TBX21 and intervertebral disk degenerative disorder: Although mechanistic studies on T cell function in IDD remain limited, evidence from endplate inflammation—a key pathological process of IDD—suggests that the transcription factors TBX21 (encoding T‐bet, a Th1 lineage marker) and RORC2 (encoding RORγt, a Th17 lineage marker) in activated CD4+ T cells are critical contributors.