Purified Pasteurella multocida protein toxin reduces acid phosphatase-positive osteoclasts in the ventral nasal concha of gnotobiotic pigs

To study the in vivo response of conchal (turbinate) osteoclasts to Pasteurella multocida toxin, four gnotobiotic pigs (7 days of age) were inoculated subcutaneously with 0.2 microgram/kg of purified toxin. One toxin-treated pig along with one control pig were necropsied at 2, 5, 9, and 14 days postinoculation. The entire length of nasal concha from the nasal planum toi ethmoid region was removed, blocked by transverse cuts into five areas, decalcified, sectioned, and then stained with tartrate-resistant acid phosphatase (TRAP) to identify osteoclasts. In each section, total area of concha, total osteoclast cytoplasmic area, and number of osteoclasts were determined using an image analysis morphometric unit. Also collected from pigs were blood and serum for complete blood counts, electrolyte levels, liver enzymes, and TRAP levels. Conchal atrophy increased in severity with time after 2 days postinoculation. In general, the ventral conchae from toxin-treated pigs at 9 and 14 days postinoculation had decreased surface area, osteoclast cytoplasmic area, and numbers of osteoclasts. Serum levels of TRAP were mildly elevated when compared with age-matched controls. No other significant alterations in blood cells or chemistries occurred and no lesions were present histologically in tissues (liver, kidney, lung, heart, and spleen) other than concha. This study shows that the P. multocida toxin induces rapid bone resorption and increases serum levels of acid phosphatase but leads to diminished acid phosphatase expression and presumably, numbers of osteoclasts.