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From the Department of Medicine,*University of Vermont School of Medicine, Burlington, Vermont; the Department of Neurology,
Oregon Health and Science University and Neuroimmunology Research, Veterans Affairs Medical Center, Portland, Oregon; the Department of Veterinary Pathobiology,
University of Illinois at UrbanaChampaign, Urbana, Illinois; the Department of Microbiology and Immunology,¶Drexel University College of Medicine, Philadelphia, Pennsylvania; and the Medical Institute of Bioregulation,
Kyushu University, Fukuoka, Japan
| Abstract |
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and more interleukin (IL)-4 in in vitro recall assays compared to wild-type controls. H1RKO mice are also less susceptible to acute early-phase experimental allergic encephalomyelitis indicating that H1R signaling in CD4+ T cells plays a central role in regulating pathogenic T-cell responses. In this study, we show that mice lacking histamine H2 receptor (H2RKO) are similar to H1RKO mice in that they develop encephalitogen-specific T-cell responses as assessed by proliferation and IL-2 production and present with less severe acute early-phase experimental allergic encephalomyelitis. However, unlike T cells from H1RKO mice, which exhibit a strong Th2 bias, T cells from H2RKO mice do not. Rather, they are uniquely characterized by a significant inhibition of Th1 effector cell responses. Given that both histamine and adjuvants such as pertussis toxin modulate antigen-presenting cell (APC) maturation and function, including T-cell-polarizing activity, we analyzed the cytokines/chemokines secreted by APCs from wild-type, H1RKO, and H2RKO mice. Significant differences in cytokine/chemokine production by APCs from unimmunized and immunized mice were delineated. APCs from H2RKO mice produce significantly less IL-12 and IL-6 and markedly greater amounts of MCP-1 compared to wild-type and H1RKO mice. Because MCP-1 is known to inhibit IL-12 production, the failure of H2RKO mice to generate encephalitogenic Th1 effector cell responses is consistent with inhibition of negative regulation of MCP-1 secretion by H2R signaling in APCs.
and tumor necrosis factor (TNF)-
whereas Th2 cells secrete interleukin (IL)-4, IL-5, and IL-13.4-6
This dichotomy is thought to be established early in T-cell antigen priming by contact with antigen-presenting cells (APCs).7,8
Signaling through histamine H1 and H2 receptors (Hrh1/H1R and Hrh2/H2R) is known to regulate Th1 and Th2 effector functions and the polarization of naïve CD4+ Th0 cells into either Th1 or Th2 cells. T cells from H1RKO mice stimulated in vitro with anti-CD3 and anti-CD28 antibodies produce lower intracytoplasmic levels of IFN-
suggesting that H1R signaling in CD4+ T cells enhances Th1 responses. In contrast, T cells from H2RKO mice stimulated in the same way produce higher intracytoplasmic levels of both IFN-
and the Th2-related cytokines IL-4 and IL-13, indicating that both Th1 and Th2 responses may be down-regulated by H2R signaling.9,10
Additionally, histamine acting primarily through H2R on APCs has been reported to strongly enhance the secretion of IL-10 and inhibit the production of IL-12, thereby influencing polarization of T-cell effector responses.11-14 Recently, we demonstrated that Bphs, an autoimmune disease gene controlling susceptibility to both experimental allergic encephalomyelitis (EAE) and autoimmune orchitis, is H1R.15 During the acute phase of disease, C57BL/6J H1RKO congenic mice exhibited a significant delay in the onset of EAE and a reduction in the severity of the clinical signs compared with C57BL/6J wild-type mice. This result was associated with immune deviation of the elicited CD4+ T-cell population from a highly encephalitogenic Th1 response to a less encephalitogenic Th2 response. In addition to the role of H1R in EAE, mRNA transcripts for molecules involved in the allergic arm of the immune response, including H1R and H2R, have been identified in central nervous system (CNS) lesions in EAE and multiple sclerosis (MS).16-18
Mast cells, the primary source of histamine in the body,19,20 have long been appreciated in EAE and MS. In 1890, Neuman21 reported their presence in MS plaques. Subsequent studies verified that the number and distribution of mast cells correlate with MS lesions and susceptibility to EAE,22,23 and have been shown to be essential for eliciting severe acute EAE.24 Histamine and histamine-releasing agents also have a dramatic effect on the blood-brain barrier, and tissue levels of histamine correlate with the onset of EAE.23,25 Inhibitors of mast cell degranulation and H1R selective antagonists have been shown to reduce the severity of EAE.26-29 Furthermore, mast cells activated in the periphery migrate to draining lymph nodes during the induction of an immune response suggesting that they have a regulatory influence on B- and T-cell responses.30-32 There is also bidirectional communication between histamine and cytokines in a variety of settings.33 Taken together, these studies suggest that histamine signaling through the H2, H3, and H4 receptors may also participate in the pathogenesis of autoimmune disease of the CNS.
