Influence of the quality of tibial plateau alignment on the reproducibility of computer joint space measurement from Lyon schuss radiographic views of the knee in patients with knee osteoarthritis.

RATIONALE: The quality of medial tibial plateau (MT-Plateau) alignment is one of the key elements for accuracy and sensitivity to change of knee radiography in knee osteoarthritis (OA). AIM: To evaluate the influence of the quality of the MT-Plateau alignment on the reproducibility of joint space width (JSW) measurement in knee radiographs. METHODS: One hundred and twenty-seven knee radiographs (99 OA), performed using a standardized radiographic procedure (Lyon schuss (LS) view). Evaluation of the quality of MT-Plateau alignment. Computerized measurement of the JSW, twice, 1-month apart, using a semi-automated and an automated method of measurement. Assessment of the reproducibility of repeated measurements: calculation of intra-observer coefficient of correlation, smallest detectable difference (SDD) and coefficient of variation (CV). RESULTS: MT-Plateau alignment was satisfactory in 99 radiographs (77.9%). Reproducibility was excellent in both satisfactory and non-satisfactory radiographs, irrespective of the method of measurement used. The automated measurement was more reproducible than the semi-automated one (CV 1.15% and 3.23%). SDD and CV were better in satisfactory than in non-satisfactory MT-Plateau aligned radiographs. CONCLUSION: These results confirm that computer measurement of the medial tibio-femoral JSW, from LS digitized radiographs, is highly reproducible, irrespective of the quality of the radiograph. However, the quality of the MT-Plateau alignment influences the reproducibility of JSW measurement. The automated measurement was more reproducible than the semi-automated one.

[Efficacy of diacerein on the symptoms and radiographic progression of osteoarthritis]. / Efficacité de la diacerhéine sur les signes fonctionnels et la progression radiologique de l'arthrose.

SYMPTOMATIC EFFECTS OF DIACEREIN: Data obtained from several clinical trials have demonstrated that relief of joint pain obtained with the interleukin-1 inhibitor diacerein is comparable with that observed with non-steroidal anti-inflammatory drugs (NSAIDS) after four to six weeks of treatment and that relief persists after treatment withdrawal. Patients taking diacerein are less handicapped, use less NSAID and/or analgesics, and have lower demands for care as well as an improved quality of life. RADIOGRAPHIC FINDINGS: The ECHODIAH study conducted to evaluate the structure-modifying effect of diacerein in hip osteoarthritis. TOLERANCE: Drug watch data and clinical trials have confirmed the safety and tolerance of diacerein, so there is no limitation on the duration of its use.

The use of different dual X-ray absorptiometry brands in a multicenter clinical trial: consequences and limits.

Accurate cross-calibration (CC) and quality control (QC) programs for dual X-ray absorptiometry (DXA) instruments are necessary in order to guarantee appropriate measurements of bone mineral density (BMD) during longitudinal studies. This article details the CC-QC program established for the STRATOS study, a multicenter clinical trial investigating the effects of strontium ranelate on osteoporotic women with vertebral fractures. Forty-five DXA instruments of different brands (namely, 27 Hologic, 9 Lunar, 5 Norland, and 4 Sopha) were cross-calibrated at the beginning of the study. Twenty-seven of these were still in use by the end of the study. The CC was performed at the beginning and at the end of the study by measuring a unique spine phantom 20 times. The in vitro reproducibility of measurements. (coefficient of variation [CV]) was calculated from the results of the phantom measurements. The in vivo CV was obtained from pairs of measurements of the lumbar spine and the hip of the patients at the time of inclusion in the study. Initial in vitro CV averaged 0.5%. At the end of the study, the CC performed for the 27 apparatus in use at the end of the trial provided long-term intrabrand in vitro CV of 0.7% for the Hologic (n = 18), 1% for the Lunar (n = 5), and 0.3% for the Norland (n = 4) DXA instruments. The in vivo short-term CV for the lumbar spine BMD measurements was suboptimal, as opposed to the hip measurements, and was most likely due to the age of the population investigated. The results of measurements of multibrand DXA apparatus in this multicenter study suggest several practical conclusions: (1) the CC should be performed by using a single phantom independent of the DXA brand tested; (2) duplicate measurements should be performed at the time of patient inclusion; (3) the most efficient QC program should include CC, central reading of in vivo scans, and central review of daily QC.

