Neuroimmunomodulation: classical and non-classical cellular activation

Activation of Conjunctiva-Associated Lymphoid Tissue in Patients With Infectious Keratitis Using In Vivo Confocal Microscopy

Purpose

We aimed to evaluate activation of conjunctiva-associated lymphoid tissue (CALT) in patients with keratitis using in vivo confocal microscopy (IVCM) and conjunctival impression cytology (CIC).

Methods

In addition to anterior segment photography and corneal fluorescein staining, IVCM revealed the palpebral conjunctiva in all subjects, and CIC and immunofluorescence staining were performed.

Results

Diffuse lymphoid tissue cell density in the eyes of patients with keratitis was significantly greater compared with healthy volunteers (P < 0.001). Similar trends were found in perifollicular lymphocyte density (P < 0.001), follicular density (P = 0.029), follicular center reflection intensity (P = 0.011), and follicular area (P < 0.001). Immunofluorescence staining showed that the proportions of CD4⁺ (61.7% ± 8.0% vs. 17.3% ± 10.2%, respectively, P < 0.001) and CD8⁺ (46.9% ± 10.0% vs. 19.6% ± 11.5%, respectively, P < 0.001) cells in patients with keratitis was greater compared with healthy volunteers. Interestingly, we also observed changes in the contralateral eye in subjects with keratitis.

Conclusions

Our research suggests that CALT, as an ocular immune structure, is activated and plays an important role in the pathogenesis of keratitis. This has been overlooked previously. CALT is also active in the contralateral eye of subjects with keratitis.

Contralateral Clinically Unaffected Eyes of Patients With Unilateral Infectious Keratitis Demonstrate a Sympathetic Immune Response

PURPOSE

To analyze the contralateral unaffected eyes of patients with microbial keratitis (MK) for any immune cell or nerve changes by laser in vivo confocal microscopy (IVCM).

METHODS

A prospective study was performed on 28 patients with MK, including acute bacterial, fungal, and Acanthamoeba keratitis, as well as on their contralateral clinically unaffected eyes and on control groups, which consisted of 28 age-matched normal controls and 15 control contact lens (CL) wearers. Laser IVCM with the Heidelberg Retinal Tomograph 3/Rostock Cornea Module and Cochet-Bonnet esthesiometry of the central cornea were performed. Two masked observers assessed central corneal dendritiform cell density and subbasal corneal nerve parameters.

RESULTS

The contralateral clinically unaffected eyes of patients with MK demonstrated significant diminishment in nerve density (15,603.8 ± 1265.2 vs. 24,102.1 ± 735.6 μm/mm²), total number of nerves (11.9 ± 1.0 vs. 24.9 ± 1.2/frame), number of branches (1.7 ± 0.2 vs. 19.9 ± 1.3/frame), and branch nerve length (5775.2 ± 757.1 vs. 12,715.4 ± 648.4 μm/mm²) (P < 0.001 for all parameters) compared to normal controls and CL wearers. Further, dendritiform cell density in the contralateral unaffected eyes was significantly increased as compared to that in controls (117.5 ± 19.9 vs. 24.2 ± 3.5 cells/mm², P < 0.001).

CONCLUSIONS

We demonstrate a subclinical involvement in the contralateral clinically unaffected eyes in patients with unilateral acute MK. In vivo confocal microscopy reveals not only a diminishment of the subbasal corneal nerves and sensation, but also an increase in dendritiform cell density in the contralateral unaffected eyes of MK patients. These findings show bilateral immune alterations in a clinically unilateral disease.

Effects of somatostatin and octreotide on cytokine and chemokine production by lipopolysaccharide-activated peripheral blood mononuclear cells

BACKGROUND

Somatostatin plays an important role in the communication between the nervous, endocrine, and immune systems. Although somatostatin or its analogues have been shown to modulate a number of immune functions, their immunomodulatory effects are not uniform and are strongly dependent on the underlying cell system.

AIM

The aim of our study was to analyze the immunomodulatory effects of somatostatin and its analogue octreotide on peripheral blood mononuclear cells (PBMC) in vitro. MATERIALS/SUBJECTS:We used lipopolysaccharide-activated cells from normal glucose tolerant (NGT) subjects and from Type 2 diabetes mellitus (T2DM) patients as T2DM is associated with chronic, low-grade inflammation, and measured immune mediator release with multiplex bead-based assays.

