Prototypical functions of the chemokine receptor CCR6 include immune regulation by manoeuvring cell chemotaxis and selective delimiting of the pro-inflammatory TH17 and regulatory Treg subsets during chronic or acute systemic inflammation. Inhibition of CCR6 is proposed to attenuate disease symptoms and promote recuperation of multiple inflammatory and autoimmune disorders. Prescription medicines with pharmacodynamics involving the inhibition of the chemokine axis CCR6-CCL20 is very limited. Developing such therapeutics is still at an early experimental stage which has mostly utilized pre-clinical models and neutralizing mono or polyclonal antibodies against either partner, CCR6 or CCL20. Other methods have been constitutive use of small molecules as peptide inhibitors or small interfering ribonucleic acid (siRNA) to interfere with transcription at the nuclear level. We in our review aim at introducing the wide array of potential CCR6-CCL20 inhibitors that have been tried to date in the research field with accent on attendant immune-modulator capacity and which are immensely promising compounds as forerunners of future curatives. 16 different tractable inhibitors of the CCR6-CCL20 duo have been identified to possess high medicinal potential to the drug developers worldwide to treat autoimmune and inflammatory diseases. A multitude of antibody preparations are already available in the current pharmaceutical market as patented treatment for diseases in which the CCR6-CCL20 axis is operative, yet must be used only as supplements with existing routinely prescribed medication as they collectively produce adverse side effects. Novel inhibitors are needed to evaluate this invaluable therapeutic target which holds much promise in the research and development of complaisant remedies for inflammatory diseases.

Inflammatory bowel disease (IBD) is a CC chemokine receptor 6 (CCR6) - associated immune mediated disorder which has attracted an extensive superfluity of experimental analyses. IBD has come to the fore of varied scrutinizing owing to its complexity by nature for comprising of two synergistic sub phenotypes; Crohn’s disease (CD) and Ulcerative colitis (UC). Both these disease entities cause potent immune dysregulation followed by intense tissue damage within the gut mucosal system, initiating symptoms which are severely debilitating. Multiple causative factors are said to be responsible for IBD but direct immune dysfunction is kindled by overplay of innate and adaptive immune responses produced against a pathogenic microbial attack through the weakened or leaky gut epithelial barrier. Once immune homeostasis is not achieved by tolerating agents, the self-assertive adaptive immunity mobilize its various T and B cell cohorts initializing their allied immune mechanisms by vigorously deploying them towards the site of infection. CCR6 and its unique solitary ligand CC-chemokine ligand 20 (CCL20) are small protein molecules which are abundantly expressed by T and B lymphocytes and act as chemotactic immune-modulatory envoys that help in the deployment of the effector lymphocyte arm of the immune system, producing two directly opposing outcomes in IBD. This dichotomous immunity consists of either immune tolerance or inflammation which then develops into a chronic state, remaining catatonic to inherent immunity or targeted clinical therapy. In this review, we have chronologically identified a plethora of experimental studies radiating into 14 different compartments highlighted in the visual depiction which have employed both mouse models and clinical subjects spanning a period of nearly two decades. In doing so, we expect the research community would further benefit by tracing through the history, thereby understanding the CCR6 –CCL20 axis in IBD and identifying the gaps in literature which can be fortuitously filled in the future.

Inflammatory bowel disease (IBD) has evoked a significant interest in human immunobiology given its tactical immune evasion methodologies resulting in acute immune destabilization. IBD comprising of Crohn’s disease and Ulcerative colitis manifest as chronic inflammation in the gut mucosa, leading to complexities involving immune dysregulation in the T helper lymphocyte arm effecting disease pathogenicity. The mucosa of the alimentary canal is constantly exposed to a myriad of food antigens and luminal microorganisms for which a consistent host-protective mechanism is operative in healthy people. Lowered mucosal immune expression which allows penetration of the epithelial barrier by infective pathogenic microbes, elicits both innate and adaptive immune responses in the gut culminating in aberrant intestinal inflammation. Interestingly, IBD leukocyte repertoire is significantly entwined with chemokine assisted chemotactic navigation into the sites of inflammation which is also thought to generate favourable immune suppressive responses. The functions of the cognate chemokine receptor, CCR6, which binds with its unique ligand CCL20, are expected to tilt the balance between upregulation of homeostatic tolerance and inflammatory pathophysiology. This review aims at critically examining the CCR6 driven immune pathways; T_H1/T_H2, T_H1/T_H17, T_H17/ T_reg, IL-23/IL-17, Akt/ERK-1 /2, ILC3 for systematic investigation of its underlying mechanisms in the future and to underpin its importance in resolving IBD aetiopathology. Thus, CCR6 occupies an exclusive position in gut immunology which renders it an invaluable therapeutic tool for the production of novel medicaments to treat IBD.

