Name: Jeffrey Eldrige  |  [from] "CCL19 Expression Quantification Assay"

Chemokine Ligand 19 is designated “2MP1” by the Worldwide Protein Data Bank. 2MP1 (commonly CCL19) is a signaling protein, key to immunological responses of lymphoid and thymic tissues. Chemokine Ligand #19 is also key to a broad class of (both) acute and chronic inflammatory processes (Gowhari Shabgah A, 2022), especially those involving lymphatic and gastrointestinal systems. Consequently, 2MP1 is associated with chronic human illnesses (including psoriasis and cancers), especially due to its involvement with immunological responses in lymphoid and vascular tissues.

The nomenclature surrounding the so-called “C-C motif” proteins (CCL19 being one) is a reference to the arrangement of their amino acid backbones, all of which have a pair of cysteine residues at their centers. Cysteine-Cysteine disulfide bridge formation is fundamental to molecular infrastructure, across the human proteome. (Wiedemann, et al., 2020) This makes the “C-C motif” proteins a particularly well-stabilized subfamily of Cytokines.

The chemokine family of biomolecules are chemotactic cytokines, meaning these are plenipotentiary secretions of immune cells; modulating, activating, and transporting immune responses. Cytokines are the surveilling praxis of chemical-induced signaling in all lymphoid organs, especially in synthesis and transport of T-Cells. Found most frequently in filament regions between related but separable organs, chemokines are dispersed throughout the layers and epithelial networks of major tissue systems; in the thymus, for instance, and also the central and peripheral nervous systems. (ELIXIR Core Data Resources, 2022) Cytokines bind to the surface of specific receptors imbedded in such connective regions, in order to secrete signals that direct subsequent transcription in processes downstream.

Human protein 2MP1 is present in epithelial networks throughout the body, making it a primary signal origin for T and B cells in a great diversity of inflammatory, reparative, and clearance processes. 2MP1 is also highly expressed in Peyer’s Patches, (Swiss Institute of Bioinformatics (SIB), 2022) the branching surveillance nodes dispersed throughout the ileum, at the base of the small intestine.

Between its high endotheleal expression and its prominence in the appendix, 2MP1 brackets the large intestine and the cecum (Swiss Institute of Bioinformatics (SIB), 2022); the cecum being a marginal structure that transports expelled salts and other waste out of the ileum. But CCL19’s modulatory importance may be further elucidated by the fact that the ileum is the primary source of B12 for neurological systems, in humans. (Bielecki B, 2015)

Not surprisingly, Chemokine Ligand #19 has a moderately-high degree of expression in neural tissues; especially the Central Nervous System (CNS), having been identified in both the cranial nerve tract (Cranial Nerve II) (Swiss Institute of Bioinformatics (SIB), 2022) and in the optic nerve itself (Wang T, 2021). 2MP1 is also prominent in the retina’s pigmentation layer (Swiss Institute of Bioinformatics (SIB), 2022), functioning as one element in the responsive transfer medium of optical data between the retina and the brain.

Further, 2MP1 expression is suffusive beneath the dermal layer, secreted (in particular) by follicular fibroblasts, directing replicative skin repair. (Topouzi & Higgins, 2020) 2MP1 fulfills a similar function in the respiratory system, (Rangel-Moreno, 2007) where it is intimately involved in Bronchus Associated Lymphoid [clearance] Tissues (iBALT). (Hwang, 2016)

2MP1 is also the indispensable secretory element of Follicle Associated Epithelium (FAE) cells in mucosal tissues throughout the gastrointestinal organs. (Noah P. Zimmerman, 2008) Recent research suggests mucosal surfaces of intestinal lymph nodes may be the primary source of the immune system in humans. (Smith, 2006) This hypothesis, along with this ligand’s aforementioned prominence for neurotaxis in the CNS indicates C-C motif Ligand #19 (CCL19, hereafter) as a key target in the emerging field of Neuro-Immune Physiology. (Yan, 2021)

CCL19 is the internalization ligand of its receptor, CCR7, (Haessler, 2011) with a strong affinity towards desensitization mechanisms in immune responses. This proficiency in affecting internalization (inside damaged tissues), unique to CCL19, is highly-attenuated; providing a viable explanation for CCR7’s importance in virion-clearance tissues in the major organ systems (gastrointestinal and respiratory). Most recently, the CCR7:CCL19 axis has been shown to be the major inductive signal leading to iBALT formation. (Nancy D. Marin, 2019)

