## 4 Discussion
Five genes were highly expressed in both B and T lymphocytes and regulate a range of functions such as cell adhesion and migration, _Cd53_; antigen receptor signaling, _Pptrcap_ and _Sash3_; and VDJ recombination, _Rag1_, and _Top2a_. Though T-lymphocytes have been found in degenerating human IVDs [5], the presence of B-lymphocytes, which accounts for the majority of the highly expressed genes in the LDP population (e.g., _Cd72_, _Blink_, _Syk_, and _Rag1_) has yet to be described during degeneration (Figure 5e,f). The involvement of immune cells and hematopoietic cells in the LDP tissue suggests that cell infiltration and differentiation were promoted by the surgical stab injury [14]. The role of lymphocytes after tissue injury had not been studied extensively; recent studies in bone fracture healing show clear roles for lymphocytes in mediating the tissue response after injury [61]. In bone fracture healing, lymphocytes were observed to infiltrate the injury site in a temporal fashion where they initially infiltrate the tissue early during the inflammation process, by 3 days post-injury, then leave and return after the peak inflammation window has passed and tissue proliferation has begun, around 14 days post-injury [61]. Lymphocytes function in the inflammation process by recruiting antigen-presenting cells, secreting cytokines to help mediate the inflammatory response, and secreting growth factors to aid in regeneration [61; 62]. We also observed that lymphocytes persisted up to 8 weeks post injury (Figure 8a,b; Table 1). B-lymphocytes act as antigen-presenting cells and dampen the inflammatory response by promoting Treg survival and secreting IL10 [62]. The lymphoid cluster contained \(Cd79b/Cd38\) positive mature B-lymphocytes [59], and the presence of \(Cd79b/Cxcr4\) positive B-lymphocytes indicates activation and trafficking (Figure 5e,f) [60]. T-lymphocytes, in contrast, modulate antigen presenting macrophages, and regulate the inflammatory response with specific subtypes such as \(Cd4\) positive Tregs [63]. \(Cd4\) positive T-lymphocytes are associated with tissue repair after injury due to eliciting immunomodulatory effects, while cytotoxic \(Cd8\) positive T cells have been shown to have a negative effect on repair [61]. We observe \(Cd3g\) broadly expressed in T-lymphocytes, \(Cd3g/Cd4\) expression in T-lymphocytes helper cells, and \(Cd3g/Cd8\) expression in cytotoxic T-lymphocytes (Figure 5e,f). Our data here reveal a novel role for B-lymphocytes in concert with T-lymphocytes as part of the immune cascade during degeneration that persists in both our model here and in humans. Moreover, the immune markers, such as \(Myb\), \(Blnk\), and \(Cd53\), remain similar over time for CON and LDP, suggesting that this is a sustained, progressive response due to degeneration rather than the acute trauma of the injury. In addition to the described differences in cell number and gene expression between cells within the clusters of control and degenerative IVDs, we observed changes in \(Ngf\) levels and expression patterns for IVD cell sub-clusters with IVD degeneration. Both \(Ngf\) and \(Ngf\) (encoding for p75 NTR) were increased in expression levels in OAF cells, and the number of OAF cells expressing \(Ngf\) was also increased. Additionally, NGF is pro-angiogenic that upregulates VEGF, and indirectly recruits endothelial cells [64]. Sustained NGF sensitizes innervating primary afferent neurons to produce hyperalgesia [65] via upregulated NGF receptor expression in ganglion neurons [66], and promotes the expression of substance P, calcitonin gene-related peptide, and neuronal ion channels that may lead to long-term adaptive effects onociceptors [67; 68]. Moreover, NGF binding to its receptor can regulate collateral sprouting of sympathetic fibers to dorsal root ganglion neurons that may relate to the maintenance of sensitization or chronic pain.