In Vitro and In Vivo Analysis of the Immune System of Vitamin D Receptor Knockout Mice

• DOI: 10.1359/jbmr.2001.16.11.2057
• Publication Date: 2006-04-27T03:34:56Z
• Authors: Chantal Mathieu; Evelyne Van Etten; Conny Gysemans; Brigitte Decallonne; Shigeaki Kato; Jos Laureys; JOS Depovere; Dirk Valckx; Annemieke Verstuyf; Roger Bouillon
• Keywords: Mice, Knockout; 0301 basic medicine; Hypocalcemia; Macrophages; T-Lymphocytes; In Vitro Techniques; Lymphocyte Activation; Diabetes Mellitus, Experimental; 3. Good health; Mice; 03 medical and health sciences; Adjuvants, Immunologic; Calcitriol; Animals; Humans; Receptors, Calcitriol; Calcium; Calcifediol

Abstract Immune cells carry receptors for 1,25-dihydroxyvitamin D3 [1,25(OH)2D3; vitamin D receptor (VDR)] and individuals with severe vitamin D deficiency have immune abnormalities. The aim of this study was to investigate the role of vitamin D in the immune system by studying VDR-knockout (VDR-KO) mice. VDR-KO mice had the same metabolic phenotype as rachitic animals with severe hypocalcemia. Leukocytosis, lymphocyte subset composition in different immune organs, and splenocyte proliferation to several stimuli were normal, except for a lower response to anti-CD3 stimulation (simulation index [SI] of 13 ± 4 vs. 24 ± 9 in wild-type mice; p < 0.01). Macrophage chemotaxis was impaired (41 ± 19% vs. 60 ± 18% in wild-type mice; p < 0.01) but phagocytosis and killing were normal. In vivo rejection of allogeneic (31 ± 12 days vs. 45 ± 26 days of survival in wild-type mice, NS) or xenogeneic (10 ± 2 days vs. 16 ± 9 days of survival in wild-type mice, NS) islet grafts was comparable with wild-type mice. Surprisingly, VDR-KO mice were protected from low-dose streptozotocin-induced diabetes mellitus (LDSDM; 5% vs. 65% in wild-type mice; p < 0.001). Correcting hypocalcemia by use of lactose-rich or polyunsaturated fat-rich diets fully restored the immune abnormalities in vitro and the sensitivity to diabetes in vivo. On the other hand, treatment with 1,25(OH)2D3 protected wild-type mice against diabetes but did not protect normocalcemic VDR-KO mice. We conclude that immune defects observed in VDR-KO mice are an indirect consequence of VDR disruption because they can be restored by calcium homeostasis normalization. This study proves that although 1,25(OH)2D3 is a pharmacologic and probably a physiological immunomodulator, its immune function is redundant. Moreover, we confirm the essential role of calcium in the immune system.