A core function for CCL19 is modulation between innate and adaptive leukocyte function, (Yan, 2021) a process affected by the protein’s complexing with dendritic cells (DCs) specific to given immunological conditions. CCL19 stimulation induces presentation of these CCR7-bearing antigens (DCs) on the surface developed by the complex; (Wenxiang Hong, 2022) ultimately transferred to the primary T-Cells the CCL19:CCR7 complex activates. Innate leukocytes are more readily activated than adaptive leukocytes because adaptive leukocytes are not already part of the thymic memory, stored in the lymph nodes. CCL19’s high level of expression in the thymus means it also has a quasi-regulatory role in determining how human immunity archives and updates itself.

These identified functions of CCL19 exemplify the signaling activities unique to this pivotal ligand. 2MP1 is expressed most prominently in the thymus and in the lymphatic/lymphoid organs, as well as the gastrointestinal systems, and is less prominently expressed in the small intestine. (ELIXIR Core Data Resources, 2022) With its receptor CCR7, 2MP1 is essential in modulation, activation, and re/circulation of T and B lymphocytes, granulocytes, and all leukocyte forms between the lymphoid organs and between layers of tissue

HYDROPHOBICITY and BINDING PATTERNS in CCL19  

The hydrophobic properties of a protein provide a vital map of the protein’s compositional and functional natures. In genetic engineering, drug design, and in planning biochemical assays, understanding the target protein’s interaction with water (& with its own polar surfaces) is necessary to accurately predicting a compound’s binding patterns, and to understanding the relevant chemoattractant behavior/s more broadly. These properties are vital data points in planning mutations, as well as for other direct structural reformation of a protein.

However, the specific charge state is not necessarily at issue, in this analysis. Water excludes all nonpolar entities, while engaging chemically with the polar (that is, hydrophillic) and sometimes “charged” (+/-) regions. For most proteins, as for the negatively-charged membranes of eukaryotic cells, this means the polar or “hydrophilic” regions will be oriented outward, facilitating the interaction with water; while the carbon-dominated hydrophobic regions will be oriented inward. Several mechanistic reasons for this dynamic are well-known. Namely, negotiation of water molecules' unfavorable "cage structure" (first) and second, utilization of the other effects of intermolecular Hydrogen bonding remain the most prominent, ubiquitous, examples of these mechanisms.

However, one imperative aspect of a protein’s structure is its three-dimensional arrangement, also referred to as its “fold.” The fold of a protein may be thought of as a contoured “plane” of reactivity, fundamental to the protein’s ability to vary its polarity across its charged surface—necessary in order to interact with its substrate, and binding to it in efficiently-specific ways. Not only water, but also receptors, immune cells, heme, and other essential biochemical components–all of which water conveys.

The “fold” of a protein clusters and partitions its polar surface so as to engineer a point of entry, or binding region, for the additional proteins (or, in the case of CCL19, its receptor) with which it must interact. Thus, polar regions of its surface (sometimes involving negatively-charged sub-regions) are interspersed in such a way as to keep part of the protein’s hydrophobic interior “exposed.” This frequently facilitates ionic binding at +/- ends of the protein’s target (polar) substrate, essentially aligning the active site of the substrate with the protein’s non-polar core.

Typically, this “fissure” of hydrophobicity takes shape in one particular area of a surface, but these regions may traverse much of the protein’s circumference—or there may be several binding regions a protein develops across its surface. Singular or not, these “fissures” of nonpolarity take shape at surface positions that are physically and geometrically (that is, energetically) advantageous for the function/s said protein will undertake.

Researchers have developed several ways of mapping hydrophobicity. I use the YRB method (Yellow Red Blue), as this approach is well known for its accuracy in delineating between charged and un-charged regions. The other major system is the Eisenberg system, which uses a 2-color gradient—between Red (Hydrophobic) and White (Polar). However, this approach provides an incomplete picture, and many negatively-charged chain termini (functionally hydrophobic in their interaction with the surface contours of the protein) are inevitably identified as simply “polar.”

Since the YRB system distinguishes between +/- polarity, a more accurate map may be determined. A YRB analysis presumes physiological pH and depicts hydrophobic surface regions in gradations of Gold/Yellow. A good molecular characterization of hydrophobicity is any region within an amino acid domain dominated by Hydrocarbon (H-C) bonds, folded so as to be separate from clusters of Nitrogen (Amine), Oxygen (Alcohol), or any of the major (+/-) polar groups. This includes any of the particular side chains to which a given “apolar” (H-C) sequence may remain bound. (Eisenhaber F, 1996)

The polar surface regions, then, are defined in a YRB map using a 3 color key. Negatively charged groups (especially where Carbon is bound to Oxygen) are depicted in Red. Positively-charged groups (especially the Nitrogen-termini) are depicted in Blue.

