This is consistent with the decrease in the number of viable intracellular bacteria in MPI cells within 24 hours of infection and is in agreement with a previous study showing colocalization of B. pertussis with late endosomal/lysosomal marker LAMP-1 and with Lysotracker, an acidotropic dye, indicating a lysosomal fusion in macrophages derived from blood mononuclear cells (34). This evidence concerns the gene LAMP1 and infection.