Expression of the murine plasma cell nucleotide pyrophosphohydrolase PC-1 is shared by human liver, bone, and cartilage cells. Regulation of PC-1 expression in osteosarcoma cells by transforming growth factor-beta.

A bone and cartilage enzyme with both 5'-nucleotide phosphodiesterase I and nucleotide pyrophosphohydrolase (NTPPPH) activity modulates physiologic mineralization and pathologic chondrocalcinosis by generating inorganic pyrophosphate. We hypothesized that, as for alkaline phosphatase, expression of an NTPPPH gene can be shared by cells from bone, cartilage, and liver and by certain leukocytes. Recently, we demonstrated the hepatocyte and murine plasma cell membrane glycoprotein PC-1 to have both 5'-nucleotide phosphodiesterase I and NTPPPH activity. We detected polypeptides cross-reactive with PC-1 in human U20S osteosarcoma cells, articular chondrocytes, homogenized human knee cartilages, human knee synovial fluids, hepatoma cells, and murine plasmacytoma cells. Constitutive low abundance PC-1 mRNA expression was detected in U20S cells and chondrocytes by a nested RNA-PCR assay and by Northern blotting. TGF beta is known to substantially increase NTPPPH activity in primary osteoblast cultures. We demonstrated that TGF beta 1 increased NTPPPH activity and the level of PC-1 mRNA and immunoprecipitable [35S]-methionine-labeled PC-1 polypeptides in U20S cells. The identification of PC-1 as an NTPPPH expressed in cells derived from bone and cartilage may prove useful in furthering the understanding of the role of NTPPPH i n physiologic and pathologic mineralization.

Molecular cloning of the murine substance K and substance P receptor genes.

The peptides substance K and substance P evoke a variety of biological responses via distinct, guanosine-nucleotide-binding-regulatory-protein-coupled receptors. We have screened a murine genomic cosmid library using oligonucleotide probes and have isolated, cloned and characterized the substance K receptor and the substance P receptor genes. The coding portion of the substance K receptor gene consists of five exons distributed over 13 kbp. The substance P receptor gene is considerably larger than that of substance K (more than 30 kbp), however, the boundaries of the four exons that have been characterized in the substance P receptor gene correspond exactly to the homologous exons in the substance K receptor gene. To verify the identity of the isolated genes, we have cloned the corresponding cDNA by means of the polymerase chain reaction and we have expressed these cDNA species in Xenopus laevis oocytes. The ligand binding characteristics determined in this system pharmacologically confirm the identity of the two receptors. The deduced amino acid sequence of the mouse substance K receptor is 94% identical to the rat sequence and 85% identical to the bovine and human sequences. The mouse substance P receptor amino acid sequence is 99% identical to the rat sequence. The cloning of the murine substance K and substance P receptor genes should contribute substantially to the generation of in vivo models for the detailed analysis of the functional significance of these receptors.

Inhibition of interleukin-1 production by 1,25-dihydroxyvitamin D3.

