Sex-biased toll-like receptor 4 signaling in nociplastic pelvic pain.

Sex differences in neuroimmune crosstalk have been identified in preclinical research, yet sex divergent immune pathways in people with chronic pain remain poorly understood. We previously identified ex vivo whole-blood stimulation of toll-like receptor-4 (TLR4), a highly conserved innate immune receptor, as a marker of nociplastic pain in female patients with urologic pain, but whether this occurs in males is unknown. Male (n=73) and female (n=135) patients with chronic urologic pain recruited from university-based tertiary urology clinics were compared on pain, urinary symptoms, and immune response to ex vivo TLR4 stimulation. Cross-sectional analyses demonstrated that female patients with widespread or comorbid pain exhibited heightened global TLR4 responses compared to female patients with pelvic-localized pain and male patients. Conversely, male patients with comorbid pain demonstrated downregulated regulatory TLR4 responses compared to male patients with pelvic-localized pain. These findings reveal distinct immunological phenotypes between male and female chronic pain patients based on pain distribution (pelvic-localized versus widespread/comorbid). This work provides foundational evidence for sex-specific immune mechanisms, with implications for the identification and treatment of nociplastic pain.