White blood cell

Leukocytes (singular of leukocyte, from Ancient Greek λευκός leukos "white" as well as ancient Greek κύτος kytos " hollow ", " vessel ", "shell" ) or white blood cells (deprecated corpuscles ) are in the blood, bone marrow, lymphoid organs and other to find body tissues of vertebrates. In contrast to the erythrocytes ( red blood cells), leukocytes do not contain the red dye hemoglobin. Particularly striking is the difference in the mammalian manage their mature red blood cells lack a nucleus ( thus called in German also red blood cells). Leukocytes fulfill specialized tasks in the defense against pathogens and non-self structures. They belong to the immune system, where they are part of the specific and nonspecific immune defenses, which is why they are also called immunocytes ( immune cells). The proportion of leukocytes in the peripheral blood is measured by a differential blood count.

Construction of leukocytes

Leukocytes are, depending on their nature, different in shape and structure. The size of leukocytes varies between 7 microns in lymphocytes and monocytes at 20 microns. Red blood cells are approximately 7.5 microns in size. The life of the cells ranges from a few days to several months. Certain white blood cells are amoeboid mobile and can actively migrate from the blood to the various tissues.

Formation of leukocytes

The formation of white blood cells is a process that begins with the adults in the red bone marrow (medulla ossium rubrum) of the sternum and pelvis. This process is called leukopoiesis (also Leukozytopoese ). In children, hematopoietic red marrow is also in the long bones of the arms and legs. The white blood cells are formed there from so-called progenitor cells of the stem cells and then further differentiate within the different categories of leukocytes, depending on their intended tasks and functions. In order to fulfill this, parts of the leukocytes must be marked after its formation in certain organs. In the lymphatic system, that is, in lymph nodes, thymus, spleen, tonsils, bone marrow, they have to learn what substances to the body of the organism belong to and what are to be regarded as foreign. The stem cells themselves have extensive opportunities to develop, they are pluripotent. In their division not two identical daughter cells, but in each case a new pluripotent stem cell and a progenitor cell of the individual blood cells are generated ( deterministic stem cell ), which further matures then. Whichever growth factor ( cytokine ) is applied, as the result, either different types of leukocytes or red blood cells, or megakaryocytes.

Tasks of leukocytes

White blood cells have the task of making the organism incompatible substances or pathogens harmless. These include bacteria, viruses, tumor cells, toxins, exogenous particles, worms, fungi, and protozoa ( single-celled ). Individual subsets of leukocytes take over various tasks within the immune system - by phagocytosis via the labeling of antigens to the fight of endogenous and foreign cells and cancer cells.

Neutrophils, monocytes, macrophages and dendritic cells, for example, are capable of as a component of nonspecific defense of phagocytosis. They take up foreign material and make it harmless. They are therefore also called phagocytes.

B lymphocytes do produce specifically directed against certain pathogens or harmful substances antibodies after appropriate stimulation. They thus belong to the specific defense.

T lymphocytes are among others, the coordination between specific and non-specific defense. Also on inflammation leukocytes are involved and able to by released mediators (mediators ) such as cytokines and leukotrienes to keep this upright to modulate or terminate. Leukocytes also play an essential role in all autoimmune diseases.

Morphology of the leukocytes

There are numerous ways to categorize the different types of leukocytes.

• Due to their origin and color in the Pappenheim staining they can be distinguished as follows. All cells of the lymphoid series go back to lymphatic progenitor cells of the myeloid series develop from myeloid progenitor cells. The red blood cells and platelets develop from myeloid precursor cells, but they are not counted among the leukocytes and are therefore not listed in the following table.

Granulocyte are different from the other immune cells ( Agranulozyten ) by their irregular lobed nuclei and by the presence of small particles in the cytoplasm. In contrast, the Agranulozyten have round or bean-shaped nuclei and no particles in the cytoplasm.

• Lymphocytes and granulocytes are divided into more cell types:

Functions of the individual leukocyte

Eosinophil granulocyte

Basophil granulocyte

Lymphocyte

Monocyte

The individual blood cells within the immune system take over different tasks, which are described briefly in the following. Further information is available under the relevant terms.

Binding of leukocytes to the blood vessels

The white blood cells are as it were the guardians of the immune system and continually patrol the entire body looking for pathogens or damaging cell structures. They use the bloodstream to move from one place to another and keys during this phase, the walls of the vessel cells systematically after stop signals from, for example, show the cancer cells. Furthermore penetrate every minute hundreds of white blood cells into the tissue and search for injury and inflammation. They do this by rolling on the walls of the cells along and search for specific structures that show such a state.

Numbers and values

• Normal values ​​of leukocytes in human blood

A norm values ​​increasing number of leukocytes per unit volume is called leukocytosis. Falling below the standard values ​​of leukocytes per volume is called leukopenia.

• The percentage of the groups in the total number of leukocytes in the body

• In seven hundred red blood cells is below normal conditions, a white blood cell.

Diseases associated with leukocytes

Leukemia

In the leukemias, individual subsets of leukocytes to tumor cells change. The most commonly affected are the lymphocytes. The origin of the disease is the bone marrow, where the tumor cells come into contact with the blood stream and are thus distributed throughout the body. Due to their mass occurrences tumor cells call disease symptoms produced in all organs. Above all, in the bone marrow, they displace the erythrocytes, normal leukocytes and platelets and inhibit in this way their education. Sufferers fall on by fatigue, pallor, bleeding tendency and general malaise. At the same time creates a susceptibility to infection because the degenerate leukocytes do not meet their real task of the immune system.

HIV

The human immunodeficiency virus multiplies primarily on T- helper cells. With time, the number of existing helper T cells is reduced until finally collapsing the complete immune response, there are symptoms of AIDS. The patients often die of opportunistic infections. A typical example of such an infection is pneumonia caused by Pneumocystis jirovecii, the healthy people rarely become ill.

Adhäsionsdefizit

This is a group (more rarely) glycoprotein biosynthesis hereditary disorders that can lead to mental and physical disabilities and an increased susceptibility to infection. Currently, nine different subtypes of the disease are known. The number of sufferers is estimated in Europe to 300. Typical leukocytosis is no apparent reason. The adhesion of leukocytes to the blood vessel wall is severely limited in this disease. The disease is also known in veterinary medicine.

Swell

• Hermann Delbrück: Chronic leukemias. Stuttgart 2004. ISBN 3-17-018369-9
• Charles A. Janeway, Jr. et al: Immunology. Spektrum Akademischer Verlag, Heidelberg 2002. ISBN 3-8274-1078-9
• Thomas Lothar (eds.): Laboratory and diagnostics. Frankfurt am Main, 2005. ISBN 3-9805215-5-9
• Arne Schaffler ( Eds.): man, body, disease. Munich 2001. ISBN 3-437-55091-8
• Dorothea sugar Franklin ( ed.): Atlas of blood cells function and pathology. Stuttgart 1990 ISBN 3-437-11299-6