS (from 0.5 to 100 pg/ml) or TNF-α (from 0.2 to 20 ng/ml), and the neoexpression of CD83 was evaluated 4 days later. VIP synergizes with TNF-α in inducing CD83 expression. This synergistic effect is maximal when VIP is used together with 0.2 ng/ml TNF-α: VIP induced-CD83 expression is significant at 10−10 M (16 ± 4% of CD83+ cells, mean ± SD, n = 5) and maximal at 10−6 M (95 ± 10% of CD83+ cells) (Fig. 1,B). In contrast, 0.2 ng/ml TNF-α alone fails to induce CD83 expression (Fig. 1). Whatever the concentration of LPS used, we report no synergistic or antagonistic effect of LPS on VIP-induced CD83 expression (data not shown).

To exclude an effect of contaminating endotoxin, cells were treated with 5 μg/ml polymixin B. Polymixin B down-regulates LPS-induced CD83 expression (decrease of 72 ± 8%, n = 3) but not VIP- or VIP plus TNF-α-induced CD83 expression (Fig. 1,A). To verify the specificity of VIP-induced CD83 expression, VIP and/or 0.2 ng/ml TNF-α were added to immature DC together with a VIP antagonist. This inhibitor does not induce CD83 expression by itself and partly prevents VIP-induced and VIP plus TNF-α-induced CD83 expression (decrease of 59 ± 11% and 66 ± 8%, respectively) (Fig. 1 A). These data obtained using VIP provided by Calbiochem have been reproduced using VIP purchased from another commercialized source (Sigma) (data not shown).

In addition to CD83 neoexpression, DC maturation is associated with a marked up-regulation of adhesion and costimulatory molecules, such as CD40, CD54, CD80, CD86, and HLA-DR (17, 18, 19). Table I shows that day 6 DC exposed to 0.2 ng/ml TNF-α still retain an immature phenotype. However, exposure of immature DC to VIP plus 0.2 ng/ml TNF-α for 4 days results in a dramatic increase in CD40, CD54, CD80, and HLA-DR expression, and in an induction of CD86 expression on virtually all the DC of the population (98 ± 8% of CD86+ cells, mean ± SD, n = 3) (Table I). Phase contrast microscopy also reveals a pronounced morphology of mature DC with large veils (data not shown). Therefore, these cells exhibit a mature phenotype similar to that of cells treated with an optimal dose of TNF-α (Table I) (17, 18, 19, 23). In contrast, 10−6 M VIP used alone induces CD86 expression on a limited number of cells (58 ± 12%) and moderately enhances CD40, CD54, CD80, and HLA-DR expression (Table I). These results indicate that VIP synergizes with suboptimal concentrations of TNF-α to confer a mature phenotype to DC.

The process of maturation is associated with the production of cytokines including IL-12 (17, 18, 19, 24, 25). We have thus analyzed the production of p75 bioactive IL-12 by VIP-treated DC. In the absence of stimulus, immature DC produce undetectable levels of IL-12. The amount of IL-12 induced by VIP remains low: 3 ± 1 and 9 ± 1.8 pg/ml (mean ± SD, n = 4) at 10−7 M and 10−6 M, respectively. Although 0.2 ng/ml TNF-α alone does not induce detectable levels of IL-12, in the presence of 0.2 ng/ml TNF-α, VIP dose dependently stimulates IL-12 production with a significant effect at 10−8 M and maximal at 10−6 M (8 ± 1.3 and 22 ± 2.5 pg/ml, respectively, mean ± SD, n = 4). Polymixin B does not affect VIP-induced and VIP plus TNF-α-induced IL-12 production (data not shown) but inhibits LPS-induced IL-12 production (decrease of 92 ± 15%, mean ± SD, n = 3). In contrast, a VIP receptor antagonist partly prevents VIP-induced and VIP plus TNF-α-induced IL-12 production (decrease of 85 ± 21% and 52 ± 13%, respectively). In additional experiments, as it has been suggested that autocrine IL-12 may affect murine bone marrow-derived DC maturation (26), we have tested the effect of a neutralizing anti-IL-12 Ab on VIP-induced and VIP plus TNF-α-induced CD86 and CD83 expression on DC. Our results show that this Ab does not modulate the effect of VIP (data not shown), thereby suggesting that endogenous IL-12 has no or a limited role in VIP-induced human monocyte-derived DC maturation. Taken together, these data indicate that VIP synergizes with TNF-α in inducing bioactive IL-12 production by DC.

