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Endocrinology Vol. 138, No. 12 5505-5510
Copyright © 1997 by The Endocrine Society

ARTICLES

Changes in 1,25-(OH)2D3 Synthesis and Its Receptor Expression in Spleen Cell Subpopulations of Mice Infected with LPBM5 Retrovirus

T. M. Nguyen, J. Pavlovitch, M. Papiernik, H. Guillozo, O. Walrant-Debray, C. Pontoux and M. Garabedian

CNRS (T.M.N., J.P., H.G., O.W.-D., M.G.), URA 583, Université Paris V, Hôpital Saint-Vincent de Paul, 75014 Paris, France; INSERM U345 (M.P., C.P.), Institut Necker, 75015 Paris, France

Address all correspondence and requests for reprints to: T. M. Nguyen, CNRS URA 583, Hôpital Saint-Vincent de Paul, 82 avenue Denfert-Rochereau, 75014 Paris, France.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
This study examines the influence of chronic retroviral infection of mice with a LPBM5 virus mixture on the paracrine system involving immune cells and 1,25-(OH)2D3 in the spleen. Plasma ionized calcium, 25-(OH)D and 1,25-(OH)2D of infected mice were unchanged. In contrast, the specific binding of 1,25-(OH)2D3 to spleen cytosol and the number of monocyte/macrophages expressing 1,25-(OH)2D3 receptors (VDR) were markedly increased. The retroviral infection also influenced the local production of 1,25-(OH)2D3 in the spleen. It did not alter this production in monocyte/macrophages but increased that in isolated T cells. Isolated B cells in control mice did not produce 1,25-(OH)2D3, but they increased the ability of isolated T cells to produce this metabolite during coculture incubations. Infection altered this cell interaction as 1,25-(OH)2D3 production in infected T cells decreased when these cells were cocultured with infected B cells.

Thus, chronic retroviral infection alters both the local vitamin D metabolism and VDR expression by immune cells in mice. These findings suggest close local interactions between 1,25-(OH)2D3 and immune system activation during retroviral infection.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
IT IS NOW widely accepted that the active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), modulates the immune system in addition to its classical role in calcium homeostasis (1, 2, 3). Vitamin D deficiency is associated with impaired immune responses and more frequent infections in humans and mice (4). 1,25-(OH)2D3 prevents the development of spontaneous, and experimental autoimmune diseases in vivo (4, 5, 6, 7, 8, 9) and influences the phenotype and function of monocytes and lymphocytes, and the synthesis of cytokines in vitro (10, 11, 12, 13, 14). In particular, it inhibits the production of interleukin-2 and interferon-{gamma}, causing the inhibition of Th1-type helper T cells (11). The 1,25-(OH)2D3 that acts on the immune cells may be synthesized in the kidney, or produced locally within the immune cells (15). Monocytes-macrophages isolated from patients with granulomatous diseases or inflammatory disorders can produce 1,25-(OH)2D3 in vitro (16, 17, 18, 19, 20, 21). Similarly, T lymphocytes from patients with a lymphoma or tuberculosis synthesize 1,25-(OH)2D3 in vitro (16, 20). Thus, the immune cells seem to both respond and synthesize 1,25-(OH)2D3 to form a paracrine system for this metabolite within the immune system.

Several observations suggest that there is an interaction between 1,25-(OH)2D3 and the activation of immune cells that occurs in retroviral infection. The serum concentration of 1,25-(OH)2D3 in early stage of acquired immunodeficiency syndrome (AIDS) is not known, but patients with a late stage of the disease have low concentration of 1,25-(OH)2D (22). Most important, their survival is positively correlated with their circulating 1,25-(OH)2D (22). In contrast, treatment of mice with 1,25-(OH)2D3 enhances the severity of mouse AIDS and increases the mortality rate (23). Lastly, the replication of HIV in lymphoid cells and macrophages is influenced by 1,25-(OH)2D3. Its effect can be stimulatory or inhibitory, depending on the cell type and their differentiation, and on whether it is given preinfection or post infection (24, 25, 26, 27).

This study was carried out to investigate the precise role of 1,25-(OH)2D3 in retrovirus-induced immunodeficiency disease. The synthesis of 1,25-(OH)2D3 and distribution of 1,25-(OH)2D3 receptors on immune cells were analyzed using the MAIDS model, which has features similar to AIDS, including immune activation, profoundly altered cytokine production and impaired B cell, T cell, and macrophage function (28, 29).


