immune disorders
Innate Immunity
Neutrophils
Neutrophils, the most common type of white blood cell in the bloodstream, are among the first immune cells to defend against infection. They are phagocytes, which ingest bacteria and other foreign cells. Neutrophils contain granules that release enzymes to help kill and digest these cells. Neutrophils circulate in the bloodstream and must be signaled to leave the bloodstream and enter tissues. The signal often comes from the bacteria themselves, from complement proteins, or from damaged tissue, all of which produce substances that attract neutrophils to a trouble spot. (The process of using substances to attract cells to a particular site is called chemotaxis.) Neutrophils also release substances that produce fibers in the surrounding tissue. These fibers may trap bacteria, thus keeping them from spreading and making them easier to destroy. 