User:Immcarle168/CCL17

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Allergies - copied from article, will be reworked as autoimmunity section with several subsections

CCL17 sometimes appears to worsen allergic diseases. CCL17 is known to help lymphocytes target areas on the skin, and could play a role in treatment of dermatitis and of other allergic reactions such as asthma. However, CCL17 is thought to trigger several Th2-mediated diseases. Atopic dermatitis(eczema) has been linked to CCL17, especially in infants whose mother does not have the disease. Studies have shown that children with allergies and atopic dermatitis have higher quantiles of CCL17 compared to children without allergies.

Autoimmunity

CCL17 is known to help lymphocytes (and especially eosinophils) target their response to skin-located pathogens. This often occurs through the CCL17-CCR4 interaction on type 2 T helper cells, which then secrete a variety of interleukins. Direct interactions between CCL17 and eosinophils has been observed but not well defined. However, overexpressed CCL17 has been linked to atopic dermatitis (eczema) and multiple sclerosis, among other autoimmune diseases. Studies have shown that children with allergies and atopic dermatitis have higher quantiles of CCL17 compared to children without allergies. As such, therapeutic approaches involving CCL17 regulation have shown some success in several cases. This intervention often involves interfering with CCR4 through monoclonal antibody treatment (such as mogamulizumab). Another option is small-molecule interaction with CCR4, which has not yet had any clinical success.

Atopic Dermatitis (eczema)

Researchers have found that type 2 helper-T cells in lesions of atopic dermatitis (AD) express more IL-4 and IL-13 than unaffected Th2 cells. Dendritic cells respond to IL-4 and IL-13 by secreting CCL17 (as well as CCL18 and CCL22), especially in "barrier-disrupted" skin (such as lesional skin). Because CCL17 is a key attractant for Th2, this creates a cycle of Th2 recruitment, IL-4 and IL-13 signaling, dendritic cell secretion of CCL17, and further recruitment of Th2 cells. Severity of AD is therefore correlated with concentration of CCL17 and CCL22 in both the blood serum and interstitial fluid of pediatric and adult patients with either acute or chronic AD. Because Th2 cells are present at elevated levels during pregnancy, a buildup of CCL17 in umbilical cord blood may summon more Th2 cells, causing the aforementioned positive feedback loop. This is correlated with a higher likelihood of developing AD (and other allergic diseases) in infants (including for mothers without AD), especially for the first two years of infancy.

In adult patients, other signals (such as IL-22) have been shown to correlate with the severity and chronicity of AD in addition to levels of CCL17, although the causal relationships between each of these other signals and CCL17 are not all yet known. Other signaling components, like TSLP, are induced by other lesional epidermal cells and directly upregulate CCL17 production.

Clinically, CCL17 has recently shown promise as a useful biomarker for AD severity as well as efficacy of treatment. Historically, physicians have used mostly visual, qualitative evaluations of lesion progress, but using CCL17 to quantify AD has allowed for more precise and accurate records of progress (or regression) during treatment. In concert with this, proposed treatments for AD include topical regulation of CCL17. Especially for infantile AD, where prolonged AD has been linked to severe food allergies, early quantification and treatment is especially important. This treatment may take the form of small-molecule inhibition of CCL17-CCR4 binding, which inhibits recruitment of Th2 cells and subsequent development of lesions.

Multiple Sclerosis (and EAE)

Multiple sclerosis (MS) (and the animal model EAE) are autoimmune diseases characterized in part by changes in the expression and regulation of CCL17 in cerebrospinal fluid. There is also evidence to suggest that certain SNPs in the CCL17 and CCL22 genes may raise the risk of MS for an individual.

While type 2 helper T (Th2) cells are a key component of AD because they are localized to the skin through the CCL17-CCR4 interaction, memory Th17 cells seem to express high levels of CCR4 in both human and murine models of MS and are therefore likely candidates for study and therapy.

Treatments of MS (such as natalizumab or methylprednisolone) seem to lower overall chemokine levels (notably including either CCL17 itself or factors that are known to induce CCL17 production) in addition to other purported primary functions. However, these findings are complicated by CCR4 up- and downregulation findings, which have sometimes seemed counter to the CCL17 localization pathways. Experimental explorations with CCL17-deficient mice have therefore counterintuitively given different information than experiments measuring CCR4 regulation for EAE.

Other Disorders

Several other disorders are also correlated with high levels of CCL17 or use CCL17 to localize Th2 cells. CCL17 can act as an inflammatory agent or as a symptom, and in either case, disrupting or manipulating the expression or ligand binding offers a therapeutic target. And, regardless of therapeutic potential, it can be used as a biomarker of disease.

• Drug rash with eosinophilia and systemic symptoms (DRESS)
• Bullous pemphigoid (BP)
• Senile erythroderma
• Eosinophilic pustular folliculitis
• Chronic spontaneous urticaria (hives)
• Maculopapular exanthema
• Stevens-Johnson syndrome/toxic epidermal necrolysis
• (Non-)episodic angioedema with eosinophilia
• Allergic asthma
• Allergic rhinitis/chronic rhinosinusitis with nasal polyps (CRSwNP)
• Eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)
• Acute and chronic eosinophilic pneumonia
• Mycosis fungoides (MF)
• Sezary syndrome (SS)
• Lymphocytic variant HES
• Acute disseminated encephalomyelitis (ADEM)
• Neuromyelitis optica (NMO) (Devic's disease)