Expression of surface and intracellular molecules in primary-culture or repeated-passage rheumatoid arthritis synovial fibroblasts (RA-SFB) and in primary-culture normal-skin fibroblasts (FB). All preparations were highly enriched for FB, as demonstrated by expression of prolyl-4-hydroxylase and CD90 (Thy-1). Contamination with endothelial cells (indicated by von Willebrand's factor), T cells (indicated by CD3), B cells (indicated by CD19), and macrophages (indicated by CD14) was below 2%, with the exception of contaminating endothelial cells in primary-culture normal-skin FB, which averaged approximately 6% (see Table 3). ??, controls; ??, cell markers; M1, gate set in order to exclude 99% of the cells stained with the respective isotype control; percentages indicate the percentage of cells positive for each marker, numbers on the x axis indicate fluorescence channels.