DDPIV/CD26, CXCL12 and CXCR4

CD26: Dipeptidyl Peptidase DPPIV known as adenosine deaminase complexing protein 2 or CD26 is an enzyme expressed on the surface of most cell types and is associated with immune regulation, signal transduction and apoptosis. CD26 has a key role in immune regulation as a T cell activation molecule and in immune-mediated disorder.

CXCL12: Stromal-derived-factor-1, SDF-1 also known as C-X-C motif chemokine 12, CXCL12 or Pre-B-Cell Growth-Stimulating Factor. A CXC chemokine that is chemotactic for T-lymphocytes and monocytes. Often induced by proinflammatory stimuli such as lipopolysaccharide, TNF, or IL1.

CXCR4: CXCR-4 is an alpha-chemokine receptor specific for stromal-derived-factor-1 (SDF-1 also called CXCL12), a molecule endowed with potent chemotactic activity for lymphocytes.

Interaction between DPPIV CD26, CXCL12 and CXCR4 is involved in inflammatory diseases.

This was studied in an experimental model of arthritis. Murine antigen-induced arthritis (AIA) induction led to reduced plasma DPPIV CD26 activity. And in CD26-deficient mice, the severity of AIA was increased. CD26-deficient mice exhibited increased levels of circulating active CXCL12, associated with increased numbers of CXCR4-positive cells infiltrating arthritic joints. Decreased circulating CD26 levels in arthritis may influence CD26-mediated regulation of the chemotactic CXCL12/CXCR4 axis.

CD26-deficient mice:
· reduced plasma DPPIV activity↓
· exhibited increased levels of circulating active CXCL12 ↑
· associated with increased numbers of CXCR4-positive cells infiltrating arthritic joints ↑

Reference: Circulating CD26 is negatively associated with inflammation in human and experimental arthritis:

What has that got to do with ME/CFS? The answer is:

Dipeptidyl peptidase IV/CD26 has been evaluated as a biomarker for ME/CFS.

Biomarkers in chronic fatigue syndrome: evaluation of natural killer cell function and dipeptidyl peptidase IV/CD26:
In the present study, we found the density of DPPIV/CD26 on lymphocyte surfaces and the concentration of the enzyme in plasma is reduced in CFS subjects, compared to controls. We hypothesize that this reduction is due to chronic lymphocyte activation in CFS patients. The present study adds to the evidence of loss of innate immune function and chronic immune activation, resulting from the long term presence of antigenic stimulus, either self or foreign.

ME/CFS:
· Density of Dipeptidyl Peptidase DPPIV/CD26 on lymphocyte surfaces ↓
· And concentration of the enzyme in plasma ↓
· CXCR4 up-regulated ↑


An up-regulation of CXCR4 in ME/CFS has been shown in other studies:
A gene signature for post-infectious chronic fatigue syndrome

Gene Expression Subtypes in Patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Assessment of a 44 Gene Classifier for the Evaluation of Chronic Fatigue Syndrome from Peripheral Blood Mononuclear Cell Gene Expression


The latest Light study Differing leukocyte gene expression profiles associated with fatigue in patients with prostate cancer versus chronic fatigue syndrome showed that mRNA expression for CXCR4 for CFS patient was elevated in relation to healthy controls, but it was not statistic significant. It would be interesting to repeat this Light study with patients after exercise, because exercise-elicited endogenous cortisol effectively augments CXCR4 expression on T lymphocytes. Reference: Cortisol-induced CXCR4 augmentation mobilizes T lymphocytes after acute physical stress


A potential up-regulation of CXCR4 in ME/CFS is worth keeping an eye on because the CXCL12-CXCR4 signaling is involved in both B cell development and development of plasmacytoid dendrite cells:

The Earliest Stages of B Cell Development Require a Chemokine Stromal Cell-Derived Factor/Pre-B Cell Growth-Stimulating Factor

Development of plasmacytoid dendritic cells in bone marrow stromal cell niches requires CXCL12-CXCR4 chemokine signaling


CXCL12-CXCR4 signaling is also involved in NK development, but it must be noted that nothing is simple in the human body. IL-15 is also involved in NK cell function, and IL15 is low in ME/CFS patients. So how all these factors affect the immune system and the dysregulated NK cells in ME/CFS is not easy to understand:

