Analysis of Infiltrating Immune Cells Following Intervertebral Disc Injury Reveals Recruitment of Gamma-Delta (????) T cells in Female Mice
Inadequate repair of injured intervertebral discs (IVD) leads to degeneration and contributes to low back pain. Infiltrating immune cells into damaged musculoskeletal tissues are critical mediators of repair, yet little is known about their identities, roles, and temporal regulation following IVD injury. By analyzing longitudinal changes in gene expression, tissue morphology, and the dynamics of infiltrating immune cells following injury, we characterize sex-specific differences in immune cell populations and identify the involvement of previously unreported immune cell types, {gamma}{delta} and NKT cells. Cd3+Cd4-Cd8-T cells are the largest infiltrating lymphocyte population with injury, and we identified the presence of {gamma}{delta} T cells in this population in female mice specifically, and NKT cells in males. Injury-mediated IVD degeneration was prevalent in both sexes, but more severe in males. Sex-specific degeneration may be associated with the differential immune response since {gamma}{delta} T cells have potent anti-inflammatory roles and may mediate IVD repair. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=92 SRC="FIGDIR/small/582950v1_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@90ba37org.highwire.dtl.DTLVardef@1b17f87org.highwire.dtl.DTLVardef@2baa2corg.highwire.dtl.DTLVardef@b155c5_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical Abstract:C_FLOATNO Schematic of the workflow to obtain longitudinal analyses of the acute IVD injury response Injured caudal IVDs, CC5/6-CC9/10, were bilaterally punctured with a 30G needle to induce a traumatic injury. Injured IVDs and neighboring uninjured internal Control IVDs, CC12/13-CC16/17, were isolated during the acute injury response every 2-3 days until 21 days post injury (dpi) and a chronic injury time point at 42 dpi in female mice. Male mice samples were only collected at key injury response time points (red numbers): 3, 7, 12, 19, and 42 dpi. Longitudinal analyses of the temporal regulation of immune cell gene expression and cell infiltration were measured with qPCR, flow cytometry, immune fluorescence, and histology analyses to identify a sex-divergent immune response. C_FIG