What Are The White Blood Cells Functions – In the previous section, Some of the chemical mediators found in plasma, the liquid part of blood, are discussed. The non-fluid part of blood contains various components, all of which are formed from the same stem cells found in bone marrow. The three main types of constituents are: red blood cells (RBCs) called erythrocytes; Blood clots called thrombocytes; and white blood cells (WBCs) called Leukocytes;

Red blood cells are primarily responsible for carrying oxygen to tissues. Platelets are cell fragments involved in blood clot formation and tissue repair. Many different types of WBC participate in various non-specific mechanisms of innate and adaptive immunity. In this section, The main focus will be on the mechanisms underlying the different types of WBCs.

What Are The White Blood Cells Functions

All the constituents of blood are derived from pluripotent hematopoietic stem cells (HSCs) in the bone marrow. When HSCs replicate themselves in the bone marrow; Individual cells receive different signals from the body that control how they grow and mature. As a result, Once mature, HSCs differentiate into circulating blood cell types in the peripheral blood. This differentiation process is called hematopoiesis. Shown in detail in Figure (PageIndex).

What Is The Function Of Red Blood Cells?

Regarding superior numbers, the majority of HSCs become erythrocytes. Smaller numbers become leukocytes and platelets. Leukocytes can be further divided into granulocytes, characterized by numerous granules visible in the cytoplasm, and agranulocytes, which lack granules. Figure (PageIndex) and their relative numbers; Provides an overview of the various organizational categories, including key functions and tenures.

Image (PageIndex): Contains the structural components of blood resulting from the differentiation of blood cells in the bone marrow.

Different characteristics; Different types of granulocytes can be distinguished from each other by the appearance of their nuclei and the composition of their granules, which provide function and staining properties. Neutrophils, called polymorphonuclear neutrophils (PMNs), have a nucleus with three to five membranes and numerous small orange granules. Each lobe of the nucleus is connected to the other lobes by thin bands of material. Eosinophils have fewer lobes in the nucleus (typically 2-3) and more small granules that stain orange-red. Basophils have bilobed nuclei and large granules that stain dark blue or violet (Figure (PageIndex)).

Figure (PageIndex): Granulocytes can be distinguished by the number of lobes in their nucleus and the staining properties of their granules. (Credit “neutrophil” micrograph: work modified by Ed Uthman)

White Blood Cell

Neutrophils (PMNs) are often involved in the removal and destruction of extracellular bacteria. They can migrate through blood vessel walls to sites of bacterial infection and tissue damage, finding and killing infectious bacteria. PMN granules contain a variety of defensins and hydrolytic enzymes that aid in the destruction of bacteria through phagocytosis (detailed in Pathogen Recognition and Phagocytosis).In addition, When neutrophils are transported to an infected site, they can be stimulated to release toxic molecules. surrounding tissue to properly clear pathogens. This is called degranulation.

Another mechanism used by neutrophils is neutrophil cellular traps (NETs), which are patches of chromatin that are closely associated with antimicrobial particles and components. Chromatin is DNA with associated proteins (usually, histone proteins that package DNA for organization and packaging within a cell). by forming and releasing a mesh or lattice-like chromatin structure that binds to antibiotic proteins; Neutrophils are capable of aggressively attacking nearby pathogens. Proteins frequently associated with NETs include lactoferrin; gelatinase including cathepsin G and myeloperoxidase. Each has a different way of promoting antimicrobial activity that helps neutrophils eliminate pathogens. Toxic proteins in NETs can kill some of the body’s own cells, along with invading pathogens. However, This collateral damage can be repaired after the risk of infection has been removed.

Because neutrophils fight infection; leukocytes visible at the site of infection; Accumulation of cellular debris and bacteria may be observed. We call this a rash (also known as an ulcer or pus or drainage). The presence of a rash is a sign of immune activation against infection. Historically, some practitioners believed that it stimulated the healing of wounds. The “complimentary wound” (for example, wrapping it in wine-soaked wool) was started by the ancient physician Galen in the 2nd century AD and was practiced in various forms until the 17th century (though not universally accepted). Although a small amount of rash may indicate a strong immune response. Artificial rash does not promote recovery.

