Efects of Bordetella bronchiseptica Dermonecrotic Toxin

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In pigs, atrophic rhinitis (AR) occurs as an upper respiratory disease caused principally by dermonecrotic toxins (DNT) of Bordetella bronchiseptica (Bb) . Turbinate atrophy is a characteristic lesion in AR.Histologically, there is a progressive loss of tubular cancellous bonein the turbinates. Severe degenerative changes in osteoblasts in the turbinates were observed by electron microscopy. The changes in osteocytes were less severe than those in osteoblasts.Osteoclasts appeared to be almost normal. Recently, a clonal MC3T3-E1 osteogenic cell line was established from newborn mouse calvaria, and has unique capacy to differentiate into osteoblasts in vitro (Kodama et al. 1981)The toxicity of Bb DNT on the structure and function of a MC3T3-E1 were investigated. The DNT induced a morphological change in the cells from a spindle shape to a spherical formwith many blebs. The toxintreated cells were viable and grew to form confluent cell layrs composed of irregularly shaped cells and multinuclear cells. The toxin inhibited elevation of alkaline phosphatase activity in the cells in a dose-dependent manner at concentrations from 1ng/ml to 1,000ng/ml. The accumulation of type 1 collagen in the cells was also reduced by the DNT.It is considered likely that Bb DNTimpairs the ability of the cells to defferentiate.