Now, once the bacterial cell is inside the tissue of our body, infection begins. And the innate immune system is the first one to actually react. And what happens is special cells, immune cells known as mast cells and basophils begin to release chemicals such as histamine. And what that does is dilates our blood vessels and it brings specialized phagocytic immune cells known as macrophages, to the site of infection. So this is what a macrophage actually looks like. So, we have different types of organelles, for example, a nucleus.