Highly lytic in vivo primed cytolytic T lymphocytes devoid of lytic granules and BLT-esterase activity acquire these constituents in the presence of T cell growth factors upon blast transformation in vitro.

Demonstration of C-like "rings," lytic granules, and the Ca2+-dependent lytic proteins--perforin/cytolysin--thereof, in certain cytocidal lymphocytes has led to the hypothesis of a mechanism of lytic granule-exocytosis and a common terminal lytic step in lymphocyte and C-induced lysis. However, neither cytolytic granules, nor formation of C-like rings during lysis have been detected in mature, highly potent, peritoneal exudate CTL (PEL) derived directly from the site of allograft rejection or in cytocidal hybridomas derived from them (PEL hybridomas). We now report that when stimulated in vitro in the presence of Con A supernatant, as a source of T cell growth factors (TCGF) or rIL-2, small in vivo primed PEL transform into large, dividing cytolytic T cells (PEL blasts) that express the same lytic specificity of the original PEL in short term lytic assays. The PEL blasts, in contrast to PEL, possess massive quantities of lytic granules, and protease (N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester esterase) (BLT-esterase) activity as well as non-specific, cell-mediated cytolytic activity in a long term (4-h) assay. These results suggest that the proposed lytic mechanism involving exocytosis of lytic granules, perforin, and BLT-esterases and the formation of 10 to 20-nm lesions may apply to lysis induced by granule-containing effectors such as large granular lymphocytes and TCGF-dependent CTL lines, such as PEL blasts. However, killing by mature, in vivo primed CTL, such as PEL or their hybridomas, appears to be effected through an alternative, contact-induced, self-destruction process(es) of the target not involving secretory lytic granules or the above lesions. Hence, although the expression of lytic granules and BLT-esterase activities in cytolytic lymphocytes devoid of these components is induced by TCGF, these cellular constituents are not necessary for the expression of CTL-mediated target cell lysis by mature effector cells.