Between the PBMC samples of 37 MDD patients (12 males and 25 females) and 42 controls (18 males and 24 females), mRNA levels of SOCS1, SIGIRR, TNFAIP3, and MyD88s were significantly different, using independent t-test (p = 1.1 × 10−5, 2.0 × 10−8, 6.0 × 10−14, and 7.2 × 10−12, respectively). Here, SIGIRR is linked to major depressive disorder.