GZMK and major depressive disorder: Moreover, the expression level of CXCR6, GZMK, and KLRG1 was consistent with the training datasets of both diseases (Figure 3D) by analyzing the validated datasets (GSE55235 for OA and GSE201332 for MDD), suggesting that CXCR6, GZMK, and KLRG1 may act as key genes related to OA and MDD.