The distribution and abnormal morphology of plasma cells in rheumatoid synovium.

This study assessed the distribution and structural features of plasma cells in rheumatoid synovial tissue. Plasma cells were found to be the predominant infiltrating mononuclear cells (mean 40%) in relation to lymphocytes and monocytes, and there was a direct relationship between their number in the infiltrates and the total number of mononuclear leucocytes (P = 0.007). Plasma cells were also seen in intimate contact with macrophages intermixed with synovial lining cells, and closely associated with small blood vessels. They often surrounded these blood vessels and sometimes were seen lying within the vessel walls themselves. Ultrastructural analysis revealed that many synovial plasma cells were considerably larger than plasma cells of a normal size and possessed a marked distension of the cisternae of rough endoplasmic reticulum. Furthermore, plasma cells in close proximity to blood vessels often appeared to be undergoing migration. These observations imply that in rheumatoid synovium, plasma cells are metabolically very active and occupy a pivotal position for the secretion of antibodies into both the vascular and the extravascular compartments.