Specific and potent inhibitor of the interleukin-1-beta converting enzyme (ICE) thereby suppressing an interleukin-1 beta response to infection. The inhibition of ICE by crmA is an example of a 'cross-class' interaction, in which a serpin inhibits a non-serine proteinase. Also inhibits granzyme B. Belongs to the serpin family. Poxviruses subfamily.