分类一：nTreg和iTreg

参考： https://www.sohu.com/a/247099502_610701

• There are two major regulatory T-cell subsets, "natural" CD4(+) Treg (nTreg) cells that develop in the thymus and "induced" Treg (iTreg) cells that develop from conventional CD4(+) T (Tconv) cells in the periphery.
• It has been indicated by various experiments that a developing T cell with an intermediate affinity TCR for a self-peptide/MHC is driven to the Treg cell lineage, while a T cell with a high-affinity TCR for the ligand is deleted, and one with a low-affinity TCR differentiates into a naive T cell