The pathway of lectin-mediated lymphocytotoxicity by Con A-coupled Sepharose beads

Soluble concanavalin A (Con A) can effectively mediate nonspecific target cell lysis by cytolytic T lymphocytes (LDCC). Because Con A bound to Sepharose beads (Con A-Seph) is also effective, it has been concluded by Z. K. Ballas, W. R. Green, and C. S. Henney. (Cell. Immunol. 59, 411, 1981) that Con A-mediated "activation" of the cytolytic cell to kill in LDCC can occur without intracellular penetration of the lectin. No preincubation of either effector or target cells with Con A-Seph has been performed. Exploiting the previous finding of G. Berke (Immunol. Rev. 72, 5, 1983) that in LDCC Con A exerts its effect(s) strictly by affecting the target rather than by bridging effector and target cells and activating the effector, identical results with Con A-Seph are shown. Preincubation of Con A-Seph with the target but not with the effector cells results in substantial killing. Moreover it is shown that the ability of Con A-Seph to mediate LDCC can be attributed to free Con A dissociating from the beads (about 1%) during the assay. Evidence is presented to indicate that the dissociated Con A, not unlike free Con A, reacts with the target cells, thereby rendering them recognizable by the effector cells. It is concluded that the activity of Con A-Seph may not be taken as evidence for Con A-mediated activation of the cytolytic cell, as suggested by Ballas et al., and that the putative Con A-mediated lymphocyte activation relevant to killing still remains to be demonstrated. Evidence contradicting Con A-mediated activation of the effector and supporting the target cell modification theory has been discussed by G. Berke, V. Hu, E. McVey, and W. R. Clark (J. Immunol. 127, 776, 1981).