Limited specific T-cell mediated cytolysis in the absence of extracellular Ca2+.

Mouse lymphocytes sensitized either in vitro or in vivo with allogeneic cells were analysed for their cytolytic activity incomplete or Ca2+-deprived medium. The deprived medium was obtained by adding EGTA in excess of the molar Ca2+ concentration but not exceeding that of Ca2+ plus Mg2+. The cytolysis in complete medium was between five and thirty-fold greater in terms of lytic units, than that in Ca2+-deprived medium. This applied equally for effectors sensitized in vivo or in vitro although the overall lytic capacity of the former was greater. The cytolysis in Ca2+-deprived medium was judged to be Mg2+ dependent, as little or no cytolysis was seen if EDTA was added to cultures in a molar concentration exceeding that of Ca2+ plus Mg2+. Direct comparison of cytolysis in complete and deprived medium showed no difference between effectors in the two situations with respect to (a) adherence to nylon wool; (b) sensitivity to lysis by anti-Thy-1.2 antiserum and complement; (c) specificity of lysis; (d) rate of cytolysis with time when effector cell numbers were adjusted to give equal levels of cytolysis at any one time; and (e) shape and angle of the slope of 51Cr release against log increase in effector cell numbers where target cell numbers were constant.