White blood cells:- Part 1 – White Blood Cells (WBC) Development, Functions, and Interpretations
White Blood Cells
Sample for White Blood Cells
- This is done on EDTA blood.
- The whole blood in EDTA is stable for 24 hours at 23° C and 48 hours at 4 °C.
- Don’t use heparin.
Indications for White Blood Cells
- This is the routine test in CBC.
- TLC differentiates acute and chronic infections.
- TLC diagnoses leukemias.
- TLC is done as a follow-up test in patients on chemotherapy.
- This will help a patient with an allergy.
Precautions for White Blood Cells:
- Physical activity and stress may cause an increase in WBCs and differential values.
- Pregnancy in the final months may cause an increase in WBC count.
- Patients with splenectomy have a persistent mild increase in the WBC count.
- Drugs that may increase the WBC county are:
- Drugs that will decrease the WBC count:
- Antithyroid drugs.
Pathophysiology of White Blood Cells
Definition of hematopoiesis:
- This is the dynamic process of blood cell production and development of the various cells of the blood.
- All these cells develop from the totipotent stem cells.
- This hematopoiesis is characterized by the constant turnover of the blood cells.
- The normal hematopoietic system maintains a cell population of erythrocytes, white blood cells, and platelets through a complex network of tissues, stem cells, organs, and regulatory factors.
Functions of the hematopoietic components (cells):
- It transports oxygen and excretes CO2 through RBCs.
- It fights infection by the WBCs.
- It performs the immune function (cellular and humoral immunity) through the lymphocytes.
- It maintains (hemostasis) the bleeding and the clotting process through the platelets.
Development of myeloid (myelopoiesis) /erythroid (erythropoiesis) cells:
- In the first few weeks of gestation, the yolk sac (mesoderm) is the hematopoiesis’s main site. The first stem cells for hemopoiesis are observed in the dorsal aorta, called an aorta-gonads-mesonephros region.
- These common precursors of endothelial and hematopoietic cells will seed the bone marrow, liver, and spleen from 6 weeks until 7 months of fetal life.
- The liver and the spleen are the major hematopoietic organs and produce blood cells until around 2 weeks after birth.
- During childhood and adulthood, marrow is the only source of new blood cells.
- In adult life, the marrow consists of approximately 50% of the fats.
- After 4 years of age, fat cells start appearing in the long bones.
- 18 to 20 years, hematopoiesis is only found in the sternum, ribs, pelvis, vertebra, and skull.
- After 40 years, the sternum, ribs, vertebra, and pelvis comprise 50% fat and 50% hematopoietic tissue.
Bone marrow activity:
- Bone marrow hematopoietic activity is divided into two pools:
- Stem cells pool.
- Bone marrow pool.
- Eventually, these cells get mature and are released into the peripheral blood.
- Hematopoiesis starts from the pluripotential stem cells.
- Hematopoietic stem cells are rare; these are 1 in every 20 million nucleated cells.
- There is self-renewal of the stem cells. So the bone marrow cellularity remains constant in a normal healthy person.
- There is an amplification of the stem cells, and one stem cell can produce about 106 mature blood cells after 20 subdivisions.
- There is various type of stem cells, and these cells develop from the totipotent cells.
- Totipotent cells, also called embryonic stem cells and gave rise to:
- Hematopoietic stem cells give rise to myeloid and lymphoid cells.
- Epithelial stem cells give rise to organs like the liver etc.
- Mesenchymal stem cells give rise to muscles, tendons, and cartilage.
- Neural stem cells give rise to neural tissue.
- These parent stem cells have CD34+ and CD38– and have the appearance of small, medium-sized lymphocytes.
- These stem cells give rise to committed stem cells, and this process takes place under the influence of CFU (colony-forming unit).
- This whole process is shown in the following diagram.
White blood cells or leukocytes are divided into :
- Granulocytic series. These cells contain granules in their cytoplasm. Because of a multilobate nucleus, these are also called polymorphonuclear leukocytes (Polys or PMN). These are of the following type:
- Agranulocytic series is without any granules in their cytoplasm. These are also called mononuclear cells. These are :
White blood cells can also be divided into:
- Phagocytic cells:
- Neutrophils (polymorphonuclear leucocytes, PMN).
- Immunocytic cells:
- Lymphocytes precursors.
- The Polys and lymphocytes comprise 75% to 90% of the total WBC count.
Polymorphonuclear leukocytes (PMN):
- The neutrophils develop from the myeloblast, transforming into promyelocytes, myelocytes, metamyelocytes, band forms, and neutrophils delivered into the peripheral blood.
The development of the neutrophils:
- These are also called segmented neutrophils or polymorphonuclear neutrophils (PMN).
- The neutrophils are of two types:
- Segmented neutrophils are found in the peripheral blood.
- Tissue neutrophils have ample cytoplasm having irregular, blunt pseudopodia that are often multi-pointed and may have hazy cytoplasmic streamers.
- These cells are not phagocytic and seldom have cytoplasmic vacuoles.
- The cytoplasm stains light blue and has a fine latticelike structure.
- Granules vary in number and stain, which will be red to blue.
- These cells have large, round, or oval nuclei with coarse chromatin.
- Nucleoli are conspicuous and stain light blue.
The cytokines involved are:
|Growth factors/cytokines||Target cells|
||The precursor of:
- The leukocytes’ total lifespan is 13 to 20 days, and they are produced in 7 to 14 days from the myeloblastic cells.
- Their life in the peripheral blood is just 7 to 10 hours and migrates to the tissue and is replenished by other cells released from the marrow.
- 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.
White blood cells granules are divided into:
- Primary granules appear at the promyelocytic stage.
- These contain myeloperoxidase, acid phosphatase, and other hydrolases.
