Antigen complexed with major histocompatibility complex class I or II molecules on the surface of antigen presenting cells interacts with the T cell receptor ( TCR ) on the surface of T cells and initiates an activation cascade .
antigen complexed with major histocompatibility complex class i or ii molecules on the surface of antigen presenting cells interacts with the t cell receptor ( tcr ) on the surface of t cells and initiates an activation cascade .
O O O O O O O O O O O O O O O B-cell_type I-cell_type I-cell_type O O O B-protein_family_or_group I-protein_family_or_group I-protein_family_or_group O B-protein_family_or_group O O O O O B-cell_type I-cell_type O O O O O O