Across the whole class of (known) proteins, it’s important to recognize several major amino groups that frequently recur in formation of these hotspots of hydrophobic interface. Specifically, Isoleucine, Valine, Leucine, Cysteine, and Phenylalanine are major contributors to hydrophobic surface states, in proteins. (Pommié, 2004) However, recent studies of folding behaviors in protein structure indicate the picture is significantly more complex. (Chongqin Zhu, 2016)

The “C-C” aspect of the nomenclature for CCL19’s family of chemokines is a reference to the pair of cysteine residues near their centers, which all “C-C motif” chemokines have. Cysteine itself is strongly hydrophobic, as previously indicated. Further, Cysteine-Cysteine disulfide bridge formation is fundamental to molecular infrastructure, across the human proteome. The importance of this structural pattern stems from the C-C bond (between the deprotonated sulfur sidechains) being uniquely stable. (Wiedemann, et al., 2020) This aspect of stability provides one explanation for CCL19’s prominence as a “recruiter” in many essential biological systems, especially in the directed transport of leukocytes. In CCL19, the disulfide bridge occurs at positions 29-30.

Cytokines bind to the surface of specific receptors imbedded in a great variety of human tissues (especially vascular and intermediary tissues). Their major function is regulation of innate immunity throughout the body. (TILO ANDUS, 1991) All Cytokine receptors are glycoproteins generally found on the membranes of cells that express them. (Holdsworth SR, 2015)

In particular, CCL19 develops 2 major binding regions across its surface. The first occupies positions 8 through 22 (with a minor gap at position 16). The second begins at position 36 and extends (roughly) to position 51 (with a minor gap around position 43). A 3^rd (minor) area of hydrophobic behavior is identifiable along the counterside of the protein, from approximately the 56th position through position 65 (again with minor gaps).

In CCL19’s 1st major binding region (positions 8-22) Cysteine, Isoleucine, and Valine are major contributors. In the 2^nd region  (36-51), Arginine, Leucine, and Threonine are all recurrent components, with the largest single contributor being Valine (at 3 positions throughout the indicated region). The two regions follow a roughly contiguous but curving trajectory. Along the underside of this curve (positions 56-65), the major amino groups comprising the minor fissure are Arginine, Valine, and Isoleucine, all 3 with at least 2 positions along the indicated trajectory.

QUANTIFYING CCL19 EXPRESSION in DYSREGULATED TISSUES

It had long been postulated that of the two ligands responsible for modulating Human Chemokine Receptor #7 (CCR7), CCL19 seems less aggressive in its activation of the receptor. CCR7 focalizes the body’s immune attacks in the lymphoid and vascular tissues, and the CCL21:CCR7 gradient out of the endothelial cells has been observed to transport more activated T-Cells during immune events, and at a faster rate. (Swartz, M. etc al., 2011)

It has also been noted that CCL21 activation of the receptor spans a greater diversity of tissues, (Hwang, 2018) at least superficially—and independent of the particular regulatory activities the CCR7:CCL21 axis may be inducing via chemotaxis to, from, and within those tissues.

In short, it’s worth noting that CCL21-activation may be more readily “available” to CCR7; (Hwang, A guide to chemokines and their receptors, 2018) complicating the exact mechanism by which CCR7 becomes instrumental in cancer metastasis, in particular.

For this reason, it’s also important to recognize the difference between CCL19 and CCL21 binding of their primary receptor (CCR7). Both ligands are known to have similar binding affinities with CCR7; but structural features of CCL21 give it a significant positively-charged tail, making it ubiquitous in long-range chemotaxis between matrix-bound signals. (Gertrud M. Hjortø†‡, 2016) The best summation of this difference in structure is that CCL19 incorporates the immune cell expressing CCR7 into the interior of dysregulation sites, whereas CCL21 activation is more likely to bind the receptor to proteoglycans in the Extracellular Matrix on the cell surface. (Haessler, 2011)

In other words, CCL21 attaches CCR7 to cell membranes, and moves CCR7 (sometimes) great distances, between membranes—whether in the presence of dysregulation (cancerous proliferation) or not. CCL21 also has a strong signal back to the peripheral lymphatic nodes, implicating it (in the light of recent studies) in a majority of lymphangiogenic metastasis events; (Detmar, 2011) so an argument may be made that many of the associations between CCR7 and the deleterious effects of metastization are due to its interactions with CCL21. Regarding disease progression, Rizeq, B. and Malki (2020) have compiled an excellent overview of CCR7’s emergence as a major target in (breast) cancer research.

