Though neutrophils are short lived, with a half-life of four to ten hours when not activated and immediate death upon ingesting a pathogen, they are plentiful and responsible for the bulk of an immune response. They are the main component of pus and responsible for its whitish color. Neutrophils are present in the bloodstream until signaled to a site of infection by chemical cues in the body. They are fast acting, arriving at the site of infection within an hour.