We speculate that the capacity of TGF-β to both independently increase AAT synthesis in hepatoma and bronchial epithelial cell lines (24, 25) as well as its capacity to enhance the response to vitamin D through increased expression of VDR and RXRα, as described here in T cells, might also contribute to the observed association between airway AAT and circulating vitamin D. Similar effects of TGF-β on VDR gene and protein expression have been reported elsewhere (26). The gene discussed is SERPINA1; the disease is hepatocellular carcinoma.