Basophils: Definition, Mediators, Mast Cells and Eosinophils

They are a type of cell produced in the bone marrow, inhabiting the blood system.

Its form is granulocyte because it contains granules in the membranes. Eosinophils, mast cells, and basophils were recognized and described for the first time by Paul Ehrlich at the end of the 19th century.

Since then, it has become clear that these three types of cells have much more in common than their recognition by the same scientist.

All three cells are involved in the pathogenesis of the allergic disease. This is a consequence of the receptors expressed on its surface and its arsenal of potent immunologically active mediators released at the activation time.

These mediators can be performed (e.g., histamine, proteases, cytotoxic proteins) and released seconds or minutes after activation, or synthesized de novo (e.g., arachidonic acid metabolites, chemokines, cytokines) and released minutes to hours or days after activation.

While mature mast cells do not appear in the blood, eosinophils circulate in the blood (usually less than 5% of leukocytes) and the hematopoietic and lymphatic organs, such as bone marrow spleen, lymph nodes, and the thymus.

Basophils

They are only found in the blood of healthy people (usually less than 1% of leukocytes). However, it is known that they are recruited rapidly in inflamed tissues, where they can reach high densities (e.g., Jones-Mote reaction, antimicrobial immunity). ticks) Moreover, play non-redundant roles.

 

Mast cells are resident in vascularized tissues throughout the body and are particularly prominent within tissues interacting with the external environment.

Pathologic features of eosinophils, mast cells, and basophils in allergy relate directly or indirectly to the presence of specific IgE allergen in allergic individuals.

Basophils the list of diseases related to basophils is somewhat shorter. Basophils have been associated with fatal asthma and acute and chronic allergy and have been shown to play an exacerbating role in lupus nephritis. It is unclear if they play any role in IgG-dependent anaphylaxis in humans.

However, its role in amplifying existing allergic responses is relatively well established due to its abundant secretion of type 2 cytokines IL-4 and IL-13 after activation.

Our understanding of basophils and their roles has been steadily increasing in recent years due to the introduction of mouse models of basophil knockout. However, there are still some questions regarding the relevance of these models for the immunobiology of human basophils.

While it may be tempting for physicians involved in treating allergic people to consider only the opposing roles of these three types of cells, it is essential to consider that causing allergic diseases is not their physiological function, and they play important protective roles.

These protective aspects of these cell types have been demonstrated in innate immunity against microbial pathogens, viruses, and helminthic parasites; and in protection against some poisons of snake, scorpion, Gila, and honey bee.

However, in the latter case, the protection of the mast cell-dependent host against bee venom may otherwise turn into individuals sensitized to bee venoms, resulting in anaphylactic shock and death.

This fact illustrates that mast cells, basophils, and eosinophils are a “double-edged sword” in the instrumentation of the immune system, highlighting the importance of developing viable strategies for the pharmacological modulation of their effects and roles in different pathological scenarios.

Mast cells

Mast cells rapidly degranulate by cross-linking specific IgE with the corresponding allergens and release preformed histamine, proteases (chymase, tryptase), and cytokines (TNF-alpha), followed by the rapid synthesis and release of prostaglandins and leukotrienes.

In general, mast cells are the main actors in the early phase of the allergic reaction due to their localization residing in places where they are more likely to encounter environmental or food allergens (for example, submucosa of the respiratory or digestive tract).

Much of the acute phase allergic reaction can be attributed to the direct effects of histamine on the surrounding tissues, for example, swelling, itching, and sneezing in allergic rhinitis; this also explains the benefits of the use of histamine receptor antagonists.

Mast cells are also associated with many other conditions such as asthma, reactions to medications, anaphylaxis, mastocytosis, and urticarial. Much less appreciated and understood are its possible secondary roles in obesity, atherosclerosis, and tumor growth and development.

Eosinophils

Eosinophils can also be associated with many disorders, such as asthma, tropical pulmonary eosinophilia, Loeffler’s syndrome, Churg-Strauss syndrome, atopic dermatitis, and eosinophilic esophagitis, hypereosinophilic syndromes, some malignancies, and adverse drug reactions.

Eosinophils are terminally differentiated granulocytic effector cells that produce and store biologically active molecules, including cytotoxic proteins, lipid mediators, chemotactic peptides, and cytokines.

They are considered multifunctional cells capable of modulating both innate and adaptive immunity.

The numbers of eosinophils in the blood and the infiltration of eosinophilic tissue often correlate with the severity of the disease. Therefore, therapies that reduce the number of eosinophils are usually effective in allergic diseases.

In addition, it has been shown that the number of eosinophils in sputum predicts the success of anti-eosinophil therapies in asthmatic patients.

However, the exact role of eosinophils in the pathogenesis of eosinophilic diseases is not clear and is currently a subject of intense research.