Retinoid X receptor beta polymorphisms do not explain functional differences in vitamins D and A response in Antineutrophil cytoplasmic antibody associated vasculitis patients

It has been suggested that the retinoid X receptor beta (RXRB) gene is a risk factor for Wegener's granulomatosis. We addressed if there is a functional difference in the response to retinoic acid (RA) and vitamin D in Antineutrophil cytoplasmic antibody (ANCA) associated systemic vasculitis (AASV) patients and if this was associated with RXRB genotypes. TNFα and IL-10 production were measured in whole blood assay from AASV patients (n = 51) and healthy controls (HC, n = 67). One micromolar of 1,25-(OH)₂ D3, 9-cis RA (9c-RA) or all-trans RA (ATRA) was added to the assay. Genotyping was performed for exons 7 and 2 of the RXRB gene and for a microsatellite in vicinity of the RXRB gene. Lipopolysaccharide (LPS) mediated TNFα production and IL-10 were significantly lower in patients. Addition of 1,25-(OH)₂ D3, ATRA or 9c-RA, blunted TNFα production, more pronounced in patients. Although all three compounds inhibited IL-10 production significantly in HC, only 1,25-(OH)₂ D3 was found to be effective in patients. Allele distribution of the RXRB microsatellite differed significantly between patients and HC. This was not found for the SNP in exons 2 and 7. Genotype of the latter correlated with the ability of 1,25-(OH)₂ D3 and ATRA to inhibit IL-10 production. We provide immunological evidence for a functional difference in vitamins D and A responsiveness in AASV patients. Since the inhibition of TNFα was more effective in patients, vitamin D supplementation might be an additional therapeutical approach.