RELATEDLY, both CCL21 & CCL19 participate in the gradient back to the lymph nodes, but CCL19 is uniquely-equipped to communicate between different immune populations. Immune cells recognize the CCL19 gradient. In particular, Dendritic Cells make use of CCL19-activated CCR7 in order to cross-regulate between other DCs and T-Cell populations. (Donnell H, et al., 2023) Some studies have suggested Leukocytes’ departure from the lymph nodes is specifically induced by CCL19. (Hansen, M. et al., 2016)

It's clear that CCR7’s differential activation patterns may be more nuanced, however, than may be recognized; especially in terminal disease progression. CCL19 is such a stronger inducer of Dendritic Leukocytes (DCs) than CCL21 (Hansen, M. et al., 2016) that CCL19 actively inhibits DC migration to CCL21 if the signal from CCL21 is “weak,” or not well established. DCs determine the form and trajectory of immune response by delineating between adaptive and innate response formation. (IQWiG, 2020)

CCL19’s fluency with the major classes of innate and adaptive immune cells (DCs, as well as T and B cells) has also been shown to confer greatly-extended immune-mediated antitumor responses when administered as the leading component of gene targeting complexes. (Xiaoxiao Liu, 2019) Further, as previously indicated, CCL19 is highly-expressed under the dermal layer by follicular fibroblasts, positively enhancing wound closure; (Topouzi & Higgins, 2020) and CCL19-expressing fibroblasts are also prominent in the lung carcinoma microenvironment, where CCL19 independently promotes anti-tumorigenic chemotaxis. (Tino Schneider, 2018) Since nearly all tumors bear Fibroblasts, (Dor Lavie, 2022) inducing CCL19 expression in Cancer Associated Fibroblasts (CAFs) is plausibly an untapped opportunity to penetrate the tumor microenvironment (TME).

Many studies suggest that explicit, therapeutic, upregulation of CCL19 may affect positive oncology outcomes in certain forms of cancer. It is a known inhibitor of tumorogenesis in gastric cancer, for instance. Definitively positive action as a result of CCL19 signaling is most typical in soft vascular tissues; like gastrointestinal system and the lungs (as with iBALT formation, previously mentioned). In short, CCL19-centeric therapeutics have shown great potential for significantly restricting and even halting tumor growth.

Recent research has also identified the specific, diseased, activities of CCR7 with mechanisms by which many persistent, terminal infections (especially HIV and cancers) obtain gain-of-[cellular] function. Speaking characteristically, these mechanisms counterfeit irreplaceable immunological components, corrupting CCR7’s functions specifically. (Brandum EP, 2021) One major reason CCR7 may be so prominent in immune dysregulation is that activation of the receptor (including its primary interactions with CCL19 and CCL21) is a critical influence for homing of leukocytes—thereby regulating white blood cell function, in addition to lymphocytic activation. (Hipkin, 2007)

For instance, the CCL19:CCR7 axis (Hwang, 2016) is, as previously indicated, one major target of HIV-1; and infected T-Cells in the early stages of HIV-1 infection similarly deform the CCR7 cell surface. (Hipkin, 2007) This results in downregulation of functional copies of CCR7, making activation by CCL19 instead a dissemination strategy for the disease. So, CCL19 can, therefore, also be hijacked (in the presence of regulatory damage, by tumorigenic disorders), particularly in follicular and breast cancers.

Many of the immunological processes CCL19 facilitates are increasingly shown to be inflammatory in nature. CCL19 frequently initiates acute inflammation processes, which have positive, antimicrobial, functions. However, replication of viral and cancerous tissues also involve inflammation.

Most human cancers, for instance, perpetuate their tumors by coopting the functionality of the so-called “H-9” [stem] cell line so as to deactivate CCR7’s recognition of the tumors as being foreign/virions to be eliminated. This requires the cancer to directly modify CCR7 so that H-9 is able to regulate the receptor in the cancer’s favor. This interaction may, in fact, also be a significant component of both metastasis and post-chemo recurrence.

