Free fatty acids are produced in and secreted from target cells very early in cytotoxic T lymphocyte-mediated killing.

Conjugation of CTL with their cognate targets elicits a number of early changes within the target cell that are thought to play an important role in the lytic mechanism. We now report that at times earlier than 5 min after conjugation with allospecific CTL, free fatty acids (FFA) are produced in and then secreted from alloantigen-bearing target cells. Using murine CTL clones with different alloantigen specificities, stimulation of FFA production from target cells was found to be Ag specific. FFA production does not appear to be specific for any particular FFA species. Indeed, a wide spectrum of cis unsaturated as well as saturated FFA are produced. FFA production is well correlated with, and specific for, CTL-mediated target cell lysis. Other means of perturbing or lysing target cells, including freeze/thaw disruption, detergent solubilization, or increasing membrane permeabilization with ionomycin, do not stimulate FFA production. In particular, FFA production is not stimulated by treatment with pore-forming granules under conditions that cause more than 90% target cell lysis. These results suggest that FFA production plays an important role in CTL-mediated lysis because stimulation of FFA release specifically requires an event that is CTL induced, occurs very early after conjugation, and is strongly correlated with CTL-mediated lysis.