The hormonal form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], inhibits the proliferation of T lymphocytes and production of growth-promoting factors (including interleukin-2) (IL2) in CTLL2 murine cells. In this study, we investigated the role of monocytes in this hormone-mediated inhibitory effect, by testing the effects of 1,25-(OH)2D3 on the ability of the mitogenic lectin phytohemagglutinin (PHA) to induce T cell activation in either a monocyte-dependent or phorbol myristate acetate (PMA)-driven (monocyte-independent) system. The results indicate that proliferation of T cells and production of growth-promoting factors are inhibited by 1,25-(OH)2D3 only in the monocyte-dependent system. Preincubation of monocytes with 1,25-(OH)2D3 for various periods of time and subsequent removal of the hormone resulted in inhibition of the PHA-driven proliferation of T cells. Preincubation for 2 h resulted in 20% inhibition, while preincubation for 36 h reduced proliferation to 50% of the control value [no 1,25-(OH)2D3 exposure]. These data suggested that monocytes are important participants in 1,25-(OH)2D3-mediated events. Therefore, we tested the effects of the hormone on the production of IL1, a monocyte-derived product thought to be involved in the induction of IL2 release and the subsequent development of the T cell proliferative response. 1,25-(OH)2D3 inhibited the production of both extracellular and cell-associated immunoreactive IL1 alpha and IL1 beta. Indomethacin, a prostaglandin synthetase inhibitor, did not alter the inhibitory properties of 1,25-(OH)2D3, suggesting that prostaglandins are not responsible for the inhibitory phenomenon. We conclude that part of the ability of 1,25-(OH)2D3 to inhibit T cell proliferation may be due to direct effects on monocytes by down-regulating IL-1 production. However, it is unlikely that the immunoregulatory properties of 1,25-(OH)2D3 on T cells are mediated solely through monocytes, and it is possible that the hormone also exerts its influence directly on T cells.

1 Alpha,25-dihydroxyvitamin D3 receptor distribution and effects in subpopulations of normal human T lymphocytes.

Receptors for 1 alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] are expressed upon activation of human lymphocytes, and the hormone inhibits in vitro the proliferation of mitogen-activated lymphocytes. In this study we examined the distribution of the 1,25-(OH)2D3 receptor protein in the two major subsets of T lymphocytes (T helper and T suppressor cells) and the effect of the hormone on their respective rates of proliferation. We activated normal lymphocytes in the presence of monocytes with phytohemagglutinin and subsequently isolated the T helper (T4-positive) and the T suppressor (T8-positive) subsets using monoclonal antibodies and complement-mediated lysis. In parallel experiments, we first isolated monocyte-depleted T4 and T8 cells and then activated them using phytohemagglutinin and a phorbol ester. Using either approach we found that both T4 and T8 lymphocytes expressed the 1,25-(OH)2D3 receptor protein upon activation. The concentration of this protein, its affinity for the ligand (Kd, approximately 10(-10) mol/L), and its sedimentation characteristics (S = 3.3) were indistinguishable in the two T cell subsets. Furthermore, the time kinetics of expression of the receptor after activation were very similar in the two subsets. Nevertheless, 1,25-(OH)2D3 inhibited in a dose-dependent fashion the rate of proliferation of the helper subset, but had no effect on the proliferation of suppressor cells. The finding of a dissimilar effect of 1,25-(OH)2D3 on the proliferation of the T helper and T suppressor cells despite their indistinguishable receptor status suggests that the 1,25-(OH)2D3 receptors of the T cells might not be involved in the effects of the hormone on T-cell proliferation, and that the 1,25-(OH)2D3-induced inhibition of mitogen-activated T4 cell proliferation could be mediated indirectly.

Distinct target cells and effects of 1 alpha,25-dihydroxyvitamin D3 and glucocorticoids in the rat thymus gland.