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Compounds tested
[26,27-3H] 25-(OH)D3 (14 Ci/mmol), [26,27-3H] 1,25(OH)2D3 (87 Ci/mmol), were obtained from Amersham (Buckinghamshire, UK). Unlabeled 25-(OH)D3 was a gift from Roussel Uclaf (Paris, France) and 1,25-(OH)2D3 was a gift from Roche Laboratory (Basel, Switzerland). Monoclonal antibody 9A7 {gamma} against 1,25-(OH)2D3 receptors was a gift from Dr. J. W. Pike.

Mice
Female C57Bl/6 mice, purchased from Charles River (France), were specific pathogen-free and were housed in an air-conditioned room in accordance with the French guidelines for care and use of laboratory animals.

LPBM5 MuLV
The virus was raised from an SC1 clone chronically infected with LPBM5 MuLV. This cell line, G6, was a gift from Dr. H. C. Morse, III (National Institutes of Health, Bethesda, MD). The mouse 3T3 cells, transformed with defective mink stomatitis virus (FG 10 S+L-) and fibroblasts transformed with defective mink S+L- virus were used to titrate helper and mink focus-forming viruses, respectively, as described by Bassin et al. (30). The LPBM5 preparation used contained 1.7 x 1010 MuLV and 1.2 x 105 mink focus-forming virus. The infectivity of the culture supernatant was tested by the incidence of splenomegaly and lymphadenopathy 6–8 weeks after challenge.

Experimental protocol
Mice were infected at 8 weeks of age with LPBM5 MuLV (0.5 ml ip/mouse). Infected and control uninfected mice were killed 5 weeks later. Their blood was collected for serum biochemical analysis, and their spleens were removed and kept on ice for cytosol or spleen cell preparation.

Measurement of plasma calcium and vitamin D metabolites
Ionized serum calcium was measured with a Hitachi 7171 analyzer (Boehringer Mannheim, Mannheim, Germany). Plasma 25-(OH)D was assayed on 50 µl of plasma extracted with chloroform/methanol (1/1). The extract was chromatographed on Amprep C-18 minicolumns (Amersham), and the 25-(OH)D in the purified samples quantified by a protein-binding assay (rat serum) (31). The lower limit of detection was 0.1 ng/ml.

1,25-(OH)2D was measured on the pooled plasma from two to three mice (0.5 ml). This sample was extracted with methanol/methylene chloride (2/1), and the extracts were chromatographed on a 1 x 20-cm column of Sephadex LH20 (Pharmacia) using an n-hexane: chloroform: methanol (90:10:10) solvent. The concentration of 1,25-(OH)2D in the purified samples was measured using a protein-binding assay (intestinal chick cytosol) (32).

Spleen cell preparation, cell-subset purification, and analysis
The spleens were weighed and homogenized in a Potter homogenizer, and the cells per spleen were counted using a hemocytometer.

Antibodies. The following monoclonal antibodies (mAb) were used: anti-CD4 (clone GK-1.5), anti-CD8 (clone 53.67), anti-Mac-1 (clone M1/70), anti-B220 (clone RA3–6B2).

Flow cytometry. Cells were washed in PBS containing 2% FCS and 0.1 M sodium azide, and incubated for 30 min with appropriate dilutions of mAb coupled to phycoerythrin or fluorescein. Flow cytometry was performed on a FACScan (Becton-Dickinson, Mountain View, CA). At least 104 lymphoid cells were acquired per sample and the results were analyzed using Lysis II software.

Purification of cell subsets. Red blood cells were lysed by osmotic shock and 4 spleen cell subpopulations were prepared by incubation for 20 min with monoclonal antibodies specific for each type of cell. The cells were then incubated for 20 min with antirat antibody or antimouse Ig-coated magnetic beads (Dynabeads, Oslo, Norway), and the magnetic beads were removed with a magnet.

