IL6R (Interleukin 6 Receptor) encodes the interleukin-6 receptor (IL-6R), a key component of IL-6 signaling that plays critical roles in immune response, inflammation, and acute phase reactions. IL-6 is a pleiotropic cytokine with diverse effects across multiple organ systems, and its signaling through IL-6R is particularly important in the nervous system where it contributes to neuroinflammation—a common feature of neurodegenerative diseases including Alzheimer's disease and Parkinson's disease[@ihle2014][@scheller2011].
The IL-6/IL-6R/gp130 signaling axis is one of the most important cytokine pathways in neuroinflammation. Activation leads to downstream signaling through JAK/STAT3, MAPK, and PI3K/Akt pathways, all of which have been implicated in neuronal survival, glial activation, and inflammatory responses in the brain[@kishimoto2010][@rose2014].
| Property |
Value |
| Gene Symbol |
IL6R |
| Full Name |
Interleukin 6 Receptor |
| Chromosomal Location |
1q21.3 |
| NCBI Gene ID |
3570 |
| OMIM |
147610 |
| Ensembl ID |
ENSG00000160712 |
| UniProt |
P08887 |
| Gene Length |
38.7 kb |
| Exons |
10 |
| mRNA Transcript |
NM_000565.4 |
| Protein Size |
468 amino acids (membrane-bound) |
| Molecular Weight |
~50 kDa (mIL-6R), ~55 kDa (sIL-6R) |
IL-6R exists in multiple forms:
- Type I cytokine receptor with extracellular, transmembrane, and cytoplasmic domains
- Extracellular region contains the IL-6 binding site
- Cytoplasmic domain is short (~90 amino acids) with limited signaling capability
- Expressed on specific cell types including hepatocytes, leukocytes, and some neuronal cells
- Generated through alternative splicing or proteolytic cleavage (ectodomain shedding)
- Can still bind IL-6 and activate cells expressing gp130
- Mediates IL-6 trans-signaling
- Elevated in various inflammatory and neurodegenerative conditions[@rose2014][@kaur2022]
- IL6ST (GP130) encodes the signal-transducing component
- Required for all IL-6R-mediated signaling
- Widely expressed including in the brain
- Triggers JAK/STAT3, MAPK, and PI3K/Akt pathways
IL-6R is a type I cytokine receptor that exists in both membrane-bound and soluble forms, mediating IL-6 signaling through multiple pathways:
- IL-6 binds to membrane-bound IL-6R (mIL-6R)
- The IL-6/mIL-6R complex recruits two gp130 molecules
- This brings associated JAK kinases (JAK1, JAK2, TYK2) into proximity
- JAKs phosphorylate gp130, creating docking sites for STAT proteins
- STAT3 (and to lesser extent STAT1) phosphorylated, dimerize, and translocate to nucleus
- Activates transcription of target genes including acute phase proteins[@ihle2014]
- Soluble IL-6R (sIL-6R) can bind IL-6
- The IL-6/sIL-6R complex can activate cells expressing gp130 but not mIL-6R
- This expands the range of IL-6-responsive cells including neurons and glia
- Particularly important in neuroinflammation and autoimmune responses
- Can be pro-inflammatory or anti-inflammatory depending on context[@rose2014]
- IL-6 can also promote anti-inflammatory responses
- Inhibits TNF-alpha and IL-1 production
- Stimulates IL-10 production
- Promotes Th2 differentiation
IL6R is expressed on various cell types:
- T cells (particularly Th17 cells)
- B cells
- Monocytes/macrophages
- Dendritic cells
- Neutrophils
- Neurons (in disease states)
- Astrocytes
- Microglia
- Oligodendrocytes
- Expression increases during neuroinflammation
- Hepatocytes (acute phase response)
- Endothelial cells
- Fibroblasts
IL-6/IL-6R signaling is significantly elevated in Alzheimer's disease:
-
Increased Expression:
- IL-6 is increased in AD brain tissue and cerebrospinal fluid
- IL-6R expression is upregulated in AD brain
- Correlates with disease severity
-
Genetic Associations:
- IL6R polymorphisms are associated with AD risk
- Asp358Ala variant (rs2228145) affects sIL-6R levels
- Modified by age and disease status
-
Pathogenic Mechanisms:
