targetcell

Target cell is a term used in biology to describe a cell that can be affected by a particular agent or process. It is used across disciplines such as virology, immunology, hematology, and pharmacology to denote cells that possess the necessary features—typically receptors or signaling machinery—to respond to a given stimulus or to be infected by a pathogen. The concept helps explain tissue and cell-type specificity, or tropism, in both normal physiology and disease.

In virology and immunology, a target cell is defined by its susceptibility to a virus or immune effector based on receptor expression. For example, HIV targets CD4-expressing cells and, depending on coreceptor usage, can infect subsets of T cells, macrophages, and dendritic cells. Other viruses, such as hepatitis C virus, preferentially infect hepatocytes through specific entry proteins. Hormones, cytokines, and other signaling molecules likewise act on target cells that display the appropriate receptors, with responsiveness governed by receptor density, affinity, and intracellular signaling pathways.

In hematology, target cells (codocytes) refer to red blood cells with a bullseye appearance on microscopic examination. This morphology arises from an altered surface-area-to-volume ratio and membrane characteristics and is commonly associated with liver disease and certain hemoglobinopathies, such as thalassemia, among other conditions.

In research and clinical practice, the term may also describe cells selected for study or those that are the intended readouts in an assay, depending on the question and context.