In this study, we directly examined the role of H2R signaling in controlling susceptibility to myelin oligodendrocyte glycoprotein (MOG) peptide 35-55 (MOG35-55)-induced EAE using C57BL/6J H2RKO congenic mice.34 We report that H2RKO mice are significantly less susceptible to acute early-phase EAE compared to wild-type C57BL/6J mice even though no significant difference in their in vitro CD4+ T-cell proliferative response or secretion of IL-2 after stimulation with MOG35-55 was detected. However, CD4+ T cells from H2RKO exhibit significantly blunted Th1 effector cell responses. An analysis of the cytokines produced by APCs from H2RKO mice revealed profiles consistent with the effector T-cell responses observed, indicating that susceptibility to EAE may in part be controlled by H2R-mediated regulation of APC function.
| Materials and Methods |
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C57BL/6J mice were purchased from the Jackson Laboratory (Bar Harbor, ME). B6.129P-Hrh1tm1Wat (H1RKO) and B6.129P-Hrh2tm1Wat (H2RKO) mice were backcrossed to C57BL/6J mice for a total of 10 generations.15,34 Wild-type controls (designated as C57BL/6J), B6.129P-Hrh1tm1Wat, B6.129P-Hrh2tm1Wat, and (B6.129P-Hrh1tm1Wat x B6.129P-Hrh2tm1Wat) F1 hybrid mice were generated at Charles Rivers Laboratory (Wilmington, MA) and shipped to either the University of Oregon Health Sciences Center (Portland, OR) or the University of Vermont (Burlington, VT).
Flow Cytometric Analysis
Single cell suspensions of thymocytes and splenocytes were prepared and the contaminating red blood cells lysed with ammonium chloride. The cells were washed twice and incubated for 20 minutes on ice with the desired fluorochrome-conjugated monoclonal antibodies or isotype control Ig at 0.5 µg/106 cells. The cells were washed twice with phosphate-buffered saline/1% bovine serum albumin, fixed in 2% paraformaldehyde, and analyzed by FACScan (BD Biosciences, San Jose, CA) using the Cell Quest program (BD Biosciences).
Induction and Evaluation of EAE
Mice were injected subcutaneously in the flanks with 0.2 ml of an emulsion containing 200 µg of MOG35-55 (Beckman Institute, Palo Alto, CA) in saline and an equal volume of complete Freunds adjuvant containing 200 µg of Mycobacterium tuberculosis H37RA (Difco Laboratories, Detroit, MI). On the day of immunization, each mouse received 25.0 ng of pertussis toxin (PTX) (List Biological Laboratories Inc., Campbell, CA) intravenously, and 67.0 ng 2 days later.15 The mice were assessed daily for clinical signs of EAE according to the following scale: 0, normal; 1, limp tail or mild hind limb weakness; 2, moderate hind limb weakness or mild ataxia; 3, moderately severe hind limb weakness; 4, severe hind limb weakness or mild forelimb weakness or moderate ataxia; 5, paraplegia with no more than moderate forelimb weakness; 6, paraplegia with severe forelimb weakness or severe ataxia or moribund condition.