Differential chemotactic receptor requirements for NK cell subset trafficking into bone marrow

CXCL12-CXCR4 chemokine signaling is essential for NK-cell development in adult mice

Mechanistic Model of Natural Killer Cell Proliferative Response to IL-15 Receptor Stimulation


Synovial fluid is a lubricating, nourishing material present in many joints of the body. CXCL12 mediates desensitization of neutrophil respiratory burst in the synovial fluid from Rheumatoid Arthritic Patients.
Reference: Stroma Cell-Derived Factor 1α Mediates Desensitization of Human Neutrophil Respiratory Burst in Synovial Fluid from Rheumatoid Arthritic Patients


Preliminary data from CFS subjects showed differences in neutrophil function based on respiratory burst and phagocytic activity when compared to the control group. These results suggest that differences in neutrophil function in CFS patients may contribute to CFS related immune dysfunction.
Reference: Analysis of Neutrophil Function in Severe and Moderately Affected Chronic Fatigue Syndrome Subjects

This is something I would like to know more about, so...

Let us look for more studies on CD26/CXCR4…

Remember the cancer study: Chronic fatigue syndrome and subsequent risk of cancer among elderly US adults? ME/CFS was associated with an increased risk of non-Hodgkin lymphoma (NHL).

This study Dipeptidyl peptidase IV: serum activity and expression on lymphocytes in different hematological malignancies showed: Significantly decreased serum DPPIV activity and a significant decrease in the percentage of: CD26 + lymphocytes, CD26 + overall white blood cells and lymphocytes in patients with NHL in comparison to healthy controls. The obtained results in the study indicate that immune disturbances that can occur in hematological malignancies might be related to the decreased expression and activity of CD26/DPPIV.

This knowledge has already come to use in this article, Targeting the CD20 and CXCR4 pathways in non-hodgkin lymphoma with rituximab and high-affinity CXCR4 antagonist BKT140: Chemokine axis CXCR4/CXCL12 is critically involved in the survival and trafficking of normal and malignant B lymphocytes. Findings suggest the possible role of CXCR4 in NHL progression and response to rituximab and provide the scientific basis for the development of novel CXCR4-targeted therapies for refractory NHL.

Data show that Cyclophilin (CYPA) has a critical role in CXCR4 signaling involved in cell proliferation and migration. Reference: Cyclophilin A Is Required for CXCR4-mediated Nuclear Export of Heterogeneous Nuclear Ribonucleoprotein A2, Activation and Nuclear Translocation of ERK1/2, and Chemotactic Cell Migration

And Cyclophilin A is up-regulated in ME/CFS:
A multidisciplinary approach to study a couple of monozygotic twins discordant for the chronic fatigue syndrome: a focus on potential salivary biomarkers

Aberrant CXCR4/CXCL12-mediated inflammatory respons is found in several disorders, such as systemic lupus erythematosus, uveitis, multiple sclerosis and inflammatory bowel diseases. Reference: Involvement of CXCR4/CXCR7/CXCL12 Interactions in Inflammatory bowel disease

And dipeptidyl peptidase IV CD26 is reduced in tissue and plasma in active Crohn's disease. This is unlikely to represent simple downregulation induced by inflammation since the key proinflammatory cytokine strongly upregulated DP4 expression in Caco-2 cells.
Reference: Dipeptidyl peptidase-4 expression is reduced in Crohn's disease
Reference: Dipeptidyl peptidase IV (DP IV, CD26) in patients with inflammatory bowel disease

Data suggest that simultaneous targeting of CXCR4 and CXCR3 may be of benefit in the treatment of the CNS autoimmune disease.
Reference: Antagonism of the chemokine receptors CXCR3 and CXCR4 reduces the pathology of experimental autoimmune encephalomyelitis

This knowledge has led to a Patent application TREATMENT OF AUTOIMMUNE DISEASE where the invention provides methods for identifying a patient suffering from and/or susceptible to autoimmune disease who might be likely to respond to treatment with CXCL12 and/or CXCR4 antagonists. The present invention provides novel CXCL12 and/or CXCR4 antagonists, methods of identifying novel CXCL12 and/or CXCR4 antagonists, and methods involving the use of these in the treatment of autoimmune disease.

