White Blood Cells
White blood cells - or leukocytes (lu'-ko-sites) - protect the body against infectious disease. These cells are colorless, but we can use special stains on the blood that make them colored and visible under the microscope.
White blood cells are the largest blood cell and can move by sticking out one part of their body and dragging the rest of themselves along. They are the "soldiers" of the blood, attacking bacteria and other invaders unfamiliar to the body. White blood cells are able to squeeze through tiny blood vessels, leaving the bloodstream to enter other tissues that are being attacked by foreign invaders.
Most white blood cells are manufactured in the red marrow of bones. Some are also made in special glands elsewhere in the body. In a healthy person, there are between 4 and 11 thousand leukocytes in every cubic inch of blood. When a person has an infection, this signals the marrow and special glands to make more white blood cells. When a medical technologist counts the white blood cells in someone's blood, they can tell the doctor if there is an infection.
There are five types of white blood cells. They are neutrophils, eosinophils, basophils, lymphocytes, and monocytes. These five types are in two main groups: The Granulocytes and The Mononuclear Cells.
The neutrophils make up the majority of the total white blood cells in a normal person's blood. Of the total white blood cells, there are usually 50-70 percent neutrophils. A mature neutrophil has a segmented nucleus and is twice the size of a red blood cell. A segmented nucleus means that you can see two to five segments (aka- lobes) of nucleus in one cell.
Neutrophils, eosinophils, and basophils are all granulocytes because they contain granules. The granules in a neutrophil are small, numerous, and are stained a light-pink to bluish-purple, "neutral" color. The cytoplasm of a neutrophil is light pink. When a person is fighting infection, the granules may be dark colored. This is called toxic granulation. One type of anemia causes the neutrophils to be hyperlobulated. This means that many of the neutrophils have six or more lobes to their nucleus. Whenever a person experiences any kind of inflammation, the neutrophils are the first to the scene.
Eosinophils are also granulocytes...so they have granules, too! Their granules are different from neutrophil granules, though. The suffix "phil" means "to love". Eosin is a type of acid red dye. Therefore, eosinophils love eosin dye. They grab onto lots of eosin dye when they're stained, making their large granules a red color. The granules in an eosinophil usually cover the nucleus, but sometimes you can see that the nucleus is segmented. Eosinophils are not as common in the blood as neutrophils. They're usually less than three percent of a person's total white blood cells. Unless you have allergies.....then they come out to fight! Depending on the severity of the allergic reaction, they can be in much higher percentages. Although their primary job is to be involved in allergic reactions, eosinophils are also increased when a person has a parasite. For example, a person with a tapeworm in their digestive tract will have an elevated eosinophil count.
Basophils, the last and least (in number) of the granulocytes. They are present as one percent or less of a person's white blood cells. Just like the eosinophils, basophils love dye. But, basophils love "basic blue" dye. Therefore, their large granules are a deep blue-purple color. Their nucleus is also segmented, but it's hard to see in the presence of those intense granules!
The lymphocytes and monocytes belong to the mononuclear cell group. This means their nucleus is in one piece. Lymphocytes are the main cells in the lymph nodes. There are almost as many lymphocytes as neutrophils in the blood. Lymphocytes are special because they can become "memory cells". When doctors talk about a person being "immune", they are referring to the ability of that person's lymphocytes to remember a foreign invader. When a person is exposed to a new infectious agent, some of their lymphocytes make antibodies against it. The rest of the lymphocytes remember that infectious agent and get the immune system working faster the next time a person is exposed to that infectious agent. Very young children have more lymphocytes than adults because they are developing immunity to the many new infectious agents around them. Lymphocytes make up 20-40 percent of an adult's total white blood cells. Small lymphocytes have a round nucleus and a small amount of blue cytoplasm. Overall, the lymphocyte looks very smooth and round. Lymphocytes vary a lot. They can be larger with a lot of cytoplasm when they are encountering an infectious agent. Sometimes they can even look wavy, like a potato chip!
Monocytes serve as part of the defense against infection by "eating" up foreign particles. When a monocyte is found in tissue, it is called a macrophage. Monocytes are large cells- three to four times the size of a red blood cell! However, there are not too many in the bloodstream. In a normal person, there are one to six percent monocytes. Monocytes can be difficult to differentiate from lymphocytes. Monocytes usually have a larger amount of cytoplasm in relation to the size of the nucleus. They are also usually more irregular in shape than the smooth lymphocytes. You can sometimes see "pseudopods" on monocytes, the "fake feet" that help it move and digest foreign particles. The cytoplasm of a monocyte is a dull blue-gray color. Even though they are not granulocytes, monocytes have granules! They are very fine and lightly stained, giving the monocyte cytoplasm a "ground-glass" appearance. You may also see vacuoles. These look like holes in the cytoplasm. When a monocyte has vacuoles, you know it has been hard at work. The vacuoles contain chemicals that digest the foreign particles. The nucleus of the monocyte is usually kidney-shaped and has brain-like convolutions (ie- the nucleus looks like it's folded).