RESULTS

Our data showed no statistically significant effects on the secretion of the cytokines interleukin (IL)-1beta, IL-6, IL-10, IL-12, interferon-gamma and tumor necrosis factor-alpha as well as the chemokines IL-8 and monocyte chemoattractant protein (MCP)-1, either on PBMC from T2DM patients or on those from NGT controls. However, a trend towards a dose-dependent biphasic effect was observed for IL- 6, IL-10 and MCP-1 with reduced immune mediator levels at low and increased/unaltered levels at higher somatostatin or octreotide concentrations. These observations could not be explained by interference with cell viability or proliferation.

CONCLUSIONS

We could not confirm immunomodulatory properties of somatostatin and octreotide on PBMC. Further analyses are necessary to explain the interaction between neuropeptides and the immune system.

Stress inhibits hair growth in mice by induction of premature catagen development and deleterious perifollicular inflammatory events via neuropeptide substance P-dependent pathways

It has been much disputed whether or not stress can cause hair loss (telogen effluvium) in a clinically relevant manner. Despite the paramount psychosocial importance of hair in human society, this central, yet enigmatic and controversial problem of clinically applied stress research has not been systematically studied in appropriate animal models. We now show that psychoemotional stress indeed alters actual hair follicle (HF) cycling in vivo, ie, prematurely terminates the normal duration of active hair growth (anagen) in mice. Further, inflammatory events deleterious to the HF are present in the HF environment of stressed mice (perifollicular macrophage cluster, excessive mast cell activation). This provides the first solid pathophysiological mechanism for how stress may actually cause telogen effluvium, ie, by hair cycle manipulation and neuroimmunological events that combine to terminate anagen. Furthermore, we show that most of these hair growth-inhibitory effects of stress can be reproduced by the proteotypic stress-related neuropeptide substance P in nonstressed mice, and can be counteracted effectively by co-administration of a specific substance P receptor antagonist in stressed mice. This offers the first convincing rationale how stress-induced hair loss in men may be pharmacologically managed effectively.

The dynamics of bone marrow stromal cells in the proliferation of multipotent hematopoietic progenitors by substance P: an understanding of the effects of a neurotransmitter on the differentiating hematopoietic stem cell

Communication within the hematopoietic-neuroendocrine-immune axis is partly mediated by neurotransmitters (e.g. substance P, SP) and cytokines. SP mediates neuromodulation partly through the stimulation of bone marrow (BM) progenitors. This study shows that SP, through the neurokinin-1 receptor, stimulates the proliferation of primitive hematopoietic progenitors: cobblestone-forming cells (CAFC, CD34+). This effect is optimal when macrophage is included within the fibroblast support. Indirect induction of IL-1 could be important in the proliferation of CAFC colonies by SP. Phenotypic and functional studies suggest that SP might directly interact with the CD34+/CD45(dim) population. These studies indicate that SP can initiate a cascade of biological responses in the BM stroma and stem cells to stimulate hematopoiesis.

Neuropeptides modulate a murine monocyte/macrophage cell line capacity for phagocytosis and killing of Leishmania major parasites

Host-parasite interactions and their outcome constitute a critical and challenging step in disease establishment in cutaneous leishmaniasis. In the present in vitro study we investigated the possible modulating effects of both sensory and autonomic neuropeptides that normally exist in human and mouse skin, on the uptake and leishmanicidal capacity of macrophages on Leishmania (L.) major parasites, using a monocyte/macrophage murine cell line (Raw 264.7). The sensory neuropeptides somatostatin (SOM), calcitonin gene-related peptide (CGRP) and substance P (SP) suppressed the macrophage capacity for phagocytosing L. major promastigotes at different concentrations, 10(-10) - 10(-5) M, however, the suppressive effect of SP does not reach a significant level. CGRP and SP enhanced the leishmanicidal capacity of macrophages at 10(-7) M, and 10(-5) M, respectively, whereas SOM was without effect. The autonomic neuropeptides vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) both suppressed the phagocytic and leishmanicidal capacities of macrophages at various concentrations, 10(-10) - 10(-5) M. The findings indicate that neuropeptides have modulating effects on macrophage-L. major interactions. These effects might be exerted by a direct action on macrophages or indirectly through induction of other mediators.

