Differential leukocyte count Enas Sabah MSc. Human Physiology

Leukocytes (White blood cells) The leukocytes, also called white blood cells, are the mobile units of the body’s protective system. specifically transported to areas of serious infection and inflammation, thereby providing a rapid and potent defense against infectious agents, the granulocytes and monocytes have a special ability to “seek out and destroy” a foreign invader.

General Characteristics of Leukocytes Types of White Blood Cells Granulocytes: Neutrophils Eosinophils Basophils Agranulocytes: Lymphocytes Monocytes

Concentrations of the Different White Blood Cells in the Blood The adult human being has about 7000 white blood cells per microliter of blood (in comparison with 5 million red blood cells).

Life Span of the White Blood Cells The life of the granulocytes after being released from the bone marrow is normally 4 to 8 hours circulating, in the blood and another 4 to 5 days in tissues The monocytes also have a short transit time, 10 to 20 hours in the blood, in the tissues, they swell to much larger sizes to become tissue macrophages, in this form, can live for months unless destroyed during phagocytic functions. The lymphocytes have life spans of weeks or months, depending on the body’s need for these cells.

The origin of Leukocytes They are formed partially in the bone marrow (granulocytes and monocytes) and partially in the lymph tissue (lymphocytes). After formation, they are transported in the blood to different parts of the body where they are needed.

The aim of this experiment is to determine the percentage of different types of leucocytes in the peripheral blood. Certain types of leucocytes may increase or decrease during certain diseases so that the test is valuable for diagnosis of these diseases.

Procedure Making a blood smear. This is done by using two slides. Put a drop of blood on one end of the first slide (horizontal slide). Then by using a second (spreader slide) slide, spread the blood on the horizontal one. The thickness of the smear is usually regulated by increasing or decreasing the angle between the slides and by controlling the speed. The film is then allowed to dry by shaking it in the air. Staining the film. Put about one pipette full of the stain (leishman’s stain) on the slide (sufficient to cover the film) and leave it for 2 minutes.

How to prepare a blood smear

Procedure 5.Add carefully an equal amount of distilled water to the stain and wait another 10 minutes. Staining occurs during this time. 6.Wash the slide with excess distilled water and dry it in the air. 7.Put a drop of cedar oil on the slide and use objective lens power -100-(oil immersion lens) to recognize the cells.

The following parameters are used to identify the leucocytes: Neutrophil: They have multilobed nucleus connected by thin strands of nuclear material. Tiny, light staining granules. Account for 55 – 75% of all leucocytes. Their count increases physiologically in heavy exercise and pregnancy and pathologically in acute bacterial infection (appendicitis) decrease in typhoid, malaria and drugs like chloramphenicol.

Eosinophil: They have bilobed nucleus which looks like a telephone receiver. Large, pinkish to red granules. Account for 1 – 4 % of all leucocytes. Their count increases in parasitic infestation (in their larval forms), and allergic conditions as bronchial asthma and hay fever decreases in stress and glucocorticoid (steroid) treatment.

Basophil: The nucleus is also bilobed but often masked by numerous, deeply stained blue to purple granules. The granules contain histamine (vasodilator) and heparin (anticoagulant) Account for 0 – 1 % of all leucocytes. Increase in type I allergic (anaphylactic) reaction, and chronic myeloid leukemia.

Lymphocyte: The nucleus is very large for the size of the cell and stains dark purple. The cytoplasm is small, clear and stains pale blue. It has a relatively small size than other leucocytes. Accounts for 20 – 40 % of all leucocytes. The T-lymphocyte acts against virus-infected cells and tumor cells. The B-lymphocyte produces antibodies. Lymphocyte count rises in infectious mononucleosis (EBV) and chronic infections. Their count decreases with steroid treatment.

• It is the largest of the leucocytes. Monocyte: • It is the largest of the leucocytes. • The nucleus is kidney shaped. • The cytoplasm is abundant and light blue. • Account for 2 – 8 % of all leucocytes. • They become macrophages that defend the body against viruses and bacteria. • Their count rises in people with typhoid fever, malaria, infectious mononucleosis and endocarditis.