1,25-Dihydroxyvitamin D3 and the immune system

Maternal vitamin D status and childhood asthma, wheeze, and eczema: A systematic review and meta-analysis

BACKGROUND

Maternal vitamin D status has been reported to be associated with childhood allergic diseases. However, this association remains to be fully elucidated.

METHODS

A systematic review and meta-analysis was conducted using prospective cohort studies that examined the association between maternal vitamin D status and childhood allergic diseases including wheeze, eczema and asthma. We searched electronic databases of PubMed, EMBASE, the Cochrane library, the Wanfang (Chinese) database, the VIP (Chinese) database, and Chinese National Knowledge Infrastructure (CNKI) up to August 2014. Odds ratios and 95% confidence intervals (CIs) from individual studies were synthesized using a fixed effects model.

RESULTS

Four studies on the association between maternal vitamin D status and childhood asthma (3666 mother-child pairs), four studies on the association between maternal vitamin D status and childhood wheeze (2225 mother-child pairs) and three papers on the association between maternal vitamin D status and childhood eczema (2172 mother-child pairs) met our inclusion criteria. Maternal vitamin D status during pregnancy was associated with childhood eczema (pooled OR=0.904, 95% CI=0.831-0.983). However, the meta-analysis showed no statistical association between maternal vitamin D status and childhood asthma (pooled OR=0.981, 95% CI=0.944-1.019) or childhood wheeze (pooled OR=0.995, 95% CI=0.982-1.009).

CONCLUSIONS

Our meta-analysis found that lower maternal vitamin D during pregnancy was associated with an increased risk of childhood eczema but was not associated with childhood asthma or wheeze. The role of maternal vitamin D as an important protective factor for the development of childhood eczema remains to be elucidated.

Efficacy of early treatment with calcimimetics in combination with reduced doses of vitamin d sterols in dialysis patients

Vitamin D is an important physiologic regulator of bone and mineral metabolism. In chronic kidney disease, reduced renal production of calcitriol contributes to secondary hyperparathyroidism (SHPT). Consequently, supplementation with vitamin D sterols is an important treatment for SHPT and its associated mineral and bone disorders. However, doses of vitamin D sterols required to suppress parathyroid hormone (PTH) secretion often promote hypercalcaemia and hyperphosphataemia. Therefore, there is a trade-off between reduced serum PTH and increased levels of serum calcium, phosphorus and calcium–phosphorus product. It has been suggested that treatment of SHPT with cinacalcet, a type II calcimimetic, with reduced doses of vitamin D sterols could enhance achievement of calcium and phosphorus treatment targets while maintaining goals for PTH. Recent clinical trials have evaluated this hypothesis and demonstrated that treatment with cinacalcet in combination with reduced doses of vitamin D sterols is an effective treatment for the management of SHPT.

Expression of calbindin-D28k and its regulation by estrogen in the human endometrium during the menstrual cycle

Human endometrium resists embryo implantation except during the 'window of receptivity'. A change in endometrial gene expression is required for the development of receptivity. Uterine calbindin-D28k (CaBP-28k) is involved in the regulation of endometrial receptivity by intracellular Ca2+. Currently, this protein is known to be mainly expressed in brain, kidneys, and pancreas, but potential role(s) of CaBP-28k in the human uterus during the menstrual cycle remain to be clarified. Thus, in this study we demonstrated the expression of CaBP-28k in the human endometrium in distinct menstrual phases. During the human menstrual cycle, uterine expression levels of CaBP-28k mRNA and protein increased in the proliferative phase and fluctuated in these tissues, compared with that observed in other phases. We assessed the effects of two sex-steroid hormones, 17beta-estradiol (E2) and progesterone (P4), on the expression of CaBP-28k in Ishikawa cells. A significant increase in the expression of CaBP-28k mRNA was observed at the concentrations of E2 (10(-9 to -7) M). In addition, spatial expression of CaBP-28k protein was detected by immunohistochemistry. CaBP-28k was abundantly localized in the cytoplasm of the luminal and glandular epithelial cells during the proliferative phases (early-, mid-, late-) and early-secretory phase of menstrual cycle. Taken together, these results indicate that CaBP-28k, a uterine calcium binding protein, is abundantly expressed in the human endometrium, suggesting that uterine expression of CaBP-28k may be involved in reproductive function during the human menstrual cycle.