Respiratory syncytial virus infection and G and/or SH protein expression contribute to substance P, which mediates inflammation and enhanced pulmonary disease in BALB/c mice

A distinct clinical presentation of respiratory syncytial virus (RSV) infection of humans is bronchiolitis, which has clinical features similar to those of asthma. Substance P (SP), a tachykinin neuropeptide, has been associated with neurogenic inflammation and asthma; therefore, we chose to examine SP-induced inflammation with RSV infection. In this study, we examined the production of pulmonary SP associated with RSV infection of BALB/c mice and the effect of anti-SP F(ab)(2) antibodies on the pulmonary inflammatory response. The peak production of pulmonary SP occurred between days 3 and 5 following primary RSV infection and day 1 after secondary infection. Treatment of RSV-infected mice with anti-SP F(ab)(2) antibodies suggested that SP may alter the natural killer cell response to primary and secondary infection. In mice challenged after formalin-inactivated RSV vaccination, SP appears to markedly enhance pulmonary eosinophilia as well as increase polymorphonuclear cell trafficking to the lung. Based on studies with a strain of RSV that lacks the G and SH genes, the SP response to RSV infection appears to be associated with G and/or SH protein expression. These data suggest that SP may be an important contributor to the inflammatory response to RSV infection and that anti-SP F(ab)(2) antibodies might be used to ameliorate RSV-associated disease.

Benzodiazepine receptors and avian macrophage activity: diazepam decreases spreading and phagocytosis

The complex interrelations between the nervous system and the immune system have led to the creation of a new research area denoted neuroimmunology. The effects of stress on the immune response have long been observed in chickens. Since benzodiazepine receptors are involved in the stress reaction, we proposed to assess the importance of these receptors in the activity of chick peritoneal macrophages. We used 420 viable embryonated eggs of the commercial Hubbard broiler line treated through the chorioallantoid membrane on the 11th day of incubation: falsely manipulated (Sham group), with 40% propyleneglycol (PG) in simple Ringer solution (Vehicle group), and treated with diazepam (DZ), 8 mg/kg (DZ group). After hatching, the chicks were housed in metal rearing cages of the "battery" type for 5 weeks. At 36 days of age, 24 chicks from each treated group were divided at random into two groups of 12 animals each which were treated with DZ (2 mg/kg) or with 40% PPG in an equal volume once a day by the oral route for 4 days. Peritoneal macrophages were collected and submitted to the spreading an phagocytosis tests. Data were analyzed statistically using the SAS software (p < 0.05). Administration of DZ in ovo did not cause a significant decrease in egg hatchability, birth weight or performance parameters during the 5 weeks of assessment. However, the rate of macrophage spreading and phagocytosis was reduced. When administered at 40 days of age, DZ did not change the spreading rate but reduced the phagocytosis rate. There was no interaction between treatments. These results indicate that benzodiazepine receptors seem to be important for macrophage activity also in birds, as previously observed in rodents and primates. Since benzodiazepine receptors are involved in the response to stress, it is possible that the effects of stress on avian immunity may be mediated in part by these receptors.

Modulating effects of sensory and autonomic neuropeptides on murine splenocyte proliferation and cytokine secretion induced by Leishmania major

The intimate, bidirectional link between neuroendocrine and immune systems is now accepted. A modulating effect of the nervous system on immune and inflammatory responses has been corroborated by identification of neuropeptide receptors on immunocompetent cells and the finding that neuropeptides can regulate leukocyte functions. The present study was undertaken to investigate the possible immunomodulatory role of sensory (SOM, CGRP and SP) and autonomic (VIP and NPY) neuropeptides in a murine model of cutaneous leishmaniasis, using two genetically different inbred mouse strains, BALB/c and C57BL/6, respectively susceptible and resistant to Leishmania (L.) major infection. The parameters studied were extent of splenocyte proliferation, as measured by thymidine uptake, and the ability of these cells to secrete IFN-gamma and IL-4 by using a two-site ELISA, upon in vitro challenge with L. major parasites and addition of the neuropeptides. The resistant mouse splenocyte proliferation was enhanced by SOM, CGRP, and VIP at 10(-5), 10(-6) and 10(-9) M concentration, respectively, but was inhibited by NPY at 10(-5) M. Proliferation of the splenocytes from the susceptible strain was inhibited by SOM (10(-11) M) and CGRP(10(-5) M). Somatostatin, at various concentrations, stimulated IFN-gamma secretion in both mouse strain splenocytes, and IL-4 production in the susceptible mouse. Calcitonin gene-related peptide enhanced IFN-gamma secretion in susceptible mouse splenocytes at 10(-6), 10(-7) and 10(-9) M, as did VIP at 10(-10) M and NPY at 10(-7) M. Vasoactive intestinal peptide also stimulated IL-4 production in BALB/c splenocytes at all concentrations used. Substance P had no effect on either cell proliferation or cytokine secretion in either of the two mouse strains. These findings indicate that the nervous system, represented by sensory and autonomic nerve terminals and their content of neuromediators, may be involved in the pathophysiology of cutaneous leishmaniasis.

