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Sequential killing of allogeneic target cells by immune cytotoxic T lymphocytes (CTL) was directly observed by time-lapse microcinematography. Target cells (EL4 lymphoma cells from C56BL/6 mice), coated with Fab fragments of goat antibody to EL4, were immobilized by binding to the floor of a polystyrene tissue culture flask that had been precoated with specifically purified anti-goat Fab. On adding immune BALB/c spleen CTL to such target cell monolayers it could be verified by direct observation that individual CTL could sequentially kill several target cells, that the CTL usually separated from the target cell before target cell death, that not all contacted target cells were killed, and that duration of contact was variable and not correlated with subsequent target cell death.

Spleen cells (from BALB/c mice immunized with the C57BL/6 lymphoma EL4, or from non-immune BALB/c) were incubated on monolayers of [C57BL/6 times BALB/cF1 (B6CF1) spleen cells on polylysine-coated polystyrene Petri plate, for 1/2 hr or for 1 hr at 37 degrees C followed by centrifugation of the monolayers for 5 min at 70 times G to 110 times G at 34 to 37 degrees C. Control monolayers were BALB/c spleen cells. As measured by the Simonsen spleen weight assay in neonatal mice, graft-vs-host (GVH) activity was partially depleted in cell populations nonadherent to B6CF1 monolayers. Residual GVH activity of these nonadherent cells was about half that of cells incubated on the control syngeneic monolayers (the mean of eight experiments was 49% +/- 11% S.D.). Two or three consecutive cycles of incubation and centrifugation did not significantly diminish the residual GVH activity, suggesting that spleen cells with GVH activity are heterogeneous with respect to binding to allogeneic target cells under the above conditions. Cell populations nonadherent to third-part [A times AL]F1 monolayers retained full activity, and cell populations partially depleted of GVH activity in B6CF1 neonates had full activity in third-party [BALB/c times AL]F1 neonates.

Mouse spleen cells could be preparatively separated into immunoglobulin positive (Ig+) and immunoglobulin-netative (Ig-)populations by incubating as many as 2 X 10(8) cells per 100 mm diameter petri plate coated with specifically purified goat anti-mouse immunoglobulin. The non-adherent population was 95% or more Ig-, and possessed graft versus host and cytotoxic effector activities, as would be expected for T cells. They could also give a mixed lymphocyte reaction and generate cytotoxic effector activity on culture in vitro. The adherent cells could not be released undamaged from plates coated with undiluted anti-Ig, but they could be released from plates coated with a 1/4 or 1/10 dilution of anti-Ig in an irrelevant antibody. The released cells were over 90% viable by trypan-blue staining, and 94% or more of the viable cells were Ig+.