Upon activation by antigens , helper T cells differentiate into one of several subsets , characterized by their distinct cytokine -production patterns .
upon activation by antigens , helper t cells differentiate into one of several subsets , characterized by their distinct cytokine -production patterns .
O O O B-protein_family_or_group O B-cell_type I-cell_type I-cell_type O O O O O O O O O O O B-protein_family_or_group O O O