CD4 and diabetes mellitus: The level of CD4 + Tregs in patients with Type 1 Diabetes decreases significantly.[28] On the other hand, the level of CD4 + CD25 + FoxP3 + Tregs in patients with Type 2 Diabetes is closely related to the disease progression, poor blood glucose control, and the risk of complications.[29] In the first step of Mediation MR, univariable MR identified a causal relationship between DM and CD4 + Tregs, i.e., diabetes was associated with a decrease of rCD4 + Treg AC (IVW method, β = −0.13; 95% CI: −0.21 to −0.05; P = 1.07e−03).