Vitamin D has essential roles in growth and calcium homeostasis, processes mediated by a specific nuclear receptor (VDR) that regulates expression of numerous target genes. In April 15 Journal of Clinical Investigation, James O'Kelly and colleagues from University of California Los Angeles, School of Medicine show that vitamin D receptors have also a signaling role in T lymphocyte development.

O'Kelly et al. used VDR knockout (KO) mice to study the importance of VDR in hematopoiesis. They observed that Vdr^-/- mice mounted only a poor Th1 response and had decreased expression of STAT4 — a Th1 cell transcription factor. But the absence of VDR did not affect the number of red and white peripheral blood cells and the percentage of bone marrow macrophages (J Clin Invest 2002, 109:1091-1099).

These results reveal "a potentially new role for VDR in the regulation of the immune response" wrote the authors....