Morphologic and functional characterization of perforin-deficient lymphokine-activated killer cells

Mice deficient in perforin, a key mediator of lymphocyte-mediated cytolysis, have recently been generated using the gene knockout technique. CTL and NK cells derived from these mice have been shown to be defective in the granule-dependent cytolytic pathway. To investigate whether the granule- formation process has been altered in these perforin-deficient cytotoxic cells, rendering them defective in using the other granule mediators, we have examined in the present study the morphologic and functional characteristics of perforin-deficient LAK cells. Perforin-deficient LAK cells, similar to wild-type LAK cells, were shown to contain a large number of granules in their cytoplasm. By electron microscopy, the morphology of the granules present in these two cell populations appeared indistinguishable. The complete depletion of perforin in LAK cells derived from perforin gene- knockout mice was further confirmed by immunoelectron microscopy using anti- perforin antiserum. The expression of other cytolytic mediators, present either within the granules (granzymes A and B) or elsewhere (Fas ligand), appeared to be unperturbed, as investigated using the reverse transcription- PCR technique. Like the CTL and NK cells isolated from perforin-deficient mice, perforin-deficient LAK cells could lyse only target cells that express high levels of Fas molecule. Furthermore, these perforin-deficient LAK cells, similar to wild-type LAK cells and a CTL clone, were resistant to perforin- mediated cytolysis.