The Killing of Tumour Cell Targets Coupled to Tuberculin (PPD) by Human and Murine PPD‐Reactive T Helper Clones

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Abstract
This paper reports on the characteristics of killing by a human and a murine tuberculin (PPD)-specific T helper clone of targets to which PPD was attached via the lectin concanavalin A (Con A). The killing was specific for PPD from M. tuberculosis; and targets coupled to Con A alone or to PPD from M. paratuberculosis were not killed. Target cells carrying Con A-PPD were more effectively lysed than PPD-pulsed cells. This form of lymphocyte killing, though highly significant, was inefficient. Maximum killing of PPD carrying targets was 30-40% at effector to target ratios of 20:1 and at 16 h. Cells carrying 2 .times. 106 molecules of PPD and less than 1.5 .times. 106 molecules Con A per cell were killed most efficiently. A major distinction between this helper T cell killing and that mediated by cytotoxic T cells was that both TH clones displayed bystander lysis and killed PPD uncoupled targets when these were cultured with syngeneic PPD-bound targets. This suggests that the mechanism of cytotoxicity may involve soluble mediators.