Effect of dietary supplementation with vitamin D metabolites in an experimental model of turkey osteomyelitis complex

Supplementation with vitamin D3 was previously shown to protect Escherichia coli challenged birds that underwent two dexamethasone (DEX) treatments at 5 and 12 wk of age in an experimental model of turkey osteomyelitis complex (TOC). The purpose of the present study was to determine the effects of dietary supplementation with 10 microg of 1,25 dihydroxyvitamin D3 (1,25D)/ kg feed or 99 microg of 25-hydroxyvitamin D3 (25D)/kg feed on disease resistance in the same model. Birds were fed the supplemented diets continuously and ad libitum. Seven hundred twenty turkey poults were placed into 24 floor pens in a 3 x 2 x 2 design (three vitamin D treatments, two DEX treatments, two E. coli treatments, with two replicate pens per treatment). At 5 wk of age, half of the birds were treated with DEX, and half of the DEX-treated birds and half of the nontreated birds were challenged with E. coli. All mortalities and lame birds were necropsied. At 9 wk, all of the DEX- or E. coli-treated birds were given another series of DEX injections; 2 wk later 10 birds per pen were necropsied. At 12 wk, survivors of the previous challenges were given a third DEX treatment, and all birds were necropsied 2 wk later. After the first series of DEX injections, mortality was increased in the 25D-supplemented birds that were given the DEX treatment and the E. coli challenge. After the second series of DEX injections, the main effect mean BW was significantly lower in birds given 1,25D as compared to controls and 25D-supplemented birds. Mortality was higher in 1,25D-supplemented birds that were challenged with E. coli at 5 wk and treated with DEX at 9 wk as compared to 25D-supplemented birds. The 1,25D-treated birds that were treated with DEX at 5 and 9 wk and challenged with E. coli at 5 wk had higher mortality and air sacculitis scores as compared to controls and 25D-treated birds. The main effect mean mortality was significantly higher in birds given 1,25D as compared to controls and 25D-treated birds. The percentage of birds with TOC lesions was decreased from 27% to 0 by 25D and 1,25D in the groups given two DEX treatments and E. coli challenge. After the third DEX treatment, BW of 1,25D-suppplemented birds was decreased, and mortality and air sacculitis scores were increased. Bone strength was generally increased by supplementation with 1,25D, whereas 25D supplementation increased bone strength only in birds challenged at 5 wk and treated with DEX at Weeks 9 and 12. In this study, supplementation with vitamin D metabolites decreased TOC incidence in E. coli-challenged birds given two DEX treatments. However, toxic effects were observed in most supplemented DEX-treated birds and may be attributed to an additive effect of DEX treatment, E. coli septicemia, and vitamin D supplementation.

The effect of vitamin D3 on resistance to stress-related infection in an experimental model of turkey osteomyelitis complex

