Difference between <Antisense RNA> & <RNAi>? - (Oct/31/2011 )

Is it correct to say that:

RNAi involves the cleavage of dsRNA into small fragments and the recruitment of RISC; while

Antisense RNA is the mere inhibition of translation by complementary pairing?

If that's correct, wouldn't antisense RNA always lead to RNAi?

Thanks.

There are two main classes of antisense: RNase-H competent antisense and steric-blocking antisense. When an RNase-H competent antisense strand binds to an RNA, it activates RNase-H activity to cleave the RNA. When a steric-blocking antisense strand binds to an RNA, it does not mediate cleavage of the RNA but instead simply binds and gets in the way of other processes.

RNAi is the alteration of gene expression involving the RISC system. Since neither RNase-H competent antisense nor steric-blocking antisense involves RISC activity, these are not RNAi. However, they do alter gene expression though their different pathways.

This paper discusses these kinds of antisense & siRNA: www.benthamscience.com/ctmc/openaccessarticles/ctmc7-7/0003R.pdf