Thymocytes are known to possess receptors for glucocorticoids (GC) as well as for alpha, 25-dihydroxyvitamin D3 [1,25-(OH)2D3]. We have now investigated the distribution of the receptors for GC and 1,25-(OH)2D3 in rat thymocytes and compared the effects of the two steroid hormones on short term primary cultures of these cells. We report that in thymic cells, as in other tissues, 1,25-(OH)2D3 and GC bind specifically to distinct receptor molecules which exhibit sedimentation coefficients of 3.3S and 3.7S, respectively. Furthermore, the thymocytes that express the 1,25-(OH)2D3 receptor belong to a different and distinct subpopulation than the cells that express the glucocorticoid receptor. Specifically, by separating the thymocytes into two subsets by means of agglutination with the lectin peanut agglutinin (PNA), we have determined that the 1,25-(OH)2D3 receptor-positive cells belong to the PNA-negative medullary mature subset, whereas the GC receptor-positive cells belong to the PNA-positive cortical immature subset of thymocytes. Finally, we have compared the effects of the two steroid hormones on primary cultures of each of the two subsets as well as on unseparated thymocytes and found that GC act on PNA-positive cells to induce cell lysis; this leads to an enrichment in 1,25-(OH)2D3 receptor-positive thymocytes, as indicated by an apparent increase (6-fold) in the 1,25-(OH)2D3 binding in the cells surviving at the end of the culture. In contrast, we found that 1,25-(OH)2D3 acts on the PNA-negative cells to decrease the rate of cell lysis. These data indicates that the target cells for GC and 1,25-(OH)2D3 in the thymus are distinct and that these two hormones exert a different regulatory influence on the gland.

1 alpha,25-Dihydroxyvitamin D3 receptors in human thymic and tonsillar lymphocytes.

In vitro activated human peripheral blood lymphocytes possess the receptor protein for 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3). In the present study we have examined whether activated lymphocytes that occur in vivo in human thymuses and tonsils also possess receptors for 1,25(OH)2D3. Freshly isolated lymphocyte preparations, from five separate surgical specimens of thymus and tonsil, were depleted of monocytes and examined, before and after fractionation on a density gradient of Percoll, for [3H] 1,25(OH)2D3 binding by means of sucrose density gradient sedimentation, by saturation analysis of the binding, and by DNA-cellulose chromatography. The state of activation of the lymphocyte preparations was determined using [3H] thymidine incorporation, DNA and RNA quantitation (using acridine orange), and by determining the presence or absence of markers of activation (interleukin-2 receptor, transferrin receptor, and HLA-DR molecules). In both the thymic and the tonsillar lymphocyte preparations we detected a 1,25(OH)2D3-binding molecule possessing sedimentation coefficient of 3.3 S and dissociation constant of 10(-10) M as well as DNA binding capability. In thymic lymphocytes, the 1,25(OH)2D3 receptor concentration correlated positively with the number of lymphocytes expressing the transferrin receptor (r = 0.84; p less than 0.05). In addition, in both thymic and tonsillar lymphocytes the concentration of 1,25(OH)2D3 receptors correlated positively with the number of cells in the G1a phase of the cell cycle (r = 0.79, p less than 0.01, and r = 0.88, p less than 0.001 for thymic and tonsillar lymphocytes, respectively). In contrast, the 1,25(OH)2D3 receptor concentration in these preparations did not correlate with the rate of cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a human osteoblastic osteosarcoma cell line (SAOS-2) with high bone alkaline phosphatase activity.

We characterized the alkaline phosphatase activity of the human osteogenic sarcoma cell line, SAOS-2, and studied the regulation of this enzyme and 3',5'-cyclic adenosine monophosphate levels by 1,25-dihydroxyvitamin D3 and triamcinolone acetonide. We report that the basal alkaline phosphatase activity of SAOS-2 cells was 100-1000 times greater than that of other established human osteogenic sarcoma cell lines. The enzymatic activity was thermolabile, could be inhibited by levamisole and L-homoarginine, but not by L-phenylalanine, and was immunoprecipitable with anti-bone/liver/kidney, but not with anti-placental antibody, confirming that it is the tissue-unspecific or bone/liver/kidney isoenzyme. However, in contrast to other established human osteosarcoma cell lines (TE-85, SAOS-1), in which alkaline phosphatase activity is stimulated several-fold by the steroid hormones 1,25-dihydroxyvitamin D3 and hydrocortisone, the alkaline phosphatase activity of SAOS-2 cells was not affected by 1,25-dihydroxyvitamin D3 treatment despite the presence of classical receptors for this hormone. Furthermore, administration of the potent glucocorticoid analogue, triamcinolone acetonide, induced only a modest increase in activity. The SAOS-2 cell line expressed low basal cAMP levels (28 pmol/10(6) cells) which could be increased 25-40 times by pretreatment with parathyroid hormone. However, unlike other osteoblastic models, in which PTH-induced cAMP stimulation is modulated by 1,25-dihydroxyvitamin D3 and glucocorticoids, neither of these hormones had an effect on the PTH-stimulated cAMP levels in SAOS-2 cells. We conclude that the SAOS-2 cell line is an osteoblastic cell model which expresses high levels of tissue-unspecific alkaline phosphatase activity and exhibits limited responsiveness to two steroid hormones.(ABSTRACT TRUNCATED AT 250 WORDS)