Male turkeys immunosuppressed by injection with dexamethasone (DEX) were given supplemental vitamin D3 in their drinking water in two experiments. In Experiment 1, vitamin D3 was supplemented at a dosage of either 2,064 IU/kg (low level) or 4,128 IU/kg (high level) in drinking water provided ad libitum only from Days 1 through 5 after hatch. In Experiment 2, vitamin D3 was provided at the low dosage for the first 5 d after hatch, followed by treatment with the high dosage for 12 h before and 12 h after each stressful event, which included weekly weighings and two DEX treatments. In both experiments, at 5 wk of age half of the birds were given intramuscular injections of 2 mg/kg DEX on 3 alternating d. In Experiment 1, 100 cfu of Escherichia coli was inoculated into the left thoracic airsac at the time of the third DEX injection. All mortalities were examined, and 10 birds per pen were necropsied 2 wk after treatment and examined for lesions of airsacculitis and turkey osteomyelitis complex (TOC). Four birds per pen were bled before necropsy, and white blood cell total counts, differential white blood cell counts, and clinical chemistry values were determined. In Experiment 2, healthy surviving birds were grown for an additional 5-wk period, after which the DEX-treated birds were given a second series of DEX injections and were bled and necropsied 2 wk later. There were no significant effects of vitamin D3 treatment in combined general linear models analysis of Experiment 1; however, when birds not treated with DEX or E. coli were compared with those treated with both DEX and E. coli, supplementation with the low level of vitamin D3 significantly decreased TOC incidence. There were no significant effects of vitamin D3 treatment in birds treated with DEX at 5 wk of age in Experiment 2. However, when surviving birds were given a second DEX treatment at 12 wk, vitamin D3 treatment resulted in significantly lower incidence of mortality, TOC, green liver, isolation of bacteria from tissues, and lower airsacculitis scores and heterophil-to-lymphocyte ratios than controls. Vitamin D3 also improved BW, relative weights of the liver and heart, and serum levels of glucose and alanine aminotransferase (ALT) of birds receiving two treatments with DEX. The ability of vitamin D3 supplementation to protect turkeys from the immunosuppressive effects of multiple DEX treatments emphasizes the role of vitamin D3 as a prohormone that affects health and disease resistance in turkeys.

Evidence for the impairment of the vitamin D activation pathway by cyclosporine A

Cyclosporine A (CsA) is a potent immunosuppressant with the drawback of renal side effects. We reported that CsA markedly decreases calcium-binding protein calbindin-D28k mRNA levels in rat kidneys, and showed that this decrease is associated with its adverse renal effects. The transcription of the calbindin-D28k gene is activated via the vitamin D pathway. In this work, the potential CsA-mediated impairment of the vitamin D pathway was investigated. Wistar rats were treated for 12 days with 50 mg/kg/day CsA or for 20 days with 50 mg/kg/day of the non-immunosuppressant and non-nephrotoxic SDZ PSC 833, which had been previously shown not to affect calbindin-D28k mRNA levels. The expression of the three vitamin D-regulated genes calbindin-D28k, 1,25-dihydroxyvitamin D3-24-hydroxylase (24-OHase), and vitamin D receptor (VDR) were quantified in rat kidney homogenates by real-time reverse transcription-polymerase chain reaction. Plasma parathyroid hormone (PTH) as well as plasma and kidney 1,25 dihydroxyvitamin D3 (calcitriol) levels were monitored in all animals. CsA induced a 85% decrease in calbindin-D28k mRNA levels as well as a 40% and 69% decrease in VDR and 24-OHase mRNA levels, respectively. Plasma and kidney 1,25 dihydroxyvitamin D3 as well as plasma PTH levels were increased by CsA, but not by SDZ PSC 833. The treatment with SDZ PSC 833 did not affect calbindin-D28k or VDR expression, but did cause a 73% decrease in 24-OHase mRNA levels. Taken together, these results indicate an association between CsA-mediated down-regulation of rat renal calbindin-D28k mRNA and the decrease in other 1,25 dihydroxyvitamin D3-regulated genes, suggesting an impairment of the vitamin D pathway by CsA which may be related to its adverse renal side effects and its immunosuppressive activity.

