Vasoactive intestinal polypeptide modulates the in vitro immunoglobulin A production by intestinal lamina propria lymphocytes

Unexpected Discoveries Should Be Reconsidered in Science-A Look to the Past?

From the past, we know how much “serendipity” has played a pivotal role in scientific discoveries. The definition of serendipity implies the finding of one thing while looking for something else. The most known example of this is the discovery of penicillin. Fleming was studying “Staphylococcus influenzae” when one of his culture plates became contaminated and developed a mold that created a bacteria-free circle. Then he found within the mold, a substance that proved to be very active against the vast majority of bacteria infecting human beings. Serendipity had a key role in the discovery of a wide panel of psychotropic drugs as well, including aniline purple, lysergic acid diethylamide, meprobamate, chlorpromazine, and imipramine. Actually, many recent studies support a step back in current strategies that could lead to new discoveries in science. This change should seriously consider the idea that to further focus research project milestones that are already too focused could be a mistake. How can you observe something that others did not realize before you? Probably, one pivotal requirement is that you pay a high level of attention on what is occurring all around you. But this is not entirely enough, since, specifically talking about scientific discoveries, you should have your mind sufficiently unbiased from mainstream infrastructures, which normally make you extremely focused on a particular endpoint without paying attention to potential “unexpected discoveries”. Research in medicine should probably come back to the age of innocence and avoid the age of mainstream reports that do not contribute to real advances in the curing of human diseases. Max Planck said “Science progresses not because scientists change their minds, but rather because scientists attached to erroneous views die, and are replaced”, and Otto Warburg used the same words when he realized the lack of acceptance of his ideas. This editorial proposes a series of examples showing, in a practical way, how unfocused research may contribute to very important discoveries in science.

Neural networks in intestinal immunoregulation

Key physiological functions of the intestine are governed by nerves and neurotransmitters. This complex control relies on two neuronal systems: an extrinsic innervation supplied by the two branches of the autonomic nervous system and an intrinsic innervation provided by the enteric nervous system. As a result of constant exposure to commensal and pathogenic microflora, the intestine developed a tightly regulated immune system. In this review, we cover the current knowledge on the interactions between the gut innervation and the intestinal immune system. The relations between extrinsic and intrinsic neuronal inputs are highlighted with regards to the intestinal immune response. Moreover, we discuss the latest findings on mechanisms underlying inflammatory neural reflexes and examine their relevance in the context of the intestinal inflammation. Finally, we discuss some of the recent data on the identification of the gut microbiota as an emerging player influencing the brain function.

Tissue-based class control: the other side of tolerance

In this Essay, we offer a new perspective on how immune responses are regulated. We do not cover how they are turned on and off, but focus instead on the second major aspect of an immune response: the control of effector class. Although it is generally thought that the class of an immune response is tailored to fit the invading pathogen, we suggest here that it is primarily tailored to fit the tissue in which the response occurs. To this end, we cover such topics as the nature of T helper (T(H)) cell subsets (current and yet to be discovered), the nature of privileged sites, the difference between oral tolerance and oral vaccination, why the route of immunization matters, whether the T(H)1-type response is really the immune system's primary defense, and whether there might be a different role for some regulatory T cells.