Association between the expression of the c-myc oncogene mRNA and the expression of the receptor protein for 1,25-dihydroxyvitamin D3.

Studies in lymphocytes have indicated similarities in the state of activation, the time kinetics, and the pathologic states associated with the expression of the c-myc oncogene, and the expression of the 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] receptor protein. Here, we have sought evidence for an association between c-myc and the 1,25-(OH)2D3 receptor protein in mammalian cells other than lymphocytes. Comparing two rat osteogenic sarcoma cell lines, one that produces constitutively relatively high levels of the 1,25-(OH)2D3 receptor protein (ROS 17/2.8) and one in which the 1,25-(OH)2D3 receptor protein is practically undetectable (ROS 2/3), we found that the 1,25-(OH)2D3 receptor-expressing cell line also expressed c-myc mRNA. In contrast, the cell line in which the 1,25-(OH)2D3 receptor was undetectable did not express c-myc mRNA. Furthermore, we transfected mouse skin fibroblasts (NIH 3T3) with a recombinant plasmid carrying the human c-myc oncogene. We found a dramatic increase in the 1,25-(OH)2D3 receptor concentration in five separate clonal lines of NIH 3T3 cells transfected with the c-myc-carrying plasmid compared to their nontransfected counterparts or to NIH 3T3 fibroblasts transfected with the vector plasmid alone. The receptor protein of the transfected cells exhibited biochemical characteristics indistinguishable from those of classical receptors for 1,25-(OH)2D3. The increased expression in the transfected cells appeared specific for the receptor for 1,25-(OH)2D3; receptors for sex steroids were not detected in the nontransfected NIH 3T3 cells and remained undetectable after transfection with c-myc. Moreover, the level of the glucocorticoid receptor protein, which was expressed in the nontransfected cells, did not change upon transfection with c-myc.

1,25-Dihydroxyvitamin D3 receptors in lymphocytes from patients with rheumatoid arthritis.

It has been previously found that activation of human lymphocytes in vitro causes the expression of receptors for the hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and that 1,25(OH)2D3 has immunoregulatory properties including the ability to inhibit interleukin-2, to suppress lymphocyte proliferation, and to inhibit antibody production. In the present study we found that 13 of a group of 17 (76%) seropositive patients with rheumatoid arthritis had lymphocytes that possessed 1,25(OH)2D3 receptors (without activation in vitro) compared with only three of 17 (18%) normal individuals. The biochemical characteristics of the 1,25(OH)2D3 receptor, including affinity, sedimentation coefficient, and DNA-binding properties in the rheumatoid arthritis lymphocytes were indistinguishable from those established for this receptor in the classic target tissue of the hormone. This finding raises the possibility that 1,25(OH)2D3, acting through its receptor, might play a previously unsuspected role on lymphocytes of patients with rheumatoid arthritis.

The antiproliferative effect of calcitriol on human peripheral blood mononuclear cells.

