 These APCs include dendritic cells, B cells, and macrophages which are specially equipped not only with MHC class II but also with co-stimulatory ligands which are recognized by co-stimulatory receptors on helper T cells.Without the co-stimulatory molecules, the adaptive immune response would be inefficient and T cells would become anergic.Several T cell subgroups can be activated by professional APCs, and each T cell is specially equipped to deal with each unique microbial pathogen.