The transaction also activates H-9 to actually repair, at the molecular level, any previous damage done to tumors. Neither the CCL21 gradient nor its activation functions are affected. And since CCL19 activation tends to integrate solubilize and degrade CCR7, CCL19 can become downregulated in such condition. NONETHELESS, some research indicates that CCL19 is uniquely equipped, in certain scenarios, to untie this twisted knot by which many human cancers metastasize and spread. (Hipkin, 2007)

As indicated, CCL19 is known to “desensitize” its receptor to further modulation by the H-9 line. (Hipkin, W., 2007) The ligand accomplishes this “desensitization” by phosphorylation of CCR7. But phosphorylation is a complicated mechanism.

Both CCL21 and CCL19 phosphorylation of CCR7 has also been implicated in studies of ERK ½ activation. The ERK ½ cascade is a primary driver of tumorigenesis in at least 40% of all human cancers, and it has been shown (Roskoski Jr., 2012) CCL19 regulation directly results in activation of ERK. But in some cancers, CCL21 expression is “four times more potent” than CCL19 in activation of the ERK ½ cascade, (Rizeq and Malki, 2020). Further, this same signaling from CCL19 (phosphorylation of CCR7), when it occurs on a CD4+ cell surface very clearly reduces ERK ½ activation. (Yan, 2019) In fact (relative to metastasis in particular), for CCL19 signaling, “activation” may only be part of the story.

It's important to understand what CCR7 phosphorylation fundamentally achieves: In most circumstances “desensitization” means CCR7 (a cell surface receptor) will allow cell entry, usually internalizing antigens. CCR7 desensitization is, in fact, fundamentally important to innate immunity. CCL19 is (now) known to be alone in its ability to induce internalization. But “internalization” can also mean facilitation of physiological signaling cascades.

Further, the mechanism by which the CCL19-mediated activation of the ERK ½ cascade occurs (binding the Ser/Thr bridge at position 296 on CCR7, (Otero C, 2008)) suggests CCL19 exhibits agonist behavior, as the binding patterns specifically results in upregulation of Arrestin Beta-3 (β3AR). Β3AR effectively disperses the ERK activity by cleavage of a set of tail positions on the CCR7:CCL19 complex. (Otero C. et al., 2006)

Β3AR is an intracellular protein expressed at high levels throughout the central nervous system, (National Library of Medicine, 2022) again indicating CCL19 as an important element in emerging physiologies of Neuro-Immunity.

In circumstances where CCL19’s phosphorylation of its receptor upregulates a (harmful) signaling pathway, the flipside of that activation is that the receptor (ultimately the cell) becomes entirely subject to the action of the relevant pathway. This regulatory outcome may simplify treatment of the relevant dysregulation.

A second major origin of tumor metastasis has recently been identified in upregulation of the so-called PI3K/Akt pathway, which is a proliferation cascade that transpires on dysregulated cell surfaces, (Mo Chen, 2022) presumably via proteoglycan-bonding. The dysregulated interaction results in conditions favorable to activities of phosphatidylinositol-4-phosphate 5-kinase (PIPKI) to activate PI3K/Akt inside the cell.

Though the exact interaction between CCL19 and PIPKI isn’t currently known, it is known that the characteristic outcome of CCL19-activated CCR7’s involvement with PI3K/Akt is upregulation of an entirely different protein: Matrix metalloproteinase-9 (MMP9). (Wei Zhanga, 2017)

MMP9 is known to pathologically degrade cell membranes and to enlist chemokines to repair the damage—it has also been indicated as a driver of metastasis. (Huang, 2018) However, since the primary means of CCR7-instigated cellular repair, related to cancer cells, involves the receptor’s ability to be modified by (cancer-activated) H9 stem cells, and CCL19 activation removes the receptor’s capacity for this interaction, it’s unclear that MMP9 activation under conditions of CCL19 mediation would lead to metastasis.

Particularly considering that the CCL19 gradient towards the peripheral lymph nodes is quite weak compared to CCL21-active conditions.

Localization issues aside, CCL19 is nonetheless alone in its ability to stop its receptor from consuming bad programming.

Part of CCL19’s uniquely-effective activation pattern is its ability to downregulate its own receptor, under specific conditions. And its receptor, CCR7, is increasingly shown to be ubiquitous in terminal disease progression throughout the body.

