CTLA4 and diphtheria: Furthermore, CD4+ T cells responsive to T. cruzi-antigens in T. cruzi-infected adults display high expression of the inhibitory receptor CTLA-4 which is a feature of exhausted T cells [41], while few T cells responsive to tetanus and diphtheria toxoids expressed CTLA-4 [29], supporting that impairment in T cell responses in T. cruzi-infected adults was confined to those specific for T. cruzi.