One thing i can not still comprehend about the immune system is the following:
A bacteria is first recognized by neutrophiles. But then neutrophiles have to have the ability to release chemotaxines upon the recognition (or the bacteria?)? Its not mentioned anywhere in my script how macrophages and other non abundant innate immune cells come to the source of an infection in details.
On the contrary it's not neutrophils that initially recognize a threat, but rather distressed epithelium, and immune cells like DCs or macrophages that are already distributed in the tissue that recognize pathogen- or damage-associated molecular patterns (see PAMPs and DAMPs). The primary response to these patterns is the secretion of cytokines.
Among the many cytokines secreted include a subset known as chemokines, from the Greek work for movement. The combination of chemokines and cytokines induce chemotaxis of immune cells circulating in the blood, such as neutrophils, by telling these cells that the nearby tissue is inflamed. IL-1ß, IL-6 and CXCL2 are examples of neutrophil attractants secreted by macrophages and monocytes. Complement fragments like C5a are also known to induce an inflammatory response, inducing the secretion of these molecules.
