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The effects of inflamed nasal mucosa from pigs with atrophic rhinitis (AR), cell extract from Bordetella bronchiseptica, conditioned medium from Pasteurella multocida, and purified dermonecrotic toxin (DNT) from P. multocida on mouse fetal long bones in organ culture were studied. Inflamed nasal "AR mucosa" stimulated the release of 45Ca from prelabeled cultures, while histologically the formation of calcified matrix was impaired as well. B. bronchiseptica cell extract only transiently increased 45Ca release, but also impaired the formation of matrix. 45Ca release was also stimulated by DNT-containing conditioned medium from P. multocida and by purified DNT. The effect of DNT was biphasic: low doses (1 to 25 ng/ml) slightly stimulated bone resorption, higher doses were inhibitory. The stimulatory action of DNT on 45Ca release was accompanied by an increase in numbers of preosteoclasts and osteoclasts. The significance of these findings for the pathogenesis of AR is discussed.

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Osteoclast formation in vitro from human progenitor cells was studied in cocultures of periosteum-free murine long-bone rudiments and human fetal tissues. No osteoclasts were generated from chorionic villi or from fetal liver, but bone marrow and purified bone-marrow fractions gave rise to multinucleated cells that resorbed calcified cartilage matrix. These polykarya react very strongly for tartrate-resistant acid phosphatase (TrAP) and upon ultrastructural examination show large ruffled borders in areas of resorption. Resorption of murine calcified cartilage matrix by human osteoclasts was less than resorption. by osteoclasts formed from murine fetal bone-marrow cells. Our results show that the murine long-bone rudiment can be used to generate osteoclasts from human sources of progenitor cells and to assess the biological activity of the formed osteoclasts. This coculture system thereby offers possibilities to study human osteoclast pathology in vitro. The use of TrAP as marker for osteoclasts in cell cultures is discussed.