CD74 and major depressive disorder: In our study, RT-PCR analysis confirmed that CD74 was increased in OSA patients compared to normal controls, WGCNA analysis confirmed a strong association between CD74 and OSA and MDD phenotypes, ROC analysis verified the diagnostic value of CD74 in both OSA and MDD conditions, ssGSEA analysis confirmed the association between infiltration of immune cells and the expression of CD74, collectively establishing its therapeutic potential for comorbid OSA-MDD.