Increased Responsiveness of Peripheral Blood Mononuclear Cells to In Vitro TLR 2, 4 and 7 Ligand Stimulation in Chronic Pain Patients

Abstract

Glial activation via Toll-like receptor (TLR) signaling has been shown in animals to play an important role in the initiation and establishment of chronic pain. However, our ability to assess this central immune reactivity in clinical pain populations is currently lacking. Peripheral blood mononuclear cells (PBMCs) are an accessible source of TLR expressing cells that may mirror similarities in TLR responsiveness of the central nervous system. The aim of this study was to characterize the IL-1β response to various TLR agonists in isolated PBMCs from chronic pain sufferers (on and not on opioids) and pain-free controls. Venous blood was collected from 11 chronic pain sufferers on opioids (≥ 20 mg of morphine / day), 8 chronic pain sufferers not on opioids and 11 pain-free controls. PBMCs were isolated and stimulated in vitro with a TLR2 (Pam3CSK4), TLR4 (LPS) or TLR7 (imiquimod) agonist. IL-1β released into the supernatant was measured with ELISA. Significantly increased IL-1β expression was found in PBMCs from chronic pain sufferers (on and not on opioids) compared with pain-free controls for TLR2 (F (6, 277) = 15, P<0.0001), TLR4 (F (8, 263) = 3, P = 0.002) and TLR7 (F (2,201) = 5, P = 0.005) agonists. These data demonstrate that PBMCs from chronic pain sufferers were more responsive to TLR agonists compared with controls, suggesting peripheral cells may have the potential to become a source of biomarkers for chronic pain.

Inflammation and inflammatory control in interstitial cystitis/bladder pain syndrome: Associations with painful symptoms

“…Further, IC/BPS is marked by inflammatory dysregulation, indicated by flattened diurnal cortisol rhythmicity, elevated plasma IL-6 and an exaggerated IL-1β response to TLR-2 stimulation in PBMCs. TLR-2 stimulated IL1-β responses in PBMCs were recently shown to be capable of differentiating a population of chronic pain patients from HCs [19]. This study extends that finding to a chronic pelvic pain population.…”

“…Plasma cytokines were assayed with high sensitivity Quantikine ELISAs. Similar approaches in populations with complex presentations of pain have been reported and are able to distinguish patients from healthy controls [5,16,17,19]. …”

“…Evidence in animal models of chronic pain suggests that inflammatory signaling secondary to TLR-4 stimulation plays a critical part in the development of hyperalgesia and allodynia [10,14,24]. Preliminary evidence suggests that heightened inflammatory responses to TLR stimulation may be a feature of human pain syndromes as well [19], but these have not been evaluated in IC/BPS. Further, no studies have determined if inflammatory responses to TLR stimulation are associated with the magnitude of painful symptoms.…”

Biological stress systems, adverse life events and the onset of chronic multisite musculoskeletal pain: a 6-year cohort study

“…One prospective study found that a blunted diurnal cortisol rhythm and non-suppression of the HPA axis were associated with new-onset chronic widespread pain among psychologically at-risk subjects 5. Also, IMS dysfunction has been demonstrated in chronic pain 11. We recently found unaltered levels of basal inflammatory markers but elevated levels of lipopolysaccharide (LPS)-stimulated inflammatory markers in chronic multisite musculoskeletal pain, possibly indicative of an enhanced innate immune response 12.…”

Medication-overuse headache and opioid-induced hyperalgesia: A review of mechanisms, a neuroimmune hypothesis and a novel approach to treatment

“…These findings are, suggestive of immune alterations in human pain states and enhancement by opioids. 114 …”