CD4+ αβ T cell infiltration into the leptomeninges of lumbar dorsal roots contributes to the transition from acute to chronic mechanical allodynia after adult rat tibial nerve injuries

Abstract

Background: Antigen-specific and MHCII-restricted CD4+ αβ T cells have been shown or suggested to play an important role in the transition from acute to chronic mechanical allodynia after peripheral nerve injuries. However, it is still largely unknown where these T cells infiltrate along the somatosensory pathways transmitting mechanical allodynia to initiate the development of chronic mechanical allodynia after nerve injuries. Therefore, the purpose of this study was to ascertain the definite neuroimmune interface for these T cells to initiate the development of chronic mechanical allodynia after peripheral nerve injuries. Methods: First, we utilized both chromogenic and fluorescent immunohistochemistry (IHC) to map αβ T cells along the somatosensory pathways for the transmission of mechanical allodynia after modified spared nerve injuries (mSNIs), i.e., tibial nerve injuries, in adult male Sprague-Dawley rats. We further characterized the molecular identity of these αβ T cells selectively infiltrating into the leptomeninges of L4 dorsal roots (DRs). Second, we identified the specific origins in lumbar lymph nodes (LLNs) for CD4+ αβ T cells selectively present in the leptomeninges of L4 DRs by two experiments: (1) chromogenic IHC in these lymph nodes for CD4+ αβ T cell responses after mSNIs and (2) fluorescent IHC for temporal dynamics of CD4+ αβ T cell infiltration into the L4 DR leptomeninges after mSNIs in prior lymphadenectomized or shamoperated animals to LLNs. Finally, following mSNIs, we evaluated the effects of region-specific targeting of these T cells through prior lymphadenectomy to LLNs and chronic intrathecal application of the suppressive anti-αβTCR antibodies on the development of mechanical allodynia by von Frey hair test and spinal glial or neuronal activation by fluorescent IHC.

Mechanical allodynia in mice with tenascin-X deficiency associated with Ehlers-Danlos syndrome

“…We performed von Frey filament tests to assess the response to mechanical stimulation using two methods: the first response method and the up-down method. In comparison to wild-type mice, TNX −/− male mice showed significantly lower thresholds of nociceptive responses, as assessed by either the lowest force required to elicit a withdrawal reflex (the first response method; wild-type male: 1.07 ± 0.10 g (n = 14) versus TNX −/− male: 0.14 ± 0.04 g (n = 13), P < 0.001, one-way ANOVA with post hoc Bonferroni test F (3,45) = 15.15, P < 0.001, Fig. 2a) or the 50% withdrawal threshold (the up-down method; wild-type male: 0.87 ± 0.09 g (n = 11) versus TNX −/− male: 0.46 ± 0.07 g (n = 9), P < 0.05, one-way ANOVA with post hoc Bonferroni test F (3,38) = 11.94, P < 0.0001, Fig.…”

“…A relationship between leptomeninges and neuropathic pain has been reported. Selective infiltration of CD4+ αβ T cells into the dorsal root leptomeninges of somatosensory pathways induces the mechanical allodynia after peripheral nerve injury 45 . Taken together, the data suggest that TNX-mediated regulation of the construction and function of the leptomeninges may induce mechanical allodynia, although this possibility requires further investigation.…”

Characterization of lumbar lymph node, a CNS-specific draining lymph node, after spinal cord injury in rats

“…Surgical excision of lumbar lymph nodes and cervical lymph nodes prior to experimental allergic encephalomyelitis (EAE) induction, reduces EAE severity by interfering with immunological priming [5], supports the concept that the CNS-draining lymph nodes are essential in the induction and severity of neuroinflammation versus non-draining lymph nodes [11]. Moreover, interestingly, lumbar lymph node-originated Lymphocytes at dorsal root leptomeninges has an important role in the development of chronic mechanical allodynia after tibial nerve injuries in rat, whereas lymphadenectomy of cervical and other CNS non-draining lymph node did not show any significant effect [6]. This implies that the nearest CNS-draining lymph node has the most potent immuneboosting capabilities against injury.…”

“…Tissue-draining lymph nodes, which could serve as sinks for cellular and solute transportation, are essential active-site for generating immune responses during inflammations, as well as in maintaining tolerance to minimize tissue damage [1][2][3][4]. The central nervous system-draining lymph nodes are thus likely vital for the balancing of protective versus harmful immune responses in experimental models of neuroinflammation [5][6][7][8]; however, surprisingly identification and functional characterization of CNS-draining lymph nodes during spinal cord injury have remained unclear.…”

C-X-C Motif Chemokine 10 Contributes to the Development of Neuropathic Pain by Increasing the Permeability of the Blood–Spinal Cord Barrier

“…Past studies have reported that CXCL10 promotes the entry of peripheral immune cells into the spinal cord (24,25). On the other hand, some studies and our recent report have shown that T cell infiltration of the dorsal horn may contribute to the onset of neuropathic and inflammatory hyperalgesia (11,12,26,27). However, it is unknown whether these processes contribute to hyperalgesia following peripheral nerve injury.…”