The Guardians in Our Blood: White Blood Cells
White blood cells are one type of blood cell and a common item in our blood-panel tests. In a normal person, the white-blood-cell count is about (3.5-9.5) x 109/L. Among our blood cells, white blood cells number only about one-thousandth as many as red blood cells. Thus, under the electron microscope, white blood cells are scattered sparsely among the vast numbers of red blood cells.
White blood cells are nucleated, spherical cells, so we also customarily call them white corpuscles. After entering the blood from the bone marrow, they generally within 24 hours pass through the walls of small vessels or capillaries by amoeboid movement and enter connective tissue or lymphoid tissue to perform their defensive and immune functions. White blood cells are an important part of our immune system; like guardians in our blood, they help the body resist many kinds of external invasion.
Medicine divides white blood cells into two major categories according to whether they contain specific granules: granulocytes and agranulocytes.
Granulocytes can in turn be divided by the staining properties of their granules into eosinophils, basophils, and neutrophils. Among them, neutrophils are the most numerous white blood cells, accounting for 50%-70% of the total. Basophils are the fewest, accounting for only 0%-1%. Eosinophils account for 0.5%-5%.
Agranulocytes include monocytes and lymphocytes. Agranulocytes are not actually without granules; in fact they contain fine azurophilic granules. These granules can be stained purplish-red by azure dye, hence the name azurophilic granules. Azurophilic granules are a kind of lysosome containing acid phosphatase, myeloperoxidase, and various acid hydrolases, which can digest phagocytosed bacteria and foreign matter; they are also present in neutrophils.
The main function of white blood cells is to digest and phagocytose bacteria and foreign matter, and neutrophils make up the largest proportion of white blood cells. What we commonly call leukocytosis generally refers to neutrophilia.
Neutrophils have strong chemotaxis and phagocytic capacity. In neutrophils, azurophilic granules account for only about 20% of the total granules. Neutrophils also contain small granules called specific granules, which account for about 80% of neutrophil granules. These are secretory granules containing lysozyme and phagocytin. Phagocytin, also called defensin, has a bactericidal effect. After neutrophils phagocytose bacteria they turn into pus cells; the pus that appears around infected tissue is the product of neutrophils phagocytosing bacteria.
During bacterial infection, the number of neutrophils in the blood rises; we usually use this indicator to determine bacterial infection. Because viral infection generally does not increase neutrophils, whereas bacterial infection usually does. But this is not absolute: after the COVID-19 outbreak, neutrophilia did appear in the blood panels of those infected, so at the beginning of the pandemic some medical workers suspected it was a bacterial infection.
Basophils and mast cells arise from the same hematopoietic progenitor cells in bone marrow, and their functions are basically the same. Basophil cytoplasm contains granules of histamine, heparin, and eosinophil chemotactic factor, and can synthesize and secrete leukotrienes—an important trigger of allergic reactions.
Basophils can initiate the inflammatory response against pathogens and also participate in allergic reactions. Allergic inflammation is an over-defensive response of immune substances to harmless substances, and may cause skin redness and swelling, breathing difficulty, and even shock.
The function of eosinophils is exactly the opposite of basophils: they can suppress allergic reactions. Eosinophils are a special kind of lysosome; besides ordinary lysosomal enzymes, they also contain cationic proteins, histaminase, and arylsulfatase. At the site where an allergic reaction occurs, the histaminase released by eosinophils can break down histamine, and arylsulfatase can inactivate leukotrienes, thereby suppressing the allergic reaction. In patients with schistosomiasis and allergic diseases, eosinophils in the blood increase. So in a blood panel, eosinophilia usually means an allergic reaction has occurred.
Besides the three granulocytes above, white blood cells also include the two agranulocytes: monocytes and lymphocytes.
Monocytes account for about 3%-8% of white blood cells. Among the various types of white blood cells, monocytes are the largest, reaching 14-20 micrometers in diameter; their nuclei are kidney-shaped, horseshoe-shaped, or irregular, lightly stained, with abundant cytoplasm containing many azurophilic granules. Monocytes have chemotaxis and phagocytic capacity; they have a special ability to migrate out of vessels into other body tissues and differentiate into the famous macrophages, which are the body's main phagocytes. Macrophages that enter the liver are also called Kupffer cells, where they phagocytose various foreign matter and bacteria; macrophages that enter the lungs phagocytose various foreign matter and bacteria within the alveoli.
Lymphocytes are the second most abundant white blood cells, accounting for about 20%-40% of the total. But lymphocytes do not all come from bone marrow: bone-marrow-derived lymphocytes account for only about 25%, while the other 75% come from the thymus. Thymus-derived lymphocytes are also called T lymphocytes; bone-marrow-derived lymphocytes are of two kinds: B lymphocytes and NK lymphocytes.
Although these three kinds of lymphocytes are all immune cells, their functions differ. T lymphocytes produce cellular immunity, B cells produce humoral immunity, and NK lymphocytes (also called natural killer cells) can directly kill tumor cells and virus-infected cells.
B cells are the body's own "vaccine." After being stimulated by antigen, B cells can proliferate and differentiate into memory cells (antibodies) and plasma cells. Plasma cells perish together with the antigen, while memory cells remain in our bodies for a long time; when the same pathogen is encountered next time, they quickly differentiate into new memory cells and plasma cells, repeating this process.
There is a saying in TCM that the human body contains a great medicine; this means that within the body there naturally exist "great medicines" that fight disease, and white blood cells are just such a "great medicine."
When we keep regular hours and do not overexert ourselves, the white blood cells in our bodies can be produced normally and exert their immune-barrier function, and many diseases can resolve without drugs. This accords with the TCM idea that "when the righteous qi is stored within, pathogen cannot invade." But if our habits are poor and we destroy this natural barrier of the body, it becomes hard to resist the invasion of external bacteria, viruses, and foreign matter, and we become weak and frequently ill.