- Secondary (specific) granules appear at the myelocytic stage and predominate in the mature neutrophils.
- These granules contain collagenase, lactoferrin, and lysozyme.
The role of the lysosomal enzyme in the destruction of the bacteria by the neutrophils are:
- Bacteria are phagocytosed into cells and fuse with the primary lysosomes to form a phagosome.
- Primary granules attack the bacteria.
- Secondary granules fuse with the phagosomes, and secondary enzymes attack the bacteria.
- Activated oxygen generated by glucose metabolism will kill the bacteria.
- Undigested, killed residual bacterial products are excreted by exocytosis.
The function of Poly (PMN) is:
- The poly (PMN) gives immunity by fighting against infections and reacting against foreign bodies by various methods:
- Phagocytosis is the killing and digestion of bacteria.
- Eosinophils are involved in allergic reactions.
- Eosinophils have a role in parasitic infestation.
- Basophils of the peripheral blood are also rich in histamine granules; they play a role in allergic reactions.
- Monocytic cells have the property of phagocytosis. They can kill bacteria and remove debris.
- Monocytes produced interferon.
- They have a longer life than neutrophils.
Summary of the difference between various types of granulocytic series (neutrophils) cells:
- Monocytes develop from the monoblast in the bone marrow.
- These macrophagic cells measure 25 to 80 µm with round or reniform nuclei and contain one or two nucleoli.
- There is clumped chromatin, abundant cytoplasm with vacuoles, and numerous azurophilic granules.
- These monocytes enter the circulation for a short time and then migrate to the tissue and transform into tissue macrophagic cells.
- Monocytes are also called histiocytes which means histio = tissue and cyte= cells.
- When these monocytes are mature, they become too large to pass readily through the capillaries, so these settle in the tissue and convert into tissue macrophages in many organs like:
- In the lungs are called pulmonary alveolar macrophages.
- In the peritoneum are called peritoneal macrophages.
- In the spleen are called splenic macrophages.
- In the liver are called Kupffer’s cells.
- In the connective tissue are called tissue macrophages.
- These are also phagocytic cells.
- Monocytes don’t enter the circulation but can go back to circulation in case of inflammation.
- The function of monocytes:
- Their function as phagocytosis is similar to neutrophils.
- Monocytes can produce more rapidly than neutrophils and spend a longer time than neutrophils.
- These cells all pass through the same stages as the neutrophils.
- These are also called mast cells when present in the tissue.
- The cells have large basophilic granules.
- The maturation of the basophils in the bone marrow takes more than 7 days.
- Basophils circulate in the peripheral blood for a few hours, then migrate to the tissue, skin, mucosa, and serosal surfaces.
- Eosinophils spend 3 to 6 days developing in the bone marrow before appearing in the peripheral blood.
- These are stored in the bone marrow and released to the peripheral blood circulation when needed.
- The mean time in the circulation is about 8 hours.
- Eosinophils migrate from blood to bronchial mucosa, skin, GI tract, and vagina in about 12 days.
- Eosinophils can migrate back to blood and bone marrow.
- Eosinophils are motile and can migrate between the endothelial cells into tissue or area of inflammation.
- Granules of the eosinophils contain hydrolytic enzymes like:
- Acid phosphatase.
- Aryl sulfatase.
- But eosinophils lake the enzymes like:
- Alkaline phosphatase.
- Cationic proteins.
- There are tissue eosinophils, and these have prominent nucleoli.
Lymphocytes are of two types:
- B – lymphocytes give rise to antibody-dependent immunity.
- T – lymphocytes give cell-mediated immunity; their subtypes are:
- T – cytotoxic cell. (T – killer).
- T – suppressor cell.
- T – helper cell.
- The primary function of T–cells is to fight chronic bacterial and viral infections.
Normal Total leucocytes count
- Adult /child = 5000 to 10,000 /cmm
- Child ≤2 years = 6200 to 17000 /cmm.
- Newborn = 9000 to 30,000 /cmm
- Adult and child = 5000 to 10,000/cmm.
- Child under 2 years = 6200 to 17,000/cmm.
- Newborn = 9000 to 30,000/cmm.
|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:
- The TLC is >11000/cmm.
- Mostly in the case of infections that may be bacterial or viral.
- Localized infections are:
- Generalized infections:
- Acute rheumatic fever.
- Localized infections are:
- In the case of leukemias.
- After the strenuous exercise.
- Pain and anorexia.
- Epileptic seizures.
- Emotional reaction.
- Mild leucocytosis in pregnancy.
- Acute hemorrhage.
- Intoxications like:
- Poisoning by drugs, chemicals, and venoms (black widow spider).
- Metabolic diseases include uremia, acidosis, eclampsia, and acute gout.
- Parenteral proteins and vaccines.
- Acute hemolysis of red blood cells.
- Myeloproliferative diseases.
- Tissue necrosis:
- Necrosis of the tumor.
- Acute myocardial infarction.
- Necrosis due to bacteria.
- Physiologic conditions are:
- Emotional stress.
- Obstetrical labor.
Decreased leucocytosis (neutropenia) is seen in:
- The TLC is <4000/cmm.
- This may be seen in fever, malaise, and chills.
- Bacterial Infections.
- Miliary tuberculosis.
- Typhoid fever.
- Paratyphoid fever.
- Viral infections are:
- Infectious mononucleosis.
- Hematological diseases:
- Aleukemic leukemia.
- Pernicious anemia.
- Gaucher’s disease.
- Felty’s syndrome.
- Aplastic anemia.
- Deficiency of vitamin B12.
- Drugs and chemicals:
- Antithyroid drugs.
- Marrow depressant.
- Malignant infiltration of the bone marrow.
- Bone marrow aplasia.
- Bone marrow depression by radiations.
- 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.
Questions and answers:
- Please see more details in CBC part 1.