Low-Dose Interleukin-2 Resolves Stress-Induced Chronic Sensitization Independent of Opioid Receptor Signaling

Stress is a common trigger of headache and widespread somatic pain. Repeated exposure to stress establishes latent sensitization that is tonically suppressed by endogenous inhibitory systems. Using brain-penetrating and peripherally restricted receptor antagonists in a mouse model of repetitive restraint stress, we systematically identified these protective pathways. Peripheral kappa opioid receptors as well as GABA type A and type B (GABA_A and GABA_B) receptors, alongside central opioid and cannabinoid signaling, actively suppress headache-related facial mechanical hypersensitivity in stressed mice. Blocking any pathway quickly reinstated cephalic allodynia. Peripheral opioid and GABA_A receptor signaling also inhibited stress-induced latent sensitization on hindpaw. In contrast, depletion of anti-inflammatory regulatory T (Treg) cells prolonged facial but not hindpaw sensitization, suggesting that Tregs preferentially limit stress-induced chronic headache. Next, we administered low-dose interleukin-2 (LD-IL-2) to stressed mice to preferentially expand and activate Treg cells. Following LD-IL-2 treatment, neither subthreshold pain triggers nor blockade of endogenous inhibitory pathways reinstated cephalic or hindpaw allodynia in either sex, indicating elimination of stress-induced sensitization. Mechanistically, LD-IL-2 acted through Treg cells to recruit multiple peripheral cytokine pathways without engaging endogenous opioid, GABA, or cannabinoid receptor signaling. Notably, LD-IL-2 was more effective than anti-CGRP (calcitonin gene-related peptide) therapy in preventing headache-related chronic sensitization in stressed mice. Collectively, these findings reveal multiple central and peripheral pathways that act concertedly to mask stress-induced latent sensitization and strongly support further evaluation of LD-IL-2 as a novel treatment for stress-induced headache and widespread pain with a distinct mechanism of action.