Regulation of IgA responses in cattle, humans and mice

Secretory IgA (SIgA) constitutes the largest component of the humoral immune system of the body with gram quantities of this isotype produced by mammals on a daily basis. Secretory IgA (SIgA) antibodies function by both blocking pathogen/commensal entry at mucosal surfaces and virus neutralization. Several pathways of induction of IgA responses have been described which depend on T cells (T cell dependent or TD) pathways or are independent of T cells (T-independent or TI) and are mediated by dendritic cells (DCs) and/or epithelial cells. Many elements of IgA regulation readily cross species barriers (adjuvants, soluble and cognate factors) and are highly conserved whereas other pathways may be more specific to any given species and must be evaluated. Regulation of IgA production in cattle is not completely understood and thus we have focused in part on highly conserved factors such as transforming growth factor beta, Type I and Type 2 interferons, neuropeptides which interdigitate mucosal tissues (vasoactive intestinal peptide or VIP), and a small peptide (IgA inducing peptide or IGIP) which can serve as targets for modulation and increasing SIgA virus-specific antibodies. We have evaluated the potential utility of modulating these factors in vitro in regulation of qualitative aspects of antibodies of the IgM, IgG and IgA isotypes at mucosal surfaces and in secretions of the upper and lower respiratory tract to a virus of economic and public health importance, foot and mouth disease virus (FMDV). IgA responses in cattle are essential for host defense in response to various infectious agents. In cattle, IgA is not released into the colostrum, as is the case for other mammals but only IgG1 is selectively transported. In previous studies in cattle, IgA has been shown to be regulated by several cytokines including IFN-gamma, Type I interferons such as IFN-alpha and IFN-tau, transforming growth factor beta, IgA inducing peptide and other potential factors such as APRIL and BlyS which have not yet been fully evaluated in cattle. Many of these factors, namely TGF-beta and Type I interferons block cell cycle progression which is an essential component of Ig class switching and thus these factors require additional regulatory factors such as IL-2 to drive cells through cell cycle resulting in class switch recombination. Among these factors, IgA inducing peptide was originally identified from a bovine gut associated lymphoid tissue expression library and is highly conserved in pigs and humans at >90% at the amino acid level. The factor is regulated differently in various species but is consistently produced by dendritic cells.

Immunomodulation by commensal and probiotic bacteria

Over the past decade there has been an increasing awareness of the role played by commensal bacteria in modulating mucosal immune responses and as a consequence there is now great interest in the therapeutic potential of probiotics and other bacteria based strategies for a range of immune disorders. Here we review current understanding of the mechanisms underlying the immunomodulatory actions of commensal and probiotic bacteria and probiotic organisms. We discuss prominent cell types involved in transducing signals from these bacteria, including epithelial cells, dendritic cells and T regulatory cells. We also draw attention to emerging data indicating interplay between the gut microbiota, enteric neurons and the immune system. There is a focus on the specific aspects of bacteria-host interactions that may influence the ability of a specific organism to confer potentially beneficial changes in immune responses. It is clear that there is still much to learn regarding the determinants of the diverse immune responses elicited by different bacterial strains by building on our current knowledge in these areas it may be possible to design clinically effective, bacteria based strategies to maintain and promote health.

Human IgA-inducing protein from dendritic cells induces IgA production by naive IgD+ B cells

Over the last several years, there has been a great deal of progress in characterizing the role of dendritic cells (DCs) in the activation and modulation of B cells. DC-secreted chemokines can induce B cell trafficking to the lymph nodes. DC-produced survival factors such as B cell-activating factor of the TNF family and a proliferation-inducing ligand have been shown to be essential for B cell maturation, but have also been implicated in class-switch recombination and B cell lymphoma survival. Recently added to this list of DC-derived factors effecting B cells is IgA-inducing protein (IGIP). In this study, we characterize production of IGIP by human DCs, and examine its capacity to induce IgA class switching and differentiation of naive B cells in vitro. Monocyte-derived DCs were cultured in vitro with TLR agonists (TLR3, 4, 5, and 9) and other factors, including CD40 ligand, GM-CSF, and IL-4 as well as the neuropeptide vasoactive intestinal peptide. Under in vitro stimulation with vasoactive intestinal peptide and CD40L, IGIP mRNA expression could be up-regulated as much as 35-fold above nonstimulated samples within 12-48 h. Naive B cells cultured with exogenous recombinant human IGIP produced IgA in greater quantities than nonstimulated controls. Finally, we demonstrate that IGIP stimulation drives the production of mu-alpha switch circles from IgM(+)IgD(+) naive human B cells, indicating its role as an IgA switch factor.