Taking this and other research into account, it should be taken to be a primary goal of subsequent human oncology to quantify the expression state and specific localization, in patients’ bodies, of the CCL19 chemokine. This immunological promotor is a natural counter to a cancer’s ability to repair its own DNA. So the importance to next stage immunotherapies, of finding ways to recirculate and/or otherwise enhance diseased immune systems via upregulating this frontline barrier to metastasis, should be self-evident.

Quantification of CCL19 concentration in patients’ bodies should be more readily assessed for these reasons. Induced activation of CCL19 pathways, and of CCL19-mediated phosphorylation is an unexplored potential in halting tumorigenesis.

Upregulation of CCL19, or of specific CCL19-mediated pathways, should also be part of vigorous preventative strategies against metastasization & recurrence, for instance.

The assay described here undertakes the quantification of CCL19 expression for these reasons.

Works Cited

Andreas, K. (2014, September). Toward in Situ Tissue Engineering: Chemokine-Guided Stem Cell Recruitment. Trends in Biotechnology, 32(9), 483–492. doi:10.1016/j.tibtech.2014.06.008

Bielecki B, J.-P. I. (2015). Central Nervous System and Peripheral Expression of CCL19, CCL21 and Their Receptor CCR7 in Experimental Model of Multiple Sclerosis. Archivum Immunologiae et Therapiae Experimentalis., 367-76. doi:10.1007/s00005-015-0339-9

Brandum EP, J. A. (2021, August 3). Dendritic Cells and CCR7 Expression: An Important Factor for Autoimmune Diseases, Chronic Inflammation, and Cancer. Journal of Molecular Science. doi:10.3390/ijms22158340

Chongqin Zhu, Y. G. (2016). Characterizing hydrophobicity of amino acid side chains in a protein environment via measuring contact angle of a water nanodroplet on planar peptide network. Proceedings of the National Academy of Sciences, 113(46), 12946-12951. doi:10.1073/pnas.1616138113

Cotterill, S. J. (n.d.). CCL19. Retrieved from Cancer genetics web: http://www.cancerindex.org/geneweb/CCL19.htm

Delano, W. L. (2000). PYMOL. CCL19 (Electric Potential Surface View). Palo Alto, California, United States.

Detmar, A. C. (2011). Lymphangiogenesis and Cancer. Genes Cancer, 2(12), 1146–1158. doi:10.1177/1947601911423028

Dor Lavie, A. B.-S.-S. (2022). Cancer-associated fibroblasts in the single-cell era. Nature Cancer, 3, 793–807. doi:10.1038/s43018-022-00411-z

Eisenhaber F, A. P. (1996, December). Hydrophobic regions on protein surfaces: definition based on hydration shell structure and a quick method for their computation. Protein Engineering, 1121-33. doi:10.1093/protein/9.12.1121

ELIXIR Core Data Resources. (2022). Tissue expression of CCL19 - summary. (The Knut & Alice Wallenberg Foundation) Retrieved from The human protein atlas: https://www.proteinatlas.org/ENSG00000172724-CCL19/tissue

Gertrud M. Hjortø†‡, O. L. (2016). Differential CCR7 Targeting in Dendritic Cells by Three Naturally Occurring CC-Chemokines. Frontiers in Immunology. doi:10.3389/fimmu.2016.00568

Godinho-Silva, C. C.-F. (2019). Neuro–Immune Cell Units: A new paradigm in physiology. Annual Review of Immunology, 37(1), 19–46. Retrieved from https://doi.org/10.1146/annurev-immunol-042718-041812

Gowhari Shabgah A, A.-O. Z. (2022). Does CCL19 act as a double-edged sword in cancer development? Clinical Experimental Immunology, 207(2), 164-175. doi:10.1093/cei/uxab039

Haessler, U. P. (2011). Dendritic cell chemotaxis in 3D under defined chemokine gradients reveals differential response to ligands CCL21 and CCL19. Proceedings of the National Academy of Sciences, 108(14), 5614–5619. doi:https://doi.org/10.1073/pnas.1014920108

Hipkin, W. (2007). CCR7 Chemokine Receptor. In W. Hipkin, & D. B. S.J. Enna (Ed.), Pharm: The Comprehensive Pharmacology Reference (pp. 1-10). Amsterdam, Netherlands: Elsevier. doi:https://doi.org/10.1016/B978-008055232-3.60191-6

Holdsworth SR, G. P. (2015). Cytokines: Names and Numbers You Should Care About. Clinical journal of the American Society of Nephrology, 10(12), 2243–2254. doi:10.2215/CJN.07590714