Due to higher levels of costimulatory molecule expression and cytokine production, mature DC are more efficient than immature ones in stimulating T cells (17, 21). Based on the observation that VIP-treated DC have a mature phenotype, we have analyzed their accessory cell capacities. In allogenic mixed lymphocyte reaction assays, allogenic T cells from two subjects were cultured with DC that were previously exposed to VIP and/or TNF-α for 4 days. Results show that DC treated with 10−6 M VIP plus 0.2 ng/ml TNF-α or with 20 ng/ml TNF-α are the most potent in stimulating T cell proliferation (PI = 24 and 15, and 25 and 20, respectively) (Fig. 3). DC treated with VIP alone also enhance T cell proliferation, but to a lesser extent (PI = 8 and 3), whereas DC treated with 0.2 ng/ml TNF-α have no significant effect compared with untreated DC (Fig. 3). Thus, immature DC stimulated with VIP plus a suboptimal concentration of TNF-α present potent costimulatory properties.

FIGURE 3.

VIP synergizes with TNF-α in enhancing the T cell stimulatory properties of DC. Day 6 DC were recultured in cytokine-containing CM in the absence or presence of 10−6 M VIP, 0.2 or 20 ng/ml TNF-α, or 10−6 VIP plus 0.2 ng/ml TNF-α. After 4 days, the cells were irradiated and cultured with freshly isolated allogenic T cells from two different donors. T cell proliferation was measured at day 5. Results are expressed in cpm (mean ± SD of quintuplicate values).

FIGURE 3.

VIP synergizes with TNF-α in enhancing the T cell stimulatory properties of DC. Day 6 DC were recultured in cytokine-containing CM in the absence or presence of 10−6 M VIP, 0.2 or 20 ng/ml TNF-α, or 10−6 VIP plus 0.2 ng/ml TNF-α. After 4 days, the cells were irradiated and cultured with freshly isolated allogenic T cells from two different donors. T cell proliferation was measured at day 5. Results are expressed in cpm (mean ± SD of quintuplicate values).

Close modal

VIP is a neuropeptide found in tissues throughout the body, which presents various immunomodulatory properties. In the present study, we show that VIP induces human DC maturation. Although its effect is modest when used alone, it cooperates with suboptimal concentrations of TNF-α in inducing full DC maturation. The treatment of immature DC with VIP plus TNF-α results in the induction of CD83 expression and IL-12 production, in the up-regulation of different adhesion and costimulatory molecule expression, and in the acquisition of potent T cell stimulatory capacity.

DC residing in the peripheral tissues are immature. The presence of inflammatory mediators prompts DC to migrate to the secondary lymphoid organs. During their migration, DC are thought to undergo a maturation process controlled by different factors. Inflammatory mediators such as TNF-α, IL-1β, PGE2, and LPS induce DC maturation; the ligation of CD40 expressed on DC also results in the generation of hyperactivated DC (17, 18, 19, 24, 25). In contrast, IL-10 converts immature DC into tolerogenic APC (19, 27). Based on our results, VIP appears as a novel DC maturation factor.

Data from the literature suggest that VIP has a dual role on T cell stimulation. Although VIP decreases proliferation and IL-2 but not IFN-γ production by murine and human T cells stimulated with anti-CD3 mAb (with or without phorbol ester) or with mitogenic lectins (5, 6, 7), it enhances IL-2 and IFN-γ production by T cells specifically stimulated by Ag-pulsed APC (28, 29). In agreement with our results, this last observation suggests that VIP acts on APC to favor Ag-dependent T cell stimulation (29). In addition, as VIP is found in the skin, its effect on murine Langerhans cells (LC), the immature DC of the epidermis, has been investigated. In agreement with our observation, LC express VIP-RI and -RII mRNA (30). Moreover, the VIP receptors are coupled to adenylate cyclase, and it has been observed that VIP increases cAMP in murine LC (31). In agreement with the absence of effect of SP on DC reported here, others have also observed that SP does not affect the APC capacity of LC (32). Finally, all these data suggesting that VIP may act on APC are reinforced by the observation that VIP induces human DC maturation.

The binding of VIP to different immune cells results in an increase in intracellular cAMP (1, 2, 3). Agents that increase intracellular cAMP (forskolin, dibutyryl cAMP, and PGE2) have been recently shown to induce CD83 expression and IL-12 production by immature DC, suggesting that the cAMP signaling pathway is involved in the DC maturation process (25). Therefore, it is tempting to speculate that this pathway is involved in VIP-induced DC maturation.