Intestinal bacteria condition dendritic cells to promote IgA production

Immunoglobulin (Ig) A represents the predominant antibody isotype produced at the intestinal mucosa, where it plays an important role in limiting the penetration of commensal intestinal bacteria and opportunistic pathogens. We show in mice that Peyer's Patch-derived dendritic cells (PP-DC) exhibit a specialized phenotype allowing the promotion of IgA production by B2 cells. This phenotype included increased expression of the retinaldehyde dehydrogenase 1 (RALDH1), inducible nitric oxide synthase (iNOS), B cell activating factor of the tumor necrosis family (BAFF), a proliferation-inducing ligand (APRIL), and receptors for the neuropeptide vasoactive intestinal peptide (VIP). The ability of PP-DC to promote anti-CD40 dependent IgA was partially dependent on retinoic acid (RA) and transforming growth factor (TGF)-beta, whilst BAFF and APRIL signaling were not required. Signals delivered by BAFF and APRIL were crucial for CD40 independent IgA production, although the contribution of B2 cells to this pathway was minimal. The unique ability of PP-DC to instruct naïve B cells to differentiate into IgA producing plasma cells was mainly imparted by the presence of intestinal commensal bacteria, and could be mimicked by the addition of LPS to the culture. These data indicate that exposure to pathogen-associated molecular patterns present on intestinal commensal bacteria condition DC to express a unique molecular footprint that in turn allows them to promote IgA production.

Morphological relationships between peptidergic nerve fibers and immunoglobulin A-producing lymphocytes in the mouse intestine

Immunoglobulin A (IgA) lymphocytes are present close to the nerve fibers in the lamina propria of the small intestine, and the administration of lipopolysaccharides (LPSs) increases the number of these cells and IgA secretion to the lumen. In the present study, we demonstrated that the nerve fibers immunoreactive for vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) were close to the IgA lymphocytes in the mouse ileum lamina propria. Three hours after intraperitoneal administration of LPSs, IgA lymphocytes close to VIP nerve fibers, those close to basement membrane, and those close to both VIP nerve fibers and basement membrane were increased in number. Further, all IgA lymphocytes seen in the ileum lamina propria expressed the receptors for VIP, VIPR1, and VIPR2. Electron microscopy revealed that varicosities were in close apposition to the lymphocyte plasma membrane. The present study suggests that VIP/NPY/CGRP neurons in the submucosal plexus have a close anatomical relationship to IgA lymphocytes, playing a role in the secretion of IgA and intestinal fluid in response to stimulation by lipopolysaccharides, pathogens, or toxins.

Role of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

Mucosal B cells: phenotypic characteristics, transcriptional regulation, and homing properties

Mucosal antibody defense depends on a complex cooperation between local B cells and secretory epithelia. Mucosa-associated lymphoid tissue gives rise to B cells with striking J-chain expression that are seeded to secretory effector sites. Such preferential homing constitutes the biological basis for local production of polymeric immunoglobulin A (pIgA) and pentameric IgM with high affinity to the epithelial pIg receptor that readily can export these antibodies to the mucosal surface. This ultimate functional goal of mucosal B-cell differentiation appears to explain why the J chain is also expressed by IgG- and IgD-producing plasma cells (PCs) occurring at secretory tissue sites; these immunocytes may be considered as 'spin-offs' from early effector clones that through class switch are on their way to pIgA production. Abundant evidence supports the notion that intestinal PCs are largely derived from B cells initially activated in gut-associated lymphoid tissue (GALT). Nevertheless, insufficient knowledge exists concerning the relative importance of M cells, major histocompatibility complex class II-expressing epithelial cells, and professional antigen-presenting cells for the uptake, processing, and presentation of luminal antigens in GALT to accomplish the extensive and sustained priming and expansion of mucosal B cells. Likewise, it is unclear how the germinal center reaction in GALT so strikingly can promote class switch to IgA and expression of J chain. Although B-cell migration from GALT to the intestinal lamina propria is guided by rather well-defined adhesion molecules and chemokines/chemokine receptors, the cues directing preferential homing to different segments of the gut require better definition. This is even more so for the molecules involved in homing of mucosal B cells to secretory effector sites beyond the gut, and in this respect, the role of Waldever's ring (including the palatine tonsils and adenoids) as a regional inductive tissue needs further characterization. Data suggest a remarkable compartmentalization of the mucosal immune system that must be taken into account in the development of effective local vaccines to protect specifically the airways, eyes, oral cavity, small and large intestines, and urogenital tract.