Calcitriol directly sensitizes renal tubular cells to ATP-depletion- and iron-mediated attack

Vitamin Ds have been reported to have diverse effects on cell homeostasis, leading to suggestions that they have therapeutic applications extending beyond their traditional actions on the Ca2+/parathyroid/bone axis. As some of these potential indications carry an inherent risk of acute renal failure (ARF; eg, cancer chemotherapy and organ transplantation), the goal of this study was to assess whether vitamin Ds directly affect renal tubule injury responses. Cultured human proximal tubular (HK-2) cells were exposed to physiological or pharmacological doses of either calcitriol (D3) or a synthetic vitamin D2 analogue (19-nor) for 3 to 48 hours. Their impact on cell integrity (percent lactate dehydrogenase (LDH) release and tetrazolium dye MTT uptake) under basal conditions and during superimposed injuries (ATP depletion/Ca2+ ionophore or iron-mediated oxidant stress) were determined. As vitamin Ds can be anti-proliferative, cell outgrowth ([3H]thymidine uptake and crystal violet staining) was also tested. Finally, the action of D3 on in vivo ARF (glycerol-induced myoglobinuria) and isolated proximal tubule injury responses were assessed. D3 induced a rapid, dose-dependent increase in HK-2 susceptibility to both ATP-depletion/Ca2+-ionophore- and Fe-mediated attack without independently affecting cell integrity or proliferative responses. In contrast, D2 negatively affected only Fe toxicity and only after relatively prolonged exposure (48 hours). D3 dramatically potentiated in vivo ARF (two- to threefold increase in azotemia), suggesting potential in vivo relevance of the above HK-2 cell results. Proximal tubules, isolated from these glycerol-exposed mice, suggested that D3 can worsen tubule injury despite a parodoxic suppression of H2O2 production. In contrast, D3 had a mild negative impact on cellular energetics (depressed ATP/ADP ratios), and it accentuated plasma membrane phospholipid breakdown. The latter was observed in both glycerol-treated and control tubules, suggesting a primary role in the injury- potentiation effect of D3. Vitamins D(s) may directly, and differentially, increase proximal tubule cell susceptibility to superimposed attack. This property should be considered as new uses for these agents are defined.

Vitamin D, thyroid hormones and muscle mass influence natural killer (NK) innate immunity in healthy nonagenarians and centenarians

Increasing evidence has demonstrated that the immune system closely interacts with other physiological systems, whose communications are mediated by circulating cytokines and hormones. The aim of our study was to test whether the number and cytolytic activity of NK cells in a group of relatively healthy Italian nonagenarians and centenarians were affected by the modifications of endocrine, metabolic and functional parameters that occur during ageing. Because of the extreme age of the study population, a cross-sectional analysis was performed. This study revealed that the group of oldest subjects with the highest number of NK cells and the best preserved cytolytic function also presented a preserved metabolism of thyroid hormones and vitamin D and integrity of muscle mass. In fact, the NK cell number and/or cytolytic activity of healthy subjects > 90 years old was positively associated with serum levels of vitamin D, while T3, FT4, i-PTH hormones and lean body mass were associated only with NK cell number. In conclusion, our results stress the paramount importance of nutritional evaluation in the clinical assessment of elderly people.

1Alpha,25-dihydroxyvitamin D3 up-regulates Bcl-2 expression and protects normal human thyrocytes from programmed cell death

Apoptosis is thought to play an important role in the pathogenesis of autoimmune thyroid disease. 1alpha,25-dihydroxyvitamin D3 (VD3) has been shown to suppress several autoimmune diseases. However, the mechanism by which VD3 has these effects is not known. We evaluated the alterations in apoptosis, induced by VD3. Thyrocytes were treated with VD3, and the expression of the Bcl-2 family molecules was studied at both the messenger RNA and protein levels. It was found that VD3 significantly induced the expression of Bcl-2 messenger RNA and protein in thyrocytes but had no effect on the expression of Bcl-xl and Bax. The increase in Bcl-2 expression, mediated by VD3, correlated with protection of thyrocytes against the induction of apoptosis by either staurosporine or UV irradiation. VD3-induced increases in the expression of Bcl-2 could be mimicked by VD3 analogs with high nuclear receptor affinity, but not by analogs only with nongenomic actions. These data indicate a role for Bcl-2 in the regulation of apoptosis in thyrocytes and raise the possibility that VD3 or its agonists may have therapeutic benefit in thyroid disorders.

