- Influenza A mutant viruses with altered NS1 protein function provoke caspase-1 activation in primary human macrophages, resulting in fast apoptosis and release of high levels of interleukins 1beta and 18. Stasakova, J., Ferko, B., Kittel, C., Sereinig, S., Romanova, J., Katinger, H., Egorov, A. J. Gen. Virol. (2005)