Huang, H. (2018, October). Matrix Metalloproteinase-9 (MMP-9) as a Cancer Biomarker and MMP-9 Biosensors: Recent Advances. Sensors (Basel), 18(10), 3249. doi:10.3390/s18103249

Hwang Ji Young, R. T.-S. (2016). Inducible Bronchus-Associated Lymphoid Tissue: Taming Inflammation in the Lung. Frontiers in Immunology , 7. doi:10.3389/fimmu.2016.00258

Hwang, J. Y.-S. (2016). Inducible Bronchus-associated lymphoid tissue: Taming inflammation in the lung. Retrieved from Fronteirs In Cell And Developmental Biology: https://www.frontiersin.org/articles/10.3389/fimmu.2016.00258/full#:~:text=Following%20pulmonary%20inflammation%2C%20leukocytes%20that%20infiltrate%20the%20lung,stromal%20cells%2C%20high%20endothelial%20venules%2C%20and%20lymphatic%20vessels

Hwang, J. Y.-S. (2018). A guide to chemokines and their receptors. The FEBS journal. Retrieved from https://pubmed.ncbi.nlm.nih.gov/29637711/

Institute for Quality and Efficiency in Health Care (IQWiG). (2020, July 30). The innate and adaptive immune systems. Retrieved from InformedHealth.org [Internet]: https://www.ncbi.nlm.nih.gov/books/NBK279396/

Jafarnejad, M. Z. (2017). A novel computational model predicts key regulators of chemokine gradient formation in lymph nodes and site-specific roles for CCL19 and ACKR4. Journal of Immunology. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5602158/

Jumper, J. e. (2021). Highly accurate protein structure prediction with AlphaFold. Nature .

Lalor, S. J. ( 2010, July 27). Lymphoid chemokines in the CNS. Journal of neuroimmunology. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2910210/

Lin, F. W. (2022). Combinatorial Guidance by CCR7 Ligands for T Lymphocytes Migration in Co-Existing Chemokine Fields. Retrieved from https://www.researchgate.net/figure/T-cell-migration-in-CCL19-gradients-A-Angular-histograms-show-T-cells-orient_fig3_51000182

Marion Leick, J. C. (2010, April). CCL19 is a specific ligand of the constitutively recycling atypical human chemokine receptor CRAM-B. Immunology, 129(4), 536–546. doi:10.1111/j.1365-2567.2009.03209.x

Mo Chen, S. C. (2022, July). A p53–phosphoinositide signalosome regulates nuclear AKT activation. Nature Cell Biology. doi:10.1038/s41556-022-00949-1

Moser, B. &. (2004, November 1). Chemokines: Role in inflammation and immune surveillance. Annals of the Rheumatic Diseases. Retrieved from https://ard.bmj.com/content/63/suppl_2/ii84

Nancy D. Marin, M. D. (2019, May). Friend or Foe: The Protective and Pathological Roles of Inducible Bronchus-Associated Lymphoid Tissue in Pulmonary Diseases. Journal of Immunology, 2519-2526. doi:10.4049/jimmunol.1801135

National Institute of Health. (2022, May 31). BLAST: Basic Local Alignment Search Tool. Retrieved from NIH.gov: blast.ncbi.nlm.nih.gov/protein/CAG33149.1

National Library of Medicine. (2022). ARRB2 arrestin beta 2 [ Homo sapiens (human) ]. National Center for Biotechnology Information. Retrieved from https://www.ncbi.nlm.nih.gov/gene/409

Noah P. Zimmerman, R. A. (2008). Chemokines and chemokine receptors in mucosal homeostasis at the intestinal epithelial barrier in inflammatory bowel disease. Inflammatory Bowel Disease, 14(7), 1000–1011. doi:10.1002/ibd.20480

Otero C, E. P. (2008, August 15). Distinct motifs in the chemokine receptor CCR7 regulate signal transduction, receptor trafficking and chemotaxis. Cell Science, 121(16). doi:doi: 10.1242/jcs.029074

Pettersen EF, G. T. (2021, January). UCSF ChimeraX: Structure visualization for researchers, educators, and developers. Protein Science, 30(1), 70-82.

Pommié, C. e. (2004). Physicochemical' classes of the 20 common amino acids. Journal of Molecular Recognition, 17-32.

