Mononuclear cells of rabbit synovial effusion: morphology and DNA synthesis

Mononuclear cells from rabbit joint fluid were studied after synovitis was induced by various means, including the intra-articular injection of bacterial endotoxin or of aggregated human gamma globulin in normal rabbits, or of HGG in rabbits previously sensitized to this material. The large majority of mononuclear cells in all groups were monocytoid rather lymphocytoid, and these cells were most readily labeled with tritiated thymidine on the first day after injection. On day 2 and 3, the numbers of labeled cells decreased, except for the animals previously sensitized with HGG, in which there was an upswing of labeling on day 3. This upswing was associated with a considerable increase in numbers of cells resembing synovial cells, and may possibly be a reflection of synovial proliferation. Macrophages loaded with engulfed polymorphonuclear cells were observed in all experimental groups, a finding which emphasizes the lack of specificity of this reaction.