The term "target cell" can be defined in more than one way. In hematology, it refers to an abnormal blood cell common in patients without a spleen and patients with anemia and other blood disorders. Otherwise, a target cell may be any cell affected by a specific drug, hormone or virus.
Abnormal Red Blood Cells
Under the microscope, the human red blood cell is red throughout. In some diseases or anemias, these cells appear thin and pale, and light can shine through them and create a white ring inside the red circular cell that looks like a bull's-eye or target. These are know as target cells, or codocytes. This usually occurs when the cell has insufficient or poorly formed hemoglobin.
Other Target cells
The term "target" may also be used to describe a cell that has a receptor for a specific drug, virus, hormone or other signaling molecule. This means the target cell has the ability to be identified by -- and can respond to -- the drug, hormone, virus or other signal. In this way, cells inside a large organism can communicate with one another even if they are far apart.