CD Markers

Author: Nat Pernick, M.D. (see Authors page)

Revised: 25 July 2018, last major update August 2013

Copyright: (c) 2002-2018,, Inc.

PubMed Search: CD9[title]

Cite this page: Pernick, N. CD9. website. Accessed October 16th, 2018.
Definition / general
  • Member of transmembrane 4 superfamily (tetraspanin family); tetraspanins have 4 hydrophobic domains, organize multimolecular complexes in plasma membrane; each tetraspanin associates specifically with integrins and other tetraspanins, forming primary complexes and leading to molecular network of interactions, the "tetraspanin web"
  • Regulates cell motility, development, activation, growth and adhesion (Blood 2011;117:1840), differentiation (OMIM #143030), fertilization (oocyte CD9 is required for sperm-egg fusion)
  • Regulates paranodal junction formation (between neurons and glia)
  • Required for microparticle release from coated-platelets (Platelets 2009;20:361); triggers platelet activation and aggregation
  • Supports myotube maintenance and promotes muscle cell fusion
  • Downregulation in ovarian carcinoma may promote tumor dissemination (Cancer Res 2005;65:2617)
  • May suppress metastasis in small cell lung cancer by promoting apoptosis via calretinin expression (Cancer Res 2010;70:8025, FEBS Open Bio 2013;3:225)
  • May mediate invasion by upregulating MMP9 (PLoS One 2013;8:e67766)
Clinical features
Diagrams / tables

Image hosted on other servers:


Uses by pathologists
  • No significant clinical use by pathologists
Microscopic (histologic) images

Images hosted on other servers:

Normal tissue:


Cervical squamous epithelium (fig A)

Various tumors:

Bone marrow: primary myelofibrosis (fig E)

Cervical carcinoma

CNS nonneuroepithelial tumors

well differentiated


Skin: basal and
squamous cell
carcinoma and
actinic keratosis

Small cell lung cancer

Spleen: extramedullary hematopoiesis

Positive staining - normal
  • Pre B cells, B cell subset, activated T cells, basophils, eosinophils (Am J Respir Cell Mol Biol 2012;46:188), macrophages, megakaryocytes, plasma cells, plasma cell precursors in germinal centers (Biochem Biophys Res Commun 2013;431:41), platelets
  • Brain, cardiac muscle, GI system, kidney (glomeruli, tubules and collective ducts), liver, lymphatic epithelium, ovarian surface epithelium, peripheral nerve, skin, spleen, thyroid, tonsil
Positive staining - disease
Negative staining
  • Red blood cells, renal collecting duct carcinomas (almost all)