A macrophage-enriched population was obtained by depletion of CD4, CD8, and B cells after incubation with anti-CD4, anti-CD8, following by incubation with antirat Ig coated magnetic beads and then with antimouse Ig coated magnetic beads to remove B cells. Lymphocyte populations containing B cells, CD4, and CD8 T cells were obtained by removing macrophages by incubation with anti-Mac-1 antibody and then with antirat antibody-coated beads. B cell-enriched population was prepared by depletion of CD4 cells, CD8 cells, and macrophages; cells were incubated with purified anti-CD4, anti-CD8, and anti-Mac-1 antibodies, and then with antirat antibody-coated magnetic beads. Finally, a CD4 and CD8 T-enriched population was obtained by depletion of macrophages and B cells; cells were incubated with anti-Mac-1 antibody, then with antirat antibody-coated beads, then with antimouse Ig-coated beads to remove B cells. The treatment removed 97–99% of the targeted cell populations.

1,25-(OH)2D3 receptors in mouse spleen — 1-Measurement of 1,25-(OH)2D3 specific binding to spleen cytosols
Cytosol preparation. Three spleens from each experimental group were pooled, rinsed with ice-cold 0.9% NaCl, cut in small pieces, and washed twice with 5 vol of isotonic buffer (0.05 M KCl, 0.05 M KH2PO4, 1 mM DTT). They were homogenized in 2 vol of high salt buffer (0.3 M KCl, 1.5 mM EGTA, 0.01 M Na2 MoO4, 1 mM DTT), and the homogenate centrifuged for 15 min at 480 x g. The resulting supernatant was then centrifuged at 100,000 x g for 1 h in a 50 Ti rotor using a Beckman (Berkeley, CA) L8–55 ultracentrifuge. The pellet and floating lipid layer were discarded, and the cytosol was frozen immediately in liquid nitrogen and stored at -80 C. Protein concentrations were determined using BSA as standard (33).
Binding studies.The binding of 1,25-(OH)2D3 to specific receptors was studied by incubating 0.2 ml spleen cytosol (1 mg protein/ml) with 0.2–4 nM 3H 1,25-(OH)2D3 (Scatchard analysis) or with 2 nM 3H 1,25-(OH)2D3 (binding studies) for 1 h at 25 C with or without a 50-fold or 500-fold excess of unlabeled 1,25-(OH)2D3. After labeling, a 50-fold excess of unlabeled 25-(OH)D3 was added, and the incubation was continued for 1 h at 0 C to eliminate binding of 3H 1,25-(OH)2D3 to the contaminating serum vitamin D binding protein (DBP) (34). Bound and unbound 3H 1,25-(OH)2D3 were separated by adsorption of bound hormone onto hydroxylapatite in 10 mM Tris-HCl, pH 7.5 (35). Aliquots (0.2 ml) of hydroxylapatite were added to cytosol at the end of incubation. Samples were centrifuged (10,000 x g) for 10 min and the pellets were washed two times with 10 mM Tris-HCl + 0.5% Triton X100. 3H 1,25-(OH)2D3 was extracted from the washed pellets by shaking with 1 ml absolute ethanol at 30 C for 30 min. The extract solutions were cleared by centrifugation at 10,000 x g for 5 min and the radioactivity in aliquots (0.6 ml) of supernatant was measured in scintillation fluid (Ultimagold F, Packard). Results are expressed as fmol 3H 1,25-(OH)2D3 bound/mg protein.

Immunocytochemical distribution of 1,25-(OH)2D3 receptors. Spleen cells were centrifuged for 10 min in a Cytospin and collected on glass coverslip. The cells were then fixed in Bouin’s fluid (picric acid:formaldehyde:glacial acetic acid 30:2:1, vol/vol) for 1 h and washed twice in 0.1 M Tris-HCl, pH 7.5. Endogenous peroxidase was blocked by incubation with 1% H2O2 for 10 min, and cells were incubated overnight at 4 C with 9A7 {gamma}, a monoclonal antibody against 1,25-(OH)2D3 receptors, or with normal rat IgG (negative controls). They were then washed and incubated with biotinylated rabbit antirat IgG (1:100, Pharmacia) for 2 h at room temperature, followed by biotinylated protein-A(1:200) and streptavidin-biotin horseradish peroxidase (1:1000). Receptors were visualized by immersion in 0.1 M Tris containing (0.5%) diaminobenzidine-tetrahydro-chloride with (0.3%) hydrogen peroxide (36). A minimum of 400 cells was evaluated for each coverslip. Results are expressed as the relative percent of cells bearing 1,25-(OH)2D3 receptors.