Brains and spinal cords were dissected from calvaria and vertebral columns, respectively, and fixed by immersion in 10% phosphate-buffered formalin (pH 7.2). After adequate fixation, brain and spinal cord were trimmed and representative transverse section embedded in paraffin, sectioned at 5 µm, and mounted on glass slides. Sections were stained with hematoxylin and eosin for routine evaluation and Luxol fast blue-periodic acid-Schiff for demyelination. Sections from representative areas of the brain and spinal cord (SC) were scored in a semiquantitative manner for the various histopathological parameters as previously described.35
Proliferation Assays
Draining lymph node cells were surgically removed from immunized mice at the peak of clinical disease (day 16 after immunization), and single cell suspensions were prepared.15,36 draining lymph node (DLN) cells (4 x 105/well) were plated on standard 96-well flat-bottom tissue culture plates for 72 hours at 37°C and 7% CO2 with and without antigen and in the presence of 0.5 µCi of 3H-thymidine during the last 18 hours. Cells were harvested onto glass fiber filters and thymidine uptake was determined by liquid scintillation.
Cytokine Assays
Spleens were surgically removed from immunized mice at the peak of clinical EAE (day 16 after immunization) and single cell suspensions were prepared. Splenocytes were suspended at 4 x 106 cells/ml in stimulation media with 20 µg/ml of MOG35-55. Cell culture supernatants were recovered at 48 hours and frozen at -70°C until needed for cytokine assays. Cytokine levels were measure by enzyme-linked immunosorbent assay (ELISA)15,36
using cytokine-specific capture and detection antibodies (PharMingen, San Diego, CA). Capture antibodies for IFN-
were diluted to 2 µg/ml in bicarbonate coating buffer (0.1 mol/L NaHCO3, pH 8.2). IL-4 was quantified using an IL-4 ELISA (PharMingen). Standard curves for each assay were generated using recombinant mouse cytokines (PharMingen), and the concentration of cytokines in the cell supernatants was determined by interpolation from the appropriate standard curve. Mean and standard curves were determined using triplicate cultures from pooled splenocytes from each group.
IFN-
, TNF-
, IL-2, and IL-5 were also simultaneously detected using the mouse Th1/Th2 cytokine CBA kit from BD Biosciences (San Jose, CA). Fifty µl of sample was mixed with 50 µl of the mixed capture beads and 50 µl of the mouse Th1/Th2 PE detection reagent. The tubes were incubated at room temperature for 2 hours in the dark, followed by a wash step. The samples were then resuspended in 400 µl of wash buffer before acquisition on the FACScan. The data were analyzed using the CBA software. Standard curves were generated for each cytokine using the mixed bead standard provided in the kit and the concentration of cytokine in the cell supernatant was determined by interpolation from the appropriate standard curve. Means and standard deviations were determined using data from individual animals.
In some experiments cytokine production was assessed using RayBio Mouse Cytokine Array 1 (RayBiotech, Inc., Norcross, GA). Cell culture supernatants were collected and assayed as per the manufacturers specifications. Complete media was used as the negative control in all assays. The results were normalized and the data presented as the relative abundance with respect to the cytokine/growth factor being produced in the highest concentration.
Assessment of Antibody Responses
Antibody reactivity to MOG35-55 was determined by indirect ELISA.15,36 Dilutions of mouse sera from MOG35-55-immunized C57BL/6J wild-type control and H2RKO mice were incubated in MOG35-55-coated wells, and bound antibody was detected spectrophotometrically with peroxidase-conjugated anti-mouse Ig, anti-mouse IgG1, and anti-mouse IgG2a and o-phenylene-diamine as a substrate.
Peritoneal Exudate (PE) Macrophages
PE cells were collected on days 7 to 8 after immunization by peritoneal lavage 3 days after the intraperitoneal injection of 1.5 ml of sterile thioglycolate (3%). The cells were suspended at a concentration of 1 x 106 macrophages/ml in media and the nonadherent cells removed after 3 hours of plating. The adherent PE macrophages (>95%) were subsequently cultured for 24 hours in media.
