Respiratory syncytial virus (RSV) infection causes bronchiolitis in infants with seasonal frequency, for which vitamin D deficiency and a well-described polymorphism in the vitamin D receptor (VDR) FokI are important risk factors. Recent studies suggest that vitamin D regulates immune pathways in airway epithelial cells during RSV infection. It is not understood why the VDR FokI polymorphism predisposes to severe RSV bronchiolitis. We investigated how the VDR FokI polymorphism regulates the epithelial response to RSV infection. To this end, we over-expressed the normal and FokI VDR variants in A549 airway epithelial cells. Vitamin D restrained the expression of both NFκB- and STAT1-induced antiviral genes. However, while NFκB control by vitamin D remained intact, both RSV-induced phosphorylation of STAT1 and expression of its downstream targets, IRF1 and IRF7, escaped vitamin D control in FokI epithelial cells. The poor capacity of vitamin D to regulate IRF1 in FokI VDR-expressing cells was recapitulated using blood samples from normal and FokI VDR-genotyped healthy donors. Hence, we provide mechanistic insight that the FokI VDR polymorphism renders STAT1-mediated antiviral immune reactions to RSV infection non-responsive to vitamin D control, resulting in enhanced immunopathology and exacerbated RSV bronchiolitis.

Defective control of vitamin D receptor-mediated epithelial STAT1 signalling predisposes to severe respiratory syncytial virus bronchiolitis.

Interleukin 6 (IL-6) is a multifunctional cytokine with an important role in immunity. We analyzed the effect of recombinant human IL-6 in combination with 1 alpha,25-dihydroxyvitamin D3 (Vit. D3) on differentiation of the human myeloid leukemic cell lines U937 and HL-60 with respect to alterations in antigen expression and functional activity. Of a panel of antigens analyzed, only CD11b (the alpha chain of CR3), and CD14 (a cell surface protein recognizing the lipopolysaccharide-binding protein-lipopolysaccharide complex) had significantly increased expression. Expression of ICAM-1 (CD54), a ligand for LFA-1, was also found to be enhanced with a concomitant increase of ICAM-1 mRNA levels. Enhanced nonspecific esterase levels and induction of respiratory burst activity confirmed that cell differentiation was induced. Furthermore, IL-6 and Vit. D3 had a profound effect on functional activities, as shown by enhancement of rosetting between sheep erythrocytes, sensitized with C3bi (EAC), and either U937 or HL-60 cells. Also, phorbol myristate acetate-induced homotypic adhesion of U937, which is ICAM-1 dependent, was markedly induced by these agents. These results indicate an important role of IL-6 and Vit. D3 in myeloid cell function and development.

Synergism of interleukin 6 and 1 alpha,25-dihydroxyvitamin D3 in induction of myeloid differentiation of human leukemic cell lines.

Cooperative effects of interferon-γ on the induction of NADPH oxidase by retinoic acid or 1,25(OH)2-vitamin D3 in monocytic U937 cells

Functional comparison of the inductions of NADPH oxidase activity and Fcγ RI in IFNγ-treated U937 cells☆

The recognition of the process of terminal differentiation by haemopoietic cells bas led to the concept of a maturation block occurring in leukaemic tissue. Subsequent failure to differentiate is associated with continued proliferation of the leukaemic population. Evidence suggests that the maturation block in the leukaemic cell is a relative phenomenon and can be overcome by changes in cellular environment (Guimaraes et al, 1985). In some cases the leukaemic cell shows multipotent differentiation producing cells in the granulocytic, erythrocytic or megakaryocytic lineages (Fialkow et al, 1987). From this has evolved the concept that human leukaemia may be more effectively treated by inducing differentiation rather than the traditional method of cell killing. In 1981 Abe et a1 described the induction of monocytic differentiation in a murine leukaemia cell line by 1.25 dihydroxycholecalciferol (1,25(OH)2-D3). findings which have since been reproduced in the human promyelocytic leukaemia cell line HL-60 and the human histiocytic lymphoma line U937 (Munker et al, 1986; Daniel etal, 1987). In vitro, both cell lines undergo monocytoid differentiation over a period of 3-4 d on incubation with 1,25(OH)2-D3. a process which is associated with almost total cessation of cell proliferation. At concentrations as low as lo-' M this hormone induces differentiation of nearly 8 5% of HL-60 cells to morphologically and functionally mature monocytes and macrophages (Snipes et al. 1987; McCarthy et al, 1983). Normal human marrow in culture shows a similar monocytoid differentiation on exposure to 1,25(OH)2-D3 (Clohisy et al. 1987). Monocytic differentiation of acute and chronic human myeloid leukaemias cultured from patients has also been demonstrated (McCarthy et al, 1984). The precise mechanism of action of 1,25(OH)2-D3 is unclear. Initially there is binding to a high affinity, analogue specific cytosolic receptor on the target cell (Ostrem et al, 1987a). The gene coding for the vitamin D receptor in chick intestine has been cloned. It has been found to display considerable homology with those for other steroid receptors and with the gag-erbA oncogene of the avian erythroblastosis virus (McDonnell et al. 1987) as well as with the c-erbA gene which may play a role in normal mammalian erythroid differentiation (Debuire et al. 1984). The receptor1,25(OH)2-D3 complex then enters the nucleus, binding to a DNA sequence altering transcriptional control of the cell. Synthesis of monocyte surface antigen is stimulated (Ball et al, 1986) leading to phenotypic differentiation. These two mechanisms seem to be independent of each other (Brelvi & Studzinski, 1986). Induction of leukaemic cell differentiation

Vitamin d and human leukaemia

The metabolite 1 alpha,25-dihydroxyvitamin D3 enhances lymphokine-mediated activation of the oxidative metabolism of the U937 cell line and phosphorylation of a 48-kD respiratory burst-associated protein.

K. Ways

Papers

The metabolite 1 alpha,25-dihydroxyvitamin D3 enhances lymphokine-mediated activation of the oxidative metabolism of the U937 cell line and phosphorylation of a 48-kD respiratory burst-associated protein.