3H 25-(OH)D3 metabolism in spleen cells
Isolated spleen cells were plated into 24-well tissue culture dishes (Costar, Cambridge, MA), at 3 x 105 cells per well. They were covered with 1 ml MEM without FCS and incubated with 10 µl ethanol containing 50 nCi [26,27- 3H] 25-(OH)D3 (2.5 x 10-9 M; specific activity: 14 Ci/mmol) for 90 min (37 C, 95% air/5% CO2). In some experiments where B and T lymphocytes were reassociated in vitro at a ratio of 1/2 T/B cells, cells were incubated for 2 h, at 37 C and under 95% air/5% CO2 before incubation with 3H 25-(OH)D3 to study the conversion of 3H 25-(OH)D3 to 3H 1,25-(OH)2D3.

Vitamin D metabolites were extracted from the media by adding 2 ml methanol plus 2 ml chloroform. The chloroform phases were dried under a stream of nitrogen, and the residues were redissolved in chromatography solvents. One hundred nanograms unlabeled synthetic 1,25-(OH)2D3 were added to each extract before chromatography. Samples were chromatographed (flow rate 1.6 ml/min) using a straight phase HPLC system (Beckman) equilibrated with n-hexane: isopropanol (90:10). Absorbance at 254 nm was monitored continuously and effluent fractions were collected every minute. Radioactivity was determined by liquid scintillation spectroscopy on an aliquot of each fraction. The vitamin D derivatives eluting in the 1,25-(OH)2D3 region were pooled and rechromatographed using a methylene chloride: isopropanol (95:5) solvent system (flow rate 1.1 ml/min). Aliquots of each fraction were evaporated to dryness, dissolved in scintillation fluid (Ultimagold F, Packard) and their radioactivity was measured. The rate of conversion of 3H 25-(OH)D3 to 3H 1,25-(OH)2D3 was determined by calculating the percentage of total radioactivity with an appropriate elution profile after the two chromatographic separations. Results are expressed as fmol/3 x 105 cells per 90 min, based on the assumption that the specific activity of the product was the same as that of the substrate. Thus, conversion of 1% of substrate to 3H 1,25-(OH)2D3 corresponds to the production of 37 fmol.

Statistical analysis
Statistical significance was assessed using Student’s t test.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Infected mice had a lower body weight than controls 5 weeks after infection with LPBM5 MuLV (Table 1Go). They developed splenomegaly and the total number of spleen cells was increased. The percentages of CD4+ T cells and B cells were not different from those of control mice, but the percentage of CD8+ T cells was lower. The concentrations of plasma calcium and vitamin D metabolites in the two groups of mice were not significantly different (Table 2Go).


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  		Table 1. Spleen cell phenotype of control and LPBM5 MuLV infected mice

 

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  		Table 2. Serum calcium and vitamin D metabolites in control and LPBM5 MuLV infected mice

 
1,25-(OH)2D3 receptors in spleen cells
Incubations of spleen cytosols with increasing amounts of 3H 1,25-(OH)2D3 (0.2–4 nM) in the absence or presence of 500-fold excess unlabeled 1,25-(OH)2D3 demonstrated specific binding sites that were saturable by low concentrations of 1,25-(OH)2D3. The apparent equilibrium dissociation constant (Kd) calculated from Scatchard analysis in spleen of infected mice was not different from that in spleen of control mice (Fig. 1Go). It was similar to the previously reported Kd for specific 3H 1,25-(OH)2D3 binding (37). The number of 1,25-(OH)2D3 binding sites calculated from the Scatchard plot was significantly higher in infected mice than in control mice (6 fmol/mg protein vs. 2 fmol/mg protein). Results were similar when estimated from binding assays in 4 separate populations of infected and control mice (9.0 ± 1.2 fmol/mg protein in infected spleens vs. 4.5 ± 0.8 fmol/mg protein in control spleens, P < 0.02).



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  		Figure 1. Scatchard analysis of the specific binding of 3H 1,25-(OH)2D3 to control or infected spleen cytosol. Aliquots of cytosol (0.2 ml and 0.2 mg protein) were incubated with increasing concentrations (0.2 nM–4 nM) of 3H 1,25-(OH)2D3 at 25 C for 1 h. The Kd for specific 3H 1,25-(OH)2D3 binding was determined from the slope of the plotted regression line.

