Anti-CD3 antibody-induced activated killer cells subsets of killer cells that mediate fast or slow lytic reactions

The present study has characterized two sets of alpha CD3-induced activated killer cells (CD3-AK). A 2 to 4-h 51Cr release assay or triton-treated 125IUdR release assay demonstrated that CD3-AK cultured in the continuous presence of alpha CD3 (CD3-AK+) mediated fast lysis. A 20-h 51Cr or 125I-deoxyuridine release assay demonstrated that CD3-AK cultured in the absence of alpha CD3 (CD3-AK-) mediated slow lysis. Activating the TCR-CD3 complex of CD3-AK- cells with alpha CD3 for 2 h enabled the killer cells to mediate fast lysis. The activation process was inhibited by H-7, a protein kinase C (PKC) inhibitor. Conversely, removal of alpha CD3 from CD3-AK+ cell cultures for 24 h resulted in almost complete loss of the ability of CD3-AK+ cells to mediate fast lysis, but they still retained the ability to mediate slow lysis. It appeared that constant perturbation of CD3 by alpha CD3 maintained the CD3-AK+ cells in an active state, and thus, they were able to mediate fast lysis. On the other hand, activation by a 2-h incubation with PMA could convert the noncytolytic CD3-AK- cells to be cytolytic in slow lysis and to augment the slow lytic reactions mediated by CD3-AK- cell with low cytolytic activity. These results were confirmed by triton-treated 125IUdR release assay which could detect early DNA-release. Thus it appeared that activation of CD3-AK cells with T cell activation signals that bypassed TCR (such as PMA) could induce slow lysis. In the effector phase of lytic reactions, the fast lytic reaction was relatively resistant to inhibition by H-7, whereas the slow lytic reaction was susceptible to H-7 inhibition, indicating that fast lysis was PKC independent and slow lysis was PKC dependent. It was further found that H-7 inhibition was at an early stage of slow lysis, suggesting that a PKC dependent activation process preceded the PKC independent lytic process. These findings indicated that the CD3-AK- cells were in a less activated state which required further activation to turn on their lytic machinery to initiate the lytic reaction.