The patent application include

Dysautonomia malfunction of the autonomic nervous system, including such disorders as postural orthostatic tachycardia syndrome (POTS); though dysautonomia appears to have multiple causes, post-viral autoimmune damage appears to be a frequent cause.

and

Chronic fatigue immune disorder whose primary symptom is usually intense fatigue; dysfunction syndrome though the syndrome likely has multiple causes, some (CFIDS) maintain that autoimmune damage to the brain stem is the principal mechanism in a significant subset of cases.

Note that POTS is mentioned! And this article suggest that this chemokine CXCR4 may contribute to autonomically mediated pathophysiological events:CXCR4 receptors in the dorsal medulla: implications for autonomic dysfunction

Oxygen availability is a determinant parameter in the setting of chemotactic responsiveness to CXCL12. Low oxygen concentration induces high expression of CXCR4 in different cell types (monocytes, monocyte-derived macrophages, tumor-associated macrophages, endothelial cells, and cancer cells), which is paralleled by increased chemotactic responsiveness to its specific ligand. CXCR4 induction by hypoxia is dependent on both activation of the Hypoxia-inducible factor 1 α and transcript stabilization. In a relay multistep navigation process, the Hypoxia–Hypoxia-inducible factor 1 α–CXCR4 pathway may regulate trafficking in and out of hypoxic tissue microenvironments.
Reference: Regulation of the Chemokine Receptor CXCR4 by Hypoxia

And it is hypothesized that autonomic dysfunction/cerebral hypoxia could be involved in ME/CFS. Postural Orhtostatic Tachycardia Syndrome (POTS) is a very common ME/CFS co-morbidity, and POTS-patients are markedly sensitized to hypoxia when upright.
Reference: Brain dysfunction as one cause of CFS symptoms including difficulty with attention and concentration
Reference: Baroreceptor unloading in postural tachycardia syndrome augments peripheral chemoreceptor sensitivity and decreases central chemoreceptor sensitivity


Chemokines are also involved in pain. Increased signaling by CXCL12 and its receptor, CXCR4, has been shown to contribute to chronic pain behavior. Activation of another chemokine CCR2 by monocyte chemoattractant protein-1 MCP-1 elicits membrane depolarization, trigger action potentials and sensitizes nociceptors via transactivation of transient receptor potential channels TRPA1 and TRPV1.
Reference: Chemokines as pain mediators and modulators.

...there are many puzzle pieces to keep an eye on! Which pieces belong to the ME/CFS puzzle and which pieces do not fit in?

P2X7 in ME/CFS and other diseases

I have previously referred to articles about TRPA1 involvement in inflammation, vasodilation, central sensitization and hypothesized that TRPA1 has a role in ME/CFS/POTS/MCS/pain and more.

TRPA1 is of course only a small part of what is affected in the human body during these diseases. Many other receptors must also be involved. The latest article from Light et al mentions higher expression of P2RX7, so let us take a closer look at the P2X7 receptor.

The P2X7 receptor (P2X7R) is a nonselective cation channel that is activated by extracellular ATP and triggers the secretion of several proinflammatory substances, such as IL-1β, IL-18, TNF-α, and nitric oxide.

Quotes from P2X7 articles:

Following the activation of P2X7R through high concentrations of and/or prolonged exposure to ATP, a large conductance channel is elicited, which leads to dynamic changes in the membrane potential that include an intracellular potassium efflux. This cationic efflux induces inflammasome complex assembly and subsequent pro-caspase-1 maturation into caspase-1 through the NOD-like receptor protein (NLRP3). Caspase-1 plays a key role in the cleavage of pro-IL-1β to form mature IL-1β, which plays a principal role in nitric oxide synthase (NOS), cyclooxygenase-2, and tumor necrosis factor-alpha (TNF-α) activities
Reference: Physiological Roles and Potential Therapeutic Applications of the P2X7 Receptor in Inflammation and Pain

The expression of the purinergic, P2X7 receptor (P2X7R), is known to be enhanced in many brain pathologies where presence of activated microglia is a concurrent feature. This review focuses on the links between P2X7R expression and microglial activation and proliferation. The P2X7R is identified as a key player in the process of microgliosis, where by driving microglial activation, it can potentially lead to a deleterious cycle of neuroinflammation and neurodegeneration.
Reference: Microglia: Proliferation and activation driven by the P2X7 receptor