 
Immunostaining of isolated spleen cells with a monoclonal antibody to purified avian 1,25-(OH)2D3 receptor showed very few positive cells in control spleens. No B cells, and only a few of T cells and macrophages bored 1,25-(OH)2D3 receptors (Table 3Go, Fig. 2aGo). Any positive reaction was restricted to the nuclei. No immunostaining was detected in cells treated with normal rat IgG (Fig. 2bGo). Infected mice had few positive cells in the T and B lymphocyte-enriched populations (Table 3Go). In contrast, over 30% of monocytes-macrophages bore 1,25-(OH)2D3 receptors (Table 3Go, Fig. 2cGo).


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  		Table 3. Expression of 1,25-(OH)2D3 receptors in isolated spleen cells from control and infected mice

 


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  		Figure 2. Immunocytochemical localization of VDR with monoclonal antibody 9A7 {gamma} in macrophage of control mice spleen (a) or infected mice (c); background staining in macrophage incubated with normal rat IgG as negative control (b). Cells were counterstained with blue toluidine. Magnification, x340.

 
Conversion of 3H 25-(OH)D3 to 3H 1,25-(OH)2D3 by spleen cells
The monocyte/macrophage-enriched populations and unseparated lymphocytes from control uninfected mice produced a 3H 25-(OH)D3 derivative that eluted with synthetic 1,25-(OH)2D3 in the two HPLC systems. This production was not significantly different between the two spleen cell subpopulations (Fig. 3Go). Isolated B cell-enriched population produced no 1,25-(OH)2D3. Isolated T cell-enriched population converted 3H 25-(OH)D3 to 3H 1,25-(OH)2D3, but this production was lower than that by unseparated lymphocyte populations (P < 0.01) (Fig. 3aGo). This suggests that both B and T cells are required for the full expression of 1{alpha}-hydroxylase activity by T cells. This was checked by a 2-h coculture of isolated B and T lymphocytes. As shown in Fig. 3bGo, the reassociated B and T lymphocytes had greater 1,25-(OH)2D3-producing capacity than T lymphocytes alone (P < 0.05). B cell-enriched populations derived from control and infected mice had similar abilities to stimulate 1,25-(OH)2D3 production when cocultured with normal T cell-enriched population.



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  		Figure 3. Conversion of 3H 25-(OH)D3 to 3H 1,25-(OH)2D3 by isolated spleen cells. Cells were incubated with 2.5 nM 3H 25-(OH)D3 for 90 min (3 x 105 cells/incubation) and 1,25-(OH)2D3 was quantified after double step straight phase HPLC as described in Materials and Methods. A, Values obtained in spleen cells from control (open bars) or infected mice (hatched bars). Bars represent mean ± SE of mean values obtained in three or four different experiments (two to eight cell incubations per experiment). ***, Values significantly different from controls (P < 0.01). B, Left panel, 1-hydroxylase activity in control cells: B lymphocytes alone (B); T lymphocytes alone (T); T cells cocultured with homologous B cells (T + B); control T cells cocultured with B cells from infected mice (T + Bi). B, Right panel, 1-hydroxylase activity in infected cells: B lymphocytes alone (Bi); T lymphocytes alone (Ti); T cells cocultured with homologous B cells (Ti + Bi); infected T cells cocultured with B cells from control mice (Ti + B). Barsrepresent mean ± SE of mean values obtained in two or three different experiments two to four cell incubations per experiment). *, Values significantly different from isolated T cells of control mice (P < 0.05). **, Values significantly different from isolated T cells of infected mice (P < 0.02).

 
Like in control mice, monocytes/macrophages and unseparated lymphocytes from infected mice produced a comparable amount of 1,25-(OH)2D3 (Fig. 3aGo). In contrast, isolated T cell-enriched population from infected mice produced much more 1,25-(OH)2D3 than did control T cell-enriched population (P < 0.01), and was as active as unseparated lymphocytes. B cells from control mice did not further increase 1,25-(OH)2D3 production by infected T cells, whereas B cells from infected mice decreased the 25-(OH)D3 1{alpha}-hydroxylase activity of infected T cells (Fig. 3bGo).


