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

Differential requirement of protein tyrosine kinase and protein kinase C in the generation of IL-2-induced LAK cell and alpha CD3-induced CD3-AK cell responses

This study examined the role of protein tyrosine kinase (PTK) and protein kinase C (PKC) in the signal transduction pathways for lymphocyte activation through IL-2R to generate LAK cells and through TCR-CD3 to generate CD3-AK cells. Two PTK inhibitors [herbimycin A and genistein (PTK-I)] and two PKC inhibitors [calphositin C and staurosporine (PKC-I)] were used in the experiments. It was found that the primary activation pathway through IL-2R was PTK-dependent; that is, generation of both the IL-2-induced proliferative and the cytotoxic responses was completely abrogated by PTK-I and not by PKC-I. Quite different results were obtained with the alpha CD3-induced CD3-AK cell response. First, the alpha CD3-induced proliferation was only partially inhibited by PTK-I or PKC-I alone. Second, generation of CD3-AK cytotoxic response was primarily PKC-dependent; that is, only PKC-I induced significant inhibition. Genistein was found to reduce protein tyrosine phosphorylation in both LAK cells and CD3-AK cells, indicating that CD3-AK cells were also susceptible to PTK-I treatment. Further studies showed that PTK-I and not PKC-I suppressed perforin mRNA expression and N-2-benzyoxycarbonyl-L-lysine thiobeneylester esterase production in LAK cells, and the opposite was true for CD3-AK cells. These results indicate that different pathways were employed in lymphocyte activation through IL-2R and TCR-CD3. The former pathway is primarily PTK-dependent. Activation through TCR-CD3 is a more complex event.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of protein kinase C and cytokines on the function and production of cytolytic granules in alpha CD3-activated killer-cell-mediated killing of tumor cells

The effects of PMA and staurosporine (PKC depletor/antagonist) and IL-2/IL4 were used to determine the role of PKC and cytokine on alpha CD3-induced activated killer cells (CD3-AK). The present study examines their effects on the production of BLT-esterase and on the effector function of CD3-AK cells as well as the cytolytic granules. The production of BLT-esterase generally correlated with the cytolytic activity of CD3-AK cells and was reduced by PKC depletor/inhibitor but increased by IL-4. In studying the effector function of CD3-AK cells, we found that adding PMA or SSP at the effector phase inhibited the PKC-dependent slow lysis. PMA, but not SSP, also reduced fast lysis, which was shown to be a PKC-independent event. Additional experiments were performed to determine the effect of PKC on the lytic granules and to ascertain whether PMA has other effects on the effector-to-target relationship unrelated to PKC. It was found that neither PMA nor SSP affects the function of cytolytic granules, as measured by hemolytic assay against anucleated target (SRBC). These findings indicate that PKC has no direct effect on the granules. During testing against the nucleated tumor target through a novel approach using non-cytolytic surrogate killers, the lytic activity of the granules was inhibited by PMA, suggesting that exocytosis or delivery of granules to nucleated target cells may require mobilization of intracellular Ca2+ in the killer cells, and this process is inhibited by PMA. Our findings indicate that PKC and cytokines regulate the production but not the lytic activity of cytolytic granules. Nonetheless, delivery of cytolytic granules from killer cells to the nucleated tumor target appears to be a Ca(2+)-dependent event unrelated to PKC.

Improved short- and long-term XTT-based colorimetric cellular cytotoxicity assay for melanoma and other tumor cells

A tetrazolium compound, XTT, bioreducible to a water-soluble formazan was used to develop a simplified cellular cytotoxicity assay. Most (13/15 melanoma and 2/3 colon carcinoma cell lines tested metabolized XTT greater than 50 times more efficiently than the lymphoid effector cells, and thus the test could be performed without separation of the effector from the target cells. The XTT assay (XTT-A) was compared to the standard 51chromium-release assay (51CrA) in terms of sensitivity as well as intra- and interassay variability using low effector to target cell (E:T) ratios and both short and long incubation periods. The correlation coefficient (r) for percent specific lysis (%SL: 35.0 +/- 15.0 versus 30.2 +/- 15.8) or lytic units (LU20/10(7) effector cells: 405 +/- 208 versus 357 +/- 227) between XTT-A and 51CrA was 0.86 for 4 h XTT-A and 51CrA (n = 37). Due to a poor performance of the 51CrA after 24 h incubation of effector and target cells, the correlation coefficient for 24 h assays was reduced to 0.79 (n = 44,%SL = 63.3 +/- 23.9 versus 55.5 +/- 26.6, and LU = 1267 +/- 982 versus 1017 +/- 691). Inter- and intra-assay variability of XTT-A were significantly lower than those for 51CrA. The total background values for XTT-A and 51CrA were similar in 4 h cytotoxicity assay and lower for XTT-A in assays with 24 h incubation. The sensitivity, in terms of discrimination between effector cells with different lytic capacity and targets with different susceptibility, was identical. The XTT-A was simpler, cheaper, and safer to perform than the 51CrA. Furthermore, the XTT-A was suitable for long-term assays and allowed experiments without requiring trypsinization of tumor cells grown in 96-well plates prior to testing.

