Different capacity of purified Klebsiella pneumoniae-stimulated respiratory DC subsets to activate OVA TCR-transgenic naive CD4+responder T cells in a CFSE-dilution assay. Respiratory DC subsets were sorted to high purity (>98%), pulsed with the model antigen OVA and matured with Klebsiella pneumoniae lysate (Kp). Naïve CD4+ responder T cells were sorted from OVA TCR transgenic animals and labeled with CFSE. Negative controls included DC without Klebsiella lysate (control), responder T cells cultured without DC (no DC) and DC-T cell co-cultures without OVA (no OVA). Proliferation was quantitated by CFSE-dilution of responder T cells (A,B). Mean ± SEM; n ≥ 3.