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Evidence has accumulated over the past several years for a close association between an activated immune system, the local synthesis of 1,25-(OH)2D3 and the presence of its receptors on immune cells. The activation of macrophages and T lymphocytes that occurs in granulomatous, several infectious diseases and in viral disease such as HTLV-I-lymphoma, makes them able to synthesize 1,25-(OH)2D3 (16, 17, 18, 19, 20), whereas normal macrophages produce 1,25-(OH)2D3 only after exposure to interferon {gamma} or liposaccharides (38, 39). In addition, the activation of human T lymphocytes that occurs in sarcoidosis and tuberculosis is associated with an increased number of cells bearing 1,25-(OH)2D3 receptors (40).

The present study on purified cell populations shows that an inflammatory disease, such as that induced by LPBM5 MuLV complex, also changes 1,25-(OH)2D3 synthesis and the production of its receptor.

Over 30% of the monocyte/macrophage cell-enriched population from infected mice bore 1,25-(OH)2D3 receptors, whereas fewer than 1% of the control cells did so. This suggests that the activation of the monocyte/macrophages is required for their full expression of 1,25-(OH)2D3 receptors (VDR), similarly to what has been described for lymphocytes (41). Although the exact signals triggering receptor production remain to be defined, there is a correlation between the increase in functional receptor protein and an increased response to 1,25-(OH)2D3 in many cell systems (42, 43). Thus, the greater expression of VDR in monocyte/macrophages may be partly responsible for the higher mortality rate observed in 1,25-(OH)2D3-treated infected mice (23).

In contrast to monocyte/macrophage population, the number of 1,25-(OH)2D3 receptors on lymphocytes from infected mice was not increased. The cell activation signals required for up-regulation of 1,25-(OH)2D3 receptors differ with the cell population(44). Thus, whereas monocytes constitutively produce the receptor, a specific signal cascade must be activated to trigger 1,25-(OH)2D3 receptor production in cells like B lymphocytes (44). Some components of this cascade may be missing in the activation of B and T lymphocytes induced by LPBM5 MuLV.

The circulating 1,25-(OH)2D concentration did not indicate any profound change in vitamin D metabolism due to LPBM5 MuLV infection because plasma concentrations of infected and uninfected mice were similar. Neither was there any difference in the local production of 1,25-(OH)2D3 by spleen macrophage and heterogeneous lymphocyte populations of infected and uninfected mice. Yet retroviral infection had a marked effect on 1,25-(OH)2D3 synthesis when isolated lymphoid cell subtypes were studied. T cell-enriched population in control mice had a low ability to produce 1,25-(OH)2D3 as compared with that of unseparated lymphocytes. B cell-enriched population did not produce the metabolite but they potentiated the 1,25-(OH)2D3 production by T cell-enriched population. The situation was different in infected mice. First, the ability of T cell-enriched population to produce 1,25-(OH)2D3 was significantly higher than in control mice. It was similar to that found in unseparated lymphocyte populations of either infected or control animals. Second, the capacity of T cell-enriched population to produce 1,25-(OH)2D3 did not respond to B cell stimulation. It is possible that the 1{alpha}-hydroxylase activity in infected T cells was maximal, and could not therefore be increased further by B cells. Last, the T cell responses to B cells differed with the origin of these cells. Control B cells did not influence the 1,25-(OH)2D3 production by infected T cells, whereas infected B cells significantly decreased this production. The LPBM5 MuLV complex directly infects B cells (28, 29), and increases IgM, IgG and IgE production. We have yet to determine whether these changes are responsible for the observed interactions between B and T cells in infected mice. Neither do we know whether the infection itself or B cells hyperactivity is responsible for the inhibition of T cell 1{alpha}-hydroxylase activity by infected B cells. But it is clear that chronic retroviral infection alters both the local vitamin D metabolism and VDR expression by immune cells in mice. These findings suggest close local interactions between 1,25-(OH)2D3 and immune system activation during retroviral infection.


   Acknowledgments
 
The authors acknowledge Dr. J. W. Pike for the generous gift of 9A7 {gamma} monoclonal antibody and Dr. M. Sinet from INSERM U13 for her help.

Received January 7, 1997.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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X. Dong, T. Craig, N. Xing, L. A. Bachman, C. V. Paya, F. Weih, D. J. McKean, R. Kumar, and M. D. Griffin
Direct Transcriptional Regulation of RelB by 1{alpha},25-Dihydroxyvitamin D3 and Its Analogs: PHYSIOLOGIC AND THERAPEUTIC IMPLICATIONS FOR DENDRITIC CELL FUNCTION
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