Influence of enteral and parenteral nutrition on splanchnic hemodynamics in septic patients

BACKGROUND

Enteral nutrition is believed to augment splanchnic perfusion, thereby preserving splanchnic integrity, whereas parenteral nutrition does not offer this benefit. In an effort to study this, we compared splanchnic oxygen exchange and blood flow in critically ill, septic patients to normal controls during enteral or total parenteral nutrition.

METHODS

Splanchnic oxygen exchange and hepatic blood flow characteristics in 14 critically ill, septic patients were compared to 19 normal controls while fasting and during nutrient administration. Nutrients were delivered as intraduodenal feedings or parenteral nutrition. Splanchnic hemodynamics were measured at baseline, 90 min, and 210 min during nutrient administration. Hepatic blood flow index (HBFI) by indocyanine green dye (ICG) clearance, splanchnic oxygen consumption index (SplVO(2)I), and hepatic venous oxygen saturation (ShvO(2)) were measured using hepatic venous catheterization. Plasma volume (PV) was measured from the volume of ICG distribution. Results were analyzed using population means (+/-SD) and one-way analysis of variance.

RESULTS

There was no statistical change in HBFI, SplVO(2)I, PV or ShvO(2) over the study time interval within any group (p < 0.05), irrespective of whether enteral or parenteral nutrition was the nutrient source. Septic patients, whether fasting or receiving nutrition, demonstrated higher HBFI and SplVO(2)I levels, whereas ShvO(2) levels were uniformly lower throughout the study compared to normal controls.

CONCLUSIONS

Critically ill patients exhibited a hyperdynamic splanchnic state as indicated by the marked increase in HBFI and SplVO(2)I. However, neither nutrient regimen at clinically relevant rates altered splanchnic hemodynamics over the course of study. Thus, enteral nutrients do not appear to offer hemodynamic protection to the splanchnic system in critically ill patients.

Interactions between the enteric nervous system and the immune system: role of neuropeptides and nutrition

Neuropeptidergic synthesis occurs in enteric nerves and immune cells of the gut-associated lymphoid tissue. Lymphocytes, macrophages, mast cells, and intestinal epithelial cells are capable of responding to these neuropeptides. Neuropeptides generate proliferative or antiproliferative responses of mucosal lymphocytes and intestinal epithelial cells, affect cytokine production and immunoglobulin synthesis by immune cells, and control secretion of water and electrolytes. Some neuropeptides, particularly cholecystokinin, gastrin-releasing peptide, and neurotensin, appear promising to maintain mucosal immunity in patients who cannot receive enteral feeding during critical illness or after GI tract loss. Exogenous administration of neuropeptides to preserve normal immune defenses represents a potential new field of pharmacotherapeutics against bacterial invasion.

Neurotransmitter coding of enteric neurones in the submucous plexus is changed in non-inflamed rectum of patients with Crohn's disease

Knowledge of the neurochemical coding of submucosal neurones in the human gut is important to assess neuronal changes under pathological conditions. We therefore investigated transmitter colocalization patterns in rectal submucosal neurones in normal tissue (n=11) and in noninflamed tissue of Crohn's disease (CD) patients (n=17). Neurone-specific enolase (NSE), choline acetyltransferase (ChAT), vasoactive intestinal polypeptide (VIP), substance P (SP), nitric oxide synthase (NOS) and calcitonin gene-related peptide (CGRP) were detected immunohistochemically in whole-mount preparations from rectal biopsies. The neuronal marker NSE revealed no differences in the number of cells per ganglion (controls 5.0; CD 5.1). Four cell populations with distinct neurochemical codes were identified. The sizes of the populations ChAT/VIP (58% vs. 55%), ChAT/SP (8% vs. 8%), and ChAT/- (22% vs. 22%) were similar in control and CD. The population VIP/- was significantly increased in CD (12% vs. 2% in controls). Unlike in controls, all NOS neurones colocalized ChAT in CD. Thickened CGRP-fibres occurred in CD. We identified neurochemically distinct populations in the human submucous plexus. The increase in the VIP/- population, extensive colocalization of ChAT and NOS and hypertrophied CGRP fibres indicated adaptive changes in the enteric nervous system in noninflamed rectum of CD patients.

