Leukocytes, or white blood cells (WBC), are cells in the peripheral blood that act as defenses for the body. What are the types of leukocytes, what is their structure and what are their functions in the body? What are the leukocyte norms? Check

Leukocytes( white blood cells , white blood cells,WBC ) are mononuclear cells (so-called monokaryocytes) with a spherical shape. They stay in the peripheral blood for several dozen hours, then they move through the wall of capillaries and small veins to the connective tissue within various organs.

Physiologically, they are present in the amount from 4,000 to 10,000 in 1 mm3of peripheral blood.

The number of leukocytes changes with age - it is slightly higher in childhood than in adults.

Their number below 4,000 in 1 mm3blood is called leukopenia, while over 10,000 in 1 mm3blood - leukocytosis .

White blood cells can be divided into:

  • granulocytes
  • lymphocytes
  • monocytes

Moreover, a special type of fragments of white cells are platelets present in the bone marrow - the so-calledmegakaryocytes . They play an important role in the blood clotting process and their number is estimated at 200-300 thousand / mm3 of blood.

Leukocytes - granulocytes: division and functions

Granulocytesare formed in the red bone marrow and have characteristic cytoplasmic grains. Among them, the following stand out:

  • neutrophils (neutrophils) - they have neutrophilic granules in the cytoplasm and account for about 30-70% of all circulating leukocytes
  • eosinophils - have eosinophils in the cytoplasm and account for about 1-8% of leukocytes
  • basophils (basophils) - have basophil granules in the cytoplasm and account for only 0-2% of white cells

The neutrophilsare derived from the CFU-GM cell, that is, from the neutrophilic lineage stem cell that grows from the undifferentiated CFU-GEMM stem cell. The proliferation and maturation of myeloid neutrophilic lineage is possible due to the presence of growth factors such as CSF-G, CSF-1 andgrowth granulocytes and macrophages (CSF-GM).

Interestingly, the total transition time from the pluripotent stem cell through all dividing stages is approx. 6-7 days.

Cells of the eosinophilic lineage are derived from the eosinophilic stem cell (CFU-Eos) and, like neutrophils, go through the stages of maturation. These processes are due to the action of the stem cell factor (SCF), IL-3 and granulocyte growth factor (CSF-G).

Additionally, they are supported by IL-5 and granulocyte macrophage growth factor (CSF-GM).

Bone marrow cells derived from the stem cell of the basophil lineage (CFU-Baso) as well as neutrophils go through the stages of differentiation and maturation sequentially. In this case, the factors that regulate these processes are CSF, interleukins and NGF (nerve growth factor).

After leaving the bone marrow, granulocytes live for about 30 hours. They have the ability to pass from blood to tissues. Interestingly, they form two pools of cells:

  1. The first of them is the so-called wall pool- it is loosely bound to the inner surface of the endothelium of the vascular wall and constitutes about 60% of all granulocytes.
  2. The second pool of granulocytes is called freely circulating pool- accounts for about 40% of all granulocytes.

It is worth mentioning here that in the peripheral blood, apart from the mature forms of granulocytes (the so-called segmental granulocytes), there are immature forms - single metamyelocytes and rod-shaped granulocytes.

The percentage ratio of these three forms of granulocytes is used to determine the blood picture according to Arneth-Schilling. The so-called a shift of the Arneth-Schilling image to the left means that granulocytopoiesis is more intense and that more younger forms of granulocytes (2- and 3-segmented) pass from the bone marrow into the blood.

In the case of inhibition of granulocytopoiesis, the Arneth-Schilling image shifts to the right - then in the peripheral blood there are forms with a 4- or 5-segment nucleus.

Granulocytes show the ability to move (diapedesis), amoebic movement, chemotaxis, degranulation, phagocytosis and radicalogenesis.

What is the role of neutrophils in the body?

Neutrophils protect our body against the invasion of microorganisms.Those that are present in the blood leave the vascular bed (diapedesis) and go to the centers of bacterial reproduction, inflammation and dead tissues. In addition, they react to the chemokines they produce (so-called chemotaxis).

They phagocytose bacteria, damaged cells and then digest them in lysosomes thanks to the presence of enzymeshydrolytic. What's more, after reaching the foci of inflammation, the so-called degranulation reaction - then the enzymes contained in the granules are released in the process of exocytosis to the environment surrounding the neutrophils.

In addition, neutrophils have the ability to generate oxygen radicals that destroy microorganisms. This is done with the participation of dihydronicotinamide adenine dinucleotide phosphate (the so-called NADPH).

What role do eosinophils play in the body?

Eosinophils have the same diaperesis, chemotaxis and phagocytosis properties as neutrophils.Physiologically they counteract the inflammatory reaction by inhibiting inflammatory mediators, but in the case of a developed disease process - they intensify the inflammatory reaction.

They have the same properties in relation to parasites as neutrophils in relation to bacteria - i.e. they have a parasiticidal effect.

What role do basophils play in the body?

Basophils are mainly involved in hypersensitivity and anaphylactic reactions . Under the influence of class E immunoglobulins, the content of their granularity - heparin and histamine - is released.

Released heparin activates, among others lipoprotein lipase - an enzyme necessary for the purification of blood and lymph from fats. In addition, basophils, like neutrophils and eosinophils, show the ability to phagocytosis.

