The 1918 Influenza Pandemic Was Notable for the Number of People

The 1918 influenza pandemic was notable for the number of people who died,particularly young people with healthy immune systems.Scientists believe that the deaths may have been caused by an overreaction of the immune system to infection.An out-of-control positive feedback loop can occur,because helper T cells and macrophages can both respond to and also secrete __________.

A) cytokines
B) immunoglobulins
C) perforin
D) proteases
E) T cell receptors