Purified CD4 T cells were treated with medium alone or CD3/ CD28 beads (cells:beads 2:1) in the presence or absence of 50 mM TAPI-1. After 24 hours, the supernatants were collected and AR was measured using the human Amphiregulin DuoSet ELISA Development kit (R&D Systems). The detection limit of the assay was 7.8 pg/mL. Because the antiserum for the ELISA was produced by immunization with bacterial recombinant human AR, and the standard is also non-glycosylated AR, this ELISA probably underestimates the concentration of normal human glycosylated AR.