Leukocytes - lymphocytes: division and functions

Lymphocytes are the main cells of the immune system. Their lifespan ranges from several days to several months or even several years. They are found in the blood, lymph and all tissues of the body, except the tissue of the central nervous system.

They are cells with a large, round nucleus and a small amount of cytoplasm. Morphologically, they can be divided into small, medium and large lymphocytes.

Functionally, lymphocytes form a heterogeneous group of cells in terms of formation, life cycle and function.

They are created in the process of the so-called lymphocytopoiesis in central lymphoid tissues (red bone marrow, thymus) and in peripheral lymphoid tissues (lymph nodes, gastrointestinal lymph nodes, tonsils, spleen).

Lymphocytes can be divided into:

  • T (thymic-dependent) lymphocytes- constitute approx. 70% of all circulating lymphocytes, their main function is to participate in cell-type immune reactions. In addition, they are responsible for the transplant rejection reaction and the late hypersensitivity reaction
  • B (myeloid-dependent) lymphocytes- constitute approx. 15% of all lymphocytes circulating in the blood, are responsible for the humoral typeimmunity - that is, the production of antibodies
  • NK lymphocytes (natural killers)- constitute approx. 15% of all lymphocytes, show strong cytotoxic properties - they destroy foreign cells through the proteins they produce

The CD (Cluster Designations) differentiating molecules on the surface of lymphocytes enable their recognition and differentiation in the peripheral blood. For example, T lymphocytes are divided into:

  • CD4 + (positive), i.e. having CD4 differentiating molecules: these are the so-called T-helper lymphocytes, of which approx. 40%
  • CD8 + (positive), i.e. having CD8 differentiating molecules: these are the so-called T-cytotoxic lymphocyte, which is about 30%

The main function of T-helper cells is to secrete cytokines or interleukins in response to the action of immunogenic substances. On the other hand, the secreted interleukins activate T-cytotoxic lymphocytes and B lymphocytes responsible for the production of antibodies.

Leukocytes - monocytes: features

Monocytes are the largest blood cells and have abundant cytoplasm. It is formed mainly in the red bone marrow and the spleen. After exiting the marrow, it remains in the blood for about 8 to 72 hours.

Interestingly, the pool of the so-called of the wall monocytes - embedded in the endothelium of blood vessels - is more than three times greater than the pool of monocytes circulating in the blood.

Moreover, monocytes, after passing from blood to tissues, become macrophages and assume characteristic functions depending on the tissue in which they are located.

Macrophages include, for example, reticuloendothelial cells in the liver, osteoclasts, and macrophages in the lungs, peritoneal cavity and joint capsules.

The function of monocytes and macrophages is to regulate antibacterial, antiviral, antiparasitic and antifungal responses.

In addition, they remove damaged tissues, regulate the synthesis of immunoglobulins and the activity of connective tissue cells and fibroblasts.

In addition, they synthesize growth factors and are responsible for angiogenesis - the process of creating blood vessels.

Excess of leukocytes - leukocytosis

Leukocytosis means an increase in the total number of leukocytes - over 10,000 / μl. As a rule, it applies to neutrophils - cells that make up the highest percentage of peripheral blood leukocytes. It usually indicates an infection or a proliferative disease.

Reasons for an increase in the number of neutrophils (neutrophilia)

  • acute bacterial infections
  • sterile inflammation associated with tissue necrosis (e.g. in the course of burns, heart attack)
  • myeloid leukemias
  • steroid therapy
  • injuries (stress)
  • states after massive blood loss

Reasons for the increase in eosinophilia (eosinophilia)

  • allergic diseases (asthma, hay fever)
  • parasitic diseases (rarely bacterial or viral)
  • lung diseases (e.g. pulmonary eosinophils)
  • systemic connective tissue diseases (e.g. Churg-Strauss syndrome, deep eosinophilic fasciitis)
  • cancers from the so-called secondary reactive eosinophilia (e.g. T-cell lymphomas, mastocytosis, acute lymphoblastic leukemias)

Reasons for increasing the number of basophils (basophilia)

  • chronic myeloid and myelomonocytic leukemia
  • acute basophilic leukemia
  • polycythemia real

Reasons for the increase in the number of lymphocytes (lymphocytosis)

  • chronic bacterial infections
  • lymphocytic leukemias
  • viral infections (e.g. mumps, measles, hepatitis A, cytomegalovirus infection)
  • multiple myeloma

Reasons for the increase in monocytes (monocytosis)

  • bacterial (e.g. syphilis, tuberculosis), viral, parasitic (e.g. malaria) infections
  • systemic diseases of connective tissue (e.g. systemic lupus erythematosus, rheumatoid arthritis)
  • granulomatous diseases (e.g. sarcoidosis)
  • inflammatory bowel disease (ulcerative colitis, Crohn's disease)
  • leukemias (e.g. acute monocytic leukemia, chronic myeloid leukemia)
  • pregnancy

Not enough leukocytes - leukopenia

Leukopenia means a reduction in total leukocyte counts below 4,000 / μl. It usually applies to neutrophils and lymphocytes - the two largest subpopulations of leukocytes.
Reasons for the decrease in neutrophil count (neutropenia):

  • viral infections
  • chemotherapy
  • radiation therapy
  • aplastic anemia
  • autoimmune diseases

Reasons for the reduction in the number of lymphocytes (lymphopenia):

  • HIV infection
  • chemotherapy
  • radiation therapy
  • leukemias
  • sepsis

Category:

Cardiology