Unit D

Module 7 ~ Lesson 3

White Blood Cells

White blood cells are less numerous than red blood cells by a ratio of about 1:700. White blood cells contain a nucleus and are able to divide, unlike red blood cells. The role of white blood cells is to participate in protecting the body from infection.

There are three groups of white blood cells: lymphocytes, monocytes, and granulocytes.

Lymphocytes are B-cells and T-cells. B-cells are responsible for making antibodies. T-cells assist B-cells in making antibodies, kill invading viruses or other pathogens by phagocytosis, regulate B-cell response, or remember returning pathogens.

Monocytes leave the blood and become macrophages. Macrophages are large, phagocytotic cells that engulf and destroy foreign material that enter the body, or they destroy dead or dying body cells.

Granulocytes consist of three different cell types: the neutrophils, the eosinophils, and the basophils.

Neutrophils are the most abundant of the white blood cells. Neutrophils squeeze through the capillary walls and into infected tissue where they kill the invaders, such as bacteria, and then engulf the remnants. This is a never-ending task; even in healthy people-throats, nasal passages, and colons contain vast numbers of bacteria.

Most of these bacteria do people no harm because neutrophils keep the bacteria in check. However, heavy doses of radiation, chemotherapy, and many other forms of stress can reduce the numbers of neutrophils so that formerly harmless bacteria begin to proliferate. The resulting opportunistic infection can be life-threatening.

Eosinophils store many toxins in the granules within the cell. These cells circulate in the blood and migrate to inflamed sites or specific areas of parasitic worm infection. Unless there is an infection or a parasitic worm, the levels of eosinophils in the blood are very low (0-450/µl). When they are needed, the eosinophil releases toxic granules that will kill the invading parasite or pathogen.

Basophils are also in relatively low concentrations unless the body is fighting an infection. Basophils leave the bloodstream and accumulate at the site of an inflammation or infection. The contents of granules are released, which, instead of killing invaders, increase blood flow to an area. Increased basophil concentrations are evident during an allergic reaction.