target cell

Examples of target cell in the following topics:

• Target Cell Specificity

  • Hormones target a limited number of cells (based on the presence of a specific receptor) as they circulate in the bloodstream.
  • An XY fetus will develop along a female pathway if the target cells fail to respond to androgen.
  • In endocrinology, target cells can refer to the cells where hormones have an effect.
  • Target cells are capable of responding to hormones because they display receptors to which the circulating hormone can bind.
  • Modulation of these factors can control target cell response.

• Mechanisms of Hormone Action

  • A hormone is a chemical messenger that enables communication between cells.
  • The hormones then diffuse to the bloodstream via capillaries and are transported to the target cells through the circulatory system.
  • Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins).
  • The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production.
  • Transport of the hormone to the target cells, tissues, or organs.

• Interactions of Hormones at Target Cells

  • In biology, permissiveness is a certain relationship between hormones and the target cell.
  • It can be used to describe situations in which the presence of one hormone, at a certain concentration, is required to allow a second hormone to fully affect the target cell.
  • For example, thyroid hormones increase the number of receptors available for epinephrine at the latter's target cell, thereby increasing epinephrine's effect at that cell.
  • Bundles of cells in the pancreas, called the islets of Langerhans, contain two kinds of cells: alpha cells and beta cells.
  • Differentiate among the interactions (permissiveness, antagonism, and synergy) of hormones at target cells

• Hormone Receptors

  • Hormones activate a cellular response in the target cell by binding to a specific receptor in the target cell.
  • Upon hormone binding, the receptor can initiate multiple signaling pathways that ultimately lead to changes in the behavior of the target cells.
  • The hormone activity within a target cell is dependent on the effective concentration of hormone-receptor complexes that are formed.
  • These molecules are not lipid-soluble and therefore cannot diffuse through cell membranes.
  • The receptors for these hormones need to be localized to the cells' plasma membranes.

• Comparing the Nervous and Endocrine Systems

  • The nervous system responds rapidly to stimuli by sending electrical action potentials along neurons, which in turn transmit these action potentials to their target cells using neurotransmitters, the chemical messenger of the nervous system.
  • The endocrine system relies on hormones to elicit responses from target cells.
  • Upon reaching their target, hormones can induce cellular responses at a protein or genetic level.
  • This process takes significantly longer than that of the nervous system, as endocrine hormones must first be synthesized, transported to their target cell, and enter or signal the cell.
  • Additionally, the target cells can respond to minute quantities of hormones and are sensitive to subtle changes in hormone concentration.

• Monoclonal Antibodies

  • Monoclonal antibodies (mAb or moAb) are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell.
  • Monoclonal antibody therapy is the use of monoclonal antibodies (or mAb) to specifically bind to target cells or proteins.
  • It is possible to create a mAb specific to almost any extracellular/ cell surface target, and thus there is a large amount of research and development currently being undertaken to create monoclonals for numerous serious diseases (such as rheumatoid arthritis, multiple sclerosis, and different types of cancers).
  • For example, mAb therapy can be used to destroy malignant tumor cells and prevent tumor growth by blocking specific cell receptors.
  • Variations also exist within this treatment, such as radioimmunotherapy, where a radioactive dose localizes on a target cell line, delivering lethal chemical doses to the target.

• Natural Killer Cells

  • Natural killer cells (NK cells) are cytotoxic lymphocyte critical to the innate immune system.
  • The role of NK cells is similar to that of cytotoxic T cells in the adaptive immune response.
  • NK cells provide rapid responses to virally infected cells and respond to tumor formation by destroying abnormal and infected cells.
  • Unlike phagocytes, NK cells do not need their targets to be opsonized (marked) by antibodies before they can act allowing for a much faster immune reaction, however opsonins do speed up the process.
  • Upon binding to a cell slated for killing, perforin forms pores in the cell membrane of the target cell, creating an aqueous channel through which the granzymes and associated molecules can enter, inducing either apoptosis or osmotic cell lysis, which is a form of cell necrosis.

• Specific T-Cell Roles

  • T helper cells assist the maturation of B cells and memory B cells while activating cytotoxic T cells and macrophages.
  • Differentiation into helper T cell subtypes occurs during clonal selection following T cell activation of naive T cells.
  • They recognize their targets by binding to antigen associated with MHC class I, which is present on the surface of nearly every cell of the body.
  • The cytotoxic enzymes and proteases travel to their target cell through a microtubule cytoskeleton.
  • Memory T cells comprise two subtypes: central memory T cells (TCM cells) and effector memory T cells (TEM cells), which have different properties and release different cytokines.

• Antigen-Presenting Cells

  • Antigen presentation is a process where immune cells capture antigens and then enable their recognition by T-cells.
  • Dendritic cells, B cells and macrophages play a major role in the innate response, also acting as professional antigen-presenting cells (APC).
  • Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.
  • Cytotoxic T cells (also known as TC, killer T cell, or cytotoxic T-lymphocyte (CTL)) are a population of T cells that are specialized for inducing the death of other cells.
  • Recognition of antigenic peptides through Class I by CTLs leads to the killing of the target cell, which is infected by virus, intracytoplasmic bacterium, or are otherwise damaged or dysfunctional.

• Desmosomes

  • A desmosome is a type of cell junction that attaches to keratin in the cytoplasm and is a localized structure adjoining two cells.
  • A desmosome , also known as macula adherens, is a type of cell junction that attaches to filaments of keratin in the cytoplasm and is characterized by a localized patch that holds two cells tightly together.
  • The cell adhesion proteins of the desmosome - desmoglein and desmocollin - are members of the cadherin family of cell adhesion molecules.
  • Blistering diseases such as Pemphigus vulgaris and Pemphigus foliaceus are autoimmune diseases in which auto-antibodies target the desmoglein proteins.
  • A desmosome, also known as macula adherens (Latin: adhering spot), is a cell structure specialized for cell-to-cell adhesion in animal cells.