Hematology

In hematology

Hematology

Hematology, also spelled haematology , is the branch of biology physiology, internal medicine, pathology, clinical laboratory work, and pediatrics that is concerned with the study of blood, the blood-forming organs, and blood diseases...

, target cells are very abnormal red blood cells, that have a bullseye

Bullseye (target)

The bullseye, or bull's-eye, is the centre of a target , and by extension the name given to any shot that hits the bullseye...

 appearance (See main article: codocyte). These target cells (from red blood cells) are associated with Hemoglobin C

Hemoglobin C

Hemoglobin C is an abnormal hemoglobin with substitution of a lysine residue for a glutamic acid residue at the 6th position of the β-globin chain.-Clinical significance:...

 (HbC) disease, Asplenia

Asplenia

Asplenia refers to the absence of normal spleen function and is associated with some serious infection risks. Hyposplenism is used to describe reduced splenic functioning, but not as severely affected as with asplenism.-Congenital:...

, Liver Disease

Liver disease

Liver disease is a broad term describing any single number of diseases affecting the liver.-Diseases:* Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons , autoimmunity or hereditary conditions...

, Thalassemia

Thalassemia

Thalassemia is an inherited autosomal recessive blood disease that originated in the Mediterranean region. In thalassemia the genetic defect, which could be either mutation or deletion, results in reduced rate of synthesis or no synthesis of one of the globin chains that make up hemoglobin...

 and severe Iron deficiency anemia

Iron deficiency anemia

Iron-deficiency anemia is a common anemia that occurs when iron loss occurs, and/or the dietary intake or absorption of iron is insufficient...

. 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.

Immunology

In immunology

Immunology

Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders ; the...

, target cells are cells which present the antigenic peptide

Antigen

An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

 combined with MHC class I

MHC class I

MHC class I molecules are one of two primary classes of major histocompatibility complex molecules and are found on every nucleated cell of the body...

 molecules to Cytotoxic T cell

Cytotoxic T cell

A cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or...

s. These cells have MHC molecules on their surface (in contrast to Antigen Presenting Cells, which in addition also have MHC class II

MHC class II

MHC Class II molecules are found only on a few specialized cell types, including macrophages, dendritic cells and B cells, all of which are professional antigen-presenting cells ....

 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.

Endocrinology

In endocrinology

Endocrinology

Endocrinology is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions called hormones, the integration of developmental events such as proliferation, growth, and differentiation and the coordination of...

, target cells can refer to the cells where hormone

Hormone

A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s have their effect. Target cells are capable of responding to hormones because they bear receptors

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

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:

1. Endocrine action: the hormone is distributed in blood and binds to distant target cells.
2. Paracrine action: the hormone acts locally by diffusing from its source to target cells in the neighborhood.
3. Autocrine action: the hormone acts on the same cell that produced it.