Real-Time Polymerase Chain Reaction (PCR) Analysis of Gene Expression
Total RNA was extracted from PE macrophages obtained after 3 hours of plating using Ultraspec RNA isolation reagent (Biotecx Laboratory, Houston, TX) as recommended by the manufacturer. Total RNA (1.0 µg) was used as a template to synthesize first strand cDNA using random primers (Promega, Madison, WI) with Superscript II reverse transcriptase (Invitrogen, Carlsbad, CA). Real-time PCR was performed using the TaqMan system (Applied Biosystems, Foster City, CA). PCRs were performed using the TaqMan Universal PCR Master Mix and the ABI PRISM 7700 sequence detection system. MCP-1 and
-actin (Actg) (internal reference) were measured by real-time PCR using probes labeled with 6-carboxyfluorescein (FAM) and Black Hole Quencher (BHQ). The MCP-1 probes and primer set sequences used were as previously described.37
The Actg probe and primer sequences were: probe, 5'-6-FAM-d(CATTGCTCCCCCTGAGCGCAA)-BHQ-1-3'; forward primer, 5'-d(GCACCTAGCACGATGAAGATTAA GA)-3'; reverse primer, 5'-d(AGCCACCGATCCAGACTGAGT)-3' (Biosearch Technologies, Novato, CA). MCP-1 and Actg mRNA levels were analyzed separately using the standard curve method. A no-reverse transcriptase control was also prepared for each sample and no genomic DNA was detected. Total RNA was isolated and reverse-transcribed into first strand cDNA. One µl of sample cDNA was used in the PCR reactions, three comparative threshold cycle (CT) values obtained and the average ratio of MCP-1:Actg calculated.
| Results and Discussion |
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and TNF-
and the Th2 cytokine IL-5 was decreased in H2RKO mice compared to wild-type mice (Figure 2, A and B)
production (Figure 4B)
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Cytokines, chemokines, and growth factor production by PE macrophages from unimmunized or immunized wild-type, H1RKO, and H2RKO mice was assessed using cytokine arrays. The results for 15 cytokines, chemokines, and growth factors on the arrays that are known to be expressed by macrophages43,44
are presented in Figure 6
. Clearly, there are significant differences in the cytokine profiles of PE macrophages among the strains form both unimmunized (Figure 6A)
and MOG35-55-immunized (Figure 6B)
mice. The most dramatic difference seen in the unimmunized mice was the increased secretion of sTNFR1 by H1RKO PE macrophages compared to wild-type cells, and the decreased level of sTNFR1 expression by PE macrophages from H2RKO mice (Figure 6A)
. Significant differences were also seen in the levels of IL-10 (WT > H1RKO = H2RKO), IL-12p70 (WT = H1RKO < H2RKO), IFN-
(WT = H2RKO > H1RKO), MCP-1 (WT = H1RKO < H2RKO), MCP-5 (WT = H1RKO < H2RKO), RANTES (WT = H2RKO > H1RKO), and SCF (WT = H1RKO < H2RKO) secretion by PE macrophages among the three strains.
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.50
In addition, MCP-1 has been shown to selectively alter cytokine-driven APC differentiation and maturation without altering their T-cell-stimulating activity.46
Interestingly, MCP-1 has been shown to be an essential mediator during the effector phase of EAE,33
and PTX treatment of mice overexpressing MCP-1 exhibit a reversible encephalopathy.51
Clearly, the effect of MCP-1 depends on the context in which it is acting.52
Cimetidine, which was originally described as an H2R selective antagonist but is in reality an inverse agonist,53
does not prevent or inhibit EAE.26
Rather, it increases disease severity54
as well as Th1-mediated delayed type hypersensitivity reactions in general,55
and the production of IL-12 by human mononuclear cells.56
Dimaprit, an H2R agonist, has been reported to ameliorate EAE57
and inhibit the production of TNF-
and IL-12.58
The seemingly paradoxical results between our findings and pharmacological based approaches may be because of several factors. The phenotypic differences in knockout mice reflect both developmental and adult gene functions. Therefore, the differences seen in H2RKO mice not only reflect the effects of H2R signaling during adulthood but they also reflect the role that the absence of H2R signaling plays in the development of the normal innate and anticipatory components of the immune system. With respect to histamine, this paradox is exemplified by the mast cell abnormalities seen in histidine decarboxylase-deficient mice59
and the abnormalities in cytokine production seen in unimmunized PE macrophages form H1RKO and H2RKO mice in this study (Figure 6A)
. The life-long absence of histamine signaling through H2R may well show a different outcome than would be predicted using pharmacological agents in an intact mouse with a normal immune repertoire.
Additionally, it has been shown that tissue-specific expression of H2R in the mouse is under the control of histamine, and that exogenous histamine present in the diet modulates receptor expression.60 Differences in dietary histamine and in vitro culture conditions can therefore significantly impact the immunological read outs associated with pharmacological approaches. For example, the effects of histamine on T- and B-cell antigen-specific proliferative responses can only be observed by using histamine-free media and depleting c-Kit-positive cells from spleen and lymph node cell preparations.61
Regarding cytokine production by T cells, our results differ from those of Jutel and colleagues.9
They reported that splenic T cells from H2RKO mice stimulated with anti-CD3 and anti-CD28 antibodies exhibited increased intracytoplasmic staining for IFN-
compared to wild-type mice. A slight increase in intracytoplasmic staining for IL-4 was also seen at 48 hours after stimulation. When histamine-pretreated spleen cells were stimulated with anti-CD3 antibody and supernatants assayed for cytokine production 72 hours later, they observed increased production of both Th1 and Th2 cytokines. The different results obtained in the present study may be because of histamine-signaling differences in T cells from mice that have been actively immunized with complete Freunds adjuvant and PTX compared to naive T cells subjected to in vitro stimulation protocols. In this regard, the effect of histamine on IFN-
production by Th1 cells has been shown to be dependent on the stimulating signals and mode of cellular activation.62
Similarly, there is increasing evidence indicating that microbial products drive the development of T-cell effector functions via their effects on APCs.63
Indeed, histamine-dependent changes in cytokine production by APCs is highly dependent on the presence or absence of LPS, a toll-like receptor (TLR) ligand with known adjuvant activity,13
and PTX as shown in this and other studies.39-42
Collectively, the results of our studies on Bphs/Hrh115 and the studies reported herein indicate that histamine signaling through H1R and H2R significantly influence the T-cell responses in EAE, particularly with respect to immune deviation and the nature of the cytokines they produce. Our results also suggest that Th1-dependent autoimmune diseases such as MS may be amenable to treatment with combinations of either H1R- and H2R-selective antagonist or agonists. Typically, H1R is coupled to the PLC/intracellular Ca2+ signaling pathway whereas H2R is considered to be coupled to the adenylate cyclase/cAMP pathway.53,64 However, an accumulating body of evidence indicates that signaling through H2R can result in the activation of the adenylyl cyclase/cAMP and PLC/intracellular Ca2+ second messenger systems. Multiple signaling is common among Gs-coupled receptors and has been suggested to be because of receptor density.65 In this regard, it was recently shown that H2R signaling through the PLC second messenger pathway is inhibited during cellular differentiation, and that this inhibition is correlated with decreased H2R expression.66 Thus, signaling through H2R may regulate immune deviation using different second messenger pathways as a function of the developmental state of either the T cells, APCs, or both. Although the details concerning the interplay between H1R- and H2R-signaling pathways and known signaling pathways regulating the polarization of T cells remains obscure, this interplay is nevertheless an avenue of investigation that has the potential to provide significant insight into the interactions between the environment, cells of the innate immune system, and the generation of effector T cells leading to disease.
| Footnotes |
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Supported by the National Institutes of Health (grants NS36526 to C.T. and E.P.B., AI4515 to C.T., AI41747 to C.T.) and the National Multiple Sclerosis Society (grants RG-3129 to C.T and E.P.B., AI42376 to H.O., NS23444 to H.O., and RG-3108 to H.O.).
Accepted for publication November 14, 2003.
| References |
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and IL-12 by macrophages via H2-receptors. Int Immunopharmacol 2001, 1:1867-1875[Medline]
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