- Contributes to chronic neuroinflammation and gliosis
- Promotes microglial activation
- May affect amyloid processing
- Contributes to tau pathology through STAT3 activation
-
Biomarker Potential:
- CSF IL-6 levels correlate with disease progression
- sIL-6R as potential biomarker[@cholerton2018][@parnispour2019]
IL-6/IL-6R contributes to dopaminergic neuron loss in Parkinson's disease:
-
Elevated Cytokines:
- Elevated IL-6 in PD serum and CSF
- IL-6R expression increased in PD substantia nigra
-
Microglial Activation:
- IL-6/STAT3 signaling in microglia promotes neurotoxic phenotype
- Contributes to chronic neuroinflammation
-
Neuronal Effects:
- Direct effects on dopaminergic neurons
- May accelerate disease progression
- STAT3 activation leads to pro-apoptotic gene expression[@lin2018][@chen2023]
IL-6 is critical for multiple sclerosis pathogenesis:
-
Th17 Differentiation:
- IL-6 drives Th17 cell differentiation
- Th17 cells are key autoimmune effector cells in MS
-
Therapeutic Target:
- IL-6R is a therapeutic target in MS
- Blocking IL-6R is beneficial in some MS patients
-
B Cell Function:
- IL-6 promotes B cell survival and antibody production
- May contribute to autoantibody production
-
Blood-Brain Barrier:
- IL-6 increases BBB permeability
- Facilitates immune cell entry into CNS[@godeny2019][@harada2020]
IL-6R is a major therapeutic target in rheumatoid arthritis:
-
Therapeutic Blockade:
- Tocilizumab (humanized anti-IL-6R antibody)
- Sarilumab (fully human anti-IL-6R antibody)
- Highly effective in RA treatment
-
Mechanism of Action:
- Blocks IL-6 binding to both mIL-6R and sIL-6R
- Reduces downstream JAK/STAT signaling
- Decreases acute phase response
The IL-6R/gp130 complex activates multiple signaling pathways:
- Primary pathway activated by IL-6R
- JAK1, JAK2, and TYK2 associated with gp130
- STAT3 is primary transcription factor
- STAT1 also activated in some cell types
- Negative regulation by SOCS3
- Activated through RAS/RAF/MEK/ERK cascade
- Contributes to cell proliferation and differentiation
- Involved in acute phase response
- Promotes cell survival
- Anti-apoptotic effects in some contexts
- May be neuroprotective or neurotoxic depending on context
- Microglial activation through STAT3
- Enhanced production of other cytokines
- Chemokine production
- Matrix metalloproteinase expression
-
Tocilizumab:
- FDA-approved for RA and other autoimmune conditions
- Being investigated for neuroinflammatory diseases
- May reduce neuroinflammation in AD and PD
-
Sarilumab:
- Similar mechanism to tocilizumab
- Under investigation for neurological applications
-
Novel Agents:
- Small molecule JAK inhibitors
- STAT3 inhibitors
- Soluble gp130 constructs
- Blood-brain barrier penetration
- Balancing pro-inflammatory vs. anti-inflammatory effects
- Timing of intervention
- Patient selection
- Ihle JN, et al., Cytokine signaling and the JAK-STAT pathway in immune cells (2014)
- Rose-John S, IL-6 trans-signaling via the soluble IL-6R (2014)
- Scheller J, et al., The IL-6 family of cytokines (2011)
- Kishimoto T, IL-6: from its discovery to clinical applications (2010)
- Ershler WB, Keller ET, Age-associated increased interleukin-6 in disease (2014)
- Campbell IL, et al., Transgenic IL-6 in the CNS (2013)
- Cholerton F, et al., IL-6 in Alzheimer's disease CSF and postmortem brain (2018)
- Parnetti L, et al., CSF IL-6 as a biomarker in neurodegenerative diseases (2019)
- Rothaug M, et al., IL-6 trans-signaling in microglia and neuroinflammation (2015)
- West PK, et al., IL-6 and cognitive decline in aging (2020)
- Lin J, et al., IL-6 and Parkinson's disease risk (2018)
- Godeny M, et al., IL-6 in multiple sclerosis pathogenesis (2019)
- Harada K, et al., Tocilizumab in neuroinflammatory disease (2020)
- Kaur K, et al., Soluble IL-6R in neurodegeneration (2022)
- Chen X, et al., IL-6/STAT3 pathway in dopaminergic neurons (2023)