On first encounter with antigen , naive CD4+ T helper ( Th ) cells differentiate into cytokine -producing effector cells .
on first encounter with antigen , naive cd4+ t helper ( th ) cells differentiate into cytokine -producing effector cells .
O O O O O O B-cell_type I-cell_type I-cell_type I-cell_type I-cell_type I-cell_type I-cell_type I-cell_type O O B-protein_family_or_group O O O O