Leukocytes – whatare they?

Leukocytes together with red blood cells and platelets are among the most important components of blood. They are one of the immune system elements, which they create along with special proteins and the lymphatic organs: bone marrow, spleen, thymus, lymph glands and lymphoid nodules. The immune system is responsible for the protection of our organism against substances and microbes which may, in any way, put it at risk. The main task of leukocytes is searching for all types of enemies and combating them, as well as immunological supervision of the organism’s cells, i.e. eliminating cells which have died or act differently than they should.

White blood cells vary both in terms of structure as well as the functions performed.Considering the presence or the lack of granularity in cytoplasm, two groups were distinguished: granulocytes and agranulocytes.

Among granulocytes we identify:
• neutrophilic – in other words neutrophils, cells having the capacity for phagocytosis and ameboid movement. They are responsible for the protection of our organism against microbes, which is facilitated by the capacity for phagocytosis – the absorption and then decomposition of substances and microbes. They are activated by pro-inflammatory cytokines for the process of phagocytosis. In the granularity of neutrophils there are enzymes necessary for the digestion of the absorbed ‘alien’. Many mediators present in granularity may get outside of the cell and their concentration in serum is used in inflammatory state diagnostics.

• eosinophilic– in other words eosinophils. They also have the capacity for phagocytosis and ameboid movement. They are responsible for the destruction of parasites attacking the organism, but they also participate in allergic reactions. The presence of eosinophils is confirmed mainly in tissues exposed to contact with external environmental factors of the organism (e.g. skin, digestive tract mucosa, respiratory tract). Impaired interaction of eosinophilswith mast cells (mastocytes), whose relatives are peripheral blood basophils, leads to allergic reactions. Their quantity in cells is 100 times higher than in peripheral blood.

• basophilic – in other words basophils. Due to histamine, heparin and proteolytic enzymes as well as being influenced by IgE immunoglobulins, they are stimulated to allergic and anaphylactic reactions.

Whereas agranulocytes are divided into:

• lymphocytes:

B Lymphocytes– are produced in bone marrow and mature in lymph glands. They are responsible for hormonal response, therefore, for producing antibodies. Contact with antigens allows them to transform into memory cells and plasma cells.

B1 Lymphocytes – the quantitatively dominant population of B lymphocytes. They are responsible for the primary response (first contact with pathogen) and, thanks to transformation into memory cells, also the secondary one (another contact with pathogen). They produce antibodies in IgM and IgG classes.

B2 Lymphocytes – 20% of the B lymphocytes population. They situate themselves within mucous membranes. They produce antibodies mainly of IgD and IgM classes. They are, therefore, responsible for producing autoantibodies.

T Lymphocytes – are also produced in bone marrow but they mature and diversify in the thymus. They are responsible for the direct destruction of harmful microorganisms and additionally regulate the work of other cells protecting our organism. Their lifespan ranges from a few months to a few years.

Tc Lymphocytes – are responsible for killing cells infected by pathogens or cancer cells.

Th  Lymphocytes –  support the immunological response and release cytokines.

Treg Lymphocytes – hamper the immunological response, including self-aggression, and release cytokines. They build organism tolerance to alien antigens.

NKT Lymphocytes– cells having features of both lymphocytes andNK cells.

• NKCells– in the past they were classified as lymphocytes and, even though they are formed from the same stem cell as lymphocytes, they don’t go through the phase of maturity in the thymus or lymph nodes. Their composition and manner of acting are similar to T lymphocytes, however, they can’t recognize antigens, only differentiate them as safe or unsafe.The main task of NK cells is participation in the early phases of non-specific response and immunologic supervision, which relies on detecting and and killing cancer-changed cells or damaged cells no longer performing their function.
• Monocytes– the largest white blood cells having the capacity for phagocytosis and ameboid movement. They can also move outside of the vascular lumen. They clean blood of pathogens and the remains of dead cells, and release cytokines. This diversity of white blood cells allows for quick and precise defensive reactions. Unfortunately, sometimes the immune system detects its own tissue as alien (autoimmune diseases), as well as food particles (allergies and hypersensitivity to foods).