The B-cell system of human mucosae and exocrine glands

The mucosae and exocrine glands harbour the largest activated B-cell system of the body, amounting to some 80-90% of all immunoglobulin (Ig)-producing cells. The major product of these immunocytes is polymeric (p)IgA (mainly dimers) with associated J chain. Both pIgA and pentameric IgM contain a binding site for the polymeric Ig receptor (pIgR), or secretory component (SC), which is a requirement for their active external transport through secretory epithelia. The pIgR/SC binding site depends on covalent incorporation of the J chain into the quaternary structure of the polymers when they are produced by the local immunocytes. This important differentiation characteristic appears to be sufficient functional justification for the J chain to be expressed also by most B cells terminating at secretory effector sites with IgD or IgG production; they probably represent a "spin-off" from sequential downstream CH switching on its way to pIgA expression, thus apparently reflecting a maturational stage of effector B-cell clones compatible with homing to these sites. Observations in IgA-deficient individuals suggest that the magnitude of this homing is fairly well maintained even when the differentiation pathway to IgA is blocked. Certain microenvironmental elements such as specific cytokines and dendritic cells appear to be required for induction of IgA synthesis, but it remains virtually unknown why this isotype normally is such a dominating product of local immunocytes and why they have such a high level of J chain expression. Also, despite the recent identification of some important requirements in terms of adhesion molecules (e.g. integrin alpha 4 beta 7 and MAdCAM-1) that explain the "gut-seeking" properties of enterically induced B cells, the origin of regionalized homing of B cells to secretory effector sites outside the gut remains elusive. Moreover, little is known about immune regulation underlying the striking disparity of both the class (IgD, IgM) and subclass (IgA1, IgA2, IgG1, IgG2) production patterns shown by local immunocytes in various regions of the body, although the topical microbiota and other environmental stimuli might be important. Rational design of local vaccines will depend on better knowledge of both inductive and migratory properties of human mucosal B cells.

Regional specialization in the mucosal immune system: what happens in the microcompartments?

Mucosal immunity is an important arm of the immune system because it operates in tissues involved in everyday infectious defence as well as in tolerance against innocuous environmental and dietary antigens. Here, Per Brandtzaeg and colleagues discuss compartmentalized regulation of mucosal B cells and mechanisms that might explain the strikingly regionalized effector disparity of the human mucosal immune system.

Enhancement by vasoactive intestinal peptide of gamma-interferon production by antigen-stimulated type 1 helper T cells

Vasoactive intestinal peptide (VIP) is a neuroendocrine mediator in immune tissues that affects many T cell functions through two homologous high-affinity G-protein-coupled receptors, termed VIPR1 and VIPR2. Antigen-stimulated secretion of gamma-interferon (IFN-gamma) by sperm whale myoglobin-specific Th1 cells of DBA/2 mouse I-Ed-restricted clones, which express VIPR1 and VIPR2, was enhanced by 10(-10) M to 10(-7) M VIP. Enhancement of IFN-gamma secretion reached a mean maximum of fourfold for VIP and threefold for a VIPR2-selective agonist, without any effect of a VIPR1-selective agonist. Secretion of IFN-gamma by PMA and ionomycin-stimulated clones of Th1 cells was not altered by VIP. Antigen-stimulated secretion of IFN-gamma by T cell receptor-transgenic, influenza hemagglutinin-specific, and cytokine-differentiated mouse lymph node Th1 cells, which also express VIPR1 and VIPR2, was enhanced by 10(-10) M to 10(-8) M VIP. Enhancement of IFN-gamma secretion increased to a maximum of 14-fold for VIP, 14-fold for the VIPR2-selective agonist, and 20-fold for the VIPR1-selective agonist. In contrast to VIP suppression of interleukin production and lack of effect on IFN-gamma production by T cells stimulated with anti-CD3 antibody or a mitogenic lectin, generation of IFN-gamma by antigen-stimulated T cells is enhanced significantly by physiological concentrations of VIP.

