White blood cell:- Part 1 – White Blood Cells (WBC) Development, Maturation, Functions, and Interpretations

Sample

1. This is done on EDTA blood.
2. The whole blood in EDTA is stable for 24 hours at 23° C and 48 hours at 4 °C.
3. Don’t use heparin.

Indications

1. This is the routine test in CBC.
2. TLC  differentiates acute and chronic infection.
3. TLC diagnoses the leukemias.
4. TLC is done as a follow-up test in patients on chemotherapy.
5. This will help a patient with an allergy.

Precautions:

1. Physical activity and stress may cause an increase in WBCs and the differential values.
2. Pregnancy in the final months may cause an increase in WBC count.
3. Patients with splenectomy have a persistent mild increase in the WBC count.
4. Drugs that may increase the WBC county are:
   1. Aspirin.
   2. Allopurinol.
   3. Steroids.
   4. Quinine.
   5. Epinephrine.
   6. Adrenaline.
   7. Chloroform.
   8. Heparin.
5. Drugs that will decrease the WBC count:
   1. Antibiotics.
   2. Anticonvulsant.
   3. Antimetabolites.
   4. Antithyroid drugs.
   5. Diuretics.
   6. Sulfonamides.
   7. Barbiturates.
   8. Chemotherapy.

Pathophysiology

1. Definition of hematopoiesis:
   1. This is the dynamic process of blood cell production and development of the various cells of the blood.
   2. These all cells develop from the totipotent stem cells.
   3. This hematopoiesis is characterized by the constant turnover of the blood cells.
   4. The normal hematopoietic system continuously maintains a cell population of erythrocytes, white blood cells, platelets through a complex network of tissues, stem cells, organs, and regulatory factors.
2. Functions of the hematopoietic components (cells):
   1. It transports oxygen and excretes CO2 through RBCs.
   2. It fights infection by the WBCs.
   3. It performs the immune function (cellular and humoral immunity) through the lymphocytes.
   4. It maintains (hemostasis) the bleeding and the clotting process through the platelets.
3. Development of myeloid (myelopoiesis) /erythroid (erythropoiesis) cells:
   1. In the first few weeks of gestation, the yolk sac (mesoderm) is the hematopoiesis’s main site. The first stem cells for the hemopoiesis are observed in the dorsal aorta, called an aorta-gonads-mesonephros region.
   2. These common precursors of endothelial cells and hematopoietic cells will seed the bone marrow, liver, and spleen from 6 weeks until 7 months of fetal life.
   3. The liver and the spleen are the major hematopoietic organs and continue to produce blood cells until around 2 weeks after birth.
   4. During childhood and adult life, marrow is the only source of the new blood cells.
   5. In adult life, the marrow approximately consists of 50% of the fats.
   6. After 4 years of age, fat cells start appearing in the long bones.
   7. 18 to 20 years hematopoiesis only found in the sternum, ribs, pelvis, vertebra, and skull.
   8. After 40 years of age, in the sternum, ribs, vertebra, and pelvis, composed of 50% fat and 50% hematopoietic tissue.
      

      Hematopoiesis in fetal life

   9. Bone marrow hematopoietic activity is divided into two pool:
      1. Stem cells pool.
      2. Bone marrow pool.
      3. Eventually, these cells get mature and are released into the peripheral blood.
         

         Bone marrow pool and their maturation into peripheral blood cells

4. Hematopoiesis:

   1. Hematopoiesis starts from the pluripotential stem cells.
   2. Hematopoietic stem cells are rare; these are 1 in every 20 million nucleated cells.
   3. There is self-renewal of the stem cells. So the bone marrow cellularity remains constant in a normal healthy person.
   4. There is an amplification of the stem cells, and one stem cell can produce about 10⁶ mature blood cells after 20 subdivisions.
   5. There is various type of stem cells, and these cells develop from the totipotent cells.
      1. Totipotent cells also called embryonic stem cells and gave rise to:
         1. Hematopoietic stem cells give rise to myeloid and lymphoid cells.
         2. Epithelial stem cells give rise to organs like the liver etc.
         3. Mesenchymal stem cells give rise to muscles, tendons, and cartilage.
         4. Neural stem cells give rise to neural tissue.
            