We show that the effect of VIP on DC maturation is potentiated by TNF-α. VIP is released locally in functionally relevant concentrations during immune and inflammatory responses (1, 2). TNF-α is produced early by different cell types in response to stimulation with LPS or inflammatory mediators (33). Thus, in inflammatory sites, VIP and TNF-α might be present concomitantly. The mechanism by which these molecules cooperate to induce the maturation of resident DC remains undetermined. As the 5′-flanking regions of the VIP-R genes contain cytokine-related elements (34), TNF-α may up-regulate VIP-R expression. Nevertheless, previous data showing that TNF-α synergizes with cAMP in up-regulating IL-1β synthesis by human monocytes (35) and with PGE2 in inducing human DC maturation (25), also suggest a possible cooperation between cAMP and TNF-α transduction pathways. Although PGE2 and other cAMP-inducing agents synergize with TNF-α in inducing IL-12 production by DC (25), they inhibit LPS-induced IL-12 production by monocytes and DC (9, 25). Thus, cAMP-inducing agents may have a dual effect on IL-12 production when used in combination with TNF-α or LPS. In agreement with this hypothesis, we report that VIP synergizes with TNF-α in inducing IL-12 production by DC, whereas others have shown that VIP down-regulates LPS-induced IL-12 production by macrophages (9, 10).

VIP prevents mice from endotoxemia (11). Moreover, VIP inhibits TNF-α and increases IL-10 production by LPS-stimulated macrophages (10, 11, 36). As these molecules enhance and prevent DC maturation, respectively (27, 37), VIP may limit the potent effect of LPS on DC maturation in vivo. In addition, the recent observation that cAMP-inducing agents decrease LPS-induced IL-12 production by DC (25) also suggests that VIP may have a direct inhibitory effect on LPS-stimulated DC.

In response to inflammatory mediators, DC migrate from the peripheral tissues to the T cell areas of the secondary lymphoid organs where they present Ag to recirculating T cells. The observation that VIP potentiates TNF-α-induced DC maturation and IL-12 production suggests that VIP, in combination with proinflammatory cytokines, may amplify the initiation of specific T cell responses and the generation of IFN-γ-producing T cells. This point is reinforced by the recent observation that VIP strikingly enhances IFN-γ production by Ag-stimulated T cells (29). In addition, VIP has been shown to favor T cell migration through basement membranes and connective tissues by increasing expression of adhesive proteins, stimulating chemotaxis, and inducing secretion of matrix metalloproteinases (1). Based on these data, it is tempting to speculate that VIP may favor the development of specific T cell responses by enhancing DC activation and T cell trafficking. Nevertheless, in vitro experiments performed with murine T cells, in the absence of APC, using mitogenic lectin or phorbol ester as stimulus (4, 5, 6, 7), also suggest a potential down-regulatory effect of VIP on previously activated T cells.

In conclusion, these data show that VIP synergizes with TNF-α in inducing human DC maturation and thereby suggest that VIP may participate in the control of specific T cell responses. As a consequence, by acting on the DC maturation process, VIP-targeted pharmacological agents may have interesting therapeutic applications.

FIGURE 2.

VIP synergizes with TNF-α in inducing IL-12 production by DC. Day 6 DC were recultured in cytokine-containing CM and stimulated with different concentrations of VIP in the absence (□) or presence (•) of 0.2 ng/ml TNF-α. Bioactive IL-12 (p75 heterodimer) was quantified in the 2-day supernatants. Results are expressed in pg/ml (mean ± SD, n = 4).

FIGURE 2.

VIP synergizes with TNF-α in inducing IL-12 production by DC. Day 6 DC were recultured in cytokine-containing CM and stimulated with different concentrations of VIP in the absence (□) or presence (•) of 0.2 ng/ml TNF-α. Bioactive IL-12 (p75 heterodimer) was quantified in the 2-day supernatants. Results are expressed in pg/ml (mean ± SD, n = 4).

Close modal
3

Abbreviations used in this paper: VIP, vasoactive intestinal peptide; DC, dendritic cells; SP, substance P; SOM, somatostatin; MFI, mean fluorescence intensity; PI, proliferation index; LC, Langerhans cells; CM, culture medium.

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