The role of type interferons in combating infectious agents

Scientists have generated type receptor knock-out mice to understand the role of type interferons in combating infectious agents. One group of knock-out mice was challenged with a virus, while another group of mice with Streptococcus pneumoniae. The mice that were exposed to bacteria were able to quickly recover from the Infection, while the mice that were exposed to the influenza virus suffered from severe symptoms. Based on these observations, which processes are defective the type receptor knock-out mice that are essential for combating viral infection, and why?