Now, these lipoproteins that the human cell contains are easily recognized by the cells of our immune system. And so these membrane protein of human cells can be used by the immune system in self recognition and that ensures that our own immune system doesn't actually destroy our own cells. On the other hand, these foreign macromolecules, or antigens, can be recognized by the immune cells as foreign objects. And so our immune system can initiate a series of internal defense mechanisms that ultimately destroy our foreign object, our bacterial cell. Now, if we take our immune system, the immune system can basically be divided into two types. The first type is known as the nonspecific, or the innate immune system.