            Totipotent stem cells develop into other tissues.

   6. These parent stem cells have CD34⁺ and CD38^– and have the appearance of small, medium-sized lymphocytes.
   7. These stem cells give rise to committed stem cells, and this process takes place under the influence of CFU (colony forming unit).
   8. This whole process is shown in the diagram.
      

      Bone marrow maturation of myeloid, erythroid, and lymphoid cells

5. White blood cell or leukocytes are divided into :
   1. Granulocytic series. These cells contain granules in their cytoplasm. Because of the presence of a multilobate nucleus, these are also called polymorphonuclear leukocytes (Polys or PMN). These are of the following type:
      1. Neutrophils.
      2. Eosinophils.
      3. Basophils.
   2. Agranulocytic series is without any granules in their cytoplasm. These are also called mononuclear cells. These are :
      1. Lymphocytes.
      2. Monocytes.
      3. Platelets.

2. White blood cells can also be divided into:
   1. Phagocytic cells:
      2. Neutrophils (polymorphonuclear leucocytes, PMN).
      3. Eosinophils.
      4. Basophils.
      5. Monocytes.
   2. Immunocytic cells:
      1.  Lymphocytes.
      2. Lymphocytes precursors.
3. The Polys and lymphocytes make up 75% to 90% of the total WBC count.

Polymorphonuclear leukocytes (PMN):

1. The neutrophils develop from the myeloblast, which transforms into promyelocytes, myelocytes, metamyelocytes, band forms, and ultimately neutrophils delivered into the peripheral blood.
   

   White blood cells development

2. The development of the neutrophils:
3. These are also called segmented neutrophils or polymorphonuclear neutrophils (PMN).
4. The neutrophils are of two types:
   1. Segmented neutrophils are found in the peripheral blood.
5. Tissue neutrophils have ample cytoplasm having irregular, blunt pseudopodia that are often multi-pointed and may have hazy cytoplasmic streamers.
   1. These cells are not phagocytic and seldom have cytoplasmic vacuoles.
   2. The cytoplasm stains light blue and have a fine latticelike structure.
   3. Granules vary in number and stain, which will be red to blue.
   4. These cells have large, round, or oval nuclei with coarse chromatin.
   5. Nucleoli are conspicuous and stain light blue.
6. The cytokines involved are:
   

   Growth factors/cytokines	Target cells
   GM-CSF (Granulocyte-macrophage colony-stimulating factor	Neutrophils, eosinophils, and monocytes
   M-CSF (Monocyte-macrophage CSF)	Mononuclear phagocytic system
   IL-3	The precursor of neutrophils, monocyte, eosinophil, basophil, platelets, and stem cells
   IL-7	Early granulocytes
   IL-8	Neutrophils, basophils, and T-lymphocytes

   1. The leukocytes’ total lifespan is 13 to 20 days where they are produced in 7 to 14 days from the myeloblastic cells.
   2. Their life in the peripheral blood is just 7 to 10  hours and migrates to the tissue and replenished by other cells released from the marrow.
7. The polys have a characteristic dense nucleus consisting of 2 to 5 lobes and pale cytoplasm, with many fine pink-blue (azurophilic granules) or grey-blue granules. These granules are present in the lysosomes.
8. These granules are divided into:
   1. Primary granules appear at the promyelocytic stage.
      1. These contain myeloperoxidase, acid phosphatase, and other hydrolases.
   2. Secondary (specific) granules appear at the myelocytic stage and predominate in the mature neutrophils.
      1. These granules contain collagenase, lactoferrin, and lysozyme.
         

         Development of white blood cells

9. The role of the lysosomal enzyme in the destruction of the bacteria by the neutrophils are:
   1. Bacteria are phagocytosed into cells and fuse with the primary lysosomes to form a phagosome.
   2. Primary granules attack the bacteria.
   3. Now secondary granules fuse with the phagosomes, and secondary enzymes also attack the bacteria.
   4. Activated oxygen generated by the glucose metabolism will kill the bacteria.
   5. Undigested killed residual bacterial products are excreted by exocytosis.
      

