Knockdown studies using a red fluorescent protein (RFP)-tagged, doxycycline (Dox)-inducible lentiviral shRNA targeted against activin A and FSTL3 in primary BECs. (A) Secretion of activin A by primary BECs transduced with Dox-inducible shRNA targeting activin A and nontargeting (NT) control shRNA (n = 10). Addition of Dox to the media led to a 68% reduction of activin A secretion (n = 11 asthmatic BEC lines, n = 5 healthy BEC lines; 62.6 pg/ml vs. 159.8 pg/ml; P < 0.0001). (B) Secretion of FSTL3 by primary BECs transduced with Dox-inducible shRNA targeting FSTL3 and NT control shRNA. Addition of Dox to the media led to a 46% reduction of FSTL3 secretion (n = 6 asthmatic BEC lines, n = 11 healthy BEC lines; 3,048 pg/ml vs. 5,750 pg/ml; P < 0.0001). (C and D) RFP expression in FSTL3 shRNA lentiviral-transfected BECs without and with the addition of Dox, respectively.