CD34

Hematopoietic progenitor cell antigen CD34 also known as CD34 antigen is a is_associated_with::protein that in humans is encoded by the CD34 gene.

CD34 is a is_associated_with::cluster of differentiation in a cell surface is_associated_with::glycoprotein and functions as a cell-cell is_associated_with::adhesion factor. It may also mediate the attachment of is_associated_with::stem cells to is_associated_with::bone marrow extracellular matrix or directly to is_associated_with::stromal cells.

Function
The CD34 protein is a member of a family of single-pass transmembrane sialomucin proteins that show expression on early is_associated_with::hematopoietic and vascular-associated tissue. However, little is known about its exact function.

CD34 is also an important adhesion molecule and is required for is_associated_with::T cells to enter is_associated_with::lymph nodes. It is expressed on lymph node endothelia, whereas the is_associated_with::L-selectin to which it binds is on the T cell. Conversely, under other circumstances CD34 has been shown to act as molecular "Teflon" and block mast cell, eosinophil and dendritic cell precursor adhesion, and to facilitate opening of vascular lumens. Finally, recent data suggest CD34 may also play a more selective role in chemokine-dependent migration of eosinophils and dendritic cell precursors. Regardless of its mode of action, under all circumstances CD34, and its relatives podocalyxin and endoglycan, facilitates cell migration.

Tissue distribution
Cells expressing CD34 (CD34+ cell) are normally found in the is_associated_with::umbilical cord and is_associated_with::bone marrow as hematopoietic cells, a subset of is_associated_with::mesenchymal stem cells, is_associated_with::endothelial progenitor cells, is_associated_with::endothelial cells of blood vessels but not is_associated_with::lymphatics (except pleural lymphatics), is_associated_with::mast cells, a sub-population is_associated_with::dendritic cells (which are is_associated_with::factor XIIIa-negative) in the interstitium and around the adnexa of is_associated_with::dermis of skin, as well as cells in soft tissue tumors like DFSP, GIST, SFT, HPC, and to some degree in MPNSTs, etc. The presence of CD34 on non-hematopoietic cells in various tissues has been linked to progenitor and adult stem cell phenotypes. It is important to mention that Long-Term Hematopoietic Stem Cells [LT-HSCs] in mice and humans are the hematopoietic cells with the greatest self-renewal capacity. Human HSCs express CD34 marker but mice HSCs do not express CD34 marker. [needs source]

Clinical applications
CD34+ cells may be isolated from is_associated_with::blood samples using immunomagnetic or immunofluorescent methods.

Antibodies are used to quantify and purify is_associated_with::hematopoietic is_associated_with::progenitor stem cells for research and for clinical bone marrow transplantation. However, counting CD34+ mononuclear cells may overestimate is_associated_with::myeloid blasts in bone marrow smears due to is_associated_with::hematogones (B lymphocyte precursors) and CD34+ is_associated_with::megakaryocytes.

Cells observed as CD34+ and CD38- are of an undifferentiated, primitive form; i.e., they are is_associated_with::multipotential hemopoietic stem cells. Thus, because of their CD34+ expression, such undifferentiated cells can be sorted out.

In tumors, CD34 is found in is_associated_with::alveolar soft part sarcoma, is_associated_with::preB-ALL (positive in 75%), AML (40%), is_associated_with::AML-M7 (most), is_associated_with::dermatofibrosarcoma protuberans, gastrointestinal is_associated_with::stromal tumors, is_associated_with::giant cell fibroblastoma, is_associated_with::granulocytic sarcoma, is_associated_with::Kaposi’s sarcoma, is_associated_with::liposarcoma, is_associated_with::malignant fibrous histiocytoma, malignant peripheral nerve sheath tumors, mengingeal is_associated_with::hemangiopericytomas, is_associated_with::meningiomas, is_associated_with::neurofibromas, is_associated_with::schwannomas, and is_associated_with::papillary thyroid carcinoma.

A negative CD34 may exclude is_associated_with::Ewing's sarcoma/PNET, is_associated_with::myofibrosarcoma of the breast, and is_associated_with::inflammatory myofibroblastic tumors of the stomach.

Injection of CD34+ is_associated_with::hematopoietic Stem Cells has been clinically applied to treat various diseases including Spinal Cord Injury, Liver Cirrhosis and Peripheral Vascular disease. Research has shown that CD34+ cells are relatively more in men than in women in the reproductive age among Spinal Cord Injury victims.

Interactions
CD34 has been shown to interact with is_associated_with::CRKL. It also interacts with is_associated_with::L-selectin, important in is_associated_with::inflammation.