Cytotoxicity and cytokine production by bovine alveolar macrophages challenged with wild type and leukotoxin-deficient Mannheimia haemolytica

Leukotoxin (LKT) is a virulence factor for Mannheimia haemolytica. In this study, bovine alveolar macrophages (BAMs) were challenged with wild type (wt) and LKT deficient (lkt?) M. haemolytica at a concentration of 1 bacterium/BAM and the cytokine response was quantified by ELISA and real-time reverse transcriptase-PCR. Significant increases in protein concentrations of tumor necrosis factor (TNF)-? and interleukin (IL)-10 were observed in supernatants obtained from BAMs challenged with the lkt? strain of M. haemolytica compared with wt challenged BAMs. There were no significant differences in mRNA expression of TNF?, IL-1ß, IL-6, IL-8 or IL-10 between BAMs challenged with the lkt? strain of M. haemolytica compared with wt challenged BAMs. BAMs challenged with the wt strain exhibited, on average, 43% more cytotoxicity than lkt? challenged BAMs (P < 0.01).