1,25-Dihydroxyvitamin D3 enhances degranulation of mast cells

The mast cell lines rat basophilic leukemia (RBL) and mouse C57 cells respond to IgE/antigen complexes by degranulation. Treatment of these cells with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), (10-100 nM) for 24-48 h enhanced IgE/antigen-induced exocytosis as monitored by release of hexosaminidase. A short term incubation with the hormone did not affect exocytosis, ruling out a rapid non genomic mechanism. The presence of vitamin D receptors, demonstrated by immunoblotting and the lack of effect of 24,25(OH)2D3 suggest a role for these receptors in the enhancing effect. 1,25(OH)2D3 also enhanced exocytosis induced by the calcium ionophore A23187 in the presence or absence of phorbol ester indicating modulation of events distal to signal transduction. 1,25(OH)2D3 enhanced exocytosis in the presence of cytochalasin D, indicating that the action of the hormone is not due to effects on microfilament structure. The results of this study suggest that 1,25(OH)2D3 may affect the allergic or pro-inflammatory potential of mast cells.

Natural immunity and bone and muscle remodelling hormones in the elderly

Increasing evidence has demonstrated that the immune system is closely integrated with two other physiological systems: endocrine and nervous. They communicate through circulating humoral factors such as cytokines, hormones and neurotransmitters. We undertook a cross-sectional analysis in a group of elderly subjects over 90 years to demonstrate that a functional relationship exists among the number and cytolytic activities of NK cells, bone and muscle remodelling hormones, anthropometric parameters and physical ability. Peripheral blood samples collected from 62, 90-106 years-old subjects underwent biochemical (bone and muscle remodelling hormone levels) and immunological determinations (Natural Killer cell distribution and activity), anthropometric and functional assessment. Significant associations were found among NK cell number and cytolytic activity and serum concentrations of vitamin D, anthropometric parameters, while functional independence in daily activity was only associated with NK cell number. In general a high level of physical ability was correlated with preserved body stores and vitamin D levels. In conclusion, our results stress the importance of nutritional evaluation in the clinical assessment of elderly people. The magnitude of the NK immune response, which constitutes the first line of defence against infected and neoplastic cells, is best preserved in oldest-old people with the best hormonal parameters and nutritional measures.

17 beta-Oestradiol and 1 alpha,25-dihydroxycholecalciferol modulate constitutive and bone matrix-induced interleukin-1 beta (IL-1 beta) production by peripheral blood mononuclear cells isolated from postmenopausal women

Local production and release of interleukin-1 (IL-1) may be of importance for bone remodeling, since this cytokine is known to stimulate bone resorption. We have studied the effect of bone matrix constituents on IL-1 beta production by peripheral blood mononuclear cells (PBMCs) isolated from 20 postmenopausal non-osteoporotic women. Hydroxyapatite (0.5 mg/ml) and heat-denaturated collagen (25 micrograms/ml) stimulated IL-1 beta production 5-fold and 520-fold, respectively, compared to control (p < 0.01). In contrast, transforming growth factor-beta (TGF-beta, 10 ng/ml), a cytokine which is abundant in bone matrix, suppressed median IL-1 beta release to 13% of control value (p < 0.01). The bone matrix-induced changes in IL-1 beta production were modulated by 10 nmol/1 17 beta-oestradiol and 10 nmol/1 1 alpha,25-dihydroxy-cholecalciferol (1,25(OH)2D3). Specifically, 17 beta oestradiol stimulated constitutive IL-1 beta release with 89% (p < 0.01) and nullified the suppressive effect of TGF-beta. Moreover, 1,25(OH)2D3 had a synergistically stimulatory effect with both hydroxyapatite and collagen, although there was no effect of this hormone when added alone. The adherent cells were slightly more elongated after treatment with 1,25(OH)2D3 and collagen, while TGF-beta and 17 beta-oestradiol had no effect on cellular morphology. Addition of hydroxyapatite resulted in long and spindle-shaped cells, and phagocytosis of the particles occurred. The modulatory effects of oestrogen and vitamin D on constitutive and bone-matrix induced IL-1 beta production by PBMCs may be of importance for bone remodelling during postmenopausal bone loss and at a site of fracture.