Activation of lymphocytes leads to the expression of receptors for the calcitropic hormone calcitriol [1,25(OH)2D3], and calcitriol is a potent inhibitor of interleukin-2 (IL-2) and of lymphocyte proliferation. We used peripheral blood mononuclear cells (PBM) activated in vitro with phytohemagglutinin to study 1) the relationship between 1,25(OH)2D3 receptor expression, IL-2 production, and 1,25(OH)2D3-induced inhibition of PBM proliferation in connection with the cell cycle; 2) the effect of 1,25(OH)2D3 on PBM activation and on the expression of activation-related molecules including the IL-2 receptor, and 3) the role of calcium in the antiproliferative effect of the hormone. 1,25(OH)2D3 receptor expression occurred when PBM entered the G1a phase of the cell cycle. The concentration of the receptor protein reached a peak at G1b and declined during the S phase. 1,25(OH)2D3 inhibited cell proliferation by blocking PBM at the G1a-G1b border. The antiproliferative effect of calcitriol was not caused by hormonal interference with the calcium-dependent activation process nor with the expression of activation-related molecules including the IL-2 receptor. Moreover, this effect was not influenced by extracellular calcium, suggesting that the hormonal action cannot be due to calcium translocation. These findings support the contention that 1,25(OH)2D3-induced inhibition of PBM proliferation is mediated through selective inhibition of IL-2 production.

1 alpha,25-Dihydroxyvitamin D3-binding macromolecules in human B lymphocytes: effects on immunoglobulin production.

Previous studies have indicated that upon in vitro activation with mitogenic lectins, human peripheral blood T lymphocytes express receptors for the steroid hormone 1 alpha, 25-dihydroxyvitamin D3(1,25(OH)2D3). Furthermore, the hormone can inhibit interleukin 2 production by the activated cells. In this investigation, we report that human peripheral B lymphocytes activated in vitro with the B lymphotropic Epstein-Barr virus (EBV) also express 1,25(OH)2D3 receptor-like macromolecules. These receptors are localized in the cell nucleus and exhibit properties similar to those found in classical target tissues for 1,25(OH)2D3. They sediment on sucrose gradients at 3.3 S, display a dissociation constant (Kd) of 4 X 10(-10) M, and can bind to DNA. In addition to the 1,25(OH)2D3 receptors, however, EBV-activated lymphocytes express a second class of 1,25(OH)2D3-binding proteins that appear to occur mainly in the cell cytosol and exhibit distinct biochemical properties from the receptor, including higher sedimentation coefficients (3.7 S to 4 S) and the lack of ability to bind to DNA. The addition of 1,25(OH)2D3 to cultures of EBV-infected cells inhibited the production of IgM and IgG by the B cells. The vitamin D3 analog 24,25(OH)2D3 did not inhibit Ig production, thus suggesting that the effect is probably mediated through the high affinity receptor macromolecule localized in the nucleus. Because the EBV-induced Ig production is independent of T cell participation, the data also suggest that the effects of 1,25(OH)2D3 are exerted directly on the B cell. The present results add to the evidence of the importance of 1,25(OH)2D3 as an immunoregulatory hormone.

Interferon-gamma-induced IA expression in WEHI-3 cells is enhanced by the presence of 1,25-dihydroxyvitamin D3.

It has been suggested recently that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is involved in the regulation of the immune functions of lymphocytes and in the differentiation of monocytic cells. This report examined the possibility that 1,25(OH)2D3 influences immune functions mediated by monocytic cells by studying its effect on the murine myelomonocytic line WEHI-3. We found that WEHI-3 cells possess 3.3S receptor proteins with high affinity (Kd = 3.3 X 10(-10) M) for 1,25(OH)2D3 that are capable of binding to DNA. Also we found that 1,25(OH)2D3 enhances the interferon-gamma (IFN-gamma)-induced expression of the class II major histocompatibility complex antigens (Ia molecules), and such enhancement leads to increased capacity of the WEHI-3 cells to stimulate antigen-specific Ia-restricted T cell activation. Finally, 1,25(OH)2D3 inhibits the proliferation of WEHI-3 cells, and this inhibition is enhanced in the presence of IFN-gamma. The 1,25(OH)2D3 modulation of IFN-gamma induction of Ia antigens suggests that the hormone might promote monocytes to function more efficiently as antigen-presenting cells.

