User:Immcarle78/sandbox

Article Evaluation of "CD69"
The article appears to be neutral in tone, and the content is relevant to the subject. All of the links work and appear to be connected to fairly reliable sources. However, this article is incredibly short and could definitely be expanded. There is a fairly extended "Further Reading" section, but few of these sources are actually cited in the article. The only one that is cited is from 1992, which leaves ample room to add updated information. There is no conversation occurring on the Talk page, and the article is currently rated as a "Stub".

To understand this article and contribute to it, I will need to start by learning more about T lymphocytes and Natural Killer cells as well as their receptors, lymphoid activation, and downstream signaling (that may result in proliferation). This article needs a lot of work, but I think that I will be able to contribute more information to it after doing some survey research.

Bibliography for "CD69"
Here are five sources that I plan to use when adding material to my article:

Cibrián, D., and Sánchez-Madrid, F. (2017). CD69: from activation marker to metabolic gatekeeper. European Journal of Immunology 47, 946-953.

Cyster, J.G., and Schwab, S.R. (2012). Sphingosine-1-Phosphate and Lymphocyte Egress from Lymphoid Organs. In Annual Review of Immunology, Vol 30, W.E. Paul, ed. (Palo Alto: Annual Reviews), pp. 69-94.

Hanazawa, A., Lohning, M., Radbruch, A., and Tokoyoda, K. (2013). CD49b/CD69-Dependent Generation of Resting T Helper Cell Memory. Frontiers in immunology 4, 183.

Kimura, M.Y., Hayashizaki, K., Tokoyoda, K., Takamura, S., Motohashi, S., and Nakayama, T. (2017). Crucial role for CD69 in allergic inflammatory responses: CD69-Myl9 system in the pathogenesis of airway inflammation. Immunol Rev 278, 87-100.

Radulovic, K., and Niess, J.H. (2015). CD69 is the crucial regulator of intestinal inflammation: a new target molecule for IBD treatment? Journal of immunology research 2015, 497056.

Although these sources cover a wide range of topics, preliminary reading has helped me choose a few specific sections that I want to add to the page. For example, I plan to write sections on CD69 structure and function, CD69's role in activation of an inflammatory response, CD69 and memory T helper cell differentiation, and CD69's role in promoting lymphocyte retention in secondary lymphoid organs. Some of these sections might change in the future, but this is my plan for the moment.

CD69 Structure and Ligands
The gene encoding CD69 is located in the NK gene complex on chromosome 6 and chromosome 12 in mice and humans respectively. Activation signaling pathways in lymphocytes, NK cells, dendritic cells and other cell types upregulate transcription factors, such as NF-κB, ERG-1 (erythroblast transformation-specific related gene-1), and AP-1 (activator protein), in order to promote the transcription of the CD69 gene. The CD69 protein is subject to post-translational modifications. Namely, it is differentially glycosylated to produce either a 28 kDA peptide or a 32 kDa peptide. Two of these peptides randomly combine to form a homodimer linked by a disulfide bond. These subunits have a C-type lectin domain (CTLD) that binds ligands, a transmembrane domain, and a cytoplasmic tail that relays signals to the cell interior.

CD69 lacks the characteristic Ca2+ binding residues in CTLDs, indicating that it might bind to proteins rather than carbohydrates, the usual ligand of CTLDs. It has been shown that CD69 binds to Gal-1, a carbohydrate binding protein located on some dendritic cells and macrophages, in addition to Myl9/12. Other ligands have yet to be identified. However, it is known that binding of the ligands initiates the Jak/Stat signaling pathway as well as the mTOR/HIF1-α pathway. CD69 is also known to interact with and mediate S1P and LAT1 receptors, which influence lymphocyte egress in lymphoid organs among other responses. More work must be done to fully characterize CD69-ligand interactions as well as CD69’s method of transducing intracellular signals.

CD69 and T cell Differentiation
CD69 expression has been associated with both regulatory T cell (Treg) and memory T cell precursors. Treg precursors exit the thymus expressing CD69 and complete differentiation into Treg cells in peripheral tissues when they encounter antigens and other cytokines, like IL-2. Through the JAK/STAT signaling pathway, CD69 activation also induces the production of TGF-β as well as IL-2, which contribute to the differentiation of Treg cells as mentioned above. CD69 is also known to be upregulated by NF-κB signaling at the onset of an immune response. A prolonged immune response is then maintained by the non-canonical NF-κB pathway, which in turn is associated with Treg differentiation.

In addition to Treg differentiation, CD69 is a common marker of precursor and mature resident memory T cells (TRM) that are localized in peripheral tissues. TGF-β is also responsible for the development of TRM, thus promoting TRM  differentiation in a manner similar to Treg differentiation.

CD69 and Lymphocyte Egress
Most lymphocytes express sphingosine-1-phosphate receptors (S1P1-5), which G-coupled protein receptors located in the cell membrane that bind to the ligand sphingosine-1-phosphate (S1P). S1P is a sphingolipid metabolite that is abundant in the bloodstream and, upon binding to S1P1, promotes lymphocyte egress from lymphoid organs so they can travel to affected tissues. However, when a T cell is activated in a lymphoid organ through cytokine and TCR signaling, CD69 is expressed and forms a complex with S1P1 (not S1P3 or S1P5). This interaction is dependent on the interaction between the CD69 transmembrane domain and helix-4 of S1P1. Following formation of this complex, S1P1 is internalized and is destroyed within the cell, inhibiting its ability to bind S1P and initiate downstream signaling. This in turn results in temporary lymphocyte retention in the lymph organs. It is thought that retention of lymphocytes in the lymph nodes may increase the chance of successful lymphocyte activation, especially if the initial activation signal was weak. Similarly, CD69 expressed in thymocytes following positive selection may ensure that T cells fully mature in the thymus prior to entering circulation.

Some research has shown that S1P1 and CD69 co-regulate so that when CD69 is in greater abundance, it results in the removal of S1P1 from the membrane as mentioned above. However, if S1P1 is more abundant than CD69, as would be the case in mature T cells, CD69 membrane localization is reduced. In this manner, regulation of CD69 and S1P1 expression and localization impacts lymphocyte egress and migration.