CD4 and pertussis: Hence, consistent mixed Th1/Th2 cytokine production was detected after PBMC stimulation with individual CD4+ T cell peptides, suggesting either that multiple clonal CD4+ T cell populations for a single specificity with either a Th1 or a Th2 cytokine profile coexist, or that single pertussis-epitope specific CD4+ T cells are capable of producing Th1 and Th2 cytokines simultaneously.