IgG Rheumatoid Factor‐Secreting Lymphocytes in Rheumatoid Arthritis: Evaluation of a Haemolytic Plaque‐Forming Cell Technique

A haemolytic plaque-forming cell (PFC) assay detecting human B lymphocytes secreting IgG rheumatoid factor (RF) was established using sheep erythrocytes (SRBC) sensitized with rabbit IgG, developing rabbit anti-human IgG, and complement. IgG-RF PFC were only demonstrated with IgG-depleted guinea-pig serum as the source of complement. Cells spontaneously secreting IgG-RF were found among synovial fluid mononuclear cells (mean, 134/10(6)) and synovial tissue mononuclear cells (mean, 1775/10(6)) from patients with rheumatoid arthritis, whereas few were recorded among blood lymphocytes (mean, 3/10(6)). The experiments revealed that the RF-IgG PFC were protein-synthesizing B lymphocytes. The antibody specificity of the secreted IgF-RF was verified by the inhibitory effect of exogenous human and rabbit IgG on PFC formation.