Distribution of substance P positive cells and nerve fibers in the rat thymus

The immune and nervous systems communicate through an array of signalling molecules which includes substance P. This work investigates the anatomical relationship between substance P nerve fibers, receptors, and substance P positive cells in the thymus. Thymuses from rats were frozen or paraformaldehyde fixed. In vitro autoradiography was used to map the distribution of SP receptors. Immunostaining was used to localize SP positive cells and nerve fibers by transmitted light and confocal microscopy. SP receptors exhibited a broader distribution than previously reported, being present throughout the organ with a preferential concentration in the cortico-medullary zone. While SP fibers were frequently associated with the blood vasculature, they were also present throughout the organ independent of blood vessels and were most prominent in the cortico-medullary zone. SP positive cells followed a similar pattern of distribution as the SP fibers and were present as single cells or aggregates of SP positive cells. Confocal microscopy revealed close spatial contact between the SP positive nerve fibers and the SP positive thymic cells. The close spatial relationship between the SP positive thymic cells and SP positive nerve fibers supports the concept of a structural-functional unit between SP nerve fibers and their potential receptor-bearing target cells in the thymus.

Secretoneurin and chemoattractant receptor interactions

Secretoneurin (SN) is a 33-amino acid peptide derived from secretogranin II (chromogranin C) which induces chemotaxis of monocytes but not neutrophils. In this study, we found that SN interacted with specific cell surface binding sites on human monocytes. The chemoattractants MCP-1, MCP-2 or fMLP could not compete for SN binding sites suggesting SN may bind to a novel chemotactic receptor. Additional studies showed that neither SN nor MCP-2 induced a rise in cytosolic Ca2+, and chemotaxis to SN was inhibited by cholera toxin (CT) and pertussis toxin (PT). Chemotactic desensitization studies demonstrated that fMLP, MCP-1, SN, and MCP-2 could all desensitize monocytes to subsequent SN stimulation. Our results indicate that SN binds to a cell surface receptor expressed on monocytes and activates signaling pathways which are sensitive to CT and PT.

Distribution of calcitonin gene-related peptide, somatostatin, substance P and vasoactive intestinal polypeptide in experimental colitis in rats

Immunohistochemistry was used to examine the distribution of calcitonin gene-related peptide (CGRP), substance P, somatostatin and vasoactive intestinal polypeptide (VIP) in experimental colitis induced with trinitrobenzene sulphonic acid (TNBS) in rats. CGRP immunoreactivity was observed throughout the colonic wall. A significant reduction of CGRP-immunoreactive (IR) nerve fibres was observed in the mucosa after the induction of colitis. After TNBS treatment substance P immunoreactivity was reduced throughout the colon; however, after 7 days there was a marked re-innervation of the circular muscle. Somatostatin immunoreactivity was distributed sparsely within the colonic wall, and was comparatively less affected by colitis. VIP immunoreactivity was abundantly distributed in the colonic wall and underwent an immediate reduction in the mucosa after TNBS treatment. After 2 days, there was a consistent and progressive increase in the number and density of VIP-IR nerve fibres in the inflamed colon, particularly the circular muscle. This change was associated with a proliferation of nerve fibres within the muscle layers. It was concluded that the early decrease in these neuropeptides was consistent with release from peripheral nerve terminals or the loss of nerves during the initial stages of colonic inflammation, which may be an essential condition for the development of colitis in this model. The observation that the intensity and density of substance P and VIP-IR nerve fibres increased in the circular muscle 7 days after the induction of colitis suggests their possible involvement in tissue repair.

