vating receptor-induced formation of GM1 20020776 rafts, which indeed are microdomains of cell membrane involved in calcium signalling . Thus, one may propose that the reduction of cholesterol content in NK cell membrane can affect the mobility of surface receptors able to recruit signal transducers, leading to an impairment of early i increase consequent to receptor triggering. In a previous report, it has been shown that activating receptormediated i increase was not affected after inhibition of HMG-CoA reductase. These results, apparently are in contrast with ours. These discrepancies may be dependent on the heterogeneity of primary NK cell populations obtained from different donors and stimulated 27326330 in vitro with IL2 or on the method used for i evaluation. However, we found that fluvastatin can inhibit i increase using two different calcium probes. This inhibiting effect is in line with the idea that 10 HMG-CoA Reductase Inhibitors and NK Cell Cytolysis co-engagement of activating receptors in rafts is not efficient in fluvastatin treated NK cells. In addition, we found that the percentage of responding cells, in which i increase was detected, diminished in fluvastatin-cultured NK cells depending on the triggering molecule: indeed, low concentrations of fluvastatin can significantly affect NKG2D- or DNAM1-mediated i increase while CD16 signal was affected only at high doses. The different sensitivity to statins of the different activating receptors in NK cells was confirmed analyzing NK cell mediated cytolysis. Indeed, NKG2D- and DNAM1-, but not FccRIIIA-triggered tumor cell lysis, are strongly inhibited also at low fluvastatin concentration. This may be related to a different threshold of activation among NKG2D or DNAM1 and FccRIIIA on NK cells, as triggering through NKG2D or DNAM1 engagement can be achieved only using amounts of specific antibody 100200 fold higher than those needed for triggering FccRIIIA. This would indicate that the engagement of a few molecules of FccRIIIA can deliver an efficient activating signal for cytotoxicity; accordingly, short-term cytolysis of tumor targets through the humanized Celgosivir biological activity antibodies rituximab or trastuzumab, is not inhibited at 1 mM fluvastatin concentration and only a 50% inhibition was found at 10 mM. It has been shown that statins down-regulate the binding of antiCD20 antibodies to CD20+ lymphoma cell lines or primary lymphoma cells, impairing the consequent ADCC and/or complement dependent cytotoxicity triggered with rituximab. We found that fluvastatin can markedly downregulate CD20 expression on lymphoma cell lines but not on primary CLL cells. However, this downregulation was not able to diminish the ADCC of CD20+ tumor cells exerted by ex-vivo NK cells triggered with rituximab, even if NK cells were treated with fluvastatin. On the other hand, fluvastatin only marginally decreased the expression of HER2 on breast adenocarcinoma cell lines without affecting ADCC elicited by trastuzumab. Altogether, these findings suggest that ADCC can be still efficient when HMG-CoA reductase is inhibited in both tumor and NK cells. The discrepancies between our results and those reported previously may depend on the different leukocyte populations and dose of rituximab used in ADCC assay. Indeed, in the above mentioned paper, PBMC-mediated ADCC was evaluated and the effect of statin was found when suboptimal doses of rituximab were used , whereas we focused on NK cells, the strongest ADCC effectors, at rituximab do