Spinal disk injury induces germinal center formation, pronociceptive antibody production, and chronic nociceptive sensitization in a male mouse back pain model.

Abstract

Accumulating evidence suggests that spinal intervertebral disk damage is associated with activation of the adaptive immune system. Key unknown features of this response are the mechanism and time course for the generation of pronociceptive antibodies and the antibody classes involved. This study used the lumbar spinal disk puncture (DP) model in male wildtype (WT) and muMT mice (lacking mature B cells) to evaluate pronociceptive immune responses. Sera collected up to 33 weeks after DP were purified for immunoglobulin (Ig)M and IgG intrathecal injections and antigen binding experiments. Spinal cords and disks were collected for quantitative polymerase chain reaction, western, and immunohistochemical analyses. Disk puncture injury in muMT mice had minimal effect, but in WT mice, it induced hindpaw allodynia, hyperalgesia, and grip weakness that gradually resolved after 6 months. Spinal cord expression of inflammatory cytokines and complement components was chronically upregulated after DP, peaking at 1 to 3 weeks. Increased IgM and IgG autoantigen binding and deposition in the spinal cord peaked at 10 to 20 weeks after DP injury. Lumbar lymph node immunostaining demonstrated B-cell germinal center formation beginning at 3 weeks and peaking at 10 to 20 weeks after DP injury. Intrathecal injection of IgM and IgG collected between 3 and 20 weeks after DP in WT mice was pronociceptive in muMT DP mice. Preemptive pharmacologic intervention targeting B cells had no effect on early nociceptive sensitization but reduced sensitization when administered at 10 weeks after DP injury in WT mice. Collectively, these data support the pronociceptive autoimmunity hypothesis for the transition from tissue injury to chronic musculoskeletal pain state.