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The Hematologist

leukocytes (white blood cells)

After many years of looking through a microscope at human blood slides, a hematologist in a hospital laboratory is very excited that he found five different types of leukocytes (white blood cells) in a row. The hematologist gives you the following hints so that you can identify the white cells:

  1. The lymphocyte is immediately to the right of the basophil.
  2. The neutrophil is immediately to the left of the monocyte.
  3. The eosinophil is not adjacent to the monocyte, the neutrophil, or the basophil.
Can you name the white cells from left to right?


The logic puzzle can be solved by letting the letters N, M, B, L, and E represent the neutrophil, monocyte, basophil, lymphocyte, and eosinophil, respectively. From Clue 1 we know that L is to the right of B; this is the sequence BL. Clue 2 tells us that NM is another sequence. Clue 3 only allows the sequences LE and EL, but EL is not possible because of Clue 1. Combining BL and LE, we now have the sequences BLE and NM. From Clue 3 we know that E is not adjacent to N, therefore the sequence of the lymphocytes is NMBLE.

The white cells are: 1) neutrophil, 2) monocyte, 3) basophil, 4) lymphocyte, 5) eosinophil. The background shows some erythrocytes (red blood cells) which have no nucleus.

Microscopic blood analysis can be very useful for identifying or diagnosing many types of diseases such as anemia, malaria, syphilis, heavy metal poisoning, leukemia, appendicitis, etc.

Leukocytes are the first line of defense of the immune system. Leukocytes are derived from bone marrow stem cells and have three main categories: Lymphocytes, Phagocytes, and Auxiliary Cells. Neutrophils, basophils, and eosinophils are called granulocytes because they have granules in their cytoplasm.

There are two types of lymphocytes: T-Cells and B-cells. T-cells develop in the thymus, a lymphatic organ in the chest behind the breastbone, whereas B-cells develop in the adult bone marrow. T-cells produce cytokine proteins which are interpreted by phagocytes as commands to destroy the material that they have taken up. The T-lymphocytes act against tumor cells and cells infected with viruses. B-cells produce antibodies that help phagocytes to recognize foreign material. Lymphocytes have agranular clear cytoplasm that stains pale blue, whereas the nucleus stains dark purple. Lymphocytes are smaller than the three granulocytes. Lymphocytes account for 25-35% of the white blood cells. A relative increase in the proportion of lymphocytes is typical of infectious mononucleosis or a chronic infection.

Named from the Greek word "phagein" (to eat), phagocytes are cells that engulf foreign particles, including infectious agents, such as bacteria. Monocytes, neutrophils, and eosinophils are the main phagocytic cells. They search and embrace foreign particles, and then destroy them. Neutrophils account for 50-70% of all leukocytes. Elevated numbers of neutrophils are usually due to an acute infection such as appendicitis. Eosinophils account for less than 5% of the white blood cells. Eosinophil levels may increase due to parasitic diseases, bronchial asthma or hay fever. Monocytes are agranular and bigger than other leukocytes. These phagocytic cells defend the body against viruses and bacteria and account for 3-9% of all leukocytes.

Malaria trophozoites
Red blood cells infected
 with malaria parasite

Auxiliary cells
Basophils, along with mast cells and platelets, secrete inflammatory mediators which attract leukocytes to the point of infection. Basophils represent less than 1% of all leukocytes. The large basophilic granules stain deep blue, and contain histamines that cause vasodilation and heparin that acts like an anticoagulant.

Malaria is caused by the protozoan parasites of the genus Plasmodium which are transmitted by the bite of an infected Anopheles mosquito. Malaria parasites evade the body's immune system defenses by reproducing inside of the red blood cells. In this way, they avoid being detected and destroyed by the white blood cells.

The following video shows a neutrophil chasing bacteria.

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© Copyright  - Antonio Zamora