Eosinophils are granulocytes that protect against protozoa and helminths. They also play a role in allergic reactions. histamine in the granules of eosinophils, which readily absorb the acid red dye eosin; It contains degrading enzymes and a compound known as major basic protein (MBP) (Figure (PageIndex)). MBP binds to carbohydrates on the parasite’s surface, This binding disrupts the cell membrane and membrane permeability.

The Benefits Of The Adaptive Immune Response

Basophils have cytoplasmic granules of various sizes, named for the ability of their granules to absorb the basic dye methylene blue (Figure (PageIndex)). Their stimulation and suppression can result from a myriad of events. The activation fragments of complement proteins include C3a and C5a, acidic fragments; This type of cell is important in allergic reactions and other inflammatory responses. One of the most abundant components of basophil granules is histamine, which is released along with other chemical factors when the basophil is stimulated. These chemicals can be chemotactic and help open the spaces between cells in blood vessels. Other mechanisms are required for basophil activation, as discussed in B Lymphocytes and Humoral Immunity.

Hematopoiesis is driven by neutrophils; It also gives rise to mast cells that appear to be derived from the same common myeloid progenitor cell, such as eosinophils and basophils. Functionally, Mast cells are very similar to basophils in that their granules contain many of the same components and play a similar role in allergic reactions and other inflammatory responses. However, unlike basophils, Mast cells leave the circulating blood and reside mostly in tissues. They are found in association with blood vessels and nerves or near surfaces exposed to the external environment, such as skin and mucous membranes (Figure (PageIndex)).

Figure (PageIndex): Mast cells act similarly to basophils by stimulating inflammatory responses. (a) This image shows the twin cells in the blood. On blood smear, they are difficult to distinguish from basophils (b). Unlike basophils, Mast cells migrate from the blood to various tissues. (Credit: Greenland JR, Xu X, Sayah DM, Liu FC, Jones KD, Looney MR, Caughey GH)

Angela’s tests came back negative for all common allergens, and her sputum samples did not contain high levels of pathogenic microbes or members of the normal respiratory microflora. But she had high levels of inflammatory cytokines in her blood.

Bone Marrow: Anatomy, Function, And Treatment

Her airway inflammation has not yet responded to treatment with antihistamines or corticosteroids. Follow-up blood work shows that Angela has a slightly elevated white blood cell count but normal antibody levels. In addition, She has lower than normal levels of complement protein C4.

As their name suggests, agranulocytes lack visible granules in the cytoplasm. Agranulocytes can be classified as either lymphocytes or monocytes (Figure (PageIndex)). Lymphocytes include natural killer cells that play an important role in non-specific innate immune defense. Lymphocytes include B cells and T cells; These are discussed in the next chapter because they are central to specific adaptive immune defenses. Monocytes differentiate into macrophages and dendritic cells, collectively referred to as the mononuclear phagocyte system.

Most lymphocytes are primarily involved in the specific adaptive immune response, as will be discussed in the following chapter. Exceptions are natural killer cells (NK cells). These mononuclear lymphocytes use nonspecific mechanisms to recognize and destroy cells that are abnormal in some way. Cancer cells and virus-infected cells are two examples of cellular abnormalities targeted by NK cells. Recognition of such cells involves a complex process that activates molecular markers on the surface of the target cell. Molecular markers that include the major histocompatibility complex (MHC) are expressed by healthy cells as indicators of “self.” This will be explained in detail in the next chapter. NK cells can recognize normal MHC markers on the surface of healthy cells, and these MHC markers act as an inhibitory signal that inhibits NK cell activation. However, Cancer cells and virus-infected cells actively reduce or eliminate the expression of MHC markers on their surface. When these MHC markers are reduced or destroyed;

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