Objective To construct a psychological immune mechanism model by examining the mediating roles of rumination, anxiety symptoms, T helper cell type 2 (Th2) and the compensatory immune regulatory system (CIRS), thereby elucidating howdifferent types of childhood trauma influence depressive symptoms in adolescents. Methods From April to November 2025, 76 adolescents with depressive disorders were recruited from the Sichuan Provincial for Mental Health Center. Demographic data were collected through questionnaires including the Simplified Childhood Trauma Questionnaire ( CTQ-SF), the Rumination Response Scale(RRS), the Generalized Anxiety Disorder Scale (GAD-7) and the Patient Health Questionnaire Depression Scale (PHQ-9). Fastingblood samples were collected. Over 30 immune factors in plasma weredetected to construct an immune spectrum. Spearman correlationswere used to examine the associations between psychological and immune indicators. Partial least squares structural equation modeling(PLS-SEM) was performed using SmartPLS 4. 1. Results In thedirect pathways, rumination, anxiety symptoms, sexual abuse andTh2 significantly positively predicted depressive symptoms (β>0, P<0. 05). CIRS showed a negative predictive effect ( β = 0. 180, P =0. 006). In the indirect pathway, rumination mediated the significantimpact of emotional abuse on depressive symptoms ( β = 0. 242, P <0. 001, VAF = 65%). It also contributed to a significant chain mediation from emotional abuse → rumination → anxiety symptoms → depressive symptoms ( β = 0. 129, P = 0. 002, VAF = 35%). Anxietysymptoms also partially mediated the association between ruminationand depressive symptoms ( β = 0. 237, P< 0. 001, VAF = 35%) . In the immune pathways, Th2 fully mediated the effect of sexual abuse on CIRS (β = 0. 107, P = 0. 033, VAF = 100%). Although the total effect of Th2 on depression was not significant ( P = 0. 209), its indirect effect through CIRS showed a significant trend ( P =0. 054). Conclusions Rumination, anxiety symptoms, sexual abuse, Th2 and CIRS can directly predict depressive symptoms. Emotional abuse indirectly exacerbates depressive symptoms by increasing levels of rumination, whereas sexual abuse influences depressivesymptoms through the Th2 / CIRS immune pathway. This study suggests that the formation of depression can involve dual mechanisms ofabnormal psychological processing and immune imbalance. Comprehensive intervention in the aftermath of childhood trauma, rumination habits and immune disorders can help with early prevention and precise treatment of depression.