An Effector-Cell Independent Step in Target Cell Lysis by Sensitized Mouse Lymphocytes

Abstract Heparin was previously shown to inhibit the lysis of target cells by sensitized thymus-derived mouse lymphocytes in vitro. However, heparin failed to inhibit target cell lysis when added to the cultures after only 10% specific release of chromium-51 had occurred. For further exploration of this phenomenon, effector cells have been specifically inactivated at various times during their action on target cells. This was accomplished with alloantiserum made in target strain mice (DBA/2) against effector strain cells (C57BL/6). Treatment of effector cells with this antiserum and complement rendered them unable to initiate new cytolytic events on target cells (and incidentally did not release soluble toxins). However, when untreated cultures were incubated for about 60 min, after which the effector cells had caused 10% specific release of chromium-51 from the target population, treatment of the cultures with anti-effector serum and complement did not interfere with the subsequent lysis of more than half of the target cell population. Hence, the effector-dependent action on the target cell is completed much earlier than evidenced by chromium-51 release, and subsequent, effectorindependent steps must occur before completion of target cell lysis. Data suggest that divalent cations are required for the effector-dependent phase, but not for the effector-independent phase.