Mechanisms and functions of vitamin D

The vitamin D hormone, 1,25-dihydroxyvitamin D3, functions by way of a nuclear receptor (vitamin D receptor [VDR]) in a manner analogous to the other members of the steroid-thyroid hormone superfamily. Although the vitamin D receptor has been cloned, its three-dimensional structure remains unknown. The VDR binds to the direct repeat response elements called DR-3 in the promoter region of target genes to stimulate or suppress transcription of those genes encoding for proteins that carry out a wide variety of functions. The binding of the VDR to a DR-3 requires the presence of its ligand and a companion protein, namely the RXR group of retinoid receptors. The RXR binds to the 5' arm of the response element while the VDR binds to the 3' arm. In addition, the transcription factor TFIIB has been shown to bind VDR but there is currently no evidence that a co-repressor or co-activator of VDR is also involved. Phosphorylation of VDR in the transcription complex occurs as does bending of the DNA prior to the initiation or suppression of transcription. As VDR has been detected in cells not previously thought to be target organs, scientists continue to discover new functions of vitamin D. Among these new functions are those noted in the immune system. Experiments in mice have illustrated that the autoimmune diseases of multiple sclerosis and rheumatoid arthritis can be successfully treated with the vitamin D hormone and its analogs. New experiments illustrating the use of the vitamin D hormone and its analogs in suppressing transplant rejection indicate that these compounds may be superior to cyclosporin and may not have the side effects attributed to the cyclosporin immunosuppression therapies.

1,25-Dihydroxyvitamin D3 inhibits the expression of inducible nitric oxide synthase in rat central nervous system during experimental allergic encephalomyelitis

The inducible form of nitric oxide synthase (iNOS) generates nitric oxide of which the excessive production is associated with central nervous system (CNS) inflammatory diseases. The investigation of iNOS expression during experimental allergic encephalomyelitis (EAE) of the Lewis rat demonstrated iNOS immunoreactivity and mRNA both during inflammatory bursts (days 12 and 23 post-immunization) and during the remission phase (day 18). iNOS expression was region-specific and expanded with time along a caudo-rostral axis, thus, correlating with the development of inflammatory infiltrates. Whereas cells of the monocyte/macrophage lineage continuously contributed to iNOS expression, astrocytes only expressed iNOS immunoreactivity or mRNA during the relapse (day 23). In order to investigate possible regulatory effects of 1,25-dihydroxyvitamin D3 (1,25-D3) on iNOS expression, rats were treated with the hormone after the beginning of clinical signs (days 11, 13, 19, 21 and 23 post-immunization), and areas of the CNS were examined at day 23. 1,25-D3 exerted a drastic inhibitory effect on iNOS expression, both at the protein and the mRNA levels. However, this effect was region-specific, and was most pronounced in the cerebellum and brainstem, but non-existent in cerebral cortex. iNOS down-regulation occurred in macrophages, activated microglia and astrocytes. The inhibition of iNOS expression in some CNS structures could account for the improvement of clinical signs observed in EAE-rats treated with 1,25-D3. Since 1,25-D3 can be synthesized by activated macrophages or microglia, our results support the hypothesis that this hormone might be implicated in the control of the CNS-specific immune responses. 1,25-D3 or its analogues could, thus, be of therapeutic value in the management of iNOS-associated diseases of the CNS.

