The blood consists of a liquid part, the blood plasma, and solid parts, the blood cells. There are three large groups of cells in the blood: each of them has specific characteristics and fulfils very important tasks for our body and our survival. Leukocytes have an essential function in the human body’s immune defense, with some cells belonging to the unspecific and others to the specific immune system.
- The red blood cells (erythrocytes),
- The white blood cells (leukocytes)
- And the blood platelets (thrombocytes),
The white blood cells are called white because, unlike the erythrocytes, they do not contain the red dye hemoglobin, which is why they appear whitish next to them. Depending on their type, they can vary greatly in size. The smallest white blood cells, the lymphocytes, are about the same size as the red blood cells, about 7 μm, the largest, the monocytes, reach sizes of up to 20 μm.
They survive from a few days to several months. The development of leukocytes begins in the red bone marrow, which in adults is located in the sternum and iliac crest. In children, this red bone marrow is also found in the long tubular bones of the legs and arms.
The white blood cells are formed here from stem cells. These continue to differentiate, always creating a precursor cell (a determined stem cell, which is already going in a certain direction, so to speak) and another original stem cell, which is able to divide again and develop in any possible direction (pluripotent). From the precursor cell, the various blood cells then develop, depending on the growth factors acting on the cell.
The granulocytes, just like blood platelets and erythrocytes, originate from the myeloid stem cell, the lymphocytes from the lymphoid stem cell. After they have been formed, some white blood cells have to migrate to another organ to be imprinted before they can perform their tasks. This imprinting takes place mainly in the thymus and bone marrow, but also in the spleen, lymph nodes and tonsils.
There, the leukocytes “learn” which substance cells belong to the body and are therefore harmless and which are considered foreign and must therefore be fought. A healthy adult has an average of 4,000 to 10,000 white blood cells per μl blood. Values above this are called leukocytosis, values below this are called leukopenia.
This total number can be further subdivided into the different types of white blood cells. This is then called a differential blood count. The white blood cells can be subdivided into different types: Next come the monocytes with about 8%, which are also capable of phagocytosis.
Finally, there are eosinophil granulocytes in very small quantities, which are mainly used to defend against parasites, especially worms, and basophil granulocytes, which play an important role in allergic reactions and inflammation.
- The most common are neutrophil granulocytes, which should make up about 40-60% of the leukocytes. Like all granulocytes, neutrophils are part of the unspecific immune defense.
They are the most important cells when it comes to destroying pathogens that have entered from outside. They perform this task by means of a process called phagocytosis: they practically “eat up” the bacteria, viruses or fungi.
- In terms of quantity, lymphocytes are in second place with 20-40%, the most important component of the specific defense, which is again differentiated into B and T lymphocytes. After a certain stimulus, the B lymphocytes develop into so-called plasma cells, whose function is to form antibodies that can then bind specifically to special structures, which either destroy them directly or at least mark them so that other cells can recognize them as foreign and take action against them.
There are also various subgroups of T lymphocytes. The most important are: (1) the T-helper cells, which coordinate the body’s immune response by releasing various messenger substances by enabling “communication” between the individual components of the defense system, and (2) the T-killer cells, which are capable of directly killing tumor cells or body cells that are attacked by viruses.
- After a certain stimulus, the B lymphocytes develop into so-called plasma cells, whose function is to form antibodies that can then bind specifically to specific structures, either destroying them directly or at least marking them so that other cells can recognize them as foreign and take action against them.
- T-lymphocytes are again divided into various subgroups. The most important are: (1) the T-helper cells, which coordinate the body’s immune response by releasing various messenger substances by enabling “communication” between the individual components of the defense system and (2) the T-killer cells, which are capable of directly killing tumor cells or body cells that are attacked by viruses.
- After a certain stimulus, the B lymphocytes develop into so-called plasma cells, whose function is to form antibodies that can then bind specifically to specific structures, either destroying them directly or at least marking them so that other cells can recognize them as foreign and take action against them.
- T-lymphocytes are again divided into various subgroups.
The most important are: (1) the T-helper cells, which coordinate the body’s immune response by releasing various messenger substances by enabling “communication” between the individual components of the defense system and (2) the T-killer cells, which are capable of directly killing tumor cells or body cells that are attacked by viruses.
- Next come the monocytes with about 8%, which are also capable of phagocytosis.
- Finally, there are eosinophilic granulocytes in very small quantities, which are mainly used to defend against parasites, especially worms, and
- Basophilic granulocytes, which play an important role in allergic reactions and inflammation
Since white blood cells are essential for our body to protect itself against influences from outside (bacteria, viruses, fungi, parasites) and inside (development of tumor cells, bacteria of our own flora, which are potentially causing illness), it goes without saying that a functional disorder or a lack of leukocytes can prove to be very dangerous and even life-threatening for us. Important clinical pictures in connection with leukocytes are HIV: a virus that attacks the T-helper cells, which sooner or later causes the entire immune system to collapse and a person affected usually ends up suffering from an actually relatively banal infection or even dies because the body is no longer able to react appropriately to it. Autoimmune diseases: Disease patterns in which the white blood cells are for a mostly unknown reason no longer able to distinguish foreign cells from the body’s own cells and therefore the defense is directed against certain necessary body cells.
Important examples are systemic lupus erythematosus, Crohn’s disease, ulcerative colitis, Graves’ disease and many more.
- Leukemias: here the number of leukocytes is increased in most cases, but the cells are functionless. They also displace the remaining blood, which is why there are also deficiencies in red blood cells (anemia) and platelets.
- HIV: a virus that infects the T-helper cells, which sooner or later causes the entire immune system to collapse and a person affected usually ends up contracting a relatively banal infection or even dies because the body is no longer able to react to it appropriately.
- Autoimmune diseases: Disease patterns in which the white blood cells are for a mostly unknown reason no longer able to differentiate foreign cells from the body’s own cells and therefore the defence is directed against certain necessary body cells. Important examples are systemic lupus erythematosus, Crohn’s disease, ulcerative colitis, Graves’ disease and many more.
