Ex vivo analysis of desmoglein 1-responsive T-helper (Th) 1 and Th2 cells in patients with pemphigus foliaceus and healthy individuals

Pemphigus foliaceus (PF) is a severe autoimmune bullous disorder, characterized by autoantibodies (autoAb) against desmoglein 1 (Dsg1). As T cells may be critical in the pathology of PF, the aim of the present study was to identify and characterize autoaggressive T-helper cells reactive to Dsg1 in PF patients and healthy individuals. Eight patients with the clinical diagnosis of PF and six HLA class II-matched healthy individuals were examined. By magnetic cell-sorting (MACS) cytokine-secretion assay, Dsg1-responsive T-helper (Th) 1 and Th2 cells were isolated and cloned by limiting dilution. The generated T-cell clones (TCC) were characterized regarding proliferative response, TCR Vbeta-chain usage, and cytokine profile upon in vitro stimulation with Dsg1. Both Dsg1-reactive Th1 and Th2 cells were detected in PF patients and controls at similar frequencies. A total of 15 Th1 and Th2 clones were isolated from patients and 27 TCC from healthy controls. Analysis of TCR Vbeta-chain usage of autoreactive T cells from both groups revealed no predominance of a specific Vbeta chain. Noteworthy, the isolated TCC showed a polarized Th1- or Th2-like phenotype upon in vitro culture and stable expression of Th1 or Th2 cytokines during long-term in vitro culture. In summary, our data demonstrate that T-cell autoreactivity against Dsg1 is not restricted to patients with PF. Moreover, both Th1 and Th2 cells were present in patients and healthy donors, suggesting that the loss of B-cell tolerance against Dsg1 in PF is not exclusively determined by the presence of autoaggressive T cells.

T cell recognition of desmoglein 3 peptides in patients with pemphigus vulgaris and healthy individuals

Pemphigus vulgaris is a severe autoimmune disease caused by autoantibodies against the cutaneous adhesion molecule, desmoglein 3 (Dsg3). The aim of this study was to characterize the specificity of autoreactive Th cells, which presumably regulate Dsg3-specific autoantibody production. Ninety-seven Th1 and Th2 clones isolated from 16 pemphigus patients and 12 HLA-matched healthy donors recognized the Dsg3 peptides, DG3(78-94), DG3(96-112), DG3(189-205), DG3(205-221), and DG3(250-266). Peptide DG3(96-112), and to a lesser extent DG3(250-266), was recognized by the majority of T cells from patients and healthy donors in association with HLA-DRB1*0402 and DQB1*0503 which were prevalent in the pemphigus patients and Dsg3-responsive healthy donors. Analyzing the Vbeta-chain of the TCR of the DG3(96-112)-specific T cells showed no restricted TCR usage. Peptides DG3(342-358) and DG3(376-392) were exclusively recognized by T cell clones (n=13) from patients while DG3(483-499) was only recognized by T cell clones (n=3) from a healthy donor. All Dsg3 peptides contained conserved amino acids at relative positions 1, 4, and 6; amino acids with a positive charge at position 4 presumably represent anchor motifs for DRB1*0402. These findings demonstrate that T cell recognition of distinct Dsg3 peptides is restricted by distinct HLA class II molecules and is independent from the development of pemphigus vulgaris.

Expression of 1,25-dihydroxyvitamin D(3) receptor in the immune system

In addition to its role in calcium and skeletal homeostasis, there is increasing evidence that the hormonal form of vitamin D, 1, 25-dihydroxyvitamin D(3), appears to serve as a modulator of the immune system. We have determined the level of the 1, 25-dihydroxyvitamin D(3) receptor (VDR) in resting and activated lymphocytes by immuno- and ligand-binding assays. As expected from previous work, the total T lymphocyte population contains VDR whose levels are increased when activated and treated with 1, 25-dihydroxyvitamin D(3). Surprisingly, the highest concentrations of VDR are found in CD8 lymphocytes, although significant amounts are also present in CD4 lymphocytes. Furthermore, B lymphocytes do not contain detectable amounts of VDR. Cells of the monocyte/macrophage lineage possess small amounts of VDR that are not affected by activation but are increased by treatment with 1, 25-dihydroxyvitamin D(3). These results suggest that CD8 lymphocytes may be a major site of 1,25-dihydroxyvitamin D(3) action, while B lymphocytes are likely not directly regulated by 1, 25-dihydroxyvitamin D(3).

