B-lymphocyte antigen CD19 also known as CD19 (Cluster of Differentiation 19), is a protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the CD19 gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...



Lymphocytes proliferate and differentiate in response to various concentrations of different antigens. The ability of the B cell
B cell
B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

 to respond in a specific, yet sensitive manner to the various antigens is achieved with the use of low-affinity antigen receptors. This gene encodes a cell surface molecule that assembles with the antigen receptor of B lymphocytes in order to decrease the threshold for antigen receptor-dependent stimulation.

CD19 is expressed on follicular dendritic cells
Follicular dendritic cells
Follicular dendritic cells are cells of the immune system found in lymph follicles of secondary lymphoid organs and tertiary lymphoid organs. They are probably not of hematopoietic origin, though they look similar to true dendritic cells due to their filiform dendritic processes, but are of...

 and B cells. In fact, it is present on B cells from earliest recognizable B-lineage cells during development to B-cell blasts but is lost on maturation to plasma cells. It primarily acts as a B cell co-receptor in conjunction with CD21 and CD81
CD81 molecule, also known as CD81 , is a protein which in humans is encoded by the CD81 gene...

. Upon activation, the cytoplasmic tail of CD19 becomes phosphorylated, which leads to binding by Src
Src may refer to:* Src , a family of proto-oncogenic tyrosine kinases* In computer programming, a common abbreviation for source codeSee also*SRC...

-family kinases and recruitment of PI-3 kinase.

As on T cells, several surface molecules form the antigen receptor and form a complex on B lymphocytes. The (almost) B cell-specific CD19 phosphoglycoprotein is one of these molecules. The others are CD21 and CD81. These surface immunoglobulin (sIg)-associated molecules facilitate signal transduction. On living B cells, anti-immunoglobulin antibody mimicking exogenous antigen causes CD19 to bind to sIg and internalize with it. The reverse process has not been demonstrated, suggesting that formation of this receptor complex is antigen-induced. This molecular association has been confirmed by chemical studies. Mutations in CD19 are associated with severe immunodeficiency syndromes characterized by diminished antibody production.


CD19 has been shown to interact
Protein-protein interaction
Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

  • CD81
    CD81 molecule, also known as CD81 , is a protein which in humans is encoded by the CD81 gene...

  • CD82
    CD82 (gene)
    CD82 is a human protein encoded by the gene.-Interactions:CD82 has been shown to interact with CD19, CD63 and CD234-External links:...

  • Complement receptor 2, and
  • VAV2
    Guanine nucleotide exchange factor VAV2 is a protein that in humans is encoded by the VAV2 gene.-Interactions:VAV2 has been shown to interact with CD19 and Grb2.-Further reading:...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.