I TAC Human
Description
Introduction to I-TAC Human
Interferon-inducible T-cell alpha chemoattractant (I-TAC), also known as CXCL11, is a non-ELR CXC chemokine critical for immune regulation. It belongs to the CXC chemokine family, characterized by the presence of a conserved cysteine residue motif (C-X-C) . Synonyms include IP-9, B-R1, H174, and SCYB9B . I-TAC is expressed in peripheral blood leukocytes, pancreas, liver, thymus, spleen, lung, and placenta, with expression strongly induced by interferons (IFN-α, IFN-β, IFN-γ) and interleukin-1 (IL-1) .
Chemotaxis and Immune Regulation
I-TAC primarily attracts activated T cells and natural killer (NK) cells via interaction with the CXC chemokine receptor 3 (CXCR3) . It demonstrates higher affinity for CXCR3 compared to other ligands like CXCL9 and CXCL10 .
| CXCR3 Ligand | Affinity | Primary Target Cells |
|---|---|---|
| CXCL11 (I-TAC) | High | IL-2-activated T cells, NK cells |
| CXCL9 | Moderate | T cells, dendritic cells |
| CXCL10 | Moderate | Monocytes, neutrophils |
Role in Neuroinflammation and Disease
I-TAC is upregulated in neuroinflammatory conditions such as multiple sclerosis, where it recruits effector T cells to the central nervous system . It is also implicated in HIV-associated dementia and autoimmune responses .
Tissue-Specific Expression
I-TAC expression is constitutively low in normal tissues but significantly upregulated under inflammatory or interferon-rich conditions:
| Tissue/Cell Type | Expression Level | Key Inducers |
|---|---|---|
| Astrocytes | High | IFN-γ + IL-1 |
| Monocytes | Moderate | IFN-γ, IL-1 |
| Thymus, Spleen | Low | Constitutive |
| Pancreas, Liver | Moderate | IFN-α/β/γ |
Transcriptional Regulation
The CXCL11 gene (chromosome 4) contains multiple polyadenylation signals, enabling cell-specific expression. IFN-γ and IL-1 synergistically induce CXCL11 mRNA by 400,000-fold in astrocytes, compared to 100-fold in monocytes .
CXCR3-Mediated Pathways
I-TAC binds CXCR3 with higher efficacy than CXCL9 or CXCL10, triggering:
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Calcium Mobilization: Rapid intracellular calcium release in activated T cells .
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Chemotaxis: Directed migration of CXCR3+ T cells, critical for immune surveillance .
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Survival Signals: Anti-apoptotic effects in T cells via PI3K/Akt pathways .
Cross-Talk with Other Receptors
While CXCR3 is the primary receptor, I-TAC may interact with CXCR7 under specific conditions, though this is less well-characterized .
Experimental Tools
Recombinant I-TAC is used in:
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Chemoattractant Assays: Assessing T cell migration in vitro .
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Antibody Neutralization: Blocking I-TAC/CXCR3 interactions in neuroinflammation models .
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Gene Expression Studies: Quantifying mRNA via qPCR (e.g., TaqMan probes targeting exon 4) .
| Application | Method | Example Use Case |
|---|---|---|
| Protein Production | E. coli expression | Functional studies |
| Antibody Development | Neutralizing monoclonal antibodies | Blocking CXCR3 signaling |
Therapeutic Implications
Targeting I-TAC/CXCR3 pathways may mitigate neuroinflammatory diseases (e.g., multiple sclerosis) or enhance anti-tumor immunity by modulating T cell recruitment . Challenges include balancing immune activation and potential off-target effects in chronic inflammation.
Product Specs
Chemokine (C-X-C motif) ligand 11 (CXCL11), also known as inducible T-cell alpha chemoattractant (I-TAC) and IP-9, is a small cytokine belonging to the CXC chemokine family. I-TAC is primarily found in peripheral blood leukocytes, pancreas, and liver, with moderate levels in the thymus, spleen, and lung. Low expression levels are observed in the small intestine, placenta, and prostate. The expression of the CXCL11 gene, responsible for encoding I-TAC, is significantly upregulated by IFN-g and IFN-b, and to a lesser extent by IFN-a. I-TAC exerts its effects on target cells by binding to the cell surface chemokine receptor CXCR3, exhibiting a higher affinity compared to other ligands for this receptor, namely CXCL9 and CXCL10. I-TAC exhibits chemotactic activity towards activated T cells. Notably, the CXCL11 gene is located on human chromosome 4, clustered with numerous other members of the CXC chemokine family.
Recombinant human I-TAC, produced in E. coli, is a single, non-glycosylated polypeptide chain consisting of 73 amino acids. It has a molecular weight of 8.3 kDa. The purification of I-TAC is achieved through proprietary chromatographic techniques.
(a) Reverse-phase high-performance liquid chromatography (RP-HPLC) analysis.
(b) Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis.
Small inducible cytokine B11, CXCL11, I-TAC, IP-9, H174, Beta-R1, chemokine (C-X-C motif) ligand 11, IP9, b-R1, SCYB11, SCYB9B, MGC102770.