Chemokine C-C receptor 6 (CCR6) and its exclusive ligand CCL20 is an extremely important chemokine receptor-ligand pair which controls cell migration and immune induction during inflammatory disease. Not many scientific studies have been undertaken to study its immune mechanisms in detail, but its unique contribution to steady state cell chemotaxis in upholding immune tolerance and regulating immune homeostasis during inflammation is evident in multiple organ systems, including lung, liver, kidney, skin, brain, eye, joints, gonads and the gut in the human body. The role of CCR6 is constitutively expressed as a series of much debilitating severe inflammatory and autoimmune diseases, HIV and cancer metastasis. CD4⁺ T cells, the central organizers of adaptive immunity, are stringently mobilized by the CCR6/CCL20 axis also induced by cytokines and a host of other factors in a carefully executed immune modulation scenario, to bring about a delicate balance between pro-inflammatory T_H17 cells and regulatory T_reg cells. Although the exact immune regulatory role is not elucidated yet, CCR6/CCL20 axis is implicated as a front runner which determines the polarization of T_H17 and T_reg cells and consequently the resolution or progression of many debilitating disorders. This review therefore aims at emphasizing the pleiotropic significance of the chemokines CCR6 and CCL20 in immunologic function in multiple organ systems thereby hoping to accentuate its value in future therapeutic modalities.

The majority of cellular responses to external stimuli are mediated by receptors such as G protein-coupled receptors (GPCRs) and systems including endoplasmic reticulum stress (ER stress). Since GPCR signalling is pivotal in numerous malignancies, they are widely targeted by a number of clinical drugs. Cancer cells often negatively modulate GPCRs in order to survive, proliferate and to disseminate. Similarly, numerous branches of the unfolded protein response (UPR) act as pro-survival mediators and are involved in promoting cancer progression via mechanisms such as epithelial to mesenchymal transition (EMT). However, there are a few proteins among these groups which impede deleterious effects by orchestrating the pro-apoptotic phenomenon and paving a therapeutic pathway. The present review exposes and discusses such critical mechanisms and some of the key processes involved in carcinogenesis.

Pattern recognition receptors such as nucleotide-binding oligomerization domain (NOD)-containing protein receptors (NLRs) and the pyrin and HIN domain (PYHIN) receptors initiate the inflammatory response following cell stress or pathogenic challenge. When activated some of these receptors oligomerize to form the structural backbone of a signalling platform known as the inflammasome. The inflammasome promotes the activation of caspase-1 and the maturation of the proinflammatory cytokines, interleukin (IL)-1β and IL-18. In the gut dysregulation of the inflammasome complex is thought to be a contributing factor in the development of inflammatory bowel diseases (IBD), such as ulcerative colitis (UC) and Crohn’s disease (CD). The importance of inflammasomes to intestinal health has been emphasized by various inflammasome deficient mice in dextran sulphate sodium (DSS) models of intestinal inflammation and by the identification of novel potential candidate genes in population based human studies. In this review we summarise the most recent finding with regard to formation, sensing and regulation of the inflammasome complex and highlight their importance in maintaining intestinal health.

Age-related alterations in the gut microbiome composition and its impacts on the host’s health have been well described; however, detailed analyses of the gut microbial structure defining ecological microbe-microbe interactions is limited. One of the ways to determine these interactions is by understanding microbial co-occurrence patterns. We previously showed promising abilities of Lactobacillus acidophilus DDS-1 on the aging gut microbiome and immune system. However, the potential of the DDS-1 strain to modulate microbial co-occurrence patterns is unknown. Hence, we aimed to investigate the ability of L. acidophilus DDS-1 to modulate the fecal, mucosal and cecal-related microbial co-occurrence networks in young and aging C57BL/6J mice. Our Kendall’s tau correlation measures of co-occurrence revealed age-related changes in the gut microbiome, which were characterized by reduced number of nodes and associations across sample types when compared to younger mice. After four-week supplementation, L. acidophilus DDS-1 differentially modulated the overall microbial community structure in fecal and mucosal samples as compared to cecal samples. Beneficial bacteria such as Lactobacillus and Akkermansia acted as connectors in aging networks in response to L. acidophilus DDS-1 supplementation. Our findings provided the first evidence of the DDS-1-induced gut microbial ecological interactions revealing the complex structure of microbial ecosystems with age.

The immunomodulatory behaviour of the CCR6/CCL20 axis in multi -system pathophysiology and molecular signalling was investigated at two clinically significant time points, using a Ccr6 - deficient mouse model of spontaneous colitis. Four groups of mice, (C57BL/6J, Ccr6^-/- of C57BL/6J, Winnie x Ccr6 ^-/- and Winnie) were utilized and (I) colonic clinical parameters (2) histology of colon, spleen, kidney and liver (3) T and B lymphocyte distribution in the spleen and MLN by flowcytometry (5) colonic CCL20, phosphorylated PI3K and phosphorylated Akt expression by immunohistochemistry and (6) colonic cytokine expression by RT-PCR were evaluated. CCR6 deficiency was shown to attenuate inflammation in the spleen, liver and gut while renal histology remained unaffected. Marked focal lobular inflammation with reactive nuclear features were observed in hepatocytes and a significant neutrophil infiltration in red pulp with extra medullary hemopoiesis in the spleen existed in Winnie. These changes were considerably reduced in Winnie x Ccr6^-/- with elevated goblet cell numbers and mucus production in the colonic epithelium. Results indicate that Ccr6- deficiency in the colitis model contributes towards resolution of disease. Our findings demonstrate an intricate networking role for CCR6 in immune activation, which is downregulated by Ccr6 deficiency, and could provide newer clinical therapies in colitis.