Selectivity of effects of vasoactive intestinal peptide on macrophages and lymphocytes in compartmental immune responses

The major immunoregulatory effects of vasoactive intestinal peptide (VIP) are mediated by structurally distinct type I (VIPR1) and II (VIPR2) G protein-associated receptors on many different types of immune cells. VIP is released in functionally relevant concentrations during many immunologic and inflammatory responses. Mast cells (VIPR1), macrophages (VIPR1 and VIPR2), B cells, and T cells (VIPR1, VIPR2, or VIPR1 and VIPR2) recognize and respond to VIP in patterns that are controlled by the relative levels of expression of VIPR1 and VIPR2. VIPR2 transduces human T-cell chemotaxis, expression of matrix metalloproteinases (MMPs) 2 and 9 and consequently basement membrane and connective tissue transmigration, while signaling suppression of proliferation and cytokine production. In contrast, VIPR1 fails to transduce T-cell chemotaxis but mediates suppression of chemotaxis and MMP expression elicited by some cytokines and chemokines. The relative representation of each type of VIPR, which is presumed to be under cytokine control, thus may determine T-cell responses to VIP and other immune mediators in tissue compartments innervated by VIPergic nerves.

Vasoactive intestinal peptide enhancement of antigen-induced differentiation of a cultured line of mouse thymocytes

The prominence of vasoactive intestinal peptide (VIP) in rodent thymic neurons suggested that this potent mediator of T cell functions may alter developmental responses of thymocytes to T cell receptor (TCR) -dependent stimulation. CD4+8+ DPK cells derived from a thymic lymphoma of a TCR transgenic mouse respond to pigeon cytochrome C (PCC) antigen in association with distinct I-E MHC II haplotypes on antigen-presenting cells (APCs) by differentiating into CD4+8- T cells. The specific recognition of VIP by two types of homologous G-protein-coupled receptors (VIPR1 and VIPR2) on DPK cells was attributable predominantly to VIPR1 before and to VIPR2 after exposure to APCs and PCC, as assessed by quantification of the respective mRNAs. PCC-evoked differentiation of DPK cells was enhanced significantly by 1 to 100 nM VIP after 3 to 4 days. The effects of VIP analogs with VIPR type selectivity implied that VIP enhancement of differentiation of DPK cells was mediated principally by VIPR2. Differential reduction in the expression of each type of VIPR by transfection of DPK cells with plasmids encoding the respective antisense mRNAs confirmed the central role of VIPR2 in VIP-enhanced conversion to CD4+8- T cells. The suppression of DPK cell differentiation by inhibitors of adenylyl cyclase and protein kinase A suggested a transductional role for VIP-elicited increases in [cAMP]i. That the changes in frequency of CD4+8+ and CD4+8- DPK cells reflected principally differentiation was supported by the lack of consistent differences between the two subsets in the effects of VIP and VIPR2 agonist on cell number, viability, apoptosis, and proliferation. VIP may be one endogenous mediator that explains the unique thymic microenvironment for topographically specific development of T cells.

T-cell dysfunctions in hu-PBL-SCID mice infected with human immunodeficiency virus (HIV) shortly after reconstitution: in vivo effects of HIV on highly activated human immune cells

