A NOVEL MONOCLONAL-ANTIBODY RECOGNIZING A UNIQUE ANTIGEN OF RAT OSTEOCLASTS INDUCED BY THE CALCIFIED MATRICES

The morphology of osteoclasts, primary cells that resorb bone, is well documented; however, the precise details of their terminal differenti ation remains obscure. To date, the only morphological criterion for i dentifying activated functional osteoclasts has been the presence of r uffled borders. We have developed a rat bone marrow culture system in which osteoclast-like cells formed. These cells fulfilled most of the criteria of osteoclasts, and when they were reseeded on calcified tiss ue, formed numerous resorption lacunae in vitro. To find an immunologi cal marker for functional osteoclasts, we have used these cells in a f unctional state as antigens for the preparation of monoclonal antibodi es (mAb) that reacted with rat osteoclasts; we obtained mAb Chi and Ch 2. Interestingly, these mAbs reacted with the marginal portion of auth entic osteoclasts, where they attached to the bone surface on frozen s ections. The reactivity of Chi to rat osteoclasts was more restricted than that, of Ch2: Chi reacted with few tartrate-resistant acid phosph atase (TRAP)-positive cells on a culture plate. These TRAP-positive ce lls (including mono- and multinucleated cells) were, however, converte d to Chi-positive cells when they were reseeded on calcified tissues. These findings suggested that the antigen recognized by the Chi antibo dy was induced by some factors of matrix proteins released from calcif ied tissues.