The body responds by launching interferon , a cellular protein to inhibit viral growth , that would slow the spread of the virus,giving the immune system time to kill infected cells and provide against future invasion. But the immune system would also produce substances such as kinins, which cause runny nose, cough and scratchy throat. This is an attempt to stop the body from replicating the virus with a full-scale production of inflammatory chemicals that would cause swelling, redness or pain.