Purvanov, V. M. (2018, December 4). Fluorescently tagged CCL19 and CCL21 to monitor CCR7 and ACKR4 functions. International Journal of Molecular Sciences. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6321256/

Rangel-Moreno, J. M.-Q. (2007). Pulmonary expression of CXC chemokine ligand 13, cc chemokine ligand 19, and CC chemokine ligand 21 is essential for local immunity to influenza. Proceedings of the National Academy of Sciences, 104(25), 10577–10582. doi:https://doi.org/10.1073/pnas.0700591104

RCSB Protein Data Bank. (2015, June 10). 2MP1: Solution Structure of the Human Chemokine CCL19. Retrieved from RCSB PDB: www.rcsb.org/structure/2mp1

Roskoski Jr., R. (2012, April 27). ERK1/2 MAP kinases: structure, function, and regulation. Pharmacol Research, 66(2), 105-43. doi:10.1016/j.phrs.2012.04.005

Roskoski, R. (June). Erk1/2 Map Kinases: Structure, function, and regulation. Retrieved June 1, 2022, from Pharmacological Research: https://www.sciencedirect.com/science/article/abs/pii/S104366181200097

Rot, A. v. (2004). Chemokines in Innate and Adaptive Host Defense: Basic Chemokinese Grammar for Immune Cells. Annual Review of Immunology, 22(1), 891–928. doi:10.1146/annurev.immunol.22.012703.104543

Smith, A. J. (2006, March 20). Mesenteric lymph nodes at the center of immune anatomy. Journal of Experimental Medicine, 203(3), 497–500. doi:10.1084/jem.20060227

Sokol, C. L. (2015, January 29). The Chemokine System in Innate Immunity. Cold Spring Harbor Perspectives in Biology, 7(5), a016303. doi:10.1101/cshperspect.a016303

Swiss Institute of Bioinformatics (SIB). (2022, June 3). CCL19 (Human Protein) Expression By Anatomical Entity and Cell Type. Retrieved from Expression By Anatomical Entity: https://bgee.org/gene/ENSG00000172724

The International SSRI Pharmacogenomics Consortium (ISPC). (2022, May 31). 2MP1. Retrieved from Proteopedia, Life in 3D: www.proteopedia.org/wiki/index.php/2mp1

TILO ANDUS, J. B. (1991). Effects of Cytokines on the Liver . Freiburg: 'Medizinische Universitatsklinik, Department of Gastroenterology and Hepatology, and 'Psychiatrische Klinik der.

Tino Schneider, M. e. (2018). CCL19-producing fibroblastic stromal cells restrain lung carcinoma growth by promoting local antitumor T-cell responses. Journal of Allergy and Clinical Immunology, 142(4), 1257-1271. doi:10.1016/j.jaci.2017.12.998

Topouzi, H. B., & Higgins, C. A. (2020). Harnessing the secretome of hair follicle fibroblasts to accelerate ex vivo healing; human skin wounds. Journal of Investigative Dermatology, 140(5). doi:https://doi.org/10.1016

Wang T, L. W. (2021). The Important Role of the Chemokine Axis CCR7-CCL19 and CCR7-CCL21 in the Pathophysiology of the Immuno-inflammatory Response in Dry Eye Disease. Ocular Immunology and Inflammation, 29(2), 266-277. doi:10.1080/09273948.2019.1674891

Wei Zhanga, G. T. (2017, August). Matrix metalloproteinase-9 is up-regulated by CCL19/CCR7 interaction via PI3K/Akt pathway and is involved in CCL19-driven BMSCs migration. Biochemical and Biophysical Research Communications, 451(2), 222-228. doi:10.1016/j.bbrc.2014.07.112

Wenxiang Hong, B. Y. (2022). New Insights of CCR7 Signaling in Dendritic Cell Migration and Inflammatory Diseases. Fronteirs in Pharmacology. doi:10.3389/fphar.2022.841687

Xiaoxiao Liu, B. W. (2019). Powerful Anticolon Tumor Effect of Targeted Gene Immunotherapy Using Folate-Modified Nanoparticle Delivery of CCL19 To Activate the Immune System. ACS Central Science, 5(2), 277–289. doi:10.1021/acscentsci.8b00688

Yan, Y. Z. (2021). CCL19 enhances CD8+ T-cell responses and accelerates HBV clearance. Journal of Gastroenterology, 56(8), 769–785. doi:https://doi.org/10.1007/s00535-021-01799-8

Yutaka Nakamura, S. K. (2018). M cell-dependent antigen uptake on follicle-associated epithelium for mucosal immune surveillance. Inflammation and Regeneration, 38(15). doi:10.1186/s41232-018-0072-y