CD40LG and susceptibility to pneumonia measurement: We evaluated the efficacy of ceftazidime or colistin in combination with polyclonal IgM-enriched immunoglobulin (IgM-IG), in an experimental pneumonia model (C57BL/6J male mice) using two multidrug-resistant Pseudomonas aeruginosa strains, both ceftazidime-susceptible and one colistin-resistant.