CHANGES IN THE LEVEL OF PERFORIN AND ITS TRANSCRIPT DURING EFFECTOR AND TARGET-CELL INTERACTIONS

Perforin is a cytoplasmic granule protein expressed in cytotoxic lymph ocytes, and is capable of lysing target cells. This protein is induced as cytotoxic T cells are activated, and the mRNA expression is modula ted by various stimulators. These observations suggest possible change s in the level of perforin transcripts and protein when killer lymphoc ytes meet specific target cells leading to target cell death. To addre ss this question, we examined three murine T-cell clones and primary h uman NK cells in perforin expression. When the cytotoxic lymphocytes w ere exposed to sensitive targets, perforin mRNA disappeared within 5 t o 30 min and appeared within an hour thereafter. Among the murine T ce ll clones, L3 and OE4 showed two phases of mRNA decrease while human N K cells and the third murine T cell clone, AB.1, showed only one phase of mRNA loss during a 240 min period. The data indicate that when cyt otoxic lymphocytes receive signals from a sensitive target, the cells rapidly degrade previously accumulated perforin mRNA and synthesize ne w transcripts. Interestingly, heat shock protein 70 mRNA was induced a s the perforin mRNA levels recovered, while P55 Il-2 receptor mRNA was downregulated within 5 min after exposure to targets. The perforin pr otein level also rapidly decreased immediately after the interaction w ith the target, followed by a recovery, and then another decrease as s een in primary human NK cells, OE4 and L3 cells. However, in the AB.1 clone, no change in perforin content was detectable, despite the loss of perforin mRNA. Since all three T-cell clones had comparable levels of killing of approx. 45% by 4 h, the AB.1 effector must receive an ad equate signal to kill the target cells. These observations suggest tha t the AB.1 may be less dependent on perforin as a mechanism for killin g.