The state of activation of the immune system may be an important factor which renders a host more receptive to human immunodeficiency virus (HIV) and more vulnerable to its effects. To explore this issue with a practical in vivo model, we developed a modified protocol of HIV infection in hu-PBL-SCID mice. First, we assessed the time course of activation of human peripheral blood lymphocytes (hu-PBL) in the peritoneal cavity of SCID mice. At 2 to 24 h after the intraperitoneal injection into SCID mice, there was a clear-cut increase in the percentage of hu-PBL expressing early activation markers (CD69), concomitant with the release of soluble intercellular adhesion molecule-1 (sICAM-1) and the soluble interleukin-2 receptor (sIL-2R) and with the accumulation of mRNAs for a number of human cytokines. At 2 weeks, virtually all of the hu-PBL expressed the memory phenotype (CD45RO) and HLA-DR antigens as well. Cells collected from the SCID mouse peritoneum at 2 and 24 h after transplantation were fully susceptible to in vitro infection with HIV type 1 (HIV-1) in the absence of either IL-2 or mitogens. The injection of HIV into hu-PBL-SCID mice at 2 h after reconstitution resulted in a generalized and productive HIV infection of the xenochimeras. This early HIV-1 infection resulted in a dramatic depletion of human CD4+ cells and in decreased levels of sICAM-1 (in the peritoneal lavage fluid) as well as of sIL-2R and immunoglobulins M and A (in the serum). Enzyme-linked immunosorbent assay and/or reverse transcriptase PCR analysis showed higher levels of IL-4, IL-5, and IL-10 in the HIV-infected animals than in control hu-PBL-SCID mice, while gamma interferon levels in the two groups were comparable. When we compared the current model of HIV-1 infection at 2 weeks after the intraperitoneal injection of the hu-PBL in the SCID mice with the model described here, we found that the majority of immune dysfunctions induced in the 2-h infection of the xenochimeras are not inducible in the 2-week infection. This supports the concept that the state of activation of human cells at the moment of the in vivo infection with HIV-1 is a crucial factor in determining the immune derangement observed in AIDS patients. These results show that some immunological dysfunctions induced by HIV infection in AIDS patients can be mimicked in this xenochimeric model. Thus, the hu-PBL-SCID mouse model may be useful in exploring, in vivo, the relevance of hu-PBL activation and differentiation in HIV-1 infection and for testing therapeutic intervention directed towards either the virus or the immune system.

Vasoactive intestinal peptide induces S(alpha)/S(mu) switch circular DNA in human B cells

Vasoactive intestinal peptide (VIP), a major neurotransmitter of peripheral nerves, has been suggested to function in host defense by regulating local human immune function. Indirect evidence has been marshaled that VIP can function as a switch factor for IgA in human Ig isotype recombination. In this study we directly tested the ability of VIP to function as a factor driving human B cells into IgA producing cells by assessing its ability to induce switch circular DNA representing direct mu to alpha switching. In addition we determined the generation of alpha germ-line transcripts and measured the level of IgA protein produced. Stimulation with VIP and CD40 mAb induced IgA production by human IgD+ B cells while VIP or CD40 alone failed to do so. Stimulation of purified IgD+ B cells with VIP plus CD40 mAb induced generation of switch circular DNA representing in vitro driven isotype switching from mu to alpha. CD40 mAb alone induced alpha germ-line transcripts but not IgA switch circles. Thus VIP, a neurogenic factor, can induce alpha-specific switching in CD40-activated human B cells and may thereby play an important role in directing the humoral immune response at mucosal surfaces.

VIP modulation of immune cell functions

Neuropeptides have recently been shown to modulate the immune response. Vasoactive intestinal peptide (VIP) released from nerve endings and from immune cells modulates the mobility and adherence of lymphocytes and macrophages, phagocytic cell functions (phagocytosis and free radical production), the lymphocyte proliferative response, lymphokine and immunoglobulin production and the natural killer cell activity, with opposite effects in vitro on these immune cell functions. The VIP receptor heterogeneity and the different action mechanisms of VIP-mediated immunoregulation could explain, at least in part, the different VIP effects observed on lymphoid and phagocytic cells. The evidence supports the theory that VIP acts not as an inhibitor, but as a modulator of immune functions, as previously thought, and that this neuropeptide may play a relevant role in vivo.

Vasoactive intestinal peptide regulation of granulomatous inflammation in murine Schistosomiasis mansoni

Schistosomiasis is a parasitic disease in which focal inflammatory responses called granulomas develop in the liver and intestines. The inflammatory cells within these granulomas produce authentic vasoactive intestine peptide (VIP). VIP acts as an immune modulator. In the schistosome granuloma, VIP can suppress T cell proliferation and T lymphocyte IL-2 production. Also, it can enhance IL-5 production from granuloma T cells. The granuloma T cells bear authentic VIP receptors of both the VIPr1 and VIPr2 subclasses. It is probable that the expression of these receptors is subject to immunoregulation, which is the topic of current investigation. Moreover, differences in the structure of VIPr1 and VIPr2 suggest that each may have unique immunoregulatory functions in inflammation.