The effect of 1,25-vitamin D3 on maturation of monocytes from HIV-infected patients varies with degree of immunodeficiency

The active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 (1,25D), has been shown to induce monocyte-to-macrophage maturation in vitro as well as monocytic differentiation of bone marrow precursors and monocytic leukaemic cell lines. In this study we assessed whether 1,25D could improve the maturation defect we have previously demonstrated in monocytes from AIDS patients. In vitro growth and maturation of monocytes from 10 controls, 15 asymptomatic HIV positives (CDC group II or III) and 13 symptomatic HIV positives (CDC group IV) was examined by assessing cellular morphology, differentiation, adherence and protein content. Cells were cultured for 10 days with or without addition of 1,25D at a concentration of 100 pg/ml. In addition, patients were monitored clinically and by immunological parameters and HIV p24 antigen in serum. The present study showed that addition of 1,25D significantly improved the growth and maturation in both patient and control groups. There was a significant negative correlation between response to 1,25D and CD4+ lymphocyte count in blood in HIV-infected patients. A greater response to 1,25D was seen in monocytes from patients with advanced immunodeficiency and symptomatic disease than in monocytes from asymptomatic patients. However, in the most advanced cases of HIV infection with serious ongoing opportunistic infections the response to 1,25D was very poor, possibly reflecting profound and incorrigible dysfunction of monocytes.

1,25-Dihydroxyvitamin D3 exerts opposing effects to IL-4 on MHC class-II antigen expression, accessory activity, and phagocytosis of human monocytes

To investigate the differentiation and activation of monocytes, the combined effects of 1,25-dihydroxyvitamin D3 (D3) and IL-4 on human blood monocytes were examined with respect to expression of MHC class-II antigens, accessory activity, and phagocytic capacity. IL-4 was reported to upregulate the expression of MHC class-II antigens and accessory activity of monocytes. The experiments described here demonstrate that D3 inhibits the expression of all three subtypes of MHC class-II antigens (HLA-DR, -DP and -DQ) as well as the accessory activity of monocytes, both in a dose- and time-dependent manner. However, D3 enhances the immunoglobulin- and complement-dependent phagocytosis by monocytes in a dose- and time-dependent manner. When monocytes are treated with both IL-4 and D3, the effects of D3 are reverted by IL-4, suggesting that IL-4 induces the development of monocytes into accessory cells, whereas D3 stimulates differentiation of monocytes into classical macrophages. These findings provide further evidence for the contention that, depending on defined stimuli, monocytes may develop either into accessory cells or into classical macrophages.

1,25(OH)2D3 increases cytotoxicity and exocytosis in lymphokine-activated killer cells

The effect of 1,25-dihydroxyvitamin D3 on lymphokine-activated killer (LAK) cells activity was studied. Treatment of LAK cells with 1,25-dihydroxyvitamin D3 for 24 h increased their cytotoxic activity without affecting cell proliferation. This effect was dose-dependent, detectable already at 10(-11) M attaining 44 +/- 7% increase at 10(-8) M. 1,25-dihydroxyvitamin D3 increased LAK cell content of the cytotoxic granule granzyme A by 21%. Secretion of granzyme A by LAK cells was triggered by 12-O-tetradecanoylphorbol 13-acetate and the calcium ionophore A23187. 1,25-dihydroxyvitamin D3 decreased the lag preceding secretion, increased the rate constant of exocytosis and the fraction of granzyme A cell content secreted. The potentiation of exocytosis was more pronounced at suboptimal calcium ionophore concentration suggesting that 1,25-dihydroxyvitamin D3 affects a calcium-dependent process. Since exocytosis of cytotoxic granules is a pivotal event in the killing of tumor cells by LAK cells, it is plausible that the enhancement of this process underlies the stimulation of LAK cell cytotoxic activity by 1,25-dihydroxyvitamin D3.

