Pronociceptive autoantibodies in the spinal cord mediate nociceptive sensitization, loss of function, and spontaneous pain in the lumbar disk puncture model of chronic back pain.

Previously, we observed that B cells and autoantibodies mediated chronic nociceptive sensitization in the mouse tibia fracture model of complex regional pain syndrome and that complex regional pain syndrome patient antibodies were pronociceptive in fracture mice lacking mature B cells and antibodies (muMT). The current study used a lumbar spinal disk puncture (DP) model of low back pain in wild-type (WT) and muMT mice to evaluate pronociceptive adaptive immune responses. Spinal disks and cords were collected 3 weeks after DP for polymerase chain reaction and immunohistochemistry analyses. Wild-type DP mice developed 24 weeks of hindpaw mechanical allodynia and hyperalgesia, grip weakness, and a conditioned place preference response indicative of spontaneous pain, but pain responses were attenuated or absent in muMT DP mice. Spinal cord expression of inflammatory cytokines, immune cell markers, and complement components were increased in WT DP mice and in muMT DP mice. Dorsal horn immunostaining in WT DP mice demonstrated glial activation and increased complement 5a receptor expressionin spinal neurons. Serum collected from WT DP mice and injected into muMT DP mice caused nociceptive sensitization, as did intrathecal injection of IgM collected from WT DP mice, and IgM immune complexes were observed in lumbar spinal disks and cord of WT DP mice. Serum from WT tibia fracture mice was not pronociceptive in muMT DP mice and vice versa, evidence that each type of tissue trauma chronically generates its own unique antibodies and targeted antigens. These data further support the pronociceptive autoimmunity hypothesis for the transition from tissue injury to chronic musculoskeletal pain state.