In this video, we're going to talk some more details about neutrophils. Recall from our last lesson video that neutrophils are one of the three types of granulocytes. These neutrophils are the most abundant type of leukocyte, or the most abundant type of white blood cell in the blood. In fact, they can make up to 70% of all leukocytes in the blood, which is the overwhelming majority. Neutrophils also will be able to migrate to different locations via the bloodstream and are able to respond to a site of infection or tissue damage. Usually, they are going to be the first to respond to an infection or tissue damage. So they are the first cells to be recruited to the site of infection or damage.

The granules that these neutrophils contain are going to have a variety of different antimicrobial peptides, including defensins, as well as hydrolytic enzymes that have the ability to degrade and destroy microbes. The granules themselves can also be released into the environment. This process of releasing the granules is referred to as degranulation. These granules can either be released through degranulation, or the neutrophil could destroy the microbes during phagocytosis. Phagocytosis is the process of ingesting and digesting material that has been brought in from the outside, and this includes invading microbes. Phagocytosis is sometimes referred to as cell eating.

Another interesting action that neutrophils can execute is the release of neutrophil extracellular traps or NETs, which act as webs of chromatin. They essentially release their own DNA into the environment to serve as a net or a trap, once again trapping infecting microbes with the DNA that they release. Trapping the microbes can be an important defense mechanism.

If we take a look at our image down below, notice on the left-hand side, we're showing you our map of the granulocytes, and we're focusing specifically on these neutrophils at the moment. Neutrophils have five lobes; they have smaller granules that do not stain very well, and here is an image of what a neutrophil could look like under a microscope. Notice in this image, we're showing you a sharp object penetrating the skin. When a sharp object penetrates the tissue, it can create an area where pathogenic bacteria might enter our tissues. Neutrophils are usually the first cells to respond to the injury and are the first cells to be recruited to the site of infection or damage. These neutrophils travel through the bloodstream and are able to leave the bloodstream to enter the site of infection.

Neutrophils are geared to fight the pathogenic microbes to defend us from these pathogens. They can do this either via phagocytosis, where they ingest and degrade microbes, or they can degranulate, which means they can release their cytoplasmic granules into the environment so that those granules can act on the microbes and destroy them. They can also release those nets, or those neutrophil extracellular traps, that once again serve as webs of chromatin to trap infecting microbes. Notice here in this image, we're showing you a neutrophil releasing its net, its web of DNA to trap the microbes.

Another thing neutrophils can do is recruit other immune cells to fight the infection. Notice that wandering macrophages are also being recruited to this area so that they can help fight off the microbes that have invaded. This concludes our brief lesson on neutrophils. We'll be able to apply some of these concepts as we move forward in our course and also learn about the other granulocytes, including eosinophils and basophils, as we move forward. I'll see you all in our next video.