In vitro Leishmania major promastigote-induced macrophage migration is modulated by sensory and autonomic neuropeptides

Recruitment, migration and adherence of macrophages and their interaction with inoculated promastigotes are key steps in the initiation of the inflammatory process in cutaneous leishmaniasis. Parasite- and nervous system-derived factors might be involved in this process. In the present study the chemotactic activities of live, killed and sonicated Leishmania major promastigotes and of the promastigote culture supernatant as well as the L. major surface protease gp63 towards a murine macrophage cell line, Raw 264.7, were investigated, using the Boyden technique. The sensory neuropeptides SOM, CGRP and SP, and the autonomic neuropeptides VIP and NPY, were also investigated for possible modulatory effects on this chemotaxis, using the living promastigotes. Living promastigotes were the most efficient attractants for macrophages compared with other forms of the parasites. Prior incubation of the macrophages with the parasites completely abolished the chemotactic activity. This might indicate that the living promastigote chemotaxis is a receptor-mediated process. On the other hand, paraformaldehyde-killed promastigotes not only failed to induce macrophage chemotaxis but also inhibited it in comparison with the control. The surface protease gp63 tended to inhibit the macrophage chemotactic activity and the sonicate tended to stimulate it compared with controls. The culture supernatant had no effect, indicating that the chemoattractive factors putatively synthesized by the living promastigotes are not released to the surrounding medium. Somatostatin inhibited L. major promastigote-induced macrophage migration at a high concentration, 10(-6) M, while substance P inhibited it at both low concentrations, 10(-10) and 10(-9) M, and a high one, 10(-6) M, the last-mentioned having the greatest inhibitory effect. A stimulatory effect of calcitonin gene-related peptide was found at high concentrations, 10(-5) and 10(-6) M. Vasoactive intestinal peptide stimulated macrophage chemotactic activity at both a high, 10(-5) M, and at a low, 10(-9) M, concentration, the same concentration at which neuropeptide Y exerted its maximum inhibitory effect.

Neuroimmunomodulation in inflammatory bowel disease. How far from "bench" to "bedside"?

The chronic inflammatory bowel diseases (BID), Crohn's disease and ulcerative colitis, are characterized by recurrent periods of inflammation and tissue destruction. The clinical course is influenced by genetics, environmental factors, and the immune system. Recent insights (bench trials) benefiting from advances in genetic engineering and molecular biology have contributed to clinical care (bedside) in terms of actual or potential therapies. Does the neuroendocrine system significantly modify disease activity? Although conceptually appealing, evidence remains circumstantial. Compelling anecdotal reports exist that "stress" affects disease activity in terms of the frequency and severity of IBD flares (bedside), but the mechanisms underlying these observations are unknown. Evidence that neuroendocrine factors play a significant role in immunomodulation is progressing (bench). (i) Trinitrobenzene sulfonic acid (TNB)-induced colitis, although similar in unstressed Fisher and Lewis rats, shows marked worsening in stressed Lewis rats. (ii) Early studies of rectal pain perception suggest there are specific differences in neuroimaging studies (PET scans) in IBD patients compared to controls. (iii) Levels of substance P (SP) and its receptor are altered. (iv) Preliminary clinical studies with SP receptor antagonists show a trend toward improvement. (v) Importantly, the placebo response in clinical trials is as high as 45%. Evidence that neuroendocrine systems significantly modulate local inflammation is rapidly accumulating (bench), which will facilitate enhanced coordination of clinically relevant therapies (bedside).

