In this article by Wang et al in the June 2013 issue of Arthritis & Rheumatism (pages 1530–1540), lentivirus titration protocols were described incorrectly in the two sentences of the “Construction of lentivirus-mediated miR-29a precursor and inhibitor expression vectors” paragraph of Materials and Methods. These sentences should have read “Lentivirus particles were concentrated by ultracentrifugation, and lentiviral genomic RNA was measured by quantitative RT-PCR using LentiX qRT-PCR Titration kits according to the instructions of the manufacturer (Clontech). Lentivirus titers were calculated and expressed as infectious units/ml.”