Described herein are agents, including antibodies, antibody fragments, polypeptides and organic small molecules, that bind reversibly inactive PTP1B (designated herein in the alternative as PTP1B-SN or PTP1B-OX) and stabilize it (stabilize PTP1B-OX) in such a manner that they inhibit reactivation of reversibly oxidized, inactive PTP1B by reduction (by reducing agent) and have no substantial direct inhibitory effect on phosphatase activity/PTP1B activity (for example, as detectable in assays in vitro).