IMMUNOLOGY PRACTICAL: Differential Blood Cell Counts

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IMMUNOLOGY PRACTICAL: Differential Blood Cell Counts


To examine a prepared blood smears from humans in order to identify and count different types of white blood cell. Also to analyse and view the data, taken during the course of a parasitic infection (on mice).


The total number of white blood cell does not necessarily indicate the severity of a disease, since some serious ailment may show a low white blood cell count. For this reason, a differential white blood cell count is performed.

A differential white blood cell count consists of an examination of blood to determine the presence and the number of different types of white blood cells. This study often provides helpful information in determining the severity and extent of an infection, more than any other single procedure used in the examination of the blood.

The role of white blood cells, or leukocytes, is to control various disease conditions. Although these cells do most of their work outside the circulatory system, they use the blood for transportation to sites of infection.

There are five different types of white blood cells, which are normally found in the circulating blood. They are 1) lymphocytes, 2) neutrophils, 3) monocytes, 4) basophils and 5) eosinophils.


Lymphocytes constitute 20-40% of the body’s white blood cell and 99% of the cells in the lymph. These lymphocytes continually circulate in the blood and lymph and are capable of migrating into the tissue spaces and lymphoid organs, thereby integrating the immune system to a high degree.


To perform a differential cell count, you must be able to identify the different types of white blood cells. The ability to properly identify the different types of white blood cells is not difficult to develop, but require a thorough knowledge of staining characteristics and morphology (the study of the form and structure of organisms). This knowledge can be gained only by extensive, supervised practice.


For this practical you have to produce a blood smear of an infected animal, but due to not being able to handle blood containing parasites, you will be provided with a prepared blood smear slide. In this practical no parasites are involved.  You are only working with the blood of the infected animals so there is no infection risk.

The methodology will still be provided in order to gain understanding of the procedure.

You have been provided with clean microscope slides on which you prepare a blood smear.  For this practical you should work in pairs, one person from each pair should do a smear from the infected animals; the other should do a smear from the control animals.  Take your slides to the demonstrator who will give you a drop of blood, make a smear.

The stains used will stain your skin and are also potentially harmful if ingested.  Standard laboratory procedure applies.

Staining of Blood Smears; fix the cells on the smear in 95% methanol for 2 min. then  Immerse the slide in buffer for 5 min (remember which side of the slide the cells are on).   Shake the droplets off slide into a waste pot. Then stain in Giemsa solution for 15 - 20 min. After 15-20 min have gone by, rinse in buffer by immersing the slide several times.  Put a drop of buffer and a cover slip on the slide and examine using the X40 objective on the microscope. If the cells are over-stained (too blue) remove the cover slip and allow them to stand in buffer for 5 min.

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Cell Identification; in order to familiarise yourself with leukocyte morphology you have also been provided with a pre-stained slide of human blood. Examine under the X40 objective and identify the following cell types in your slides; lymphocytes, neutrophils, monocytes, eosinophils and basophils. Also carry out a differential cell count as described below.

Cell Counts; for differential cell counts count the number of each leukocyte cell type in the field of view of the microscope.  Look at least 5 - 10 fields of view over the slide.  (White cells tend to occur most near the edges of the smears). ...

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