1,25-Dihydroxyvitamin D3 promotes in vitro morphologic and enzymatic changes in normal human monocytes consistent with their differentiation into macrophages.

1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has been shown to promote the in vitro differentiation of established human monocytic cell lines and normal human bone marrow progenitor cells toward the macrophage phenotype. The possibility that 1,25(OH)2D3 exerts a similar effect on the differentiation of peripheral monocytes from normal individuals, has been examined in the present study. Monocytes were isolated by density gradient sedimentation on Ficoll-Paque followed by adherence to plastic. Cells were subsequently maintained in culture in 10% autologous serum for 4 weeks either with or without 1,25(OH)2D3 (10(-8) M). In five experiments using monocytes from different donors we found that cells grown in the absence of the hormone underwent morphologic changes toward the macrophage phenotype as well as a gradual increase in the activities of lysosomal enzymes (beta-acetyl-glucosaminidase and beta-galactosidase). In the presence of the hormone the morphologic changes appeared at earlier stages of the culture, and the increase in enzymatic activities occurred earlier and was one- to twofold greater than the activity of the control cells. In addition, 1,25(OH)2D3 enhanced the adherence of the cultured cells.

Interactions of 1,25-dihydroxyvitamin D3 and the immune system.

A series of recent discoveries indicate that the hormonal form of vitamin D3, namely, 1,25(OH)2D3 plays a role in the regulation of the immune system. Cells of the monocyte/macrophage lineage possess receptors for 1,25(OH)2D3 regardless of their activation stage; cells of the lymphoid lineage also express these receptors but only at certain stages of their differentiation pathway and upon activation. Further, 1,25(OH)2D3 promotes the differentiation of monocyte precursors towards monocyte/macrophages and enhances monocyte function in antigen presentation. In addition 1,25(OH)2D3 is a potent inhibitor of interleukin-2 (IL-2) and suppresses effector functions of both T and B lymphocytes via IL-2-dependent as well as via IL-2-independent mechanisms. The theoretical and clinical implications of these discoveries are discussed.

1,25-dihydroxyvitamin D3: a novel immunoregulatory hormone.

The hormonal form of vitamin D3, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], at picomolar concentrations, inhibited the growth-promoting lymphokine interleukin-2, which is produced by human T lymphocytes activated in vitro by the mitogen phytohemagglutinin. Other metabolites of vitamin D3 were less effective than 1,25(OH)2D3 in suppressing interleukin-2; their order of potency corresponded to their respective affinity for the 1,25(OH)2D3 receptor, suggesting that the effect on interleukin-2 was mediated by this specific receptor. The proliferation of mitogen-activated lymphocytes was also inhibited by 1,25(OH)2D3. This effect of the hormone became more pronounced at later stages of the culture. These findings demonstrate that 1,25(OH)2D3 is an immunoregulatory hormone.

1,25-Dihydroxyvitamin D3 receptors in a subset of mitotically active lymphocytes from rat thymus.

Lymphocytes from the rat thymus gland were separated on Percoll gradient in two subsets. The first subset was enriched in large mitotically active cells and the second in small mitotically inert cells. The former cell preparation possessed a 3.3 S macromolecule with high affinity for 1,25-Dihydroxyvitamin D3 (Kd = 3.3 X 10(-10)M) which bound to DNA cellulose and was eluted from this resin with 0.26 M KCl. In contrast, the small-cell-enriched subset of thymic cells was negative for 1,25-Dihydroxyvitamin D3 specific binding. These findings support evidence from studies in human lymphocytes that there exists an association between mitotic activity and 1,25-Dihydroxyvitamin D3 receptor expression in this class of leukocytes.