Abstract
Background:
Psychosocial stress activates innate immune pathways, leading to leukocyte trafficking alterations and systemic immune dysregulation. Toll-like receptor 4 (TLR4) plays a central role in mediating the activation of stress-induced immune cells.

Aim:
This study investigated the effect of siRNA-mediated TLR4 silencing on stress-induced hematological alterations in rats using an unpredictable vibration–noise stress model.

Methods:
Forty adult male Wistar rats were randomly assigned to 4 groups: control, stress, siRNA, and siRNA + stress (n = 10 per group). Chronic stress was induced daily for 4 weeks, followed by the intraperitoneal administration of TLR4-targeting siRNA (0.5 μg/g body weight). Hematological responses were assessed longitudinally using a mixed-effects linear model.

Results:
Chronic stress significantly increased the number of circulating neutrophils and the neutrophil-to-lymphocyte ratio (N/L), with the number of neutrophils increasing from 2.18 ×10³/μl to 4.51 ×10³/μl and N/L increasing from 0.39 to 0.85 (p < 0.001). TLR4 silencing markedly attenuated these responses, reducing the neutrophil count to 1.90 ×10³/μl and restoring the N/L ratio to baseline levels. Significant treatment × time interactions were observed for neutrophils (ηp² = 0.566, p < 0.001) and N/L (ηp² = 0.467, p < 0.001), whereas erythrocytic parameters remained unchanged.

Conclusion:
TLR4 signaling plays a mechanistic role in stress-induced leukocyte redistribution. Targeted TLR4 silencing effectively restores immune homeostasis, highlighting the role of innate immune pathways in stress adaptation. However, the absence of molecular validation of TLR4 silencing represents a limitation of this study.

Key words: Innate immune signaling; Leukocyte redistribution; Neutrophil–lymphocyte ratio; Stress-induced inflammation; TLR4 silencing.