IL-4 regulation of a protein kinase C independent pathway for the generation of alpha CD3-induced activated killer cells

alpha CD3 induced the generation of activated killer cells from resting T cells. Pretreatment of the splenic responders with PMA, a phorbol ester, depleted protein kinase C and induced unresponsiveness to the generation of alpha CD3-induced activated killer (CD3-AK) cells. Addition of exogenous IL-4 (1 U/ml) restored the cytotoxic response, with the maximal effect achieved with 30 to 100 U/ml. The phenotypes of CD3-AK cells maintained in IL-2 or in IL-4, with or without PMA, were the same: Thy1+ and CD8+. These results were reproduced with purified T cells and purified CD8+ cells, indicating that both the effectors and precursors were CD8+ cells and IL-4 had a selective effect to upregulate the CD8+ cells. Similar results were obtained by using SSP (staurosporine), another PKC inhibitor. At 2 days prior to testing, switching the lymphokine added to 2-week PMA- and IL-2-maintained CD3-AK cells reversed their cytolytic activity: switching from IL-2 to IL-4 restored cytolytic activity, and switching from IL-4 to IL-2 reduced cytolytic activity. The cytolytic activity of these CD3-AK cells correlated with their ability to produce BLT-esterase. In the absence of PMA, CD3-AK cells cultured in either IL-2 or IL-4 were cytolytic and contained high levels of BLT-esterase. In contrast, in the presence of PMA, only the IL-4-maintained CD3-AK cells were cytolytic and produced significant amounts of BLT-esterase. The effect of IL-4 was abrogated by the alpha IL-4 antibody 11B11, which reduced the cytolytic activity of CD3-AK and the ability to produce BLT-esterase. The requirement of IL-2 was less stringent and its major role appeared to be maintaining the cell growth. These findings indicate that IL-4 may participate in the regulation of a PKC-independent pathway for the generation of CD3-AK cells by regulating the production of cytolytic granules.

Anti-CD3 antibody-induced activated killer cells: cytokines as the additional signals for activation of killer cells in effector phase to mediate slow lysis

This study examines the role of cytokines in activating the effector cells to mediate slow lysis. After activation of splenocytes by alpha CD3, further culturing the cells in the absence of alpha CD3 resulted in the generation of activated killer cells (CD3-AK-) to mediate slow lysis. In contrast to fast lysis which was not affected by a PKC inhibitor H-7, slow lysis was inhibited. These findings suggested that a PKC-dependent activation phase preceded the lytic phase in slow lysis. To explore the mechanism for activating the lytic machinery in slow lysis, we examined the roles of cytokines in these reactions. First, it was found that alpha IL-2 or an alpha IL-2/alpha IL-4 combination inhibited slow lysis but had no effect on fast lysis. Secondly, IL-2, IL-4, or TNF alpha converted a noncytolytic CD3-AK- cells to mediate slow lysis, but they did not augment fast lysis. IL-2 and IL-4 had additive effect, and TNF alpha synergized with IL-2 to further augment the CD3-AK- cytolytic activity. Exogenous IL-6 and INF did not have any appreciable effect on the cytolytic activity of the killer cells. Besides TNF alpha, these cytokines were not directly cytotoxic to the target cells, indicating that they were not cytotoxic factors per se. Treatment with cycloheximide for 24 hr abrogated the cytolytic activities of CD3-AK cells, suggesting that a cytotoxic factor(s) was continuously synthesized to be stored in activated killer cells and was catabolized within 24 hr. Our results indicated that in the effector phase of slow lysis, after activating the CD3-AK- cells by the first signal (appropriate target cells), IL-2 and/or IL-4 appeared to be the second signal to initiate a cascade of events which triggered the release of other cytokines (e.g., TNF). This process resembles the secondary (memory) type of immune response. These events lead to full activation of the killer cells and converted the preformed cytotoxic factors into active form to initiate the lytic reaction and completed the lytic process.