      White blood cells role in bacterial infection

2. The function of Poly (PMN) is:
   2. To give immunity by fighting against infections and react against foreign bodies by various methods like:
      2. Phagocytosis is the killing and digestion of bacteria.
      3. Eosinophils are involved in allergic reactions.
      4. Eosinophils have a role in parasitic infestation.
      5. Basophils of the peripheral blood are also rich in histamine granules; they play a role in allergic reactions.
   3. Monocytic cells have the property of phagocytosis. They can kill bacteria and remove the debris.
      1. Monocytes produced interferon.
      2. They have a longer life than neutrophils.

Summary of the difference between various types of granulocytic series (neutrophils) cells:

Characteristics	Myeloblast	Promyelocyte	Myelocyte	Metamyelocyte	Band form	Neutrophil
Size of the cell	10 to 20 µm	10 to 20 µm	10 to 18 µm	10 to 18 µm	10 to 16 µm	10 to 16 µm
Nuclear shape	Round	Round	Oval or round	Kidney shape	The elongated, horseshoe shape	2 to 5 nuclear lobes
N/C ratio	4:1	3:1	2:1 to 1:1	1:1	1:1	1:1
Nucleoli number	1 to 3	1 to 2	+/-	None	None	None
Nuclear chromatin and color	Light reddish-blue no aggregation of material	Light reddish-blue, fine meshwork, slight aggregation may be seen at the nuclear membrane.	Light reddish-blue, fine chromatin, slight aggregation, or granular pattern	Light blue purple with basophilic chromatin	Purplish-red clumped granular pattern.	Purplish-red clumped granular pattern.
Cytoplasmic granules	Absent	Present fine azurophilic and non-specific granules	Present, fine azurophilic, specific granules	Present, fine azurophilic, specific and neutrophilic	Specific granules, fine violet-pink	Specific granules, fine violet-pink
Amount of cytoplasm	Basophilic and slight	Basophilic and increased	Bluish-pink and moderate	Clear-pink and moderate	Pink-abundant	Pink-abundant

Monocytes:

1. Monocytes develop from the monoblast in the bone marrow.
2. These macrophagic cells measure 25 to 80 µm with round or reniform nuclei and contain one or two nucleoli.
   1. There is clumped chromatin, abundant cytoplasm with vacuoles, and numerous azurophilic granules.
3. These monocytes enter the circulation for a short time and then migrate to the tissue and transform into tissue macrophagic cells.
   1. Monocytes are also called histiocytes which means histio = tissue and cyte= cells.
      

      Monocytes in the peripheral blood smear

4. When these monocytes are mature, they become too large to pass readily through the capillaries, so these settle in the tissue and converts into tissue macrophages in many organs like:
   1. In the lungs are called pulmonary alveolar macrophages.
   2. In the peritoneum are called peritoneal macrophages.
   3. In the spleen are called splenic macrophages.
   4. In the liver are called Kupffer’s cells.
   5. In the connective tissue are called tissue macrophages.
5. These are also phagocytic cells.
6. Monocytes don’t enter back the circulation but can go back to circulation in case of inflammation.
7. Their function as phagocytosis is similar to neutrophils.
8. Monocytes can produce more rapidly than neutrophils and spend a longer time than neutrophils.

Basophils:

1. These cells all pass through the same stages as the neutrophils.
2. These are also called mast cells when present in the tissue.
3. The cells have large basophilic granules.
4. The maturation of the basophils in the bone marrow takes more than 7 days.
5. Basophils circulate in the peripheral blood for few hours, then migrate to the tissue, skin, mucosa, and serosal surfaces.
   

   Morphology of the Basophil

Eosinophils:

1. Eosinophils spend 3 to 6 days developing the bone marrow before appearing in the peripheral blood.
2. These are stored in the bone marrow and released to the peripheral blood circulation when needed.
3. The mean time in the circulation is about 8 hours.
4. Eosinophils migrate from blood to bronchial mucosa, skin, GI tract, and vagina in about 12 days.
5. Eosinophils can migrate back to blood and bone marrow.
6. Eosinophils are motile and can migrate between the endothelial cells into tissue or area of inflammation.
   