P2X7 is involved in central sensitization. Purinergic signaling, involving P2X4, P2X7 and P2Y12 receptors, plays a central role in the recruitment and activation of microglia, which have emerged as key regulators of central sensitization.
Reference: Pain hypersensitivity mechanisms at a glance
Reference: Central sensitization of nociceptive neurons in rat medullary dorsal horn involves purinergic P2X7 receptors
Reference: P2X(7) inhibition in stellate ganglia prevents the increased sympathoexcitatory reflex via sensory-sympathetic coupling induced by myocardial ischemic injury


Lipid rafts are important in the control of nociceptor excitability – P2X7 is associated with lipid rafts

Lipid rafts are microdomains of the plasma membrane highly enriched in cholesterol and sphingolipids. Lipid rafts tune the spatial and temporal organisation of proteins and lipids on the plasma membrane. They are thought to act as platforms on the membrane where proteins and lipids can be trafficked, compartmentalised and functionally clustered.
Reference: Association between tetrodotoxin resistant channels and lipid rafts regulates sensory neuron excitability

Reference: Palmitoylation of the P2X7 receptor, an ATP-gated channel, controls its expression and association with lipid rafts
(Palmitoylation is the covalent attachment of fatty acids, such as palmitic acid, to cysteine and less frequently to serine and threonine residues of proteins, which are typically membrane proteins.)

Caveolae are a special type of lipid raft

It has recently been shown in epithelial cells that the ATP-gated ion channel P2X7R is in part, associated with caveolae and colocalized with caveolin-1. In the present study of the mouse heart, we show for the first time, using immunohistochemistry and cryoimmunoelectron microscopy, that P2X7R is expressed in atrial cardiomyocytes and in cardiac microvascular endothelial cells, but not in the ventricle cardiomyocytes. In cardiac tissue homogenates derived from caveolin-1 deficient mice (cav-1-/-), an increase of the P2Xrx7 mRNA and P2X7R protein (80 kDa) was found, particularly in atrial samples.
Reference: Increased P2X7R expression in atrial cardiomyocytes of caveolin-1 deficient mice

Some guessing:
Some ME patients have POTS. POTS patients may have autoimmunoreactive IgGs against proteins associated with caveolae structure. Cavelolin-1 is a protein in the caveolae. Increased P2X7R expression is found in atrial cardiomyocytes of caveolin-1 deficient mice. ME patients show increased P2RX7 expression.

P2X7 and motor neruron death/cell death:

Here we found that P2X(7) receptor activation in spinal cord astrocytes initiated a neurotoxic phenotype that leads to motor neuron death
Reference: Extracellular ATP and the P2X7 receptor in astrocyte-mediated motor neuron death: implications for amyotrophic lateral sclerosis

P2X7-induced motor neuron death was dependent on neuronal nitric oxide synthase-mediated production of peroxynitrite, p38 activation, and autocrine FAS signaling. Taken together, our results indicate that motor neurons are highly sensitive to P2X7 activation, which triggers apoptosis by activation of the well-established peroxynitrite/FAS death pathway in motor neurons.
Reference: P2X7 receptor-induced death of motor neurons by a peroxynitrite/FAS-dependent pathway

A cytofluorometric assay demonstrated that P2X7 activation induced ROS formation in EOC13 cells, via a mechanism independent of Ca2+ influx and K+ efflux. Cytofluorometric measurements of Annexin-V binding and 7AAD uptake demonstrated that P2X7 activation induced EOC13 cell death. The ROS scavenger N-acetyl-L-cysteine impaired both P2X7-induced EOC13 ROS formation and cell death, suggesting that ROS mediate P2X7-induced EOC13 death. In conclusion, P2X7 activation induces the uptake of organic cations, ROS formation, and death in EOC13 microglia.
Reference: P2X7 Receptor Activation Induces Reactive Oxygen Species Formation and Cell Death in Murine EOC13 Microglia

Let us keep an eye on P2X7 and ME/CFS research to find out what the higher expression of P2RX7 actually means in ME/CFS.

Update: 
Surface expression of P2X7R on PBMC in patients with pSS was significantly higher than controls, suggesting P2X7R may contribute to the complex pathogenesis of pSS and also anxiety and/or depression.
Reference: The expression of P2X7 receptors on peripheral blood mononuclear cells in patients with primary Sjögren's syndrome and its correlation with anxiety and depression