PROS1 and infection: Exposing T cells from recovered SARS-CoV-1 patients to peptides derived from the S protein of this virus revealed that the induction of polyfunctional T cells (T cells producing multiple effector cytokines) was higher in individuals with severe SARS-CoV-1 infection than in those with moderate infection, indicating that the level of T-cell response corresponds with the severity of this infection and time to recovery (15).