Q&A
What molecular mechanisms regulate I-TAC expression in human astrocytes?
I-TAC expression in astrocytes is primarily induced by synergistic activation of interferon-γ (IFN-γ) and interleukin-1β (IL-1β). Key methodological approaches include:
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Cytokine stimulation assays: Treating primary human astrocytes with IFN-γ (200 U/mL) and IL-1β (200 U/mL) for 12 hours induces a 400,000-fold increase in I-TAC mRNA, as quantified via reverse transcriptase PCR (RT-PCR) .
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Transcriptional profiling: Sequencing cytokine-activated astrocyte cDNA libraries identifies novel chemokine transcripts, including I-TAC, through bioinformatic clustering .
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Signal pathway inhibition: Using JAK/STAT inhibitors (e.g., ruxolitinib) to dissect IFN-γ–dependent signaling cascades.
Table 1: I-TAC Expression Levels Under Cytokine Stimulation
| Cell Type | Stimulation Condition | Fold Change in mRNA | Method Used |
|---|---|---|---|
| Astrocytes | IFN-γ + IL-1β | 400,000x | RT-PCR |
| Monocytes | IFN-γ alone | 100x | Northern blot |
How does I-TAC selectively recruit activated T cells?
I-TAC binds CXCR3 with higher affinity () compared to related chemokines IP-10 () and HuMig () . Methodological insights include:
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Calcium mobilization assays: Transient intracellular calcium flux in CXCR3-transfected HEK293 cells confirms receptor activation potency (I-TAC > IP-10 > HuMig) .
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Chemotaxis chambers: IL-2–activated T cells exhibit dose-dependent migration toward I-TAC (EC50 = 1.2 nM) using Boyden chamber assays .
What techniques validate I-TAC’s interaction with CXCR3?
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Receptor transfection models: Stable expression of CXCR3 in HEK293 cells enables binding studies via radiolabeled I-TAC (e.g., -I-TAC) .
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Competitive inhibition: Pre-incubating T cells with IP-10 reduces I-TAC–induced chemotaxis by 60%, confirming shared receptor usage .
How do contradictory data on I-TAC expression across studies arise?
Discrepancies often stem from:
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Cell type specificity: Astrocytes show 4,000x higher I-TAC induction than monocytes under identical IFN-γ/IL-1β stimulation .
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Temporal dynamics: Peak mRNA expression occurs at 12 hours post-stimulation in astrocytes but declines by 24 hours, necessitating precise time-course experiments.
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Technical variability: Northern blot vs. RT-PCR sensitivity differences account for 10–20% quantification disparities .
What experimental designs control for confounding in neuroinflammatory studies?
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Cohort stratification: In multiple sclerosis models, separate analysis of acute vs. chronic lesions clarifies I-TAC’s role in T cell infiltration .
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Knockdown models: siRNA targeting I-TAC in astrocyte cultures reduces T cell migration by 75% in transwell assays .
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Multiplex cytokine panels: Simultaneous measurement of 12 IFN-γ–associated biomarkers controls for pleiotropic effects.
How can researchers resolve I-TAC’s dual pro- and anti-inflammatory roles?
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Context-dependent assays:
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Single-cell RNA sequencing: Identifies CXCR3 splicing variants preferentially binding I-TAC in Tregs vs. Th1 cells.
What are the limitations of in vitro I-TAC models?
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Loss of tissue microenvironment: 3D astrocyte-microglia cocultures restore physiological IFN-γ gradients absent in monolayers.
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Plasma protein interference: Serum-free media precludes false positives in ELISA measurements (detection threshold: 15 pg/mL) .
How to standardize I-TAC quantification across platforms?
Product Science Overview
CXCL11 is a non-ELR CXC chemokine that consists of a 94 amino acid precursor protein. This precursor includes a 21 amino acid signal sequence, which is cleaved to form the mature 73 amino acid protein . The protein is highly expressed in peripheral blood leukocytes, pancreas, and liver, with moderate levels in the thymus, spleen, and lung . It is expressed at lower levels in the small intestine, placenta, and prostate .
The gene expression of CXCL11 is strongly induced by interferon-gamma (IFN-γ) and interferon-beta (IFN-β), and weakly induced by interferon-alpha (IFN-α) . CXCL11 functions as a chemoattractant for activated T cells by interacting with the chemokine receptor CXCR3 . It has a higher affinity for CXCR3 compared to other ligands such as CXCL9 and CXCL10 .
CXCL11 plays a crucial role in the immune response by mediating the chemotaxis of T cells. It is involved in various biological processes, including:
- Chemotaxis: The movement of cells towards the site of infection or inflammation .
- Positive regulation of leukocyte chemotaxis: Enhancing the movement of white blood cells to the site of infection .
- Chemokine-mediated signaling pathway: Facilitating communication between cells during immune responses .
- Response to lipopolysaccharide: Reacting to components of bacterial cell walls .
Recombinant human CXCL11/I-TAC is produced using Escherichia coli (E. coli) expression systems . The recombinant protein is typically purified to a high degree of purity (>97%) and is used in various research applications . It is often utilized to study its role in immune responses and its potential therapeutic applications.