Actions of calcipotriol (MC 903), a novel vitamin D3 analog, on human bone-derived cells: comparison with 1,25-dihydroxyvitamin D3

The actions of a novel vitamin D3 analog calcipotriol (MC 903), on human bone-derived cells were compared to those of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Both calcipotriol and 1,25-(OH)2D3 inhibited the proliferation of human osteoblast-like cells in a dose-dependent manner (10(-10)-10(-6) M), an effect observed at different cell densities. Lower concentrations of either agent exerted no marked effect on the growth of the cells compared to untreated cultures. Calcipotriol and 1,25-(OH)2D3 were equipotent in stimulating the activity of alkaline phosphatase and the synthesis of osteocalcin in human osteoblast-like cells. The stimulation of alkaline phosphatase activity and osteocalcin synthesis by both compounds was evident by 24 h and was increased progressively up to 96 h in a dose-dependent manner over the concentration range of 10(-10)-10(-6) M. The increment in both proteins was dependent on cell density and was attenuated at higher cell densities. In contrast to these actions, neither calcipotriol nor 1,25-(OH)2D3 (10(-14)-10(-6) M) affected the synthesis of prostaglandin E2. These studies indicate that calcipotriol and 1,25-(OH)2D3 exhibit a similar spectrum of activity on human osteoblast-like cells in vitro.

Distribution of the 1,25 dihydroxy-vitamin D3 receptor in the bursa of Fabricius of chicken

The vitamin D3 metabolite 1,25(OH)2D3 is probably involved in B lymphocyte ontogeny. We therefore determined the distribution of the 1,25(OH)2D3 receptor in the bursa of Fabricius and spleen cells of 7-day-old chicks, by immunohistochemistry using a monoclonal antibody against the chick intestinal cell 1,25(OH)2D3 receptor. The bursa cells of young (7-day-old) chicks contained large amounts of receptor while the spleen cells did not. The bursa cells of older (35-day-old) chicks contained fewer receptors, but the number of receptors in the spleen increased.

Expression of 1,25-dihydroxyvitamin D3 receptors in normal and psoriatic skin

Increasing evidence suggests an immunoregulatory function of the potent steroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) which has been successfully applied for treatment of psoriasis. The skin is both a site of production and a target of 1,25(OH)2D3. In vitro, 1,25(OH)2D3 inhibits proliferation and stimulates differentiation of keratinocytes. We investigated the in situ expression of vitamin D-receptors (VDR) in normal and psoriatic skin by immunochemical methods. The VDR were visualized using the monoclonal antibody (MoAb) 9A7g to the VDR and the labeled avidinbiotin technique. Immunoreactivity was consistently confined to nuclei in all skin biopsies. In normal skin specimens (n = 10) VDR antigens were expressed in keratinocytes of all epidermal layers (except those of the stratum corneum) and in cells of the epidermal appendages. Double labeling experiments with MoAb to cluster-defined antigens indicated that melanocytes and approximately 75% of Langerhans cells exhibit 1,25(OH)2D3 receptors in normal skin biopsies (n = 5). Depending on their localization in skin compartments 42-62% of CD11b+ positive macrophages and 45-75% of CD3+ T lymphocytes expressed VDR. Non-lesional psoriatic skin specimens (n = 8) revealed nearly identical staining patterns. Lesional psoriatic skin specimens (n = 8) exhibited a significant increase of VDR expression both in basal and suprabasal epidermal layers as measured by computer-assisted morphometry and showed a remarkable change of the immune cell pattern: the densitity and proportion of VDR positive T lymphocytes and macrophages were higher in the epidermal and the perivascular papillary loop compartment. These in vivo findings strongly support the hypothesis that 1,25(OH)2D3 modulates immune response and cell proliferation/differentiation in human skin.

1,25-Dihydroxycholecalciferol inhibits the cochemotactic activity of Gc (vitamin D binding protein)

The identification of Gc (vitamin D binding protein) with the anionic polypeptide cochemotaxin has recently been reported. In this paper we investigate its dose dependent cochemotactic activity and report the inhibition of Gc enhanced chemotaxis by vitamin D3. These results further support the role of immunomodulating hormone played by vitamin D.