Mononuclear cells in human synovial fluid. Identification of lymphoblasts in rheumatoid arthritis.

A simple method was developed to identify large mononuclear (LMN) cells in human synovial fluid based on morphology and staining with Sudan black B. All cells were classified as monocyte-derived macrophages (MDM), lymphoblasts (LB), or synovial lining cells (SLC). Lymphoblasts were seen in 58 of 60 rheumatoid fluids (mean: 69 +/- 18% LB per LMN cells). However lymphoblasts were rarely seen in synovial fluids from patients with crystal-induced synovitis or bacterial infections.