Target cell is a term given to one of three different concepts in medicine.
In hematology, target cells are very abnormal red blood cells, that have a bullseye appearance (See main article: codocyte). These target cells (from red blood cells) are associated with Hemoglobin C (HbC) disease, Asplenia, Liver Disease, Thalassemia and severe Iron deficiency anemia. Target cells may be seen on a peripheral blood smear when there is excess membrane relative to the amount of hemoglobin. Membrane may be excessive in liver disease. Intracellular hemoglobin may be lowered during iron deficiency, thalassemia, hemoglobin C or SC and other hemoglobinopathies.
In immunology, target cells are cells which present the antigenic peptide combined with MHC class I molecules to Cytotoxic T cells. These cells have MHC molecules on their surface (in contrast to Antigen Presenting Cells, which in addition also have MHC class II molecules). Target Cells are the normal cells of the body which have undergone some alteration and synthesize abnormal proteins e.g. tumor cells, virus infected cells.
In endocrinology, target cells can refer to the cells where hormones have their effect. Target cells are capable of responding to hormones because they bear receptors to which the hormone can bind. Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptors for the hormone. Hormone receptors are found either exposed on the surface of the cell or within the cell, depending on the type of hormone. A hormone may bind target cells in three general ways: