CD28 and Autoimmunity: Also, recent reports haveshown that the cytoplasmic domain of CTLA-4 (ctCTLA-4) alone is sufficient toinhibit T-cell activation and prevent autoimmunity [52-54].Taken together, these studies suggest that competing with CD28 for ligand is onlyone of several inhibitory mechanisms utilized by CTLA-4 and support the hypothesisthat there is an intrinsic inhibitory nature to CTLA-4.