The present invention provides methods of identifying the presence of or quantifying the amount of one or more of T helper (Th) cells and iTreg cells present in a sample by identifying the presence of an ADAM or the amount of an ADAM, such as ADAM12, present in a sample. The present invention also provides methods for increasing or decreasing signaling of a TGF such as TGFβ by increasing or decreasing the biological activity or expression of an ADAM. Further, the present invention provides methods for inhibiting or stimulating, downregulating or upregulating, an immune response, and for treating diseases associated with an immune response such as cancer, viral, bacterial and fungal infections, autoimmune diseases and graft versus host diseases. Still further, the invention provides screening methods effective for identifying therapeutic agents, pharmaceutical compositions containing therapeutic agents, and vaccines.