CD40LG and infection: Lastly, in a different set of experiments, mice were infected with PAO1 or PAO1ΔlasIRrhlIR embedded in agar slurry, euthanized at 22 days after initial infection and after a second dose of bacteria at day 21, and serum levels of P. aeruginosa-specific IgM, IgG1 and IgG2a measured by ELISA.