Help on Natural Killer Cells

[David Peritt]

In article <43hvho$70j at cocoa.brown.edu> Gary C. Pien, Gary_Pien at brown.edu
writes:
>specific T cell receptor (TCR) 

  
>Thus, the target specificity of NK cells is greater than that for CTLs. 

Why is target specificity greater in NK over CTL's?  So how do NK cells
know self from foreign?  The negative signaling of the class I like
recognition structures is an interesting begginning.