Differential effects of fluoride and insulin-like growth factor I on sodium-dependent alanine and phosphate transport in a human osteoblast-like cell line

The effects of fluoride and insulin-like growth factor (IGF)-I on sodium-dependent (Na(d)) alanine and phosphate (Pi) transport were compared in a human osteosarcoma cell line, SAOS-2/B-10. Fluoride stimulated Na(d) alanine but not Pi uptake in a dose-dependent manner, whereas IGF-I stimulated both alanine and Na(d)Pi transport. IGF-I and low concentrations of fluoride stimulated Na(d) alanine transport rapidly. Genistein, an inhibitor of tyrosine kinase blocked IGF-I- but not fluoride-stimulated Na(d) alanine transport. The effects of fluoride and IGF-I were additive and not associated with corresponding changes in cell number or protein content. In conclusion, low concentrations of fluoride rapidly and selectively stimulate Na(d) alanine transport in SAOS-2 cells.

Prostaglandin E2 stimulates sodium-dependent phosphate transport in osteoblastic cells via a protein kinase C-mediated pathway

Eicosanoids are released by bone cells in response to physical, hormonal, and cytokine stimulation, and they can both inhibit and stimulate bone formation. We investigated the effect of PGE2 on sodium-dependent phosphate (Na(d)Pi) transport in a rat bone-derived cell line, PyMS. PGE2 and 12-O-tetradecanoyl phorbol-13-acetate (TPA), an activator of protein kinase C, increased Na(d)Pi uptake in a dose- and time-dependent manner. There was no change in Na-dependent alanine transport, and the effects of PGE2 and TPA were not associated with corresponding changes in cell number or protein content. Their effects on Na(d)Pi uptake were not additive. Calphostin C, an inhibitor of protein kinase C (10(-8) M) completely blocked TPA- and PGE2-stimulated Na(d)Pi uptake. The results are consistent with a crucial role of protein kinase C activation in the short term stimulation of Na(d)Pi transport by PGE2 in PyMS cells.

1 alpha,25-dihydroxyvitamin D3 stimulates sodium-dependent phosphate transport in osteoblast-like cells

1 alpha,25-Dihydroxyvitamin D3 [1,25(OH)2D3] stimulates calcium and phosphate absorption in the duodenum. Because osteoblastic cells appear to be responsible for Pi deposition in bone, we analyzed the effect of 1,25(OH)2D3 on sodium-dependent phosphate (NadPi) transport in newborn rat calvaria-derived osteoblasts and in a rat bone-derived cell line, PyMS. 1,25(OH)2D3 at 10(-9) mol/L stimulated NadPi uptake 1.6-fold in PyMS and 1.8-fold in calvaria cells after 24 h, but not after 2 h and 6 h. Insulin-like growth factor (IGF)-I stimulated NadPi transport 1.8-fold in both cell types within 2 h. There was no change in Na-dependent alanine transport or in Na-independent uptake of Pi and alanine, and the effects of 1,25(OH)2D3 on NadPi transport were not associated with corresponding changes in cell number, protein content, or alkaline phosphatase activity. Actinomycin D, an inhibitor of transcription, prevented the stimulatory effect of 1,25(OH)2D3 (but not that of IGF-I) on NadPi transport; stimulation of NadPi transport by 1,25(OH)2D3 may depend on an increased de novo synthesis of transporters. Our studies confirm that IGF-I stimulates NadPi uptake and show, for the first time, a specific stimulatory effect of 1,25(OH)2D3 on NadPi transport in osteoblasts in vitro.

Expression of sodium-dependent phosphate (NadPi) transport in Xenopus laevis oocytes induced by mRNA from 1 alpha, 25-dihydroxyvitamin D3-treated rat osteoblast-like cells

Injection of messenger ribonucleic acid (mRNA) isolated from 1 alpha, 25-dihydroxyvitamin D3-treated osteoblast-like (PyMS) cells leads to an enhanced sodium-dependent phosphate (NadPi) transport in Xenopus laevis oocytes, when compared to untreated cells. After mRNA size fractionation, mRNA with an average size of 2.2-3.8 kilobases showed up to a 1.8-fold stimulation of NadPi transport encoding either directly a NadPi transporter(s) or proteins controlling their activity. No hybridization was observed in Northern blots with RNA from rat bone or PyMS cells with the recently cloned rat renal brush border NadPi transporter NaPi-2; hybrid depletion with a NaPi-2 antisense oligonucleotide did not abolish the PyMS mRNA-induced NadPi transport in oocytes. We present the first evidence for functional expression in Xenopus laevis oocytes of a new type of NadPi transport system in bone cells, which is different from the renal type.