Comparison of four immune variables and pulmonary lesions of goats with intrapulmonary exposure and subsequent intrathoracic challenge exposure with Pasteurella haemolytica
Authors: Purdy Charles W. , Foster Gene S. 
Published: January 2024

A comparison of immune variables following lung sensitization with live Pasteurella haemolytica serotype 1 (Ph1)-impregnated agar beads was done in 2 separate trials. The Phi immune variables studied were blood bactericidal activity, serum bacteriolysis, total classical complement, and indirect hemagglutination antibody. Each trial had 16 male weanling goats: 6 controls and 10 principals. In trial 1, each goat was surgically catheterized through the trachea, then the material was deposited in a bronchus. The controls received only agar beads and the principals received agar beads impregnated with live Phi. These goats were studied for 32 days, euthanatized, and necropsied. In trial 2, the controls were each transthoracically injected with agar beads into the left lung and the principals were similarly injected with agar beads impregnated with live Phi. These goats were studied for 35 days, then challenge exposed transthoracically by injection of Phi in saline solution (1.2 × 107 cfu/ml) into the right lung. Four days later, they were euthanatized and necropsied. The volume of lung consolidated tissue was an excellent measure of Phi immunity. Principal goats generated solid protective immunity to subsequent challenge exposure because minimal or no lung consolidation was observed, whereas large volumes of lung consolidation were seen in the controls.

The principal goats in trial 1 gave a weak serum indirect hemagglutination Phi antibody response, which was attributed to the bronchial method of depositing the Phi. The corresponding response of the control group remained negative. The Phi agar beads (1 × 106 cfu in 0.5 ml) protected the bacteria from immediate phagocytosis and lysis as indicated by the induced pneumonic deaths of 2 principals 5 days later. Also, live Phi were isolated on day 32 during necropsy of respiratory tracts of 3 principals. At necropsy, no Phi isolates were found in the controls. Bacteriolytic activity was not induced against Phi in either control or principal groups in this trial.

In trial 2, the indirect hemagglutination Phi antibody response of the controls remained unchanged throughout the study, but antibody titers of the principals increased to a geometric mean of 1:250 seven days after lung injection (1 × 105 cfu in 0.5 ml). Serum bacteriolytic titers on day 0 indicated that both principals and controls could be subgrouped to high or low subgroups on the basis of their bacteriolytic activity. The bacteriolytic activities of the controls remained unchanged during the experiment, and neither control subgroup was protected from Phi challenge exposure. Bacteriolytic activities of the high and low principal subgroups responded differently to Phi agar bead lung injection, but both principal subgroups were protected from lung challenge exposure. The low principal subgroup generated high titers of indirect hemagglutination Phi antibody, whereas, the high principal subgroup generated lower antibody titers. Total complement, serum bacteriolytic, and blood bactericidal profiles were similar in the principal group with high bacteriolytic activity. The immune factors that protected 2 principal subgroups did not appear to be associated with Phi serum bacteriolysis.