Substance P C-terminal octapeptide analogues augment tumor necrosis factor-alpha release by human blood monocytes and macrophages

We have investigated the effects of the substance P C-terminal octapeptide analogues [Pro4, Glu (OBzl)11] SP4-11, [Hyp4, Glu(OBzl)11] SP4-11, [cHyp4, Glu(OBzl)11] SP4-11 and [kPro4, Glu(OBzl)11] SP4-11 on the constitutive and/or lipopolysaccharide (LPS)-induced expression of tumor necrosis factor (TNF-alpha) in both freshly isolated human blood monocytes (FIBM) and monocyte-derived macrophages (MDM). The cells were treated with substance P and the substance P analogues at various concentrations (10-14 to 10-6 M) in the presence or absence of LPS and culture supernatants were analyzed for TNF-alpha as measured by an enzyme immunosorbent assay (ELISA). Monocytes and macrophages treated with the substance P analogues alone increased TNF-alpha secretion at a magnitude similar to the effect of entire undecapeptide substance P. The stimulatory effects of the substance P analogues on TNF-alpha secretion are inhibited by substance P antagonists, spantide ([D-Arg-1-D-Trp-7-D-Trp-9-Leu-11]-SP) and CP-96,345 (a nonpeptide antagonist of the substance P receptor), indicating that these effects are specific and substance P receptor-mediated. Treatment of monocytes and macrophages with the substance P analogues in combination with LPS, however, showed no synergistic interaction in upregulation of TNF-alpha. These data indicate that the biological effect of substance P on TNF-alpha production by human monocytes and macrophages depends mainly on the sequence of the C-terminal region of the molecule.

Neuromuscular regulation of T-cell activation

Recent investigations in our laboratory have shown that murine intestinal smooth muscle cells (ISMCs) can exert an immunomodulatory effect on T-cells. Therefore, we examined the effects of substance P, calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) on the ability of ISMCs to modulate T-cell proliferation and lymphokine generation. T-cell proliferation was observed when these cells were co-cultured with IFN-pretreated C57/BL6 ISMCs which expressed major histocompatibility complex II (MHC II), but not during T-cell co-culture with C2D (MHC II -/-) ISMCs pretreated in the same manner. T-cell proliferation during co-culture with C57/BL6 ISMCs was also associated with significantly enhanced T-cell synthesis of IFN. When CGRP (at 10(-9) M), but not substance P or VIP, was added to C57/BL6 ISMCs during the IFN-pretreatment period. T-cell proliferation was significantly increased. However, increased T-cell proliferation was not observed if the concentration of CGRP was increased to 10(-6) M. At the higher concentration, addition of substance P or VIP during the pretreatment period significantly inhibited the subsequent T-cell proliferation. Pretreatment of C57/BL6 ISMCs with any of the three neuropeptides and IFN resulted in the diminished production of IL-4 and IFN by co-cultured T-cells. A similar pattern of cytokine secretion was observed during T-cell co-culture with IFN- and neuropeptide-pretreated C2D ISMCs except when 10(-6) M substance P was added; IFN secretion by co-cultured T-cells was increased 4-fold under these conditions. Taken together, these data show a direct modulatory role for neuropeptides in the interaction between ISMCs and T-cells and suggest that, in general, neuropeptides may dampen immune responses in the neuromuscular layers of the inflamed intestine.

Neuroimmunomodulation via limbic structures--the neuroanatomy of psychoimmunology

During the last 20 years, mutual communications between the immune, the endocrine and the nervous systems have been defined on the basis of physiological, cellular, and molecular data. Nevertheless, a major problem in the new discipline "Psychoneuroimmunology" is that controversial data and differences in the interpretation of the results make it difficult to obtain a comprehensive overview of the implications of immunoneuroendocrine interactions in the maintenance of physiological homeostasis, as well as in the initiation and the course of pathological conditions within these systems. In this article, we will first discuss the afferent pathways by which immune cells may affect CNS functions and, conversely, how neural tissues can influence the peripheral immune response. We will then review recent data, which emphasize the (patho)physiological roles of hippocampal-amygdala structures and the nucleus accumbens in neuroimmunomodulation. Neuronal activity within the hippocampal formation, the amygdaloid body, and the ventral parts of the basal ganglia has been examined most thoroughly in studies on neuroendocrine, autonomic and cognitive functions, or at the level of emotional and psychomotor behaviors. The interplay of these limbic structures with components of the immune system and vice versa, however, is still less defined. We will attempt to review and discuss this area of research taking into account recent evidences for neuroendocrine immunoregulation via limbic neuronal systems, as well as the influence of cytokines on synaptic transmission, neuronal growth and survival in these brain regions. Finally, the role of limbic structures in stress responses and conditioning of immune reactivity will be commented. Based on these data, we propose new directions of future research.