The influence of opsonins on the bactericidal effect of bovine alveolar macrophages against Pasteurella multocida.

Monolayers of bovine alveolar macrophages were infected with smooth and rough strains of Pasteurella multocida to determine their bactericidal function. Heat inactivated normal bovine serum, fresh bovine serum, specific immune serum and a combination of specific immune serum and fresh bovine serum were used as opsonins. A substantial difference in the bactericidal effect of macrophages against the logarithmic and stationary phase p. multocida was observed. Opsonization of the rough strain of P. multocida with the combination of specific immune and fresh serum increased their association with alveolar macrophages compared to those opsonized with either normal serum, fresh serum or specific immune serum. Opsonization of the smooth strain of P. multocida with normal bovine serum resulted in substantially fewer bacteria associated with macrophages at time zero, compared with other opsonins. Regardless of the kind of opsonins used in these experiments, the number of the rough strain of P. multocida killed by macrophages was always higher than those of the smooth strain.