EFFECTS OF PASTEURELLA-MULTOCIDA TOXIN ON PORCINE BONE-MARROW CELL-DIFFERENTIATION INTO OSTEOCLASTS AND OSTEOBLASTS

The effect of Pasteurella multocida toxin (PMT) on porcine osteoclast and osteoblast differentiation was studied using in vitro cell culture systems. When grown in the presence of Vitamin D-3, isolated porcine bone marrow cells formed multinucleated cells with features characteri stic of osteoclasts. Exposure of bone marrow cells to Vitamin D-3, and PMT during growth resulted in formation of increased numbers and earl ier appearance of osteoclasts compared to controls. Ultrafiltered medi um from PMT-treated cells likewise increased osteoclast numbers, sugge sting that a soluble mediator may be involved in the action of PMT. Wh en cell cultures were treated with fluorescein-labeled PMT, fluorescen ce was found within the cytoplasm of small, round cells that did not r esemble either osteoclasts or osteoclastic precursor cells. Cultures o f porcine bone marrow cells exposed to dexamethasone, ascorbic acid, a nd beta-glycerophosphate developed into osteoblastic cells that formed multilayered, mineralized nodules. Exposure of osteoblastic cultures to low concentrations of PMT resulted in retarded cell growth, formati on of decreased numbers of nodules, and minimal to no mineralization i n the nodules; higher concentrations of PMT resulted in increased cell ular debris and poor growth of cells, with no nodule formation. These findings suggest that PMT may induce turbinate atrophy in pigs by incr easing osteoclast numbers and inhibiting osteoblastic bone formation. The effect of PMT on osteoclastic differentiation and growth may not b e due to a direct effect on preosteoclastic cells, but rather due to a lterations in the soluble mediator secretion by marrow stromal cells.