   Eosinophils structure

7. Granules of the eosinophils contain hydrolytic enzymes like:
   1. Peroxidase.
   2. Acid phosphatase.
   3. Aryl sulfatase.
   4. β-glucuronidase.
   5. Phospholipase.
   6. Cathepsin.
   7. Ribonuclease.
8. But eosinophils lake the enzymes like:
   1. Alkaline phosphatase.
   2. Lysosomes.
   3. Cationic proteins.
9. There are tissue eosinophils, and these have prominent nucleoli.

Immunocytes:

1. Lymphocytes are of two types:
   1. B – lymphocytes give rise to antibody-dependent immunity.
   2. T – lymphocytes give cell-mediated immunity; their subtypes are:
      1. T – cytotoxic cell. (T – killer).
      2. T – suppressor cell.
      3. T – helper cell.
   3. Primary Function of T–cells is to fight chronic bacterial and viral infection.

Normal Total leucocytes count

Source 2

• Adult /child = 5000 to 10,000 /cmm
• Child ≤2 years = 6200 to 17000 /cmm.
• Newborn = 9000 to 30,000 /cmm

Other sources

• Adult and child = 5000 to 10,000/cmm.
• Child under 2 years = 6200 to 17,000/cmm.
• Newborn = 9000 to 30,000/cmm.

Differential count:

Type of the cells	%	Absolute count
Neutrophils	55 to 70	2500 to 8000/cmm
Eosinophils	1 to 4	50 to 500/cmm
Monocytes	2 to 8	100 to 700/cmm
Basophils	0.5 to 1	25 to 100/cmm

Increased TLC (Leucocytosis) is seen in:

1. The TLC is >11000/cmm.
2. Mostly in the case of infections that may be bacterial or viral.
   1. Localized infections are:
      1. Meningitis.
      2. Pneumonia.
      3. Abscess.
      4. Tonsillitis.
   2. Generalized infections:
      1. Septicemia.
      2. Acute rheumatic fever.
      3. Cholera.
3. In the case of leukemias.
4. After the strenuous exercise.
5. Pain and anorexia.
6. Epileptic seizures.
7. Emotional reaction.
8. Mild leucocytosis in pregnancy.
9. Acute hemorrhage.
10. Intoxications like:
    1. Poisoning by drugs, chemicals, venoms (black widow spider).
    2. Metabolic diseases uremia, acidosis, eclampsia, and acute gout.
    3. Parenteral proteins and vaccines.
11. Acute hemolysis of red blood cells.
12. Myeloproliferative diseases.
13. Tissue necrosis:
    1. Burns.
    2. Gangrene.
    3. Necrosis of the tumor.
    4. Acute myocardial infarction.
    5. Necrosis due to bacteria.
14. Physiologic conditions are:
    1. Emotional stress.
    2. Excercise.
    3. Obstetrical labor.
    4. Menstruation.

Decreased leucocytosis (neutropenia) is seen in:

1. The TLC is <4000/cmm.
2. This may be seen in fever, malaise, and chills.
3. Bacterial Infections.
   1. Bacterial.
   2. Septicemia.
   3. Miliary tuberculosis.
   4. Typhoid fever.
   5. Paratyphoid fever.
   6. Tularemia.
   7. Brucellosis.
4. Viral infections are:
   1. Hepatitis.
   2. Influenza.
   3. Infectious mononucleosis.
   4. Psittacosis.
   5. Rubella.
   6. Measles.
5. Hematological diseases:
   1. Aleukemic leukemia.
   2. Pernicious anemia.
   3. Gaucher’s disease.
   4. Felty’s syndrome.
   5. Aplastic anemia.
6. Deficiency of vitamin B12.
7. Drugs and chemicals:
   1. Antibiotics.
   2. Analgesics.
   3. Sulphonamides.
   4. Antithyroid drugs.
   5. Arsenicals.
   6. Marrow depressant.
8. Malignant infiltration of the bone marrow.
9. Bone marrow aplasia.
10. Bone marrow depression by radiations.
11. Autoimmune diseases like SLE.

TLC counted in Neubauer chamber:

 

• Please always correlate TLC with the freshly prepared peripheral blood slide.